Transcript Chapter 19
Chapter 19 Anatomy & Physiology Fifth Edition Seeley/Stephens/Tate (c) The McGraw-Hill Companies, Inc. Blood 1. Introduction • • • • • • Blood has been the source of mysteries for thousands of years. Blood is a type of C.T. consisting of cells and liquid. Blood is circulated by pumping action of the heart, the valves in blood vessels and by the contracting action of calf muscles. The total volume of an adult female is 4 – 5 L, while that an adult is 5 – 6 L. Blood constitutes about 8% of the total body weight of the human and the components may be divided with centrifugation. Study Fig. 19.1 carefully. 2. The Functions of Blood – At least 5 major functions of blood have been identified( I have broken down the functions to 5, rather than 3 as shown in the text.) i. Transportation: for gases, nutrients, hormone, vitamins, and metabolic wastes. ii. Regulation: of the pH, electrolytes and composition of interstitial fluids throughout the body. iii. Homeothermic: keeping the organism at constant temperature. iv. Protection: of damage sites with blood clots. v. Immunogenic defense: against toxins and pathogens. • Blood Collection and Analysis • Collection of human blood is usually performed from a superficial vein via venipuncture or from the finger tip or sole. • Only when needed an arterial puncture may be performed. • The temperature of blood is about 38°C and is slightly higher than that of the body temperature. • Having a large quantity of proteins in plasma (7g/100ml) and corpuscles, bloods’ viscosity is more than five times higher than that of water. • The pH of blood is about 7.4. 3. Plasma (see Table 19.1) – The plasma volume remains relatively consistent. a. Differences between plasma and interstitial fluids – The composition of plasma and that of interstitial fluid is about the same, but the former has more proteins and dissolved gases. b. Plasma Proteins – 7g/100ml of plasma • • • Albumin: 58% of plasma proteins. Osmotic balance. Globulin: 38%. Immunoglobulins, lipoproteins and transport proteins: antibodies and thyroid hormone-binding proteins. Fibrinogen: 4%. Can form large fibrins to form blood clot. – 50% of plasma proteins are produced by plasma cells. c. The other substances in plasma – In addition of dissolved proteins, plasma contains ions, nutrients, waste products, gases and regulatory substances. 4. • • • Formed Elements – The hematocrit refers to the percentage of blood cells ( in practice the formed elements). This number is obtained by centrifuging the blood held in a thin glass tube at a high speed. The formed elements will settle down to the bottom and its ratio to the total volume is the hematocrit. – The hematocrit is about 46% for male and about 42% for females. Red blood cells – 99.9 % of the formed elements in volume or 4.2 – 6.2 million/mm³. Erythrocytes are enucleated and have little organelles. White blood cells (leukocytes) – have nuclei – Granulocytes are: neutrophils, eosinophils and basophils. – Agranulocytes are: lymphocytes, monocytes. Platelets – enucleated and have little organelles. • Production of Formed Elements – Hemopoiesis or hematopoiesis – The major production sites of the formed elements shift: – The first 8 weeks: they start at the embryonic yolk sac and they begin to settle in the liver, spleen, thymus, and bone marrow. They become stem cells. – Form the 8th week to 5th month: in the liver and spleen are the primary sites of hemopoiesis. – No nucleus or organelles, thus only glycolytic enzymes to form energy by glycolysis. – Carbonic anhydrase responsible for conversion and transportation carbon dioxide. – Phospholipids and membrane proteins and others etc…. • Erythrocytes are : • • • • • 99.9% in volume of the formed elements. 5.4 million cells/ one microliter (ul or mm³) of blood for a man. 4.8 million cells/ one microliter (ul or mm³) for a woman. 260 million RBC/drop of blood. 