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BLOOD SYSTEM


I Introduction:

The primary function of blood is to maintain a constant environment for the other living tissues of the body. Blood transports foods, gases, and wastes to and from the cells of the body. Food, digested in the stomach and small intestine, passes into the bloodstream through the lining cells of the small intestine. Blood then carries these nutrients to all body cells. Oxygen enters the body through the air sacs of the lungs. Blood cells then transport the oxygen to cells throughout the body. Blood also helps to remove the waste products released by cells. It carries gaseous waste (such as carbon dioxide) to the lungs to be exhaled. It carries solid waste, such as urea, to the kidneys to be expelled in the urine.

Chemical messengers called hormones are also carried by the blood from their sites of secretion in glands, such as the thyroid or pituitary, to distant sites where they regulate growth, reproduction, and energy production.

Finally, blood contains proteins and white blood cells that fight infection, and platelets (thrombocytes) that help the blood to clot.

II Composition and Formation of Blood

Blood is composed of cells, or formed elements, suspended in a clear, straw-colored liquid called plasma. The cells constitute 45% of the blood volume and include erythrocytes (red blood cells), leukocytes (white blood cells), and platelets, or thrombocytes (clotting cells). The remaining 55% of blood is plasma, a solution of water, proteins, sugar, salts, hormones, and vitamins.

Cells: Most blood cells originate in the marrow cavity of bones. Both the red blood cells that carry oxygen and the white blood cells that fight infection arise from the same immature cells called stem cells (hemocytoblasts). Under the influence of proteins found in the bloodstream and bone marrow, the primitive stem cells change their size and shape and assume a specialized, or differentiated, form. In this process, the cells change in size from large (immature cells) to small (mature forms) and the cell nucleus shrinks (in red cells, the nucleus actually disappears).

Erythrocytes: As a red blood cell matures (from primitive erythroblast to normoblast to reticulocyte and finally to erythrocyte), it loses its nucleus and the cell assumes the shape of a disk. This shape (a depressed or hollow surface on each side of the cell, resembling a cough drop with a thin central portion) allows for a large surface area on the erythrocyte so that absorption and release of gases (oxygen and carbon dioxide) can take place. Red cells contain the unique protein hemoglobin, which consists of an iron-containing pigment called heme and a protein part called globin. Hemoglobin in the erythrocyte enables the cell to carry oxygen. The combination of oxygen and hemoglobin (oxyhemoglobin) produces the right red color of blood.

Erythrocytes originate in the bone marrow. A hormone called erythropoietin (secreted by the kidney) stimulates their production (-poiesis means formation). Erythrocytes live and fulfill their role of transporting gases for about 120 days in the bloodstream. After this time, cells (called macrophages) in the spleen, liver, and bone marrow destroy the worn-out erythrocytes. Two to ten million red cells are destroyed each second, but because they are constantly replaced, the number of circulating cells remains constant (4 – 6 million per cu mm).

Macrophages breakdown erythrocytes and the hemoglobin within them into their heme and globin (protein) portions. The heme releases iron and decomposes into a dark green pigment called bilirubin. The iron in hemoglobin is reutilized to form new red cells or is stored in the spleen, liver, or bone marrow. Bilirubin is excreted into the bile by the liver, and from the bile it enters the small intestine where it can be excreted in the stool. The green color then turns brown in the stool.

Leukocytes: White blood cells (7000 – 9000 cells per cu mm) ar less numerous than erythrocytes, but there are five different types of mature leukocytes. Five mature types of white blood cells: three granulocytic leukocytes (basophil, neutrophil, and eosinophil) and two agranulocytic leukocytes (monocyte and lymphocyte).

The granulocytes, also known as polymorphonuclear leukocytes, are the most numerous (about 60%). Each is different and has a specialized function. Basophils contain dark-staining cytoplasmic granules that stain with a basic (alkaline) dye. The granules contain heparin (an anticlotting substance) and histamine (a chemical that is released in allergic responses). Eosinophils contain granules that stain with a red acidic dye called eosin. These granulocytes increase in numbers in allergic responses and are thought to engulf substances that trigger the allergies. Neutrophils contain granules that are neutral; that is, they do not stain intensely with either dye. Neutrophils are phagocytes (phag/o means to eat or swallow) that accumulate at sites of infection, where they ingest and destroy bacteria.

Granulocytes and their precursor cells are considered part of the myeloid (derived from bone marrow) line of cells. Their growth and proliferation in the bone marrow are stimulated by specific proteins called colony-stimulating factors (CSFs). G-CSF (granulocyte CSF), GM-CSF (granulocyte macrophage CSF), interleukin-1, and interleukin-3 have been produced commercially and are administered to promote or restore myeloid proliferation in cancer patients. Erythropoietin, like the colony-stimulating factors, is produced by recombination DNA techniques and it stimulates red blood cell production.

Although all granulocytes are polymorphonuclear (they have multilobed nuclei), the term polymorphonuclear leukocyte (poly) is used most often to describe the neutrophil, which is the most numerous of the granulocytes.

Agranulocytes are mononuclear (containing one large nucleus) leukocytes that do not have dark-staining granules in their cytoplasm. These are the lymphocytes and monocytes. Lymphocytes arise in lymph nodes and circulate both in the bloodstream and in the parallel circulating system, the lymphatic system.

Lymphocytes play an important role in the immune response that protects the body against infection. They can directly attack foreign matter and, in addition, make antibodies, which neutralize and destroy foreign antigens (bacteria and viruses). Monocytes are phagocytic cells that also fight disease. They move from the bloodstream into tissues (then they are called macrophages) and dispose of dead and dying cells and other tissue debris by phagocytosis.

Platelets: Platelets, or thrombocytes, are formed in the red bone marrow from giant multinucleated cells called megakaryocytes. Tiny fragments of the megakaryocyte break off from the cell to form platelets. The main function of platelets is to help in the clotting of blood.

Plasma: Plasma is the liquid part of the blood and consists of water, dissolved proteins, sugar, wastes, salts, hormones, and other substances. The four major plasma proteins are albumin, globulin, fibrinogen, and prothrombin (the last two proteins are clotting proteins).

Albumin maintains the proper proportion (and concentration) of water in the blood. Because albumin cannot pass easily through capillary walls, it remains in the blood and carries smaller molecules bound to its surface. It attracts water from the tissues back into the bloodstream and thus opposes the water’s tendency to leave the blood and leak out into tissue spaces. Edema (swelling) results when too much fluid from blood “leaks” out into tissues. This happens in a mild form when a person ingests too much salt (water is retained in the blood and seeps out into tissues) and in a severe form when a person is burned in a fire. In this situation albumin escapes from capillaries as a result of the burn injury. Then water cannot be held in the blood; it escapes through the skin and blood volume drops.

The globulin portion of plasma contains antibodies that destroy foreign substances called antigens. There are three different kinds of globulins in plasma. They are alpha, beta, and gamma, and they can be separated by the process of electrophoresis. Plasma is placed in a special solution and an electric current is passed through the solution. The different protein molecules in the plasma separate out as they migrate at different speeds to the source of the electricity. Specific gamma globulins called immunoglobulins are capable of acting as antibodies. Examples of immunoglobulin antibodies are IgG (found in high concentration in the plasma) and IgA (found in breast milk, saliva, tears, and respiratory mucus). Other immunoglobulins are IgM, IgD, and IgE.

Plasmapheresis (-apheresis means to remove) is the process of separating plasma from the formed elements in the blood. This separation is mechanical, not electrical, as electrophoresis is. In plasmapheresis, the entire blood sample is spun in a centrifuge machine, and the plasma, being lighter in weight than the blood cells, moves to the top of the sample.

III Blood Groups

Transfusions of “whole blood” (cells and plasma) are used to replace blood lost after injury, during surgery, or in severe shock. A patient, who is severely anemic and needs only red blood cells, will receive a transfusion of packed red cells (whole blood with most of the plasma removed). Transfusions cannot occur between any two people at random. Human blood falls into four main groups called A, B, AB, and O, and there are harmful effects of transfusing blood from a donor of one blood group into a recipient who has blood of another blood group.

Each of the blood groups has a specific combination of factors (antigens and antibodies) that are inherited. These antigen and antibody factors of the various blood types are:
Type A, containing A antigen and anti-B antibody
Type B, containing B antigen and anti-A antibody
Type AB, containing A and B antigens and no anti-A or anti-B antibodies
Type O, containing no A or B antigens and both anti-A and anti-B antibodies

The problem in transfusing blood from a type A donor into a type B recipient is that A antigens (from the A donor) will react adversely with the anti-A antibodies in the recipient’s type B bloodstream. The adverse reaction is called agglutination, or clumping of the recipient’s blood. The agglutination is fatal to the recipient because it stops the flow of blood. Similar problems can occur in other transfusions if the donor’s antigens are incompatible with the recipient’s antibodies.

People with type O blood are known as universal donors because their blood contains neither A nor B antigens. The anti-A and anti-B antibodies in O blood do not have an effect in the recipient because the antibodies are diluted in the recipient’s bloodstream. Those with type AB blood are known as universal recipients because their blood contains neither anti-A nor anti-B antibodies, so that neither the A nor the B group antigens will cause agglutination in their blood.

Besides A and B antigens, there are many other antigens located on the surface of red blood cells. One of these is called the Rh factor (named because it was first found in the blood of a rhesus monkey). The term Rh-positive refers to a person who is born with the Rh antigen on her or his red blood cells. An Rh-negative person does not have the Rh antigen. There are no anti-Rh antibodies normally present in the blood of an Rh-positive or an Rh-negative person. However, if Rh-positive blood is transfused into an Rh-negative person, the recipient will begin to develop antibodies that would agglutinate any Rh-positive blood if another transfusion were to occur subsequently.

The same reactions occur during pregnancy if the fetus of an Rh-negative woman happens to be Rh-positive.

IV Blood Clotting

Blood clotting, or coagulation, is a complicated process involving many different substances and chemical reactions. The final result (usually taking less than 15 minutes) is the formation of a fibrin clot from the plasma protein fibrinogen. Platelets are important in beginning the process following injury to tissues or blood vessels. The platelets clump, or aggregate, at the site of injury, releasing a protein, thromboplastin, which in combination with calcium and the sequential release of clotting factors (I – V and VII – XIII) promotes the formation of a fibrin clot. One of the clotting factors is a protein known as clotting factor VIII. It is missing in people who are born with hemophilia.

The fibrin threads form the clot by trapping red blood cells and platelets and plasma. Then the clot retracts into a tight ball, leaving behind a clear fluid called serum. Normally, clots (thrombi) do not form in blood vessels unless the vessel is damaged or the flow of blood is impeded. Anticoagulant substances in the bloodstream inhibit blood clotting, so thrombi and emboli (floating clots) do not form. Heparin, produced by tissue cells (especially liver cells), is an example of an anticoagulant. Other drugs (such as dicumarol) are given to patients with thromboembolic diseases to prevent the formation of clots.

VII Pathological Conditions

Any abnormal or pathological condition of the blood is generally referred to as a blood dyscrasia (disease). The blood dyscrasias discussed in this section are organized in the following manner: disease of red blood cells, disorders of blood clotting, diseases of white blood cells, and bone marrow disease.

