Blood Components And Functions PDF

56 Unit 1 Comparative Anatomy and Physiology BLOOD COMPONENTS AND FUNCTIONS including amino acids, lipids, and glucose are absorbed VetBooks.ir...

56 Unit 1 Comparative Anatomy and Physiology BLOOD COMPONENTS AND FUNCTIONS including amino acids, lipids, and glucose are absorbed VetBooks.ir from the intestinal tract and delivered to other sites in Objective the body for utilization. List Blood Components and Explain the Functions of Blood The protein portion of the blood can be divided into three types: albumin, globulins, and fibrinogen. Blood separates into a fluid portion and a formed- Albumin, the major protein in blood, maintains element portion. If blood is placed in a tube and spun the water in the bloodstream. Albumin draws water in a centrifuge, the formed elements settle to the bot- into blood vessels through osmosis. The large albumin tom of the tube (Figure 4–2). The cellular portion of the molecules do not diffuse from the blood vessels. The blood makes up about 30% to 45% of the total contents. presence of protein within the blood vessels increases This percentage varies dramatically among species the osmotic pressure, helping to retain water within the and animal ages. The remaining fluid portion is called bloodstream. The liver produces albumin and secretes plasma. Normal plasma, without the red blood cells, is it into the bloodstream. a transparent fluid that varies in color from clear to a Globulins, another type of protein in the plasma, very light yellow. are antibodies produced to fight disease. The immune Plasma consists mainly of water. For most animals, system produces these antibodies to fight specific dis- plasma contains 91% to 94% water. Protein makes up 5% ease-causing organisms. The globulins can be used to to 8% of the plasma. The protein in the plasma creates make a diagnosis in infectious diseases. A high level the pale yellow color. The remainder of the plasma is a of globulin for a particular organism is evidence that combination of electrolytes, gases, nutrients, metabolic the animal has been exposed to it. Other globulins wastes, and hormones. The electrolytes include sodium, are used for transporting certain molecules, such as potassium, calcium, magnesium, chloride, phosphorus, hormones. and bicarbonate. Oxygen, carbon dioxide, and nitrogen Fibrinogen, the third type of protein found in the are all gases transported in the blood. Many nutrients, plasma, aids in clotting blood. When a blood vessel is Plasma ( (55% of Total V Volume) ) Erythrocytes Thrombocytes (Platelets) Formed A B Elements E s ((45% of Total Neutrophil Monocyte V Volume) ) © 2017 Cengage Learning® Leukocytes Test Tube Containing Eosinophil Lymphocyte Whole Blood © 2017 Cengage Learning® Basophil FIGURE 4–2 A. Centrifuged blood separating serum from the formed elements. B. Blood and its components. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  Chapter 4 The Circulatory System 57 damaged, fibrinogen is converted to fibrin. The fibrin which oxygen must diffuse. Changes in the fluid sta- VetBooks.ir forms fibrous threads that attach to the damaged ves- tus of the animal can also affect the amount of water sel. If the clotting proteins are removed from plasma, within the RBC. Because of the biconcave disk shape, the resulting fluid is called serum. a small amount of additional fluid entering the cell The formed elements of the blood are divided into will not cause rupture of the membrane. Excessive three fractions: red blood cells, white blood cells, and changes can actually cause a rupture of the RBC. An platelets. Red blood cells are also called erythrocytes. adult dog has approximately 6 to 8 million RBCs per White blood cells are also called leukocytes. microliter (μl). Red blood cells (RBCs) carry oxygen. Mature RBCs are produced in the bone marrow. As the RBCs do not have a nucleus (Figure 4–3). The bicon- cells are produced, the immature RBCs contain a cave disk shape of RBCs provides a large surface nucleus. These immature RBCs are occasionally found area, which allows the cell to efficiently exchange in the bloodstream. This usually occurs when the body oxygen and carbon dioxide. In addition to increasing is producing a large amount of RBCs, such as an animal the surface area, the shape minimizes the distance to that recently lost a large amount of blood. Photomicrographs courtesy William J. Bacha, PhD, Photomicrographs courtesy William J. Bacha, PhD, A B and Linda M. Bacha, MS, VMD. and Linda M. Bacha, MS, VMD. Photomicrographs courtesy William J. Bacha, PhD, Photomicrographs courtesy William J. Bacha, PhD, C D and Linda M. Bacha, MS, VMD. and Linda M. Bacha, MS, VMD. Photomicrographs courtesy William J. Bacha, PhD, FIGURE 4–3 Photomicrographs of blood and bone marrow. A. A blood smear from a dog. Numerous red blood cells are visible. The large, darkly stained cell with granules is a basophil. The other white blood cell with lightly stained cytoplasm and segmented nucleus is a neutrophil. B. A E and Linda M. Bacha, MS, VMD. blood smear from a dog showing a small lymphocyte. Two platelets are also visible. The dark spots visible are deposits of stain. C. A blood smear from a dog showing an eosinophil. The cell has granules and a nucleus similar in shape to that of a basophil. The granules, however, stain differ- ently between cell types. D. A blood smear from a dog showing a mono- cyte. E. A bone marrow smear from a dog. Multiple white blood cells are visible, including an immature neutrophil or band cell. