Blood Physiology: RBC, WBC, Hemostasis (Textbook)

BLOOD PHYSIOLOGY Dr Sakineh Shafia TEXTBOOK OF MEDICAL PHYSIOLOGY GUYTON & HALL 14TH EDITION 1 Physiology Is the scientific study of the normal function in living systems The branch of biology that study all of the parts of living organisms and their various...

BLOOD PHYSIOLOGY Dr Sakineh Shafia TEXTBOOK OF MEDICAL PHYSIOLOGY GUYTON & HALL 14TH EDITION 1 Physiology Is the scientific study of the normal function in living systems The branch of biology that study all of the parts of living organisms and their various function. 2  Objectives  At the end of this lecture you should be able to: 1. Describe Cellular and non-cellular components of the blood. 2. Recognize functions of the blood. 3. Define Erythropoiesis; leucopoiesis, thrombopoiesis. 4. Recognize sites of RBC formation at different developmental age. 3  Objectives cont… 5. Describe different stages of RBC differentiation. 6. Describe features of RBC maturation. 7. Describe regulation of RBC production and erythropoietin hormone secretion in response to hypoxia. 8. Recognize clinical conditions associated with high level of erythropoietin in the blood.  Blood:is a connective tissue in fluid form. It is considered as the fluid of life because it carries oxygen from lungs to all parts of the body and carbon dioxide from all parts of the body to the lungs. Properties of the blood 1. Color: Blood is red in color. Arterial blood is Scarlet red because of Hbo2 and venous blood is purple red because of more CO2. 5  Volume: The average volume of the blood in a normal adult is 5 L. In newborn baby it is 450 ml. It increases during growth and reaches 5 L at the time of puberty. In females, it is slightly less and is about 4.5 L It is about 8% of the body weight in a normal young healthy adult weighing about 70 kg. 6 BLOOD COMPOSITION 1. Cellular components: ○ Red Blood Cells (Erythrocytes) ○ White Blood Cells (Leucocytes) ○ Platelets (Thrombocytes) 2. Plasma: ECF ○ 98% water + ions + plasma proteins e.g. (Albumin, globulin, Fibrinogen) ○ Same ionic composition as interstitial fluid. 7 FUNCTIONS OF BLOOD 1. Transport  O2, CO2, nutrient, hormones, waste product 2. Homeostasis Regulation of body temperature, ECF pH 3. Protecting against infections White Blood Cells, Antibodies 4. Blood clotting prevent blood loss 8  Blood Cells Formation Erythropoiesis: Formation of RBC (erythrocytes) Leucopoiesis: Formation of WBC (leucocytes) Thrombopoiesis: Formation of platelets (thrombocytes) 9 Hematopoiesis 10  Production of RBC In-utero: Early few weeks nucleated RBCs are formed in yolk sac. Middle trimester mainly in liver & spleen & lymph nodes. Last months RBCs are formed in bone marrow of all bones ---------------------------------------------------------------------------- After Birth: Bone marrow of flat bone continue to produce RBC Shaft of long bone stop to produce RBC at puberty while epiphysis continued 11  Hematopoiesis Begins in early embryonic life and continues throughout life  Yolk sac 3rd to 10th Week  Liver 6th to 32nd Week  Spleen 10th to 25th Week  Bone marrow 30th to 36th Week and also after birth  12 13 14 15 16 Bone Marrow Red Bone Marrow (Active Bone marrow) Yellow Bone Marrow (Inactive Bone marrow) 17 Blood is made of two parts: 1-Plasma which makes up 55% of blood volume 2- cellular elements (red and white blood cells, and platelets) which combine to make the remaining 45% of blood volume. 18  Composition of Blood Hematocrit – measure of % RBC – Males: 47% ± 5% – Females: 42% ± 5% 19 20 Composition of Whole Blood 21 Figure 19.1c 22  Straw colored, Plasma nonliving part of blood. 90% Water Helps to regulate body temperature Contains Electrolytes transports blood cells, products of digestion and hormones throughout the body. 23 PLASMA PROTEINS The plasma proteins are: 1. albumin 2. globulin 3. Fibrinogen. Globulin is of three types, α-globulin, β-globulin and γ-globulin. 24 The ratio between plasma level of albumin and globulin is called Albumin/Globulin (A/G) ratio. It is an important indicator of some liver and kidney diseases. Normal A/G ratio is 2:1. 