Diseases of Red Blood Cells

Anemia–deficiency in erythrocytes or hemoglobin
The most common type of anemia is iron-deficiency anemia; it is caused by a lack of iron, which is required for hemoglobin production. Other types of anemia include:
1. aplastic anemia–Failure of blood cell production due to aplasia (absence of development, formation) of bone marrow cells. The cause of most cases of aplastic anemia is unknown (idiopathic), but some cases have been linked to benzene exposure and to antibiotics such as chloramphenicol. Pancytopenia occurs as stem cells fail to produce leukocytes, platelets, and erythrocytes. Blood transfusions prolong life until the marrow resumes its normal functioning, and antibiotics are used to control infections. Bone marrow transplants have been successful as therapy.

2. hemolytic anemia–Reduction in red cells due to excessive destruction. One example of hemolytic anemia is congenital spherocytic anemia (also called hereditary spherocytosis). Instead of their normal biconcave shape, erythrocytes are spheroidal. This shape makes them very fragile and easily able to be destroyed (hemolysis), which leads to anemia. The spherocytosis causes increased numbers of reticulocytes in the circulating blood as the bone marrow attempts to compensate for the hemolysis of mature erythrocytes. The excessive hemolysis leads to jaundice because of accumulation of bilirubin in the circulating bloodstream. Because cells in the spleen destroy red cells, the spleen may be removed with helpful results. In some ceases, hemolytic anemia is due to production of autoimmune antibodies that destroy red cells.

3. pernicious anemia–Lack of mature erythrocytes owing to inability to absorb vitamin B12 into the body. (Pernicious means ruinous or hurtful.) Vitamin B12 is necessary for the proper development and maturation of erythrocytes. Although vitamin B12 is a common constituent of food matter (liver, kidney, sardines, egg yolks, oysters), it cannot be absorbed into the bloodstream without the aid of a special substance called intrinsic factor that is normally found in gastric juice, and the result is unsuccessful maturation of red blood cells, with an excess of large, immature, and poorly functioning cells (megaloblasts) in the circulation. Treatment is administration of vitamin B12 for life.

4. sickle cells anemia–A hereditary condition characterized by abnormal shape of erythrocytes and by hemolysis. The crescent, or sickle, shape of the erythrocyte is caused by an abnormal type of hemoglobin (hemoglobin S) in the red cell. The distorted, fragile erythrocytes are poorly oxygenated and clump together, blocking blood vessels, leading to thrombosis and infarction (dead tissue). Symptoms include arthralgias, acute attacks of abdominal pain, and ulcerations of the extremities. The genetic defect (presence of the hemoglobin S gene) is particularly prevalent in black persons of African or African-American ancestry and appears with different degrees of severity, depending on the inheritance of one or two genes for the trait.

5. thalassemia–An inherited defect in the ability to produce hemoglobin, usually seen in persons of Mediterranean (thalassa is a Greek Word meaning sea) background. This condition presents in varying forms and degrees of severity (the most severe form is called Cooley’s anemia), usually leads to hypochromic anemia (diminished hemoglobin content in red cells).

hemochromatosis—Excessive deposits of iron throughout the body. Hepatomegaly occurs and the skin is pigmented, so that it has a bronze hue; diabetes can occur and cardiac failure commonly develops. The condition is usually seen in men over 40 years of age.

polycythemia vera–General increase in red blood cells (erythremia). Blood consistency is viscous (sticky) because of greatly increased numbers of erythrocytes. The bone marrow is hyperplastic, and leukocytosis and thrombocytosis accompany the increase in red blood cells. Treatment consists of reduction of red cell volume to normal levels by phlebotomy (removal of blood from a vein) and by suppressing production with myelotoxic drugs.

Disorders of Blood Clotting

hemophilia – Excessive bleeding caused by a congenital (hereditary) lack of one of the protein substances (factor VIII) necessary for blood clotting. Although, the platelet count of a hemophiliac patient is normal, there is a marked deficiency in a plasma-clotting factor (factor VIII), which results in a very prolonged coagulation time. Treatment consists of administration of the deficient factor.

purpura – Multiple pinpoint hemorrhages and accumulation of blood under the skin. Purpura means purple, and in this bleeding condition, hemorrhages into the skin and mucous membranes produce red-purple discoloration of the skin. The bleeding is caused by a fall in the number of platelets (thrombocytopenia). The cause of the disorder may be immunological, meaning the body produces an antiplatelet factor that harms its own platelets. Idiopathic thrombocytopenic purpura is a condition in which a patient makes an antibody that destroys his or her own platelets. Bleeding time is prolonged and the cause is unknown. Splenectomy (the spleen is the site of platelet destruction) and drug therapy with corticosteroids to discourage antibody synthesis are methods of treatment. Purpura is also seen in any other condition associated with a low platelet count, such as leukemia and drug reactions.

Diseases of White Blood Cells

leukemia – An increase in cancerous white blood cells. This is a disease of the bone marrow in which malignant leukocytes fill the marrow and bloodstream. There are several types of leukemia, determined according to the particular leukocyte involved. The terms acute and chronic are used to refer to a large number of immature (in acute forms) or mature, differentiated (in chronic forms) leukocytes in the blood.

Acute leukemias have several common clinical characteristics: abrupt, stormy onset of symptoms, fatigue, fever and bleeding, bone pain and tenderness, lymphadenopathy, splenomegaly and hepatomegaly, and CNS symptoms, such as headache, vomiting, and paralysis. Four types of leukemia are:

acute myelogenous (myelocytic) leukemia (AML) – Immature granulocytes (myeloblast) predominate. Platelets and erythrocytes are diminished because of infiltration and replacement of the bone marrow by large numbers of myeloblasts.

acute lymphocytic leukemia (ALL) – Immature lymphocytes (lymphoblast) predominate. This form is seen most often in children and adolescents; onset is sudden.

chronic myelogenous (myelocytic) leukemia (CML) – Both mature and immature granulocytes are present in the marrow and bloodstream. This is a slowly progressive illness with which patients may live for many years without encountering life-threatening problems.

chronic lymphocytic leukemia (CLL) – Abnormal numbers of relatively mature lymphocytes predominate in the marrow, lymph nodes, and spleen. This form of leukemia usually occurs in the elderly and follows a slowly progressive course.

All forms of leukemia are treated with chemotherapy, using drugs that prevent cell division and selectively injure rapidly dividing cells. Effective treatment can lead to a remission (disappearance of signs of disease). Relapse occurs when leukemia cells reappear in the blood and bone marrow, necessitating further treatment.

Transplantation of normal bone marrow from closely related donors is successful in restoring normal bone marrow function in some patients with acute leukemia. This procedure is performed following high-dose chemotherapy, which is administered to eliminate the leukemic cells.

granulocytosis – Abnormal increase in granulocytes in the blood. An increase in granulocytes in the blood may occur in response to infection or inflammation of any type. Eosinophilia is an increase in eosinophilic granulocytes, which is seen in certain allergic conditions, such as asthma, or in parasitic infections (tapeworm, pinworm). Basophilia is an increase in basophilic granulocytes seen in certain types of leukemia.

mononucleosis – An infectious disease evidenced by increased numbers of lymphocytes and enlarged cervical lymph nodes. This disease is caused by the Epstein-Barr virus (EBV). Lymphadenitis is present, with fever, fatigue, asthenia (weakness), and pharyngitis. Atypical lymphocytes are present in the blood, liver (hepatomegaly), and spleen (splenomegaly).

Mononucleosis is usually transmitted by direct oral contact (salivary exchange during kissing) and affects primarily young adults. No treatment is necessary for EBV infections. Antibiotics are not effective for self-limited viral illnesses. Rest during the period of acute symptoms and slow return to normal activities is advised.

Diseases of Bone Marrow Cells

multiple myeloma – Malignant tumor of bone marrow. This is a progressive tumor of antibody-producing cell (called plasma cells). The malignant cells invade the bone marrow and destroy bony structures. The tumors cause overproduction of immunoglobulins and Bence Jones protein, an immunoglobulin fragment found in urine. Often, the condition leads to osteolytic lesions, hypercalcemia, anemia, renal damage, and increased susceptibility to infection. Treatment is with analgesics, radiotherapy, palliative (relieving, not curing) doses of chemotherapy, and special orthopedic supports.

VIII Laboratory Tests, Clinical Procedures, and Abbreviations

Laboratory Tests
Antiglobulin test (Coombs test) – Demonstrates whether the patient’s erythrocytes are coated with antibody and is useful in determining the presence of antibodies in infants of Rh- women or in patients with autoimmune hemolytic anemia.

bleeding time – The time it takes for a small puncture wound to stop bleeding. Normal time is 8 minutes or less. Bleeding time is prolonged with use of aspirin and in platelet disorders such as thrombocytopenia. There are several testing methods, but the most widely used is the Simplate (an incision is made while constant pressure is applied using a sphygmomanometer).

complete blood count (CBC) – This usually includes the following studies: red blood cell count, white blood cell count (with differential), platelet count, hemoglobin test, hematocrit, and red cell indices—MCH, MCV, MCHC. These routine tests are performed by automatic machines.

coagulation (clotting) time – Time required for venous blood to clot in a test tube. Normal time is less than 15 minutes.

erythrocyte sedimentation rate (sed rate or ESR) – Speed at which erythrocytes settle out of plasma. Venous blood is collected, anticoagulant is added, and the blood is placed in a tube in a vertical position. The distance that the erythrocytes fall in a given period of time is the sedimentation rate. The rate is altered in disease conditions, such as infections, joint inflammation, and tumor, that increase the immunoglobulin content of the blood.

hematocrit (Hct) – Percentage of erythrocytes in a volume of blood. A sample of blood is spun in a centrifuge so that the erythrocytes fall to the bottom of the sample.

hemoglobin test (Hb, Hgb) – Total amount of hemoglobin in a sample of peripheral blood.

partial thromboplastin time – Measures the presence of factors that act at early points in the coagulation pathway. This test is used to follow patients taking certain blood thinners (anticoagulants).

platelet count – Number of platelets per cu mm. Platelets normally average between 200,000 and 400,000 per cu mm.

prothrombin time – This is a test of the ability of blood to clot. It measures the time elapsed between the addition of calcium to a plasma sample and the appearance of a visible clot. The test is also used to follow patient’s taking certain blood thinners (anticoagulants).

red blood cell count (RBC) – Number of erythrocytes per cu mm of blood. The normal number is 4 – 6 million per cu mm.

red blood cell morphology – A stained blood smear is examined to determine the shape or form of individual red cells. The presence of anisocytosis, poikilocytosis, sickle cells, and hypochromia can be noted.

white blood cell count (WBC) – This is the number of leukocytes per cu mm. Automatic counting devices can record the numbers within seconds. Leukocytes normally average between 5000 and 10,000 per cu mm.

white blood cell differential – This test determines the numbers of different types of leukocytes (immature and mature forms). The cells are stained and counted under a microscope by a technician. A minimum of 100 cells is counted, and the percentages of neutrophils, lymphocytes, monocytes, basophils, and eosinophils are given.

The term “left shift” is used to describe a condition in which there is an increase in immature neutrophils and a decrease in mature forms in the blood.