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  58 Unit 1 Comparative Anatomy and Physiology oxygen. Active muscles produce lactic acid, which low- Table 4–1 Life Span of Red Blood Cells (in days) VetBooks.ir ers the pH. As a result, more oxygen is released at the Dogs 100–110 site of these active muscles. The elevated temperature that occurs in active tissues also increases the release Cats 66–78 of oxygen. Horses 150 Carbon monoxide is a gas released from poorly vented heaters and the exhaust from automobiles. The © 2017 Cengage Learning® Sheep 150 gas is colorless and odorless, so it is not detected by the animal breathing it. Carbon monoxide is extremely Cattle 160 toxic because it binds to hemoglobin with a higher Humans 120 affinity than does oxygen. It also increases the affinity of hemoglobin to oxygen so it is released less freely. The toxic effect occurs because the blood is unable The production of RBCs by the bone marrow is to carry enough oxygen to the tissues. With prompt called erythropoiesis. RBCs have a limited life span diagnosis the supplementation of high levels of oxy- and are constantly being replaced (Table 4–1). In addi- gen may be lifesaving. In the past small birds such as tion to the normal turnover of RBCs, conditions such canaries were taken into mines as sentinels for elevated as blood loss increase the need for more cells. When carbon monoxide levels. With their high metabolic rate the number of RBCs decreases, the amount of oxygen the canaries were more susceptible to poisoning by the delivered to the tissues also declines. Special receptors gas. If the miners saw the bird drop from its perch they in the kidney detect such a change and release a hor- knew to head for safer areas. Currently inexpensive mone called erythropoietin. Erythropoietin stimulates carbon monoxide detectors in enclosed areas can pre- the bone marrow to produce more RBCs. vent loss of life with early detection. The RBCs contain hemoglobin, which is the protein Hemoglobin carries only about 20% of the carbon responsible for transporting oxygen. Hemoglobin is dioxide. Most of the carbon dioxide is transported in an iron-containing molecule. It contains four subunits, the cytoplasm or the RBCs and plasma. Much of the each with a globin protein and the iron-containing carbon dioxide is converted to bicarbonate with the aid heme molecule. Each subunit can bind a molecule of of an enzyme, carbonic anhydrase (Figure 4–4). The oxygen. Thus, a complete hemoglobin can transport hemoglobin without bound oxygen helps to keep the four oxygen molecules. The globin molecule helps to pH normal by absorbing much of the free hydrogen keep the oxygen from binding securely (i.e., prevents ions. The blood then carries the bicarbonate to the complete oxidation) and allows it to be released read- lungs, where the carbon dioxide is released. ily in the tissues. The iron gives the red appearance to Leukocytes, or white blood cells (WBCs), are pres- hemoglobin. Hemoglobin is efficient at binding oxy- ent to help fight infection. The five major types of white gen, which is extremely important because oxygen is blood cells can be divided into two major classes, gran- poorly soluble in plasma. Only about 3% of the oxygen ulocytes and agranulocytes, based on the microscopic in blood is dissolved in the plasma. The hemoglobin appearance of the cytoplasm. Neutrophils, eosinophils, carries the remaining 97% of the oxygen. and basophils—the granulocytes—all have granules The oxygen concentration of hemoglobin is highest within the cytoplasm. The granules pick up different in the capillaries of the lungs. As the blood is pumped stains, which aids in the identification of these types. to tissues in which the oxygen concentration is lower, The agranulocytes—lymphocytes and monocytes— the oxygen is released from the hemoglobin. The higher have a smooth cytoplasm. the level of carbon dioxide at the tissue level, the more Like RBCs, the WBCs are also produced in the bone oxygen is released. Some of the carbon dioxide is car- marrow. WBCs spend only a portion of their time in ried by hemoglobin, which helps to release the oxygen. the bloodstream. The remainder of the time, the cells A lower pH (more acidic) also increases the release of move into tissues to fight infection. The total count of © 2017 Cengage Learning® FIGURE 4–4 The chemical form of carbon dioxide in blood. