Anatomy & Physiology Chapter 20: Blood

Composition of Blood Introduction (Figure 20-1) Blood—made up of plasma and formed elements Blood—complex transport medium that performs vital pickup and delivery services for the body Blood—keystone of body’s heat- regulating mechanism 2

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Composition of Blood Blood volume Young adult male has approximately 5 liters of blood Blood volume varies according to age, body type, sex, and method of measurement 4

Formed Elements of Blood Red blood cells (RBCs; erythrocytes) Description of mature RBCs (Figure 20-4) Have no nucleus and shaped like tiny biconcave disks Do not contain ribosomes, mitochondria, and other organelles typical of most body cells Primary component is hemoglobin Most numerous of the formed elements 5

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Formed Elements of Blood Red blood cells (cont) Function of RBCs Critical role of RBCs in the transport of oxygen and carbon dioxide depends on hemoglobin Carbonic anhydrase (CA)—enzyme in RBCs that catalyzes a reaction that joins carbon dioxide and water to form carbonic acid Carbonic acid—dissociates and generates bicarbonate ions, which diffuse out of the RBC and serve to transport carbon dioxide in the blood plasma 7

Formed Elements of Blood Red blood cells (cont) Hemoglobin (Figure 20-5) Within each RBC are approximately 200 to 300 million molecules of hemoglobin Hemoglobin is made up of four globin chains, with each attached to a heme group Hemoglobin is able to unite with four oxygen molecules to form oxyhemoglobin to allow RBCs to transport oxygen where it is needed A male has a greater amount of hemoglobin than a female Anemia—a decrease in number or volume of functional RBCs in a given unit of whole blood 8

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Formed Elements of Blood Red blood cells (cont) Formation of RBCs (review Figures 20-6 and 20-7) Erythropoiesis—entire process of RBC formation RBC formation begins in the red bone marrow as hematopoietic stem cells and goes through several stages of development to become erythrocytes; entire maturation process requires approximately 4 days RBCs are created and destroyed at approximately 200 billion per day in an adult; homeostatic mechanisms operate to balance the number of cells formed against the number of cells destroyed 10

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Formed Elements of Blood Red blood cells (cont) Destruction of RBCs (Figure 20-8) Life span of a circulating RBC averages 105 to 120 days Macrophage cells phagocytose the aged, abnormal, or fragmented RBCs Hemoglobin is broken down, and amino acids, iron, and bilirubin are released 13

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Formed Elements of Blood White blood cells (leukocytes; WBCs) (review Table 20-1) Granulocytes Neutrophils (review Figure 20-9)—make up approximately 65% of total WBC count in a normal blood sample; highly mobile and very active phagocytic cells; capable of diapedesis; cytoplasmic granules contain lysosomes 15

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Formed Elements of Blood Granulocytes (cont) Eosinophils (review Figure 20-10)—account for 2% to 5% of circulating WBCs; numerous in mucous lining of respiratory and digestive tracts; weak phagocytes; release chemicals of immunity; provide protection against infections caused by parasitic worms and help regulate allergic reactions Basophils (review Figure 20-11)—account for only 0.5% to 1% of circulating WBCs; motile and capable of diapedesis; cytoplasmic granules contain histamine and heparin 17

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Formed Elements of Blood White blood cells (cont) Agranulocytes (Figures 20-12 and 20-13) Lymphocytes—smallest of the WBCs; second most numerous WBC; account for approximately 25% of circulating WBCs; T lymphocytes and B lymphocytes have an important role in immunity—T lymphocytes directly attack an infected or cancerous cell, and B lymphocytes produce antibodies against specific antigens Monocytes—largest leukocytes; mobile and highly phagocytic cells 20

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Formed Elements of Blood White blood cells (cont) WBC numbers—1 mm3 of normal blood usually contains 5000 to 9000 leukocytes, with different percentages for each type; WBC numbers have clinical significance because they change with certain abnormal conditions (Figure 20-14) Formation of WBCs (review Figure 20-6) Granular and agranular leukocytes mature from the undifferentiated hematopoietic stem cell Neutrophils, eosinophils, basophils, and a few lymphocytes and monocytes originate in red bone marrow; most lymphocytes and monocytes develop from hematopoietic stem cells in lymphatic tissue 23