Clinical Procedures

apheresis – Separation of blood into its parts. It is performed to remove toxic substances or autoantibodies from the blood or to harvest blood cells. Leukapheresis, plateletpheresis, and plasmapheresis are examples.

blood transfusion – In this procedure, whole blood or cells are taken from a donor, and after appropriate testing to ensure a close match of red cell or platelet type, the whole blood or cells are infused into a patient. Also prior to transfusion, tests are performed to ensure that the specimen is free of hepatitis and the acquired immunodeficiency syndrome (AIDS) virus. Autologous transfusion is the collection and later reinfusion of a patient’s own (auto-means self) blood or blood components.

bone marrow biopsy – A needle is introduced into the bone marrow cavity, and a small amount of marrow is aspirated and examined under a microscope. This procedure is helpful in the diagnosis of blood disorders such as anemia, cytopenias, and leukemia.

bone marrow transplant – Bone marrow cells from a donor whose tissue and blood cells closely match those of the recipient are infused into a patient with leukemia or aplastic anemia. First the patient is given total-body irradiation or aggressive chemotherapy to kill all diseased cells and much of the normal bone marrow. The donor’s marrow is then intravenously infused into the patient, and it repopulates the patient’s marrow space with normal cells. Problems encountered subsequently may be serious infection, graft versus host disease (immune reaction of the donor’s cells to the recipient’s), and relapse of the original disease (such as leukemia) despite the treatment.


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CARDIOLOGY SYSTEM

The heart and blood vessels and the terminology related to their anatomy, physiology, and disease conditions will be explored in this chapter. The nature of blood and another body fluid called lymph will be discussed in a later chapter.

Blood Vessels and the Circulation of Blood

Blood Vessels
There are three types of blood vessels in the body. These are arteries, veins, and capillaries.

Arteries are the large blood vessels that lead away from the heart. Their walls are made of connective tissue, muscle tissue, elastic fibers, and an innermost layer of epithelial cells called endothelium. Endothelial cells, which line all blood vessels, secrete substances that affect the size of blood vessels, reduce blood clotting, and promote the growth of blood vessels. Because arteries carry blood away from the heart, they must be strong enough to withstand the high pressure of the pumping action to the heart. Their elastic walls allow them to expand as the heartbeat forces blood into the arterial system throughout the body. Smaller branches of arteries are called arterioles. Arterioles are thinner than arteries and carry the blood to the tiniest of blood vessels, the capillaries.

Capillaries have walls that are one endothelial cell thick. These delicate, microscopic vessels carry nutrient-rich, oxygenated blood from the arteries and the arterioles to the body cells. There walls are thin enough to allow passage of oxygen and nutrients out of the blood stream and into the tissue fluid surround the cells. Once inside the cells, the nutrients are burned in the presence of oxygen (catabolism) to release needed energy within the cell. At the same time, waste products such as carbon dioxide and water pass out of the cells and into the thin-walled capillaries. The waste filled blood then flows back to the heart in small veins called venules, which branch to form larger vessels called veins.

Veins are thinner walled than arteries. They conduct blood (that has given most of its oxygen) toward the heart from the tissues. Veins have little elastic tissue and less connective tissue than arteries, and blood pressure in veins is extremely low compared with pressure in arteries. In order to keep blood moving back toward the heart, veins have valves that prevent the backflow of blood and keep the blood moving in one direction. Muscular action also helps the movement of blood in veins.

Circulation of Blood
Arteries, arterioles, veins, venules, and capillaries, together with the heart, form a circulatory system for the flow of blood.

Blood deficient in oxygen flows through two large veins, the venae cavae, on its way from the tissue capillaries to the heart. The blood became oxygen-poor at the tissue capillaries when oxygen left the blood and entered the body cells.

Oxygen-poor blood enters the right side of the heart and travels through that side and into the pulmonary artery, a vessel that divides in two, one branch leading to the left lung, the other to the right lung. The arteries continue dividing and subdividing with the lungs, forming smaller and smaller vessels (arterioles) and finally reaching the lung capillaries. The pulmonary artery is unusual in that it is the only artery in the body that carries blood deficient in oxygen.

While passing through the lung (pulmonary) capillaries, blood absorbs the oxygen that entered the body during inhalation. The newly oxygenated blood next returns immediately to the heart through pulmonary veins. The pulmonary veins are unusual in that are the only veins in the body that carry oxygen-rich (oxygenated) blood. The circulation of blood through the vessels from the heart to the lungs and then back to the heart again is known as the pulmonary circulation.

Oxygen-rich blood enters the left side of the heart from the pulmonary veins. The muscles in the left side of the heart pump the blood out of the heart through the largest single artery in the body, the aorta. The aorta moves up at first (ascending aorta) but then arches over dorsally and runs downward (descending aorta) just in front of the vertebral column. The aorta divides into numerous branches called arteries that carry the oxygenated blood to all parts of the body. The names of some of these arterial branches will be familiar to you: brachial (brachi/o means arm), axillary, splenic, gastric, and renal arteries. The carotid arteries supply blood to the head and neck.

The relatively large arterial vessels branch further to form smaller arterioles. The arterioles, still containing oxygenated blood, branch into smaller tissue capillaries, which are near the body cells. Oxygen leaves the blood and passes through the thin capillary walls to enter the body cells. There, food is broken down, in the presence of oxygen, and energy is released.

One metabolic product of this chemical process is carbon dioxide (CO2). Carbon dioxide is produced in the cell but is harmful to the cell if it remains. It must thus pass out of the cells and into the capillary bloodstream at the same time that oxygen is entering the cells. As the blood makes its way back from the tissue capillaries toward the heart in venules and veins it is full of carbon dioxide and is oxygen-poor.

The circuit is thus completed when oxygen-poor blood enters the heart from the venae cavae. This circulation of blood from the body organs (except the lungs) to the heart and back again is called the systemic circulation.

Anatomy of the Heart

The human heart weighs less than a pound, is roughly the size of an adult fist, and lies in the thoracic cavity, just behind the breastbone in the mediastinum (between the lungs).

The heart is a pump, consisting of four chambers; two upper chambers called atria (singular: atrium) and two lower chambers called ventricles. It is actually a double pump, bound into one organ and synchronized very carefully. Blood passes through each pump in a definite pattern. Pump station number one, one the right side of the heart, sends oxygen-deficient blood to the lungs, where the blood picks up oxygen and releases its carbon dioxide. The newly oxygenated blood returns to the left side of the heart to pump station number two and does not mix with the oxygen-poor blood in the pump station number one. Pump station number two then forces the oxygenated blood out to all parts of the body. At the body tissues, the blood loses its oxygen and on return to the heart, to pump station number one, blood poor in oxygen (rich in carbon dioxide) is sent out to the lungs to begin the cycle anew.

Oxygen-poor blood enters the heart through the two largest veins in the body, the venae cavae. The superior vena cava drains blood from the upper part of the body, and the inferior vena cava carries blood from the lower part of the body.

The venae cavae bring oxygen-poor blood that has passed through all of the body to the right atrium, the thin walled upper right chamber of the heart. The right atrium contracts to force blood through the tricuspid valve (cusps are the flaps of the valves) into the right ventricle, which is the lower right chamber of the heart. The cusps on the tricuspid valve form a one-way passage designed to keep the blood flowing in only one direction. As the right ventricle contracts to pump oxygen-poor blood through the pulmonary valve into the pulmonary artery, the tricuspid valve stays shut, thus preventing blood from pushing back into the right atrium. The pulmonary artery then branches to carry oxygen-deficient blood to each lung.

The blood that enters the lung capillaries from the pulmonary artery soon loses its large quantity of carbon dioxide into the lung tissue, and the carbon dioxide is expelled. At the same time, oxygen enters the capillaries of the lungs and is brought back to the heart via the pulmonary veins. The newly oxygenate blood enters the left atrium of the heart from the pulmonary veins. The walls of the left atrium contract to force blood through the mitral valve into the left ventricle.

The left ventricle has the thickest walls of all four heart chambers (three times the thickness of the right ventricle). It must pump blood with great force so that the blood travels through arteries to all parts of the body. The blood is pumped out of the left ventricle through the aortic valve and into the aorta, which branches to carry blood all over the body. The aortic valve prevents the return of aortic blood to the left ventricle once it has been pumped out.

The four chambers of the heart are separated by partitions called septa (singular: septum). The interatrial septum separates the two upper chambers (atria), and the interventricular septum is a muscular wall that comes between the two lower chambers (ventricles).

The heart wall is composed of three layers. The endocardium is a smooth layer of endothelial cells that lines the interior of the heart and heart valve. The myocardium is the middle, muscular layer of the heart and its thickest layer. The pericardium is a fibrous and membranous sac surrounding the heart. It is composed of two layers, the visceral pericardium, which adheres to the heart and the parietal (parietal means wall) pericardium, which lines the outer fibrous coat. The pericardial cavity (Between the visceral and the parietal pericardia normally contains 10 – 15 ml of fluid, which lubricates the membranes as the heart beats.

Physiology of the Heart

Heartbeat and Heart Sounds
There are two phases of the heartbeat. These phases are called diastole (relaxation) and systole (contraction). Diastole occurs when the ventricle walls relax and blood flows into the heart from the venae cavae and the pulmonary veins. The tricuspid and mitral valves are open in the diastole, as blood passes from the right and left atria into the ventricles. The pulmonary and aortic valves are closed during diastole.

Systole occurs next, as the walls of the right and left ventricle contract to pump blood into the pulmonary artery and the aorta. Both the tricuspid and the mitral valves are closed during systole, thus preventing the flow of blood back into the atria.

This diastole-systole cardiac cycle occurs between 70 and 80 times per minute (100,000 times a day). The heart pumps about 3 ounces of blood with each contraction. This means that about 5 quarts of blood are pumped by the heart in 1 minute (75 gallons an hour and about 2000 gallons a day).

Closure of the heart valves is associated with audible sounds such as “lub, dub, lub, dub,” that can be heard when listening to a normal heart with a stethoscope. The “lub” is associated with closure of the tricuspid and mitral valves at the beginning of the systole and the “dub” with the closure of the aortic and pulmonary valves at the end of systole. The “lub” sound is called the first heart sound and the “dub” is the second heart sound because the normal cycle of the heartbeat starts with the beginning of the systole. An abnormal heart sound is known as a murmur.

Conduction System of the Heart

What keeps the heart at its perfect rhythm? Although the heart does have nerves that can affect its rate, they are not primarily responsible for its beat. It is known that the heart starts beating in the embryo before the heart is supplied with nerves and will continue to be in experimental animals even when nerve supply is cut.

Primary responsibility for initiating the heartbeat rests with a small region of specialized muscle tissue in the posterior portion of the right atrium, where an electrical impulse originates. This region of the right atrium is called the sinoatrial node (SA node). The SA node is called the pacemaker of the heart. The current of electricity generated by the pacemaker causes the walls of the atria to contract and force blood into the ventricle (ending diastole).

Almost like ripples in a pond of water when a stone is thrown, the wave of electricity passes from the pacemaker to another region of the myocardium. This region is at the posterior portion of the interatrial septum and is called the atrioventricular node (AV node). The AV node immediately sends the excitation wave to a bundle of specialized muscle fibers called the atrioventricular bundle or bundle of His (pronounced hiss). Within the interventricular septum, the bundle of His divides into the right and left bundle branches, which form the conduction myofibers that extend through the ventricle walls and stimulate them to contract. Thus, systole occurs and blood is pumped away from the heart. A short rest period follows, and then the pacemaker begins the wave of excitation across the heart again.

The record used to detect these electrical changes in heart muscle at the heartbeats is called an electrocardiogram (ECG or EKG, from the Greek root kardia). The normal ECG shows five waves, or deflections, the represent the electrical changes as a wave of excitation spreads through the heart. The deflections are called P, QRS and T waves. The P wave represents electrical activity in the wall of the atria (atrial depolarization). The QRS wave represents ventricular depolarization as electricity passes through the atrioventricular bundle and the ventricular wall. This is the largest wave because the ventricle contains the most muscle. The T wave represents ventricular repolarization, which is when the ventricular wall relaxes and recovers from contraction. The ECG is used to diagnose a heart attack (myocardial infarction, which causes abnormal deflections.