25 trillion RBCs in the blood of an adult = 1/3 of all the cells in the human body. (75 trillion cells) • The difference in the hematocrit mention earlier, I.e. 46 to men and 42 to women, arises from the fact that androgens in men stimulate erythropoiesis, while estrogens in women are inhibitory. • The ratio of white cells to red cells is 1 to 1000. • The hematocrit vs disease: anemia and polycythemia. • Structure of RBCs • Uniquely biconcaved and flexible (Fig 19.3), have excellent exchange of gases between the cells and the environment. Contrary to a sphere, the RBC has the maximum surface to volume ratio. • The diameter is 7.5 microns and the thickness varies at the edge (thick, 1.5 microns) and the center (thinner, 1 micron) making it possible to tumble and bend in tissue capillaries. • The primary function of RBCs is performed by hemoglobin. – 33% of RBC is hemoglobin, Hb, an oxygen and CO2 carrying protein. – Each Hb consist of two pairs of subunits (alpha and beta) and each subunit has an oxygen binding heme. (Fig. 19.4) – Since the oxygen binding to heme is reversible, the number of oxygen bound to heme depends upon the amount of oxygen is in the environment of Hb. – Thus, in the lungs, where oxygen pressure is high, Hb binds oxygen and carries the gas to the tissues where the oxygen pressure is low. – Binding of CO2 to Hb is not at the heme, but is at the alpha amino group of the N-terminal ends of four subunits. – CO2 binding is essentially opposite to that of oxygen, but again follows the amount of CO2 in plasma. – (O2 - 95% w/Hb, 5% dissolved) – (CO - 7% dissolved, 23% w/ Hb, 70% as bicarbonate) – The circulation of CO2 also relies on the chemically dissolved form of CO2, i.e., bicarbonate. This process is facilitated by carbonic anhydrase. – Thus carbon dioxide may be transported as : carboamino hemoglobin, dissolved bicarbonate and free carbon dioxide. • Life Span and Circulation • Complete circulation of an erythrocyte in a body usually takes less than a minute. • During this period, especially while negotiating through tissue capillaries of less than several microns of diameter, pulsating motion of blood flow severely stresses the erythrocytes. • In addition, despite the presence of complex protective mechanisms, carrying of oxygen would provide ample opportunities to cause oxidative damages to the contents of the cells. • As a consequence, the life span of a RBC is about 120 days. • Since the hematocrit of a normal person is relatively consistent, the loss of erythrocytes is compensated with continuous erythropoiesis. • Old or damaged erythrocytes are usually phagocytically broken down in the liver, spleen and bone marrow. • Recycled Hb, when in small quantities, its path is through the kidneys and into the urine. If this level goes up, there will be discoloration of the urine.(yellowish ---- iron) • Recycling of RBC/hemoglobin Components • Macrophages in the spleen, liver, and other lymphatic tissues phagocytically engulf erythrocytes. • Globular proteins are broken down to amino acids for resumption. • Heme is separated from its iron and becomes biliverdin (green) then to bilirubin to be absorbed in the liver, there conjugated and then excreted in bile from the intestines. A build up of bilirubin in the circulation and intestinal spaces is known as jaundice. • Iron may be stored with the plasma protein, transferrin and recycled. • Erythropoiesis is regulated with erythropoetin from the kidneys, which appears in the plasma when peripheral tissues are exposed to low oxygen concentration, hypoxia. • White Blood Cells – leukocytes – They are different from RBC because of the presence of nuclei and the lack of hemoglobin – thus the transparent or white appearance. • They are loosely divided into: (Table 19.2) – Granulocytes: Neutrophils, eosinophils, basophils – Agranulocytes: monocytes, lymphocytes • There are as many as 6-8,000 leukocytes in 1 microliter of blood, but most of the leukocytes are found on peripheral tissues. • WBC Movement – WBC are capable of amoeboid movement. – Thus, they can migrate out of the epithelia of capillary walls, diapedesis. – Positive chemotaxis leads them to the troubled spots. There they are phagocytotic. • General Functions • General defense: neutrophils, eosinophils, basophils and monocytes • Specific immunity: lymphocytes – Neutrophils: polymorphonuclear • Live in the circulatory system for only 10-12 hours, then move into tissues, where they live up to 1-2 days. • Phagocytic and secrete lysozymes to digest bacteria and others. – Eosinophils: reduce inflammation and parasitic reaction. – Basophils: releases histamines, which promotes inflammation also release heparin, which inhibits blood clotting. • In