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Formed Elements of Blood Platelets (review Figure 20-2) Structure In circulating blood, platelets are small, pale bodies that appear as irregular spindles or oval disks Three important properties are agglutination, adhesiveness, and aggregation Platelet counts in adults average 250,000/mm3 of blood; normal range is 150,000 to 400,000/mm3 25

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Formed Elements of Blood Platelets (cont) Functions of platelets Important role in hemostasis and blood coagulation; secondary role in defending against bacterial attacks Hemostasis—refers to stoppage of blood flow; however, if injury is extensive, the blood-clotting mechanism is activated to assist 27

Formed Elements of Blood Platelets (cont) Platelet plug formation Platelets adhere to damaged endothelial lining and to each other 1 to 5 seconds after injury to vessel wall, forming a platelet plug Temporary platelet plug is an important step in hemostasis “Sticky platelets” form physical plug and secrete several chemicals involved in the coagulation process Formation and life span of platelets (average of 7 days)—formed in red bone marrow, lungs, and spleen by fragmentation of megakaryocytes 28

Blood Types (Blood Groups) The ABO system (Figures 20-16 to 20-18) Every person’s blood belongs to one of four ABO blood groups Named according to antigens present on RBC membranes Type A—antigen A on RBCs Type B—antigen B on RBCs Type AB—both antigen A and antigen B on RBCs; known as universal recipient Type O—neither antigen A nor antigen B on RBCs; known as universal donor 29

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Blood Types (Blood Groups) The Rh system (Figure 20-19) Rh-positive blood—Rh antigen is present on the RBCs Rh-negative—RBCs have no Rh antigen present Anti-Rh antibodies are not normally present in blood; anti-Rh antibodies can appear in Rh-negative blood if it has come in contact with Rh-positive RBCs 33

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Blood Plasma Plasma—liquid part of blood; clear, straw-colored fluid; made up of 90% water and 10% solutes (Figure 20-20) Solutes—6% to 8% of plasma solutes are proteins, consisting of three main compounds Albumins—help maintain osmotic balance of the blood Globulins—essential component of the immunity mechanism Fibrinogen—key role in blood clotting Plasma proteins have an essential role in maintaining normal blood circulation 35

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Blood Clotting (Coagulation) Mechanism of blood clotting—goal of coagulation is to stop bleeding and prevent loss of vital body fluid in a swift and sure method; the classic theory (Figure 20-21) is as follows: Classic theory of coagulation advanced in 1905; identified four components critical to coagulation Prothrombin Thrombin Fibrinogen Fibrin 37

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Blood Clotting (Coagulation) Mechanism of blood clotting (cont) Current explanation of coagulation involves three stages (Figure 20-22) Stage 1—production of thromboplastin activator by either of the following: Chemicals released from damaged tissues (extrinsic pathway) Chemicals present in the blood (intrinsic pathway) Stage II—conversion of prothrombin to thrombin Stage III—conversion of fibrinogen to fibrin and production of fibrin clot 39

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Blood Clotting (Coagulation) Conditions that oppose clotting Clot formation in intact vessels is opposed Several factors oppose clotting Perfectly smooth surface of the normal endothelial lining of blood vessels does not allow platelets to adhere Antithrombins—substances in the blood that oppose or inactivate thrombin; prevent thrombin from converting fibrinogen to fibrin; for example, heparin 41

Blood Clotting (Coagulation) Conditions that hasten clotting Rough spot in the endothelium Abnormally slow blood flow Clot dissolution (Figure 20-23) Fibrinolysis—physiological mechanism that dissolves the clot once it has formed Plasmin—enzyme in the blood that catalyzes the hydrolysis of fibrin, causing it to dissolve; it is activated by chemicals released from damaged cells and acts slowly to dissolve the clot Substances that generate plasmin can be used as a therapy to dissolve blood clots 42

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The Big Picture: Blood and the Whole Body Blood plasma transports substances, including heat, around the body, linking all body tissues together Blood tissue contains formed elements—blood cells and platelets RBCs assist in the transport of oxygen and carbon dioxide WBCs assist in the defense mechanisms of the whole body Platelets prevent loss of the fluid that constitutes the internal environment 44

The Big Picture: Blood and the Whole Body Blood is needed by all organs and body systems to function properly, just as many body systems aid the functions of blood. Blood is useless to the body unless it continues to flow around the body and performs its functions of transport, defense, and balance (or homeostasis). 45