Normal heart rhythm (originating in the SA node and traveling through the heart) is called sinus rhythm. Sympathetic nerves speed up the heart rate during conditions of emotional stress or vigorous exercise. Parasympathetic nerves slow the heart rate when the need for extra pumping is past.

Blood Pressure
Blood pressure is the force that the blood exerts on the arterial walls. This pressure is measured by a device called a sphygmomanometer.

The sphygmomanometer consists of a rubber bag inside a cloth cuff that is wrapped around the upper arm, just above the elbow. The rubber bag is inflated with air by means of a rubber bulb. As the bag is pumped up, the pressure within it increased and is measured on a recording device attached to the cuff.

The vessels in the upper arm are compressed by the air pressure in the bag. When there is sufficient air pressure in the bag to stop the flow of blood in the artery of the arm (brachial artery), the pulse in the lower arm where the observer is listening with a stethoscope) obviously drops.

Air is then allowed to escape from the bag and the pressure is lowered slowly, allowing the blood to being to make its way through the gradually opening artery. At the point where the person listening with the stethoscope first hears the sounds of the pulse beats, the reading on the device attached to the cuff shows the higher, systolic, blood pressure (pressure in the artery when the ventricle is contracting to force the blood into the aorta and other arteries).

As air continues to escape, the sounds become progressiv3e louder. Finally, when a change in sounds from loud to soft occur, the observer makes note of the pressure on the recording device. This is called the diastolic blood pressure (pressure in the artery when the ventricles are relaxing and the heart is filling, receiving blood from the venae cavae and pulmonary veins).

Blood pressure is usually expressed as a fraction: for example, 120/80, in which the 120 represents the systolic pressure and 80 the diastolic pressure.

Pathological Conditions: The Heart and Blood Vessels

Heart
arrhythmias – Abnormal heart rhythms (dysrhythmias). Examples of cardiac arrhythmias:
1. Heart block (atrioventricular block) – Failure of proper conduction of impulses through the AV node to the atrioventricular bundle (bundle of His). Damage to the SA node may cause its impulses to be too weak to activate the AV node and impulses fail to reach the ventricles. If the failure occurs only occasionally, the heart will miss a beat in a rhythm at regular intervals (partial heart block). If no impulses reach the AV node from the SA node, the ventricles contract slower than the atria and are not coordinated. This is complete heart block. Implantation of a cardiac pacemaker can overcome heart block and establish a normal rhythm.

2. Flutter – Rapid but regular contractions of atria or ventricles. This condition can occur in patients with heart disease. The heart rhythm may reach up to 300 beats per minute.

3. Fibrillation – Rapid, random, ineffectual, and irregular contractions of the heart (350 beats or more per minute). In atrial fibrillation, the wave of excitation passes through the atrial myocardium even more quickly than in atrial flutter. In order to restore normal heart rhythm, an electrical device called a defibrillator is applied to the chest wall; this electric shock stops the heart and reverses its abnormal rhythm. This is also called cardioversion. Drugs, such as digoxin may also be used to convert fibrillation into regular rhythm.

A device called an automatic implantable cardioverter/defibrillator (AICD) can now be implanted in the chest to sense arrhythmias and correct them. These are pacemaker-sized devices that give shocks to change abnormal rhythms, such as ventricular fibrillation.

Radiofrequency catheter ablation (RFA) is a nonsurgical treatment used to treat arrhythmias, such as paroxysmal (sharp, sudden spasm) tachycardia. A catheter, placed in blood vessels leading up against the heart muscle, delivers a high-frequency current to burn a small portion of the muscle. This injury (ablation) to the muscle destroys the arrhythmias.

Cardiac arrest is the sudden and often unexpected stoppage of heart movement, caused by heart block or ventricular fibrillation (resulting from underlying heart disease).

Palpitations are uncomfortable sensations in the chest associated with different types of arrhythmias. Palpitations do not necessary indicate serious heart disease (smoking, caffeine, and drugs such as antidepressants can produce palpitations). Two cardiac causes of palpitations are premature ventricular contractions (PVCs) and premature atrial contractions (PACs).

Congenital heart disease – Abnormalities in the heart at birth. The following are congenital anomalies resulting from failure in the development of the fetal heart.

1. Coarctation of the aorta (CoA) – Narrowing (coarctation) of the aorta. Surgical treatment consists of removal of the constricted region and end-to-end anastomosis of the aortic segments.

2. Patent ductus arteriosus (PDA) – A small duct (ductus arteriosus between the aorta and the pulmonary artery, which normally close soon after birth, remains open (patent). This condition means that the oxygenated blood flow from the aorta to the pulmonary artery. The anomaly occurs most often in females and is commonly associated with intrauterine rubella (German measles) infection, prematurity, and infantile respiratory distress syndrome. Treatment is surgery to close the ductus arteriosus open.

3. Septal defects – Small holes in the septa between the atria (atrial septal defects [ASDs]) or the ventricle (ventricular septal defects [VSDs]). Although many septal defects will close spontaneously, others will require surgery. Septal defects can be closed while maintaining a general circulation by means of a heart-lung machine. This machine is connected to the patient’s circulatory system and relieve the heart and lungs of pumping and oxygenation functions during heart surgery.

Two recent procedures as alternatives to traditional surgery are transcatheter closure (a “clamshell” device is threaded through the blood via a catheter into the heart and into the septal defect, where it is fixed in place to block the hole) and minimally invasive heart surgery (through 3 or 4 small puncture holes in the chest; special instruments are used to repair the defect).

4. Tetralogy of Fallot – A congenital malformation of the heart involving four (tetra) distinct defects. The condition, named for Etienne Fallot, the French physician who described it in 1888. The four defects are:
A. Pulmonary artery stenosis. This means that blood is not adequately passed to the lungs for oxygenation.
B. Ventricular septal defect. The gap in the septum allows deoxygenated blood to pass into the left ventricle, and from there to the aorta.
C. Shift of the aorta to the right, so that the aorta overrides the interventricular septum. Oxygen-poor blood passes even more easily from the right ventricle to the aorta.
D. Hypertrophy of the right ventricle. The myocardium has to work harder to pump blood through a narrowed pulmonary artery.

An infant with this condition is described as a “blue baby” because of the extreme degree of cyanosis present at birth (other congenital conditions that involve a shunt of blood from the right to the left without passing through the lungs and receiving proper oxygenation can lead to cyanosis as well). Surgery is required to repair the various heart defects.

Congestive heart failure – The heart is unable to pump its required amount of blood (more blood enters the heart from the veins than leaves through the arteries). Blood accumulates in the lungs (left-sided heart failure) causing pulmonary edema (fluid seeps out of capillaries into the tiny air sacs of the lung). Damming back of blood resulting form right-sided heart failure results in accumulation of fluid in the abdominal organs (liver and spleen) and subcutaneous tissue of the legs. Congestive heart failure often develops gradually over several years, although it can be acute. Therapy includes lowering dietary intake of sodium and diuretics to promote loss of fluids.

Recent studies have shown that drugs known as angiotensin-converting enzyme (ACE) inhibitors can improve the performance of the heart and its pumping activity. These drugs also decrease pressure inside blood vessels and are used to treat hypertension (high blood pressure). If drug therapy and lifestyle changes fail to control congestive heart failure, heart transplantation may be the only treatment option. While waiting for a transplant, patients may need a device to assist the heart’s pumping. A left ventricular assist device (LVAD) is a booster pump implanted in the abdomen, with a cannula (tube) inserted into the left ventricle. It pumps blood out of the heart to all parts of the body. The LVAD is sometimes called a “bridge to transplant.”

Coronary artery disease (CAD) – Disease of the arteries surrounding the heart. The coronary arteries are three large vessels that arise from the aorta and supply oxygenated blood to the heart. It is interesting that the blood that constantly flows through the four hollow chambers of the heart does not itself nourish the myocardial tissue. Instead, after blood leaves the heart via the aorta, a portion is at once lead back over the surface of the heart through the coronary arteries, so that the heart muscle receives blood before any other organ. This seems logical because the energy requirements of the heart are greater than those of any other organ.

Coronary artery disease is usually the result of atherosclerosis. This is the deposition of fatty compounds on the inner lining of the coronary arteries (any other artery can be similarly affected). The ordinary smooth lining of the artery becomes roughened as the atherosclerotic plaque collects in the artery.

Atherosclerosis is dangerous for two important reasons. First, narrowing of the vessel due to atherosclerosis can cause inflexibility and plugging up of the vessel. Second, the roughened lining of the artery may rupture or cause abnormal clotting of blood, leading to a thrombotic occlusion (blocking of the coronary artery by a clot). In both cases, blood flow is decreased (ischemia) or stopped entirely, leading to death (necrosis) of a part of the myocardium. The area of dead myocardial tissue is known as an infarction. The infarcted area is eventually replaced by scar tissue.
The severity of a myocardial infarction (also known as a heart attack) depends on the size of the artery that is blocked and the extent of the blockage. If the blocked artery is small, the result may be death of only a small portion of the heart immediately fed by the artery. After scar tissue forms, the patient may be able to resume completely normal activity.

Angina pectoris is an episode of chest pain, often called precordial pain (precordial means in front of the chest), resulting from a temporary difference between the supply and the demand of oxygen to the heart muscle. Angina can be the result of low oxygen levels in the blood from smoking or respiratory disease), restricted blood flow to the heart (coronary artery disease), or an increase in the work of the heart beyond normal levels. For acute attacks of angina, nitroglycerine is given sublingually. This drug, one of several called nitrates, is a powerful vasodilator and muscle relaxant.

Treatment guidelines for CAD begin with controlling risk factors, such as smoking, obesity, and lack of exercise. Daily aspirin therapy (to prevent formation of clots) and drug therapy to lower cholesterol (HMGs or “statins” reduce the production of cholesterol in the liver) are also important to prevent heart disease. After the occurrence of an MI, patients may require maintenance and anti-ischemic therapy with drugs called beta-blockers, which reduce the force and speed of the heartbeat and lower blood pressure. Other drugs, such as nitrates and calcium channel blockers, cause dilatation of blood vessels, making it easier for the heart to pump blood through vessels.

Surgical treatment of CAD is an open-heart operation called coronary artery bypass grafting or CABG. Experimental keyhole (scopic) bypass grafting is being done on a very limited basis with limitations of a maximum of 3-vessel grafting being done. Cardiologist perform percutaneous transluminal coronary
angioplasty (PTCA), in which catheterizations with balloons and stents opens clogged coronary arteries.

An innovation method of treatment is transmyocardial laser revascularization (TMLR). A laser makes holes in the heart muscle to induce angiogenesis (growth of new blood vessels). Gene therapy (giving DNA or viruses containing DNA to promote expression of factors that lead to angiogenesis) is another new technique to restore damaged heart muscle.

Endocarditis – Inflammation of the inner lining of the heart caused by bacteria (bacterial endocarditis). This condition may be a complication of another infectious disease, an operation, or an injury. Damage to the heart valves produces lesions called vegetations (they resemble cauliflower) that break off into the bloodstream as emboli (material that travels through the blood). When the emboli lodge in the small vessels of the skin, multiple pinpoint hemorrhages known as petechiae (from the Italian petechio, meaning a fleabite) form. Antibiotics are effective in curing bacterial endocarditis.