25  ORIGIN OF PLASMA PROTEINS  In embryonic stage, the plasma proteins are synthesized by the mesenchyme cells.  In adults, the plasma proteins are synthesized mainly from reticuloendothelial cells of liver and also from spleen, bone marrow, general tissue cells.  Gamma globulin is synthesized from B lymphocytes. 26  FUNCTIONS OF PLASMA PROTEINS 1. Role in Coagulation: Blood Fibrinogen is essential for the coagulation of Blood. 2. Role in Defense Mechanism: gamma globulins play an important role in the defense mechanism by acting as antibodies. These proteins are also called immunoglobulins. 27 3. Role in Transport Mechanism: Plasma proteins are essential for the transport of various substances in the blood. Albumin, alpha globulin and beta globulin are responsible for the transport of the hormones, enzymes, etc. The alpha and beta globulins transport metals in the blood. 28 4. Role in Maintenance of Osmotic pressure : Pressure in Blood Plasma proteins exert the colloidal osmotic (oncotic) pressure. The osmotic pressure exerted by the plasma proteins is about 28 mm Hg. Since the concentration of albumin is more than the other plasma proteins, it exerts maximum pressure. 29 5. Role in Regulation of Acid-base Balance: Plasma proteins, particularly the albumin, play an important role in regulating the acid-base balance in the blood. 30  6. Role in Viscosity of Blood: The plasma proteins provide viscosity to the blood, which is important to maintain the blood pressure. Albumin provides maximum viscosity than the other plasma proteins. 31  32 Erythrocytes, leukocytes and thrombocytes SEM x1,825 Pluripotent Stem Cells in Bone Marrow and Cord Blood 33 By Ambreen Shaikh and Deepa Bhartiya  Characteristics of RBCs Biconcave discs size : 7.5 Micrometer Membrane flexible No Mitochondria, ribosome or RNA Anaerobic Glycolysis Life Span 120 days 4.7-5.2 million/ mm3 Hb = 14-16 g/dl in the blood 34  Red Blood Cells (RBC): Function: – O2 transport – CO2 transport – Buffer 35  Genesis (Production) of RBC All blood cell are formed from Pluripotential hematopoietic stem cells  committed cells: Committed stem cells for RBC Committed stem cells for WBC Growth of different stems cells are controlled by different growth factors 36  Stages of differentiation of RBC – Stages of RBC development: Committed stem cell Proerthroblast basophil erythroblast polychromatophil erythroblast orthochromatic erythroblast Reticulocytes Mature erythrocytes In cases of rapid RBC production  reticlocytes in the circulation. 37  Erythropoiesis  RBC development is characterize by:  decrease in cell size.  disappearance of nucleus.  appearance of hemoglobin (Hb) 38 39 40  Growth and reproduction of the different stem cells are controlled by multiple proteins called: growth inducers.(interleukin-3) differentiation inducers: causes one type of committed stem cell to differentiate one or more steps toward a final adult blood cell. 41  Formation of the growth inducers and differentiation inducers is controlled by factors outside the bone marrow. For instance, in the case of RBCs, exposure of the blood to low oxygen for a long time causes growth induction, differentiation, and production of greatly increased numbers of RBCs 42  Regulation of RBC production Erythropoiesis is stimulated by erythropoietin hormone produced by the kidney in response to hypoxia (low oxygen in the blood) Hypoxia ( oxygen) caused by: – Low RBC count (Anaemia) – Hemorrhage – High altitude – Prolong heart failure – Lung disease 43 Production of erythropoietin by Kidney in response to its O2 Supplies 44  Erythropoietin Is Formed Mainly in the Kidneys. erythropoietin is secreted mainly by fibroblast. fibroblast cells surrounding the tubules in the cortex and outer medulla, where much of the kidney’s oxygen consumption occurs. Renal tissue hypoxia leads to increased tissue levels of hypoxia- inducible factor–1: (HIF1) norepinephrine and epinephrine and several of the prostaglandins stimulate erythropoietin production. 