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  Chapter 4 The Circulatory System 59 WBCs in the blood of a normal dog ranges from 6,000 Many students are familiar with antihistamines taken VetBooks.ir to 17,000 per microliter. The total count and types of for hay fever. Antihistamines block the effects of hista- WBCs present can be used to help diagnose infectious mine. Histamine causes inflammation in the linings of conditions in animals. Different WBCs have different the nasal passages and respiratory tract. This inflam- functions, and changes in their number are useful in mation produces the signs of sneezing and runny nose, understanding the disease process. common among hay fever sufferers. Histamine causes The neutrophil is the predominant WBC in dogs, similar effects in animals. cats, and horses. The main function of neutrophils Lymphocytes, which have a single nucleus, are is to phagocytize (ingest in a form of endocytosis) essential in immune function (Figure 4–3B). Lympho- and destroy microorganisms and cellular debris. The cytes produce the antibodies that help fight disease. organism is taken into the cell in a membrane-bound These antibodies make up a portion of the globulin that sac that joins with granules within the cytoplasm. is found in plasma. Lymphocytes are found in all the These granules contain enzymes that can destroy tissues and organs used in fighting infection. Unlike organisms. Neutrophils generally perform this func- many of the WBCs, lymphocytes are not involved in tion in the tissues, not in the blood. The neutrophil phagocytosis. They are present in the tonsils, lymph has a nucleus that appears segmented or divided nodes, spleen, and thymus and are able to move back (Figure 4–3A). This is the typical appearance of a and forth between the bloodstream and tissues. A more mature neutrophil. If the body is attacked by an detailed discussion of the immune system is found in infection, the neutrophils move to the tissue infected Chapter 11. (such as the lungs in pneumonia). The neutrophils Neutrophils and lymphocytes make up the largest respond to chemical factors in the diseased tissue and number of WBCs found in circulating blood. Using the squeeze between the endothelial cells of the capillar- illustrations in this text, students can identify the indi- ies. (The term diapedesis describes this process of cells vidual types of cells. It will be more difficult to find the migrating out of the vessels.) Within hours the bone basophils, eosinophils, and monocytes than the com- marrow releases a large number of neutrophils that mon neutrophils and lymphocytes. Table 4–2 shows have been held in reserve. The bone marrow then the normal ranges found in domestic species. begins to increase production of the neutrophils. This Platelets are the third type of formed element. higher production level takes three to four days to be Platelets, produced in the bone marrow, aid in the fully transferred to the bloodstream. To speed up pro- normal clotting of blood. Blood clotting is a very com- duction, the bone marrow releases less-mature neu- plicated process involving the platelets and numerous trophils into the blood. These immature neutrophils, proteins and factors in the blood. also called band cells, have a nucleus that is shaped Immediately after a blood vessel is cut, there is a like a U (Figure 4–3E). A high percentage of band constriction of the vessel. Through this simple reflex cells in blood tells the veterinarian that an animal is the size of the leak is automatically decreased. Platelets actively fighting an infectious agent. then begin to attach to the edges of the damaged vessel, Monocytes, another WBC, actively phagocytize plugging the hole. In addition, a number of clotting microbes (Figure 4–3D). Monocytes are produced in factors help to convert the fibrinogen protein found in the marrow and move into the bloodstream and then the plasma into fibrin, which completes the plug. There into the tissues. In the tissues, monocytes mature into are 13 factors identified in the process of clotting blood. macrophages. Some of these macrophages are estab- Over time the fibrin clot is replaced with repaired lished in places such as the spleen, lymph nodes, lung, blood vessel. or liver. They remove microorganisms, dead cells, and The ability of an animal to clot vessels is quite foreign particles (such as inhaled dust in the lungs). impressive. Farm cats, with legs amputated by farm Eosinophils look similar in appearance to neu- equipment, have been known to stop bleeding without trophils with the segmented nucleus. Staining charac- intervention. The mammary vein on the lower abdo- teristics help to distinguish each of the granulocytes. men of a cow can be over an inch in diameter. One cow The eosinophils also have a large number of visible with a hole in its mammary vein more than an inch in granules in the cytoplasm (Figure 4–3C). Eosinophils length stopped bleeding before the veterinarian arrived play roles in fighting parasites and also in allergic reac- at the farm. However, the laceration was sutured for tions. The eosinophils help to limit inflammation by extra insurance against bleeding. The ability of animals releasing the contents of the granules at the tissue site to clot unaided is amazing. of an allergic reaction. Only the damaged blood vessel wall stimulates the Basophils are darkly staining cells with many gran- formation of a clot. The normal smooth epithelial lining ules and a segmented nucleus (Figure 4–3A). Basophils, of the vessels does not stimulate clotting. Abnormal like eosinophils, are involved in allergic reactions. clots potentially cause damage to tissues by stopping Some of the granules in basophils contain histamine. blood flow. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203