Hypertensive heart disease – High blood pressure affecting the heart. This condition is caused by the contraction of arterioles leading to increased pressure in arteries. The heart itself is affected because it has to pump more vigorously to overcome the increased resistance in the arteries. Vessels lose their elasticity, become like solid pipes, and place increased burden on the heart to pump blood through the body.

Mitral valve prolapse (MVP) – Improper closure of mitral valve when the heart is pumping blood. This condition, found most frequently in otherwise healthy young women occurs because the mitral valve enlarges and prolapses into the left atrium during systole. The physician hears a midsystolic click on auscultation (listening with a stethoscope). Most people with MVP live normal lives, but because prolapsed valves can on rare occasions become infected, persons with MVP are advised to have preventive antibiotics at the time of dental procedures if the murmur is present.

Murmur – An extra heart sound, heard between normal beats. Murmurs are heard with the aid of a stethoscope and are usually caused by a valvular defect or disease that disrupts the smooth flow of blood in the heart. They are also heard in cases of interseptal defects when blood flows abnormally between chambers through holes in the septa. A functional murmur is one that is not caused by a valve or septal defect and is not a serious danger to the patient’s health. A bruit is an abnormal sound or murmur heard on auscultation. A thrill, which is a vibration felt on palpation of the chest often accompanies a murmur.

Pericarditis – Inflammation of the membranes (pericardium) surrounding the heart. In most instances, pericarditis is secondary to disease elsewhere in the body (such as pulmonary infection). Bacteria and viruses cause the condition, or the etiology may be idiopathic. Malaise, fever and chest pain occur, as well as accumulation of fluid within the pericardial cavity. Compression of the heart due to collection of fluid is called cardiac tamponade. If a considerable amount of fluid is present, pressure on the pulmonary veins may slow the return of blood from the lungs. Excess fluid is drained by pericardiocentesis.

Rheumatic heart disease – Heart disease caused by rheumatic fever. Rheumatic fever is a disease, usually occurring in childhood that can follow a few weeks after a streptococcal infection. Damage is done to the heart, particularly the heart valves, by one or more attacks of rheumatic fever. The valves, especially the mitral valve, become inflamed and scarred (with vegetations, so that they do not open and close normally. Mitral stenosis, atrial fibrillation, and congestive heart failure, due to weakening of the myocardium, are other aspects of rheumatic heart disease. Treatment consists of reduced activity, drugs to control arrhythmias, surgery to repair a damaged valve, and anticoagulant therapy to prevent emboli from forming. Mechanical or porcine (pig) valve implants are also used to replace deteriorated heart valves.

Blood vessels

Aneurysm – Local widening (ballooning out of a small area) of an artery caused by weakness in the arterial wall or breakdown of the wall owing to atherosclerosis. Aneurysm literally means to widen (eurysm) up (ana-). It may occur anywhere in the body but most commonly in the aorta. The danger of an aneurysm is that as the wall of the artery pushes outward it becomes progressively thinner and may eventually rupture. Treatment of an aneurysm depends on the particular vessel involved, the site, and the health of the patient. In aneurysms of small vessels in the brain (berry aneurysm), treatment is occlusion of the vessel with small clips. For larger arteries, such as the aorta, the aneurysm is resected and a synthetic graft is sewn within the aneurysm.

Hypertension – high blood pressure. Most high blood pressure is essential hypertension, in which the cause of the increased pressure is idiopathic. In adults, a blood pressure equal to or greater than 140/90 mmHg is considered high. Diuretics, beta-blockers, ACE inhibitors and calcium channel blockers are used as treatment for essential hypertension. Losing weight, limiting sodium (salt) intake, stopping smoking, and reducing fat in the diet are also important in therapy.

In secondary hypertension, there is always some associated lesion, such as glomerulonephritis, pyelonephritis or disease of the adrenal glands, that is responsible for the elevated blood pressure.

Peripheral vascular disease – Blockage of blood vessels (arteries) in the lower extremities due to atherosclerosis. When arteries in the groin or upper leg narrow or become blocked, blood flow to the lower leg and foot is reduced. Often, the femoral (thigh) artery or the popliteal (back of the knee) artery is involved. An early sign of the problem is intermittent claudication (absence of pain or discomfort in the leg at rest, but pain, tension, and weakness after walking has begun). Treatment is exercise, avoidance of nicotine, which causes vessel constriction, and control of risk factors such as hypertension, hyperlipidemia and diabetes. Surgical treatment includes endarterectomy and bypass grafting (from the normal proximal vessel around the diseased area to a normal vessel distally.

Raynaud phenomenon – Short episodes of pallor and numbness in the fingers and toes due to temporary constriction of the arterioles in the skin. This condition is usually idiopathic, but it may also be secondary to some other, more serious disorder. The episodes can be triggered by cold temperatures, emotional stress, or cigarette smoking. Protecting the body from cold and use of vasodilators are effective treatment.

Varicose veins – Abnormally swollen and twisted veins, usually occurring in the legs. This condition is due to damaged valves that fail to prevent the backflow of blood. The blood then collects in the veins, which distends to many times their normal size. Because of the slow flow of blood in the varicose veins and frequent injury to the vein, thrombosis may occur as well. Hemorrhoids (piles) are varicose veins near the anus. Surgical treatment of hemorrhoids includes injection of the sclerosing solutions, ligation with rubber bands, and cryosurgery.
Treatment of varicose veins includes wearing elastic stockings, elevation of the legs if edema occurs, and surgery to ligate (tie off) and strip (remove) the twisted, swollen veins. The surgical procedure is called vein stripping.

Laboratory Tests and Clinical Procedures

Laboratory Tests

Lipid tests – Lipids are fatty substances found in foods and in the body. Examples of lipids are cholesterol and triglycerides. Lipid tests measure the amounts of these substances in a blood sample. High levels of triglycerides and cholesterol in the blood are associated with a greater risk of atherosclerosis. A cholesterol level below 200 mg/dL in a middle-aged adult is associated with a relatively low risk for coronary artery disease (CAD). A diet high in saturated fat (solid fats of animal origin such as milk, butter, and meats) tends to increase the amount of cholesterol in the blood. Polyunsaturated fats (such as corn oil and safflower oil) do not raise blood cholesterol.

The mainstay of treatment for people with hyperlipidemia is proper diet (low fat and high fiber intake with fresh fruits and vegetables) and exercise. Niacin (a vitamin) is also helpful in reducing lipids. Drug therapy includes HMG reductase inhibitors (HMGs), which lower cholesterol by reducing its production in the liver. These are known as “statins” and examples are simvastatin, lovastatin, and pravastatin.

Lipoprotein electrophoresis – Lipoproteins are proteins that carry lipids (fats) n the bloodstream. Protein electrophoresis is the process of physically separating lipoproteins from a blood sample. High levels of low-density lipoproteins (LDL and very-low-density lipoproteins (VLDL) are associated with atherosclerosis. High levels of high-density lipoproteins (HDL), which remove cholesterol and transport it to the liver, protect adults from the development of atherosclerosis. Factors that increase HDL are estrogen, exercise and alcohol in moderation.

Serum enzyme tests – During a myocardial infarction, enzymes are released into the bloodstream from the dying heart muscle. These enzymes can be measured and are useful as evidence of an infarction. The enzymes tested for are creatine phosphokinase (CPK or CK) and lactate dehydrogenase (LDH). Other blood testes measure levels of muscle proteins, myoglobin and troponin.

Clinical Procedures

X-rays
Angiography – Dye is injected into the blood stream or heart chamber, and x-ray films are taken of the heart and large blood vessels in the chest. If dye is injected into the aorta or an artery in the groin, the procedure is called arteriography.

Digital subtraction angiography (DSA) – Video equipment and a computer are used to produce x-ray pictures of blood vessels. First, an x-ray is produced of the area to be studied, and the results are stored in a computer. Next, contrast material is injected into a vein, and a second image is produced that is also recorded in the computer. The computer then compares the two images and subtracts the first image from the second (removing parts not being studied such as bone, muscle, and fat), leaving nothing but an image of the contrast medium and vessels.

Ultrasound Tests
Doppler ultrasound – An instrument is used to focus sound waves on a blood vessel; blood flow is measured as echoes bounce off red blood cells. Velocity of blood flow increases in areas of stenosis. Arteries or veins in the arms, neck or legs are examined to detect vascular occlusion (blockage due to clots or atherosclerosis).

Echocardiography (ECHO) – Pulses of high-frequency sound waves (ultrasound) are transmitted into the chest, and echoes returning from the valves, chambers, and surfaces of the heart are electronically plotted and recorded.

Nuclear Cardiology
Positron emission tomography (PET) scan – An IV radiopharmaceutical is administered, followed by an injection of glucose. These localize in the myocardium. Uptake is proportional to the glucose metabolic activity of myocardial cells. Images showing the blood flow and functional activity of the myocardium are obtained. Indications for PET scanner use include detection of CAD, assessment of myocardial viability, and differentiation of ischemia and cardiomyopathy.

Thallium 201 scintigraphy – Thallium 201 is a radioactive isotope that is taken up by myocardial tissue. After intravenous injection, the concentration of thallium 201 is measured (by perfusion scanning). Infarcted or scarred myocardium does not extract any isotope, showing up as “cold spots.” Thallium 201 imaging can be performed before or after an exercise ECG study or as a resting study only.

Technetium 99m ventriculography (multiple-gated acquisition scan, or MUGA scan) – This radioactive test studies the motion of the left ventricular wall and measures the ventricle’s ability to eject blood. It is a test of the functioning of the heart and cardiac output.

Magnetic Resonance Imaging (MRI)
Cardiac MRI – Magnetic waves are beamed at the heart, and an image is produced. The procedure is used to obtain detailed information about congenital heart disease, cardiac masses, and lesions of large blood vessels prior to surgery.

Other Procedures

Cardiac catheterization – A thin, flexible tube (catheter) is introduced into a vein or artery and is guided into the heart for purposes of detecting pressures and patterns of blood flow. Contrast can also be injected and x-ray films made (angiography).

Cardioversion (defibrillation) – Very brief discharges of electricity are applied across the chest to stop a cardiac arrhythmia and to allow a more normal rhythm to begin.

Coronary bypass surgery (CABG) – Vessel grafts, consisting of veins taken from other parts of the body, are anastomosed (connected) to existing coronary arteries to detour around blockages in the coronary arteries and keep the myocardium supplied with oxygenated blood. Minimally invasive CABG surgery is performed with smaller incisions instead of traditional sternotomy to open the chest.

Electrocardiography (ECG, EKG) – Process of recording the electricity flowing through the heart and thus the rhythm of the heartbeat. A normal sinus rhythm begins in the SA nodes and is between 60 and 100 beats per minute, with normal intervals and no ectopic beats.

Endarterectomy – This procedure involves surgical removal of the innermost (end-) lining of an artery when it is thickened by fatty deposits (atheromas) and thromboses.

Extracorporeal circulation (ECC) – A heart-lung machine (pump oxygenator) is used as a bypass to divert blood from the heart and lungs while the heart is being repaired. Blood leaves the body, enters the heart-lung machine, where it is oxygenated, and then returns to a blood vessel (artery) to circulate through the bloodstream. Extracorporeal means outside (extra-) the body (corpor/o).

Holter monitoring – A compact version (about the size of a portable tape player) of an electrocardiograph (instrument to measure the electricity flowing through the heart) is worn during a 24-hour period to detect cardiac arrhythmias.