45 Tissue oxygenation and RBC formation 46 High altitude 47 Muscular exercise. Emotional Conditions 48  Erythropoietin: Glycoprotein. 90% from renal cortex 10% liver. Stimulate the growth of early stem cells. Does not affect maturation process. Can be measured in plasma & urine.  Conditions like: anemia , High altitude , Heart failure , Lung Disease Result in High erythropoietin levels and polycythemia 49 Role of the kidneys in RBC formation 50 Hemoglobin 51 Hemoglobin 52 53 Normal Hb types: Hb A: Hb A2: Hb F (Fetal Hb): 54  Iron Metabolism Iron important part of hemoglobin, myoglobin and other structures – ~65% of total iron in hemoglobin – 4% myoglobin – 1% various heme compounds – 0.1% in plasma combined with transferrin – 15-30% stored in liver as ferritin 55 Iron Metabolism: Key to Hemoglobin O2 Transport 56  Transferrin is made in the form of apo transferrin by the liver Apo transferrin is inactive And after binding to iron, it becomes transferrin and becomes active Dietary iron is triple positive and it becomes positive twice with vitamin C 57  Factors affecting Erythropoiesis Fe Vitamins :Vit B12, Folic Acid, Vit C, Protein diet Erythropoietin 58  MATURATION FACTORS 1. Vitamin B12 (Cyanocobalamin). is essential for synthesis of DNA, cell division and maturation in RBCs. It is absorbed from the small intestine in the presence of intrinsic factor of stomach Vitamin B12 is stored mostly in liver and in small quantity in muscle. Its deficiency causes pernicious anemia in which the cells remain larger with fragile and weak cell membrane. 59  2. Intrinsic Factor It is produced in gastric mucosa by the parietal cells of the gastric glands. It is essential for the absorption of vitamin B12 from intestine. Absence of intrinsic factor also leads to pernicious anemia The deficiency of intrinsic factor occurs in conditions like severe gastritis, ulcer and gastrectomy. 60 3. Folic Acid Folic acid is also essential for the synthesis of DNA. Deficiency of folic acid decreases the DNA synthesis causing maturation failure. Here the cells are larger and remain in megaloblastic stage which leads to megaloblastic anemia. 61  erythrocyte disorders POLYCYTHEMIA ANEMIA 62  Polycythemia polycythemia is the increase in the RBC count. The count increases above 7 millions/cu mm of the blood. Polycythemia is of two types: 1.primary polycythemia 2.secondary polycythemia. 63 Primary Polycythemia — Polycythemia vera It is a disease characterized by persistent increase in RBC count above 14 millions/cu mm of blood. This is always associated with increased WBC count above 24,000/cu mm of blood. Polycythemia vera occurs because of red bone marrow malignancy. 64  Secondary Polycythemia It is the pathological or physiologic condition. A: pathological condition 1. Respiratory disorders like emphysema, Tuberculosis or pneumonia 2. Congenital heart disease 3. heart disease B:physiologic condition. 1.Exercise 2.Increase in metabolism ( Androgens) 3. Life in the highlands 65  Respiratory disorders In respiratory failure, the lungs do not have the ability to absorb enough oxygen, The created hypoxia increases the secretion of erythropoietin. Pulmonary emphysema means too much air in the lungs, which is caused by nicotine consumption and paralysis of airway cilia 66 Heart disease In heart disease, the heart does not have the ability to pump blood properly, Therefore, the cells suffer from hypoxia 67 Anemia is the blood disorder characterized by the reduction in: 1. Red blood cell count 2. Hemoglobin content 3. Packed cell volume. 68  69 ERYTHROCYTE DISORDERS ANEMIA  Insufficient of RBCs  Hemorrhagic anemia  Hemolytic anemia  Aplastic anemia  Malnutrition (Low VB12,Fe )  Pernicious anemia - macrocytic  Iron deficiency – microcytic  Abnormal hemoglobin  Thalassemia  Sickle cell Anemia  Abnormal Shape  spherocytosis  ANEMIAS 1.Blood Loss Anemia. After rapid hemorrhage, the body replaces the fluid portion of the plasma in 1 to 3 days, but this response results in a low concentration of RBCs. the RBC concentration usually returns to normal within 3 to 6 weeks. 