Cardiovascular System Blood
Composition of Blood Blood is the body’s only fluid tissue It is composed of liquid plasma and formed elements Formed elements include: Erythrocytes, or red blood cells (RBCs) Leukocytes, or white blood cells (WBCs) Platelets (Thrombocytes) Hematocrit – the percentage of RBCs out of the total blood volume
Composition of Blood Figure 18.1
Physical Characteristics and Volume Blood is a viscous, opaque fluid with a metallic taste. Color varies from scarlet (oxygen-rich) to dark red (oxygen-poor) The pH of blood is 7.35–7.45 Temperature is 38C, slightly higher than “normal” body temperature Average volume of blood is 5–6 L for males, and 4–5 L for females
Functions of Blood Transports gases, nutrients, hormones, and metabolic wastes Regulates pH and electrolyte balance Hemostasis: maintains blood volume Defends the body against toxins and pathogens Stabilizes body temperature
Blood Plasma Plasma makes up 55% of the total blood volume: 92% of plasma is water Proteins Albumins: maintain osmotic pressure of blood Globulins: antibodies and transport proteins Fibrinogens: involved in blood clotting Nonprotein nitrogenous substances – lactic acid, urea, creatinine Organic nutrients – glucose, carbohydrates, amino acids Electrolytes – sodium, potassium, calcium, chloride, bicarbonate Respiratory gases – oxygen and carbon dioxide
Erythrocytes (RBCs) Biconcave discs Lack a nucleus Filled with hemoglobin (Hb), a protein that functions in transporting Oxygen and Carbon Dioxide Normally produced in the red marrow of bones.
Erythrocyte Function Erythrocytes are dedicated to respiratory gas transport Hemoglobin reversibly binds with oxygen and carbon dioxide Hemoglobin is composed of: The protein globin, made up of two alpha and two beta chains, each bound to a heme group. Each heme group carries an atom of iron, which can bind to oxygen. As oxygen levels decrease, hemoglobin molecules release oxygen and the globin portion binds to carbon dioxide. Each hemoglobin molecule can transport four molecules of oxygen
Erythrocyte Function
Hormonal Control of Erythropoiesis Erythropoietin (EPO) release by the kidneys is triggered by: Hypoxia (low oxygen) due to decreased RBCs Decreased oxygen availability (high altitude) Increased tissue demand for oxygen (exercise) Enhanced erythropoiesis increases the: RBC count in circulating blood Oxygen carrying ability of the blood increases
Hormonal Control of Erythropoiesis Figure 18.6
Leukocytes (WBCs) Leukocytes, the only blood components that are complete cells: Are less numerous than RBCs Make up 1% of the total blood volume (normal count 6000-9000 per cubic mm.) Can leave capillaries through tissue spaces via diapedesis Leukocytosis – WBC count over 11,000 per cubic mm. Normal response to bacterial or viral invasion
Leukocytes (WBCs) Two categories: Granulocytes: Neutrophils: Phagocytic, release cytotoxic chemicals Eosinophils: attack antibody-labeled and parasitic pathogens Basophils: release histamines, enhance inflammation Agranulocytes Lymphocytes: provides specific immune response Monocytes: macrophages engulf pathogens or debris
Platelets Cell fragments Functions in the clotting mechanism (Hemostasis) Forms a temporary “Platelet Plug” that helps seal breaks in blood vessels.
White blood cells Platelets Red blood cells
Neutrophil Lymphocyte
Monocyte
Eosinophil Lymphocyte
Neutrophil Basophil Monocyte
6 3 4 2 5 1
6. Neutrophil 3. Eosinophil 4. Neutrophil 2. Lymphocyte 5. Basophil 1. Monocyte
Sickle cell anemia: abnormal formation of hemoglobin, which causes RBC’s to be deformed, and causes poor oxygen circulation, and blood clots.
Leukemia: Cancer of blood forming tissues, causing elevated levels of and abnormal formation of WBC’s.
Hemostasis A series of reactions designed for stoppage of bleeding During hemostasis, three phases occur in rapid sequence Vascular Phase Platelet Phase Coagulation (blood clotting) Phase
Hemostasis
Hemostasis Vascular Phase: Smooth muscles in the walls of blood vessels constrict The decrease in the diameter of the blood vessel slows and sometimes stops blood loss. Endothelial cells at an injury site become sticky, and cells may stick together further blocking the injury site.
Hemostasis Platelet Phase: Platelets attach to “sticky” endothelial cells at the injury site. As more platelets arrive, a “Platelet Plug” forms, a mass of cells that may block the break in the vessel wall.
Hemostasis Coagulation Phase: Coagulation = Blood Clotting Occurs when a series of steps results in the formation of fibrin. Fibrin is an insoluble protein “net” that traps blood cells and platelets which form a blood clot. The blood clot seals off the damaged portion of the blood vessel.
Blood Typing A system of categorizing blood based on the surface antigens of RBC’s (agglutinogens) Three of the most important antigens: A, B and Rh When serum containing anti-A or anti-B agglutinins is added to blood, agglutination will occur between the agglutinin and the corresponding agglutinogens Positive reactions indicate agglutination (clumping) and incompatible blood type.