Percutaneous transluminal coronary angioplasty (PTCA) – In this procedure, also called balloon angioplasty, a balloon-tipped catheter is inserted via the femoral (thigh) artery and threaded up the aorta into a coronary artery. The balloon is inflated, compressing fatty deposits or plaque against the side of the artery and opening the artery to allow for passage of blood. Balloon valvuloplasty is used to open narrowed cardiac valves and is seen as a possible alternative to surgery for valvular stenosis. Stents (expandable slotted tubes are now used instead of PTCA to create wider lumens and make restenosis less likely.


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Dermatology

STRUCTURE AND FUNCTION

Purpose of the skin
The skin covers the entire body and provides protection against injuries and infection and aids in the regulation of body temperature and prevents dehydration. It contains nerve endings that constitute the four sensory senses, touch pressure, cold, warmth, and pain. It communicates with the external openings of the digestive, respiratory, and urogenital systems through the mucous membranes. The skin is composed of five layers (strata) called stratified squamous epithelium. The top most layer is the epidermis. It consists of three sub layers known as Stratum corneum, Stratum lucidum and Stratum germinativum. The second layer is the dermis and the third layer is the subcutaneous.

The three combining forms for skin are derm/o, dermat/o, and cutane/o.

The epithelium consists of several layers of keratin-containing cells in which the surface cells are flattened and scale-like and the deeper cells are polyhedral in form. Keratin filaments become progressively more abundant toward the surface, which on the dry surfaces of the body may consist of a layer of dead corneocytes.

THE EPIDERMIS
The stratum corneum, the outermost layer of the epidermis is composed of dead cells filled with a hard protein material called keratin. This keratin prevents the evaporation of body water and also prevents the entry of water. The stratum corneum also acts as a barrier to pathogens and chemicals because most of the microorganisms and chemicals cannot penetrate the unbroken skin.

The stratum lucidum, a layer of lightly staining corneocytes in the deepest level of the stratum corneum; found primarily in the thick epidermis of the palmar and plantar skin.

The stratum germinativum is the inner epidermal layer where cells are being continuously produced. Every three to four weeks the dead cells are pushed to the surface (stratum corneum) and are replaced with new cells. Keratinocytes and melanocytes are two important types of cells produced in this layer. Keratinocytes are the cells that produce the hard protein substance called keratin. Melanocytes produce the pigment called melanin, which gives the color to skin.

Keratin is an insoluble, fibrous protein in the horny layer of the epidermis and helps to protect the body, by producing extra thickness. The thickness varies in different parts of the body and is the most in the palms and feet, resulting in callus formation with use.

Melanin is a pigment produced by the melanocytes. The more melanin present, the darker the color of skin and hair and lesser the melanin, the lighter the color of skin and hair. Melanin absorbs the ultraviolet rays of the sun protecting our skin from damage. At the same time, the ultraviolet rays react with the chemicals within the skin to convert them into vitamin D, a necessary nutrient, and is absorbed through the skin.


THE DERMIS OR CORIUM
It is the layer immediately under the epidermis and is composed of living tissues, that consist of numerous capillaries, collagen, elastic fibers, lymphatics, and nerve endings. The sweat (sudoriferous) glands, oil (sebaceous) glands, and hair roots are also located in the dermis.

The sudoriferous glands are small structures that open as pores on the surface of the skin, and are of two types. They are known as Eccrine and Apocrine.

Eccrine: is found all over the body and has ducts. A tubular structure giving exit to the secretion of a gland, or conducting any fluid that open directly onto the surface of the skin and secrete a watery fluid in response to warm temperature and helps to cool the body through evaporation.

Apocrine: becomes active at puberty and secretes a “milky” sweat that is broken down by bacteria that causes odor. Specialized apocrine glands produce cerumen (wax), found in the ear.

The sebaceous (oil) glands: produce an oily secretion that lubricates the skin and hair. The ducts of the oil glands open into the hair follicles or directly to the surface of the skin. They secrete a liquid substance called sebum, otherwise known as oil. Their function is to prevent drying of the skin and the cracking of the hair, which could be a potential entryway for bacterial invasion.


THE SUBCUTANEOUS LAYER OR HYPODERMIS
It is the connective tissue layer underlying the dermis and is composed of adipose (fat) tissue and connects the skin to underlying organs like the muscles and bones. It regulates the temperature of the body.


OTHER APPENDAGES OF THE SKIN
Hair appears all over the body except on the palms and soles and is composed of keratin. In the dermis, there are cavities known as hair follicles and hair grows from a root within these follicles. This root is known as hair root. The part of the hair that is seen above the skin is known as hair shaft. Hair grows in two phases: a growing phase known as anagen and a resting phase known as telogen.

Nails protect the fingertips and are composed of hardened keratin. The thin fold of skin at the base of the nail is known as the cuticle and the nail grows from a root within this cuticle.

TERMS

adipose: fat

albinism: deficiency or absence of pigment in the skin, hair, and eyes, or eyes only, due to an abnormality in production of melanin.

causalgia: persistent severe burning sensation

subcutaneous: beneath the skin.

diaphoresis: excessive sweating

erythema: redness of the skin due to capillary dilatation

anhidrosis: inability to tolerate heat; absence of sweat glands

ichthyosis: congenital disorders of keratinization characterized by noninflammatory dryness and scaling of the skin

keratosis: any lesion on the epidermis marked by the presence of circumscribed overgrowths of the horny layer

leukoplakia: a white patch of oral mucous membrane

lipoma: a benign neoplasm of adipose tissue, comprised of mature fat cells.

melanoma: a malignant neoplasm, derived from cells that are capable of forming melanin.

dermatomycosis: fungus infection of the skin caused by dermatophytes, yeasts, and other fungi.

onycholysis: loosening of the nails, beginning at the free border, and usually incomplete.

dermatophytosis: an infection of the hair, skin, or nails caused by any one of the dermatophytes.

pilosebaceous: relating to the hair follicles and sebaceous glands.

seborrhea: over activity of the sebaceous glands, resulting in an excessive amount of sebum.

squamous: relating to or covered with scales.

steatoma: benign tumor of fat tissue.

trichopathy: any disease of the hair.

subungual: below the nail.

xanthoma: a yellow nodule or plaque, especially of the skin, composed of lipid-laden histiocytes.

xeroderma: dry skin.


DISEASES AND CONDITIONS

cyst: a thick walled, closed sac, or pouch containing fluid or semisolid material

fissure: a groove or crack-like sore

macule: a discolored flat lesion

papule: small less than 1-cm diameter solid elevation of the skin.

polyp: mushroom-like growth extending on a stalk from the surface of the mucous membrane.

pustule: small elevation of the skin containing pus.

ulcer: open sore or erosion of the skin or mucous membrane.

vesicle: small collection of clear fluid.

wheal: smooth slightly elevated edematous area that is redder or paler than the surrounding skin.


SYMPTOMS:

alopecia: absence of hair from areas where it normally grows.

ecchymosis: bluish-black mark on the skin.

petechiae: small pinpoint hemorrhage.

pruritus: itching.

urticaria: acute allergic reaction in which red round wheals develop on the skin.

purpura: merging ecchymosis and petechiae over any part of the body.

vitiligo: loss of pigment in areas of the skin.


ABNORMAL CONDITIONS:

acne: papular and pustular eruption of the skin.

burns: injury to tissues caused by heat contact.

eczema: inflammatory skin disease with erythematous, papulovesicular lesions.

gangrene: death of tissue associated with loss of blood supply.

impetigo: bacterial inflammatory skin disease.

psoriasis: chronic recurrent dermatosis marked by itchy, scaly, red patches covered by silvery-gray scales.

scabies: a contagious parasitic infection of the skin with intense pruritus.

scleroderma: chronic progressive disease of the skin with hardening and shrinking of connective tissue.

tinea: ringworm infecting the skin.


SKIN NEOPLASM

callus: increased growth of cells in the horny layer of epidermis due to pressure or friction.

keloid: hypertrophied, thickened scar after trauma or surgical incision.

keratosis: thickened area of the epidermis.

leukoplakia: white thickened patches on mucous membrane tissues of the tongue or cheek.

nevus: pigmented lesion of the skin.

wart: epidermal growth caused by a virus.



CANCEROUS LESIONS:
basal cell carcinoma: malignant tumor of the basal cell layer of the epidermis

Kaposi sarcoma: malignant, vascular, neoplastic growth characterized by cutaneous nodules on the lower extremities.

malignant melanoma: cancerous growth composed of melanocytes.

squamous cell carcinoma: malignant tumor of the squamous epithelial cells of the epidermis.


LABORATORY TESTS AND SURGICAL PROCEDURES

bacterial analysis: samples of purulent material or exudates are sent to the laboratory for examination to determine what type of bacteria are present

fungal tests: scrapings from skin lesions are placed on a growth medium for several weeks and then examined microscopically for evidence of fungal growth.


CLINICAL PROCEDUERS

cryosurgery: tissue is destroyed by the application of intensely cold liquid nitrogen.

Mohs’ surgery: thin layers of a malignant growth are removed and each is examined under the microscope.


allergy skin testing: tests used to determine which allergens (substance causing allergy) are responsible for causing an allergic reaction.

scratch test: it is a form of skin test in which antigen is applied through a scratch in the skin.

patch tests : a test of skin sensitiveness: a small piece of paper, tape, or a cup, wet with a non-irritating diluted test fluid, is applied to skin of the upper back or upper outer arm and after 48 hours the area previously covered is compared with the uncovered surface; an erythematous reaction with vesicles occurs if the substance causes contact allergy.

intradermal tests: injection of an antigen into the skin for allergy testing.

biopsies: Obtaining a tissue sample for microscopic evaluation to establish diagnosis.
1. excisional: complete removal of skin lesion.
2. incisional: partial removal by cutting.
3. punch: partial removal by means of a special surgical instrument.


ABBREVIATIONS

AE acrodermatitis enteropathica
bx biopsy
DLE discoid lupus erythematosus
PPD purified protein derivative
subq subcutaneous

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Digestive System


I Introduction

The digestive system, also called the alimentary canal or gastrointestinal tract, begins with the mouth, where food enters the body, and ends with the anus, where solid waste material leaves the body. The primary functions of the organs of the digestive systems are threefold.

First, complex food material taken into the mouth must be digested, or broken down, mechanically and chemically, as it travels through the gastrointestinal tract (passageway). Digestive enzymes speed up chemical reactions and help in the breakdown (digestion) of complex nutrients. Complex proteins are digested to simpler amino acids; complicated sugars are reduced to simple sugars, such as glucose; and large fat molecules (triglycerides) are broken down to fatty acids and glycerol.

Second, the digested food must be absorbed into the blood stream by passing through the walls of the small intestine. In this way, valuable nutrients, such as sugar and amino acids, can travel to all the cells of the body. Cells then catabolize (burn) nutrients in the presence of oxygen to release energy stored with the food. Cells also use amino acids to anabolite (build) large protein molecules needed for growth and development. Although the walls of the small intestine also absorb fatty acids and glycerol, these nutrients enter lymphatic vessels rather than blood vessels. Digested fats eventually enter the blood stream as lymph vessels join with blood vessels in the upper chest region.

The third function of the digestive system is the elimination of solid waste materials that cannot be absorbed into the blood stream. The large intestine concentrates these solid wastes, called feces, and the wastes finally pass out of the body through the anus.

II Anatomy & Physiology

Oral Cavity
The alimentary canal begins with the oral cavity, or mouth.

The cheeks form the walls of the oral-shaped cavity and the lips surround the opening to the cavity.