2.Iron Deficiency If a person cannot absorb enough iron from the intestines to form hemoglobin as rapidly as it is lost. RBCs that are much smaller than normal and have too little hemoglobin inside them are then produced, giving rise to microcytic hypochromic anemia, 70  Anemia Due to Malnutrition: Iron deficiency Vitamin B12 deficiency Protein deficiency 71 In pathological conditions, the variations in size of RBCs are: 1. Microcytes —smaller cells 2. Macrocytes — larger cells 3. Anisocytosis —cells of different sizes. Microcytes Microcytes are present in: i. Iron deficiency anemia ii. Increased osmotic pressure in blood 72  Megaloblastic Anemia. vitamin B12, folic acid, and intrinsic factor from the stomach mucosa deficiency 73 3- Hemolytic Anemia:  hereditary spherocytosis  sickle cell anemia  erythroblastosis fetalis  Thalassemia 74  hereditary spherocytosis In this disease, the ratio of surface to volume is smaller than 1 75 sickle cell anemia, the cells have an abnormal type of hemoglobin called hemoglobin S, containing faulty beta chains in the hemoglobin molecule When this hemoglobin is exposed to low concentrations of oxygen, it precipitates into long crystals inside the RBC. These crystals elongate the cell and give it the appearance of a sickle rather than a biconcave disc. which leads to ruptured RBCs. 76  Erythroblastosis fetalis 77 erythroblastosis fetalis, Rh-positive RBCs in the fetus are attacked by antibodies from an Rh- negative mother. These antibodies make the Rh-positive cells fragile, leading to rapid rupture and causing the child to be born with a serious case of anemia. The extremely rapid formation of new RBCs to make up for the destroyed cells in erythroblastosis fetalis causes a large number of early blast forms of RBCs to be Released from the bone marrow into the blood. 78 79  Thalassemia Half of the hemoglobin is paternal and half is maternal. Thalassemia is minor if one of the parents carries the defective gene, And if both parents carry the defective gene, it is thalassemia major 80  In thalassemia major, globular lysis is high and iron deposition in the liver, heart, and adrenals is harmful. Desferal is a compound that prevents the deposition of iron in tissues Desferal causes urinary excretion of excess iron Timely transfusion and use of Desferal helps to improve them 81  82 Anemia - Aplastic Anemia Due to Bone Marrow Dysfunction A) Rays X ray UV ray Gamma ray B) Drugs Sedatives Antibiotics chemotherapy C) toxic chemicals insecticides benzene in gasoline D) autoimmune disorders E) Idiopathic aplastic.Aplastic Anemia Due to Bone Marrow Dysfunction. Bone marrow aplasia means lack of functioning bone marrow. For example, 1.exposure to high-dose radiation 2.chemotherapy for cancer treatment can damage stem cells 3.high doses of certain toxic chemicals, such as insecticides or benzene in gasoline, may cause the same effect. 83 Aplastic Anemia Due to Bone Marrow Dysfunction 4.In autoimmune disorders, such as lupus erythematosus, the immune system begins attacking healthy cells such as bone marrow stem cells, which may lead to aplastic anemia. 5.idiopathic aplastic anemia. 6. Some medications People with severe aplastic anemia usually die unless they are treated with blood transfusions—which can temporarily increase the numbers of RBCs—or by bone marrow transplantation. 84  Effects of anemia on circulatory system function The viscosity of the blood, depends largely on the blood concentration of RBCs. In persons with severe anemia, the blood viscosity may fall to as low as 1.5 times that of water rather than the normal value of about 3. This change decreases the resistance to blood flow in the peripheral blood vessels, so far greater than normal quantities of blood flow through the tissues and return to the heart, thereby greatly increasing cardiac output. 