Chapter 17: Blood

COMPOSITION OF BLOOD Blood (Figure 17-1) Blood volume Composed of plasma and formed elements Complex transport medium that performs vital pickup and delivery services for the body Keystone of body’s heat-regulating mechanism Blood volume Young adult male has approximately 5 L of blood Blood volume varies according to age, body type, sex, and method of measurement

FORMED ELEMENTS OF BLOOD Red blood cells (RBCs), also called erythrocytes Description of mature RBCs (Figure 17-4) Have no nucleus and shaped like tiny biconcave disks Do not contain ribosomes, mitochondria, or other organelles typical of most body cells Primary component is hemoglobin Most numerous of the formed elements Function of RBCs Critical role in the transport of oxygen and carbon dioxide depends on hemoglobin

FORMED ELEMENTS OF BLOOD (cont.) Hemoglobin (Figure 17-5) Within each RBC are approximately 200 to 300 million molecules of hemoglobin Hemoglobin is composed of four globin chains, 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 Males have a greater amount of hemoglobin than females Anemia: a decrease in number or volume of functional RBCs in a given unit of whole blood

FORMED ELEMENTS OF BLOOD (cont.) Formation of RBCs (Figures 17-6 and 17-7) Erythropoiesis: entire process of RBC formation 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

FORMED ELEMENTS OF BLOOD (cont.) Destruction of RBCs (Figure 17-8) 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

FORMED ELEMENTS OF BLOOD (cont.) White blood cells (WBCs), also called leukocytes (Table 17-1) Granulocytes Neutrophils: approximately 65% of total WBC count in a normal blood sample; highly mobile and active phagocytic cells Eosinophils: 2% to 5% of circulating WBCs; numerous in lining of respiratory and digestive tracts; weak phagocytes; provide protection against infections caused by parasitic worms and allergic reactions (Figure 17-10) Basophils: only 0.5% to 1% of circulating WBCs; motile and capable of diapedesis; cytoplasmic granules contain histamine and heparin (Figure 17-11)

FORMED ELEMENTS OF BLOOD (cont.) Agranulocytes (Figures 17-12 and 17-13) 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

FORMED ELEMENTS OF BLOOD (cont.) Monocytes: largest leukocytes; mobile and highly phagocytic cells 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 17-14)

FORMED ELEMENTS OF BLOOD (cont.) Platelets (Figure 17-12) Structure In circulating blood, platelets are small, pale bodies that appear as irregular spindles or oval disks 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

BLOOD TYPES: BLOOD GROUPS The ABO system (Figures 17-16 to 17-18) Every person’s blood belongs to one of four ABO blood groups Named for antigens on RBC membranes Type A: antigen A on RBCs Type B: antigen B on RBCs Type AB: both antigens A and B on RBCs; known as universal recipient Type O: neither antigen A nor B on RBCs; known as universal donor

BLOOD TYPES: BLOOD GROUPS (cont.) The Rh system (Figure 17-19) Rh-positive: 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

BLOOD PLASMA Plasma: liquid part of blood; clear, straw-colored fluid; composed of 90% water and 10% solutes (Figure 17-20) 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

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 (Figure 17-21) 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

BLOOD CLOTTING: COAGULATION (cont.) Conditions that hasten clotting Rough spot in the endothelium Abnormally slow blood flow Clot dissolution (Figure 17-23) Fibrinolysis: physiological mechanism that dissolves Fibrinolysin: enzyme in the blood that catalyzes the hydrolysis of fibrin, causing it to dissolve Additional factors are presumed to aid clot dissolution (e.g., substances that activate profibrinolysin)

THE BIG PICTURE: BLOOD AND THE WHOLE BODY Blood plasma transports substances, including heat, around the body, linking all body tissues together Substances can be transported between almost any two points in the body 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 No organ or system of the body can maintain proper levels of nutrients, gases, or water without direct or indirect help from blood Other systems assist the blood Blood is useless unless it continues to transport, defend, and maintain balance