The hard palate forms the anterior portion of the roof of the mouth and the muscular soft palate lies posterior to it. Rugae are the irregular ridges in the mucous membrane covering the anterior portion of the hard palate. Hanging from the soft palate is a small soft tissue called the uvula. The word uvula means little grape. The structure functions to aid in producing sound and speech.

The tongue extends across the floor of the oral cavity, and muscles attach it to the lower jaw bone. It moves the food around during mastication (chewing) and deglutination (swallowing). Papillae, small raised areas on the tongue, contain taste buds that are sensitive to chemical nature of foods and allow discrimination of different tastes as food moves across the tongue.

The tonsils are masses of lymphatic tissue located in depressions of the mucous membranes on both sides if the oropharynx (part of the throat near the mouth). They act as filters to protect the body from invasion of microorganisms and produce lymphocytes, which are white blood cells able to fight disease.

The gums are made of fleshy tissue and surround the sockets of the teeth. Each dental arch has 16 permanent teeth. There are 32 permanent teeth in the entire oral cavity.

Dentists use special terms to describe the surfaces of teeth. The labial surface (labio/o means lip), for incisor and canine teeth, is nearest the lips. The buccal surface (bucc/o means cheek), for premolar and molar teeth, is adjacent to the cheek. Some dentists refer to both the labial and buccal surfaces as the facial surface (faci/o means face). Opposite to the facial surface, all teeth have a lingual surface (lingu/o means tongue). Mesial surface of a tooth lies nearest the median line and the distal surface, farthest from the medial line. Premolars and molars have an additional occlusal surface (occlusion means to close) that comes in contact with a corresponding tooth in the opposing arch. The incisors and cuspids have a sharp incisal edge.

A tooth consists of a crown, which shows above the gumline and a root, which lies within the bony tooth socket. The outermost protective layer of the crown, the enamel, protects the tooth. Enamel is a dense, hard, white substance – the hardest substance in the body. Dentin, the main substance of the tooth, lies beneath the enamel and extends throughout the crown. Yellow in color, dentin is composed of bony tissue that is softer than enamel. The cementum covers, protects and holds the tooth in place in the tooth socket.

The pulp lies underneath the dentin. It is soft and delicate tissue and fills the center of the tooth. Blood vessels, nerve endings, connective tissue, and lymphatic vessels are within the pulp canal (also called the root canal). Root canal therapy is often necessary when disease or abscess (pus collection) occurs in the pulp canal. A dentist opens the tooth from above and cleans the canal of infection, nerves, and blood vessels. The canal is then disinfected and filled with material to prevent the entrance of microorganisms and decay.

Three pairs of salivary glands surround the oral cavity. These exocrine glands produce a fluid called saliva that contains important digestive enzymes. Saliva is released from the parotid gland, submandibular gland, and sublingual gland on each side of the mouth. Narrow ducts carry the saliva into the oral cavity.

Pharynx The pharynx or throat is a muscular tube, about five inches long, lined with a mucous membrane. It serves as a common passage for air traveling from the nose (nasal cavity) to the windpipe (trachea) and food traveling from the oral cavity to the esophagus. When swallowing (deglutination) occurs, a flap of tissue, the epiglottis, covers the trachea so that food cannot enter and become lodge there.

Esophagus The esophagus, meaning swallowing (phag/o) inward (eso-), is a 9- to 10-inch muscular tube extending from the pharynx to the stomach. Rhythmic contractions of muscles in the wall of the esophagus propel food toward the stomach. Peristalsis, meaning constriction (-stalsis) surrounding (peri-), is this involuntary, progressive, rhythm-like contraction of the esophagus and the other gastrointestinal tubes. The process is like squeezing a marble (the bolus, or semi-solid mass of food) through a rubber tube.

Stomach Food passes from the esophagus into the stomach. The stomach is composed of an upper portion called the fundus, a middle section known as the body, and a lower portion, the antrum. Rings of muscles called sphincters control the openings into and leading out of the stomach. The lower esophageal sphincter (cardiac sphincter) relaxes and contracts to move food from the esophagus into the stomach, whereas the pyloric sphincter allows food to leave the stomach when it is ready. Folds in the mucous membrane (mucosa) lining the stomach are called rugae. The rugae contain digestive glands that produce the enzyme pepsin (to begin digestion of proteins and hydrochloric acid.

The role of the stomach is to prepare the food chemically and mechanically so that it can be received in the small intestine for digestion and absorption into the bloodstream. Food does not enter the bloodstream through the walls of the stomach. The stomach controls the passing of foods into the first part of the small intestine so that it proceeds only when it is chemically ready and in small amounts. Food leaves the stomach in 1 to 4 hours or longer depending upon the amount and type of food eaten.

Small intestine (small bowel) The small intestine (small bowel) extends for 20 feet from the pyloric sphincter to the first part of the large intestine. It has three parts. The first section is the duodenum, only 1 foot in length, which receives food from the stomach as well as bile from the liver and gallbladder and pancreatic juices from the pancreas. Enzymes and bile help to digest food before it passes into the second part of the small intestine. The jejunum, about 8 feet long. The jejunum connects with the third section, the ileum, about 11 feet long. The ileum attaches to the first part of the large intestine.

Millions of tiny, microscopic projections called villi line the walls of the small intestine. The tiny capillaries (microscopic blood vessels) in the villi absorb the digested nutrients into the bloodstream and lymph vessels.

Large Intestine (Large Bowel) The large intestine extends from the end of the ileum to the anus. It is divided into 6 parts: ascending colon, transverse colon, descending colon, sigmoid colon and rectum. The cecum is a pouch on the right side that connects to the ileum at the ileocecal valve (sphincter). The appendix hangs from the cecum. The appendix has no clear function and can become inflamed and infected when it is clogged or blocked. The colon (large intestine), about 5 feet long, has three divisions. The ascending colon extends from the cecum to the undersurface of the liver, where it turns to the left (hepatic flexure or bend) to become the transverse colon. The transverse colon passes horizontally to the left toward the spleen, and turns downward, splenic flexure into the descending colon. The sigmoid colon, shaped like an S (resembling the Greek letter sigma, which curves like an S), lies at the distal end of the descending colon and leads into the rectum. The rectum terminates in the lower opening of the gastrointestinal tract, the anus.

The large intestine receives the fluid waste products of digestion (the material unable to pass into the bloodstream) and stores these wastes until they can be released from the body. Because the large intestine absorbs most of the water within the waste material, the body can expel solid feces (stools). Defecation is the expulsion or passage of feces from the body through the anus. Diarrhea, watery stools, can result from lack of absorption of the water through the walls of the large intestine.

Liver, Gallbladder, and Pancreas
Three important additional organs of the digestive system – the liver, gallbladder, and pancreas – play crucial roles in the proper digestion and absorption of nutrients.

The liver, located in the right upper quadrant (RUQ) of the abdomen, manufactures a thick, yellowish-brown, sometimes greenish, fluid called bile. Bile contains cholesterol (a fatty substance), bile acids, and several bile pigments. One of these pigments called, bilirubin, is produced from the breakdown of hemoglobin during normal red blood cell destruction. Bilirubin then travels via the blood stream to the livers where it is conjugated (combined) with another substance so that it can be added to bile. Thus, conjugated bilirubin enters the intestine with bile. In the colon, bilirubin is degraded by bacteria into a variety of pigments that give feces a brownish color. Bilirubin and bile leave the body in feces.

If bilirubin cannot leave the body, it remains in the bloodstream, causing jaundice (hyperbilirubinemia), yellow discoloration of the skin, whites of the eyes, and mucous membranes.

The liver continuously release bile, which then travels through the hepatic duct to the cystic duct. The cystic duct leads to the gallbladder, a pear-shaped sac under the liver, which stores and concentrates the bile for later use. After meals, in response to the presence of food in the stomach and duodenum, the gallbladder contracts, forcing the bile out the cystic duct into the common bile duct. Meanwhile, the pancreas secretes pancreatic juices (enzymes) that travel vial the pancreatic duct to join with the common bile duct just as it enters the duodenum. The duodenum thus receives a mixture of bile and pancreatic juices.

Bile has detergent-like effect on fats in the duodenum. It breaks apart large fat globules, creating more surface area so that enzymes from the pancreas can digest the fats. This is called emulsification. Without bile, most of the fat taken into the body would remain undigested.

The liver, besides producing bile, has several other vital and important functions. Some of these are:
1. Keeping the amount of glucose (sugar) in the blood at normal level. The liver removes excess glucose from the bloodstream and stores it as glycogen (starch) in liver cells. When the blood sugar levels become dangerously low, the liver can convert stored glycogen back into glucose via a process called glycogenolysis. In addition, the liver can also convert proteins and fats into glucose, when the body needs sugar, by a process called gluconeogenesis.
2. Manufacture of some blood proteins, particularly those necessary for blood clotting.
3. Release of bilirubin, a pigment in bile.
4. Removal of poisons (detoxification) from the blood.

The portal vein brings blood to the liver from the intestines. Digested foods pass into the portal vein directly after being absorbed into the bloodstream from the small intestine, thus giving the liver the first chance to use the nutrients.

The pancreas is both an exocrine and an endocrine organ as an exocrine gland, it produces enzymes to digest starch, such as amylase (amyl/o = starch, -ase = enzyme), to digest fat, such as lipase (lip/o = fat), and to digest proteins, such as protease (prote/o = protein). These pass into the duodenum through the pancreatic duct.

As an endocrine gland (secreting into the bloodstream) the pancreas secretes insulin. This hormone, needed to help release sugar from the blood, acts as a carrier to bring glucose into cells of the body to be used for energy.

V Pathology of the Digestive System

This section is divided into terms that describe symptoms (signs of illness) and terms that describe pathological conditions. The sentences following the definitions use medical words that are familiar to you and often describe the etiology (etio/o = cause) of the illness and its treatment. If the etiology is neither known nor understood, it is called idiopathic (idi/o = unknown).

Symptoms

anorexia – Lack of appetite (-orexia = appetite). Often a sign of malignancy or liver disease. Anorexia nervosa is loss of appetite owing to emotional problems such as anger, anxiety, and fear. It is an eating disorder. It can be related to a similar disorder, bulimia nervosa.

ascites – Abnormal accumulation of fluid in the abdomen. This condition, previously called dropsy, occurs when fluid seeps out of the bloodstream and collects in the peritoneal cavity. It can be a symptom of neoplasm or inflammatory disorders in the abdomen, venous hypertension (high blood pressure) caused by liver disease (cirrhosis), and heart failure.

borborygmus – Rumbling or gurgling noises produced by the movement of gas, fluid, or both in the gastrointestinal tract. These noises are often audible from a distance.

constipation – Difficult, delayed elimination of feces. Stools (feces) are dry and hard when peristalsis is slow. A medication that encourages movement of feces from the colon is called a laxative. A cathartic is a strong laxative.

diarrhea – Frequent, loose, watery stools. Rapid onset of diarrhea soon after eating suggests an acute infection or toxin. However, certain infections may not cause diarrhea for several hours. Watery or bloody stools are a symptom of inflammation or disease in the GI tract.

dysphagia – Difficulty in swallowing. This sensation occurs when a swallowed bolus fails to process, either because of a physical obstruction (obstructive dysphagia) or because of a motor disorder in which the esophageal peristalsis is not properly coordinated (motor dysphagia). Odynophagia is painful swallowing.

eructation – Gas expelled from the stomach through the mouth (belching, burping)

flatus – Gas expelled through the anus. Flatulence is the presence of excessive gas in both the stomach and the intestines. Flatulent refers to a person experiencing flatulence.

hematochezia – Bright, fresh, red blood discharged from the rectum. Hematochezia is associated with rapid bleeding, as from a duodenal ulcer, ulcerative colitis, or hemorrhoids.

jaundice – Yellow-orange coloration of the skin and other tissues due to high levels of bilirubin in the blood (hyperbilirubinemia). Jaundice (icterus) can occur in three major ways: (1) excessive destruction of erythrocytes, as in hemolysis, causes excess bilirubin in the blood; (2) malfunction of liver cells (hepatocytes) because of liver disease prevents the liver from excreting bilirubin with bile; (3) obstruction of bile flow, such as from choledocholithiasis or tumor, prevents bilirubin in bile from being excreted into the duodenum.

melena – Black, tarry stools; feces containing blood. This symptom usually reflects a condition in which blood has had time to be digested (acted on by intestinal juices).

nausea – Unpleasant sensation in the stomach and a tendency to vomit. This term comes from a Greek word meaning seasickness. Irritation of nerve endings in the stomach or other parts of the body sends a message to the vomiting reflex center in the brain. Nausea and vomiting may be symptomatic of a perforation (hole in the wall) of an abdominal organ; obstruction of a bile duct, stomach, or intestine; or toxins (poisons)

steatorrhea – Fat in the feces. Improper digestion or absorption of fat can cause fat to remain in the intestine. This may occur with disease of the pancreas (pancreatitis) when pancreatic enzymes are not excreted. It is also a symptom of disease of the small intestine that involves malabsorption of fat.