85  Moreover, hypoxia resulting from diminished transport of oxygen by the blood causes the peripheral tissue blood vessels to dilate, allowing a further increase in the return of blood to the heart and increasing the cardiac output to a still higher level—sometimes three to four times normal. Thus, one of the major effects of anemia is greatly increased cardiac output, as well as increased pumping workload on the heart 86  effect of polycythemia on function of the circulatory system Because of the greatly increased viscosity of blood in polycythemia, blood flow through the peripheral blood vessels is often very sluggish. In accordance with the factors increasing blood viscosity decreases the rate of venous return to the heart. Conversely, the blood volume is greatly increased in polycythemia, which tends to increase venous return 87  Actually, the cardiac output in polycythemia is not far from normal because these two factors more or less neutralize each other. The arterial pressure is also normal in most people with polycythemia, although in about one-third of them, the arterial pressure is elevated. 88 Extravascular Pathway for RBC Destruction (Liver, Bone marrow, & Spleen) Phagocytosis & Lysis Hemoglobin Globin Heme Bilirubin Amino acids Fe2+ Amino acid pool Excreted 89  Circulation for about 120 days 3 7 Amino Reused for protein synthesis Fe3+ Transferrin Globin acids 4 6 5 Fe3+ 2 Heme Fe3+ Ferritin Transferrin + Globin Bilirubin 9 + 1 Biliverdin Liver Vitamin B12 Bilirubin 11 Red blood cell 10 + death and Erythopoietin phagocytosis Small Kidney 8 Erythropoiesis in Bilirubin intestine 13 red bone marrow 12 Urobilin Macrophage in Urobilinogen spleen, liver, or Bacteria Key: red bone marrow in blood Stercobilin Large 14 in bile Feces intestine Urine 90 91  What is the cause of Jaundice? Jaundice also called Bilirubinemia RBC’s may breaking down at high rate Liver may not be processing bilirubin Cirrhosis Hepatitis Bile duct may be occluded (gall stones) Infants – GI tract may not be prepared to eliminate it. (Hemolytic Disease of the Newborn) 92  Pathophysiology Jaundice Under normal circumstances, bilirubin undergoes conjugation within the liver, making it water-soluble. It is then excreted via the bile into the GI tract, the majority of which is egested in the faeces as urobilinogen and stercobilin (the metabolic breakdown product of urobilingoen). 93  Around 10% of urobilinogen is reabsorbed into the bloodstream and excreted through the kidneys. Jaundice occurs when this pathway is disrupted. 94  Types of Jaundice  Pre-Hepatic There is excessive red cell breakdown which overwhelms the liver’s ability to conjugate bilirubin. This causes an unconjugated hyperbilirubinaemia.  Intrahepatic or Hepatocellular There is dysfunction of the hepatic cells. The liver loses the ability to conjugate bilirubin, but in cases where it also may become cirrhotic,  Post-Hepatic obstruction of biliary drainage. The bilirubin that is not excreted will have been conjugated by the liver 95 NORMAL BILIRUBIN METABOLISM 96 Prehepatic (hemolytic) jaundice Results from excess production of bilirubin (beyond the livers ability to conjugate it) following hemolysis Excess RBC lysis is commonly the result of autoimmune disease; hemolytic disease of the newborn (Rh or ABO- incompatibility); structurally abnormal RBCs (Sickle cell disease); or breakdown of extravasated blood High plasma concentrations of unconjugated bilirubin (normal concentration ~0.5 mg/dL) 97 Intrahepatic jaundice Impaired uptake, conjugation, or secretion of bilirubin Reflects a generalized liver (hepatocyte) dysfunction In this case, hyperbilirubinemia is usually accompanied by other abnormalities in biochemical markers of liver function 98 Posthepatic jaundice Caused by an obstruction of the biliary tree Plasma bilirubin is conjugated, and other biliary metabolites, such as bile acids accumulate in the plasma Characterized by pale colored stools (absence of fecal bilirubin or urobilin), and dark urine (increased conjugated bilirubin) In a complete obstruction, urobilin is absent from the urine 99 100  Neonatal Jaundice Common, particularly in premature infants Transient (resolves in the first 10 days) retardation known as kernicterus