new born and young children, both have mostly red bone marrow. • In adults, red bone marrow found in the skull, fibs, sternum, vertebrae, pelvis, proximal femur and proximal humorous. • Observe the hematopoiesis of stem cell in Fig. 19.2. • Stem cell are the origin of all formed elements. • Note the types of blast cells and the final cell types. – Monocytes – live 2-3 days in circulation and migrate in the tissues as macrophages, which phagocytose foreign bodies. An increased number of monocytes is an indication of an infection. – Lymphocytes – They are about the size of an RBC and they contain a nucleus. Most of the lymphocytes dwell in the lymphatic system. There are three types: • T-cells: attack foreign bodies. • B-cells: differentiate into plasma cells, which secrete antibodies. • Natural Killer cells (NK cells): destroys the bodies own abnormal cells. – Platelets – Megakaryocytes in bone marrow, which release their fragments into circulation, then called platelets. – Platelets have no nuclei. – Participate in blood clotting. – Platelets survive about 10-12 days in circulation and are about 150,000 – 300,000/ul – Thrombocytopenia is a loss of platelets and is a sign of bleeding etc.. – Thrombocytosis is excess platelets and is a sign of infection. • Hemostasis – arrest of bleeding. • Prevents loss of blood in three phases. • The vascular phase: immediate temporary closure of a blood vessel by constriction of vascular smooth muscles. • The platelet phase: formation of a platelet plug by platelet adhesion and aggregation (Fig 19.9). Platelets bind to collagen in damaged tissues. Platelets are adhered and form a plug. • The coagulation phase: for a large blood clot formation by the network of fibrin from fibrinogen. A large number of steps involving many factors are required, some of which require thrombin and Ca++. • The clotting process • Clotting is the phenomenon where blood cells are trapped in the framework of fibers. The clotting process requires Ca++ and 11 different plasma proteins, mostly enzymes. The process goes through 3-stages: 1. Activation of prothrombinase by either the extrinsic or intrinsic pathway. 2. Prothormbinase converts prothrombin to thrombin. 3. Thrombin converts fibrinogen to fibrin. Extrinsic pathway: the process is triggered by a tissue factor of damaged endothelial cells, the other enzymes are successively activated to complete the clotting process- a cascade. The process is fast and takes only 15 seconds. Intrinsic pathway: starts with the activation of factor XII by contacting the damaged blood vessels and is a slower process. • • • • • Clot retraction am Removal • The platelets begin to contract – clot retraction. • During the repair process of tissue, the clot gradually dissolves – fibrinolysis. • This process draws a lot of attention because dissolving clots in heart attack or stroke patients is clinically important. • To dissolve a clot: – Activated plasminogen by tissue plasminogen activator (t-PA) plasmin is produced plasmin digest the fibrin strands to dissolve the clot. • Blood tests and RBCs (review) • Blood types – Genetically determined RBC antigens (glycoproteins) rest on the surface of the membrane. – There are at least 50 different kinds of antigens on the surface of an RBC. – Their antibodies are found in plasma. – One set of important antigens are A and B, typed ABO. Although A/B antibodies are not found in the blood until about 2 months after birth. (Fig 19.12) • Blood Type TYPE A TYPE B TYPE AB TYPE O Rh Surface-antigen A B + + + + D US pop 40% 10 4 46 In plasma antibodies A B + + + + Blood donor and Recipient: • Blood may be received from the subject of the same blood type, but not from the other type, except one with subject with type O. • Type O subject, who has no surface A/B antigen, has been considered as a universal donor, since the donated RBC will not be coagulated. • However, the antibodies in the plasma can interact with the surface antigens of the recipient and may induce minor reactions. Thus, the word “universal donor” is misleading. • Another important antigen is the Rh factor. Rh-positive or Rh-negative. The Rh positive subjects have the D antigen on the surface of the erythrocytes. About 86% of the people in the US are RH positive. • Hemolytic Disease of the Newborn (HDN) The End.