Chapter 17 Blood

Composition of Blood Introduction 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

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

Formed Elements of Blood Red blood cells (erythrocytes) Description of mature red blood cells (RBCs) Have no nucleus and are 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

Formed Elements of Blood Function of RBCs RBCs’ critical role in the transport of oxygen and carbon dioxide depends on hemoglobin Carbonic anhydrase—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

Formed Elements of Blood Red blood cells (erythrocytes) (cont.) Hemoglobin Within each RBC are approximately 200 to 300 million molecules of hemoglobin Hemoglobin is made up of four globin chains, each attached to a heme molecule 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

Formed Elements of Blood Red blood cells (erythrocytes) (cont.) Formation of red blood cells Erythropoiesis—entire process of RBC formation RBC formation begins in the red bone marrow with hemopoietic stem cells that go through several stages of development to become erythrocytes; entire maturation process requires approximately 4 days RBCs are created and destroyed at a rate of approximately 100 million per minute in an adult; homeostatic mechanisms operate to balance number of cells formed against number of cells destroyed

Formed Elements of Blood Destruction of RBCs 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 White blood cells (leukocytes, WBCs) Granulocytes Neutrophils —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 Eosinophils —account for 2% to 5% of circulating WBCs; numerous in lining of respiratory and digestive tracts; weak phagocytes; capable of ingesting inflammatory chemicals and proteins associated with antigen-antibody reaction complexes; provide protection against infections caused by parasitic worms and allergic reactions Basophils —account for only 0.5% to 1% of circulating WBCs; motile and capable of diapedesis; cytoplasmic granules contain histamine and heparin

Formed Elements of Blood White blood cells (cont.) Agranulocytes (Figures and 17-13) Lymphocytes—smallest of the WBCs; second most numerous type of 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 type of leukocyte; mobile and highly phagocytic cells

Formed Elements of Blood WBC numbers—a cubic millimeter of normal blood usually contains 5,000 to 9,000 leukocytes, with different percentages for each type; WBC numbers have clinical significance because they change with certain abnormal conditions Formation of WBCs Granular and agranular leukocytes mature from the undifferentiated hemopoietic stem cell Neutrophils, eosinophils, basophils, and a few lymphocytes and monocytes originate in red bone marrow; most lymphocytes and monocytes develop from hemopoietic stem cells in lymphatic tissue

Formed Elements of Blood Platelets 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 per mm 3 of blood; normal range is 150,000 to 400,000 per mm 3 Functions of platelets Important role in hemostasis and blood coagulation 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 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 RBC Type B—antigen B on RBC Type AB—both antigen A and antigen B on RBC; known as universal recipient Type O—neither antigen A nor antigen B on RBC; known as universal donor

Blood Types (Blood Groups) The Rh system 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

Blood Plasma Plasma—liquid part of blood; clear, straw-colored fluid; made up of 90% water and 10% solutes Solutes—6% to 8% of plasma solutes are proteins, consisting of three main compounds: Albumins—helps 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 Plasma Plasma—liquid part of blood; clear, straw-colored fluid; made up of 90% water and 10% solutes Solutes—6% to 8% of plasma solutes are proteins, consisting of three main compounds: Albumins—helps 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; the “classic theory” is as follows: “Classic theory” of coagulation advanced in 1905 Identified four components critical to coagulation: Prothrombin Thrombin Fibrinogen Fibrin

Blood Clotting (Coagulation) Mechanism of blood clotting (cont.) Current explanation of coagulation involves three stages: Stage I—production of thromboplastin activator by one or the other 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

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; e.g., heparin

Blood Clotting (Coagulation) Conditions that hasten clotting Rough spot in the endothelium Abnormally slow blood flow Clot dissolution Fibrinolysis—physiological mechanism that dissolves fibrin 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