Pathological Conditions

Oral Cavity and Teeth
aphthous stomatitis – Inflammation of the mouth with small ulcers. This idiopathic condition is also known as canker sores. Aphth/o means ulcer.

dental caries – Tooth decay (caries means decay). Dental plaque is the accumulation of the foods, proteins from saliva, and necrotic debris on the tooth enamel. Bacteria grow in the plaque and cause the production of acid that dissolves the tooth enamel, resulting in a cavity (area of decay). If the bacteria infection reaches the pulp of the tooth (causing pulpitis), root canal therapy may be necessary.

herpetic stomatitis – Inflammation of the mouth (gingiva, lips, palate, and tongue) by infection with the herpesvirus. Commonly called fever blisters or cold sores.

oral leukoplakia – White plaques or patches (-plakia means plaque) on the mucosa of the mouth. A precancerous condition; major etiological factors are chronic tobacco and alcohol use.

periodontal disease – Inflammation and degeneration of gums, teeth, and surrounding bone; also called pyorrhea (py/o means pus). Chronic inflammation of gums (gingivitis) occurs as a result of accumulation of dental plaque (noncalcified collection of oral microorganisms and their products) and dental calculus or tartar (a white, brown, or yellow-brown calcified deposit at or below the gingival margin of teeth). Gingivectomy (a metal instrument is used to scrape away plaque and tartar from teeth) may be necessary to remove pockets of pus and allow new tissue to form. Infected areas are treated with targeted antibiotics.

Gastrointestinal Tract
achalasia – Failure of the lower esophagus sphincter (LES) muscle to relax (-chalasia means relaxation). In achalasia there is also loss of peristalsis so that food cannot pass easily through the esophagus. Both failure of the LES to relax and the loss of peristalsis cause dilation and widening of the esophagus. Physicians often recommend a bland diet low in bulk, and dilation of the LES to relieve symptoms.

anal fistula – Abnormal tube-like passageway near the anus. The fistula usually, but not always, opens into the rectum. An anal fissure is a narrow crack or slit in the mucous membrane of the anus.

colonic polyposis – Polyps (small benign growths) protrude from the mucous membrane of the colon. Two types of polyps: pedunculated – attached to the membrane by a stalk or peduncle; sessile – sitting directly on the mucous membrane. The polyps protrude into the lumen of the colon.

colorectal cancer – Adenocarcinoma of the colon or rectum, or both. Colorectal cancer can arise from polyps in the wall of the colon. Their removal by colonoscopy prevents progression to colorectal cancer. Approximately 50 percent of colorectal carcinomas develop in the rectosigmoid region. Individuals with strong family history of colorectal cancer are advised to have routine colonoscopies for screening. Prognosis depends on the stage (extent of spread) of the tumor, including size, depth of invasion of the colon, and involvement of lymph nodes.

Crohn disease – Chronic inflammation of the intestinal tract (most often the terminal ileum and colon). This chronic relapsing disease can affect any part of the GI tract from the mouth to the anus. It causes inflammation with diarrhea, cramping, and fever. Similar to ulcerative colitis, both are forms of inflammatory bowel disease (IBD). Etiology is unknown and the disease is treated by drugs or surgical removal of the diseased portion of the intestine, with anastomosis of remaining parts.

diverticula (singular: diverticulum) – Abnormal side pockets (outpouchings) in the intestinal wall (diverticulosis). A common location for diverticula to occur is in the sigmoid colon. When undigested food or bacteria becomes trapped in a diverticulum, diverticulitis occurs. Diverticula (di – aside, verti – to turn, cul – small)

dysentery – Painful, inflamed intestines. Commonly occurring in the colon, the etiology of dysentery is usually ingested food or water containing bacteria (salmonellae or shigellae), amebae (one-celled organisms), or viruses. Colitis, diarrhea, and abdominal cramps occur.

esophageal varices – Swollen, tortuous veins in the distal portion of the esophagus or upper part of the stomach. Liver disease (such as cirrhosis) can cause increased pressure in blood vessels (portal vein hypertension). This pressure can lead to enlarged, tortuous esophageal veins with danger of hemorrhage (bleeding). Treatment includes drug therapy to lower portal hypertension or using sclerosing (hardening) agents to close off veins.

gastric carcinoma – Malignant tumor of the stomach. Chronic gastritis associated with H pylori (bacterial) infection is a major risk factor for gastric carcinoma. Tumor is usually diagnosed by endoscopic examinations in high-risk patients. Cure is dependent on early detection and surgical removal.

gastroesophageal reflux disease (GERD) – Solids and fluids return to the mouth from the stomach. Heartburn is the burning sensation caused by the regurgitation of hydrochloric acid from the stomach to the esophagus. Chronic exposure of the esophageal mucosa to gastric acid and pepsin (a proteolytic enzyme) causes reflux esophagitis. Drug treatment for GERD includes acid-suppressive agents and those that increase the tone of the lower esophageal sphincter.

hemorrhoids – Swollen, tortuous veins in the rectal region. Also known as piles, hemorrhoids can be internal (within the wall of the rectum) or external (in the anal area), and they are often caused by chronic constipation and straining, which increases pressure on anal veins.

hernia – protrusion of an organ or part through the muscle normally containing it. A hiatal hernia occurs when the upper part of the stomach protrudes upward through the esophageal opening in the diaphragm. An inguinal hernia occurs when a small loop of bowel protrudes through a weak place in the lower abdominal muscle wall (groin). Muscle weakness can be inherited or acquired as part of the aging process, pregnancy, obesity, or heavy lifting and coughing.

ileus – Failure of peristalsis. This may be caused by mechanical obstruction of the bowel (adhesions, tumor, or stones) or poor neural stimulation (as in peritonitis and overuse of medications). Paralytic ileus is acute transient (brief) loss of peristalsis. Common causes are surgical, traumatic, or bacterial injury to the peritoneum.

intussusception – Telescoping of the intestines. This is a cause of intestinal obstruction and occurs most commonly in children and in the ileocecal region. Treatment involves resection of the intussusception and anastomosis.

irritable bowel syndrome – A group of GI symptoms (diarrhea and constipation, lower abdominal pain, and bloating) associated with stress and tension, also called spastic colon. No pathological lesions are found in the intestines. Treatment includes psychotherapy to manage stress and medications (antidiarrheals and bulk-forming laxatives) to relieve symptoms. A diet high in bran and fiber also helps soften stools and establish regular bowel movements.

ulcer – Open sore or lesion (wound) of skin (epithelial) tissue. Gastric or duodenal ulcers (both are peptic ulcers) are examples. Duodenal ulcers are now thought to be caused by a bacterium, Helicobacter pylori (H pylori). The combination of bacteria, hyperacidity, and gastric juice (particularly pepsin) damages epithelial linings. Treatment includes drugs to reduce the production of hydrochloric acid and protect the lining of the stomach and intestine. Antibiotics are commonly used against H pylori.

ulcerative colitis – Chronic inflammation of the colon with the presence of ulcers. This is an idiopathic, chronic, recurrent diarrheal disease (inflammatory bowel disease) with rectal bleeding and pain. Often beginning in the rectum, the inflammation spreads proximally, involving the entire colon. Resection of diseased bowel with ileostomy may be necessary as treatment. Ulcerative colitis is associated with a higher risk of colon cancer.

volvulus – Twisting of the intestine upon itself. A surgical emergency, the volvulus must be released immediately.

Liver, Gallbladder, and Pancreas

cirrhosis – Chronic disease of the liver with degeneration of liver cells. Alcoholism combined with malnutrition is a common etiological factor, but infection and poisons can affect the liver cells as well. Alcohol has a toxic effect on hepatocytes, causing fat cells to accumulate, followed by necrosis and fibrous scarring, and discoloration (cirrh/o refers to the liver’s orage-yellow color). As with other liver diseases, jaundice results when the liver cells fail to function and bilirubin is not eliminated from the body.

gallstones (cholelithiasis and choledocholithiasis) Crystallization of cholesterol and other materials to form stones in the gallbladder or bile ducts. Calculi (stones) can prevent bile from leaving the gallbladder and bile ducts to enter the duodenum. The majority of patients with gallstones remain asymptomatic and do not require treatment. However, if a patient experiences episodes of biliary colic (pain from blocked cystic or common bile duct), treatment is required. Conventional treatment has been cholecystectomy or choledocholithotomy. Currently, more cholecystectomies are performed using a laparoscopic technique (laparoscopic cholecystectomy) similar to that used to tie off the fallopian tubes.

pancreatitis – Inflammation of the pancreas. Digestive enzymes attack pancreatic tissue, leading to damage to the gland. Alcoholism and gallstones may be causative factors, but chronic or acute inflammation can develop from abdominal trauma or chemical injury. Acute pancreatitis (marked by massive swelling, bleeding, and necrosis of the pancreas) may be complicated by sacs of fluid called pseudocysts (in the pancreas) and systemic problems such as shock, renal failure, and respiratory collapse. Treatment includes medications to relieve epigastric pain, intravenous fluids, and rarely, surgery to remove portions of the pancreas.

viral hepatitis – Inflammation of the liver caused by virus. There are three major types of viral hepatitis: Hepatitis A (caused by type A virus and previously called infectious hepatitis) is a benign, acute, self-limited disorder transmitted by infected water and food (the virus is also excreted in feces). Hepatitis B (caused by type B virus and called serum hepatitis) is acquired parenterally, through blood (transfusions, hypodermic needles, and dental and surgical instruments) and via body fluids, such as tears, saliva, and semen. A vaccine that provides immunity to hepatitis B is recommended for hospital personnel, dentists, laboratory technicians, and persons requiring frequent transfusions. Hepatitis C is transmitted by blood or blood products; transmission through sexual contact and from mother to infant is rare. About 10 percent of patients develop hepatic fibrosis and cirrhosis. In all types, liver enzymes may be elevated, indicating damage to liver tissue. Symptoms include malaise, anorexia, occasional joint pain, and in severe cases, nausea and jaundice.
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