If bilirubin levels are judged to be too high, then phototherapy with light is used to convert it to a water soluble, non-toxic form If necessary, exchange blood transfusion is used to remove excess bilirubin Jaundice within the first 24 hrs of life or which takes longer then 10 days to resolve is usually pathological and needs to be further investigated 101  Transport of Bilirubin in Plasma Bilirubin on release from macrophages circulates as unconjugated bilirubin in plasma tightly bound to albumin. Albumin + free Bilirubin Bilirubin ~ Albumin Complex Why bound to albumin? ★Increase the solubility of whole molecule ★ Prevent unconjugated bilirubin freely come into other tissue, cause damage. 102 ＊normal range of bilirubin: 1～16mol/l (0.1 ～1mg/dl) 2mg/ dl jaundice 103 104 105 Characteristics of human red cells 106 Blood Film 107  White blood cell Platelet Red blood cell SEM 3500x (a) Scanning electron micrograph 108  Key: Proenitor cells CFU–E Colony-forming unit—erythrocyte CFU– Colony-forming unit— Pluripotent Meg megakaryocyte CFU– Colony-forming unit—granulocyte stem cell GM macrophage Myeloid stem cell Lymphoid stem cell CFU–E NK lymphobla st Nucleus ejected ReticulocyteMegakaryocyte Red blood cell Platelets Eosinophil Basophil Neutrophil Monocyte B lymphocyte Natural T lymphocyte (erythrocyte) (thrombocytes) (T cell) (B cell) killer Granular leukocytes Agranular (NK) cell leukocytes Mast cell Macrophage Plasma cell 109  Objectives At the end of the lecture you should be able to: 1. Describe the role of WBCs in the body defence mechanisms. 2. Describe the normal functions of the various WBCs. 3. Describe the role of diapedesis, chemotaxis, phagocytosis as function of the WBCs.  White blood cells WBC: mobile units of the body's protective system. Normal count is 4000-11,000 /µL Types: Granulocytes (Polymorphnuclear or "polys"): – Neutrophils 60 % – Eosinophils 2 % – Basophils 0.4 % Agranulocytes (mononuclear): – Lymphocytes 30 % – Monocytes 5 %  Life span Granulocytes: 4-8 hours in blood, 4-5 days in tissues. Monocytes: 10-20 hours in blood, months in tissue (tissue macrophages) Lymphocytes live for weeks or months. Neutrophils and Macrophages defend against infections  Phagocytosis Definition: Cellular ingestion of the offending agent. Most important function of neutrophils and macrophages.  Neutrophils Segmented nucleus Mature cells that can attack and destroy bacteria even in the circulating blood. Attach to the particle and project pseudopodia around it→ an enclosed chamber that contains the phagocytized particle which breaks away → free floating phagosome. Can phagocytize 3-20 bacteria before it dies.  monocytes Bean-shaped nucleus Immature in blood (1-2 days) In tissues → mature and enlarge → tissue macrophages. Much more powerful phagocytes than neutophils. Can phagocytize as many as 100 bacteria. Can engulf large particles e.g. malarial parasites. Can survive after phagocytosis for months.  Neutrophils and monocytes reach the site of infection by the following mechanisms: They squeeze through the pores of the capillaries by diapedesis. They move toward the site of infection by amoeboid movement. Different chemicals released by microbes and inflamed tissues attract neutrophils and macrophages→ chemotaxis. 122  Interstitial fluid Blood flow Neutrophil Endothelial cell Rolling Sticking Squeezing between endothelial cells Key: Selectins on endothelial cells Integrins on neutrophil 123 124 125  Basophils Similar to mast cells outside capillaries in connective tissue.( have heparin, histamine, bradykinin) Both basophils and mast cells release heparin into blood, which prevent blood coagulation. Play a role in allergic reactions. When ruptured histamine and other substances released cause local vascular and tissue reactions that are characteristic of allergic manifestations.  Eosinophils They attach themselves to the surface of the parasite and release substances that kill the invading parasite. Release of eosinophil chemotactic factor from mast cells and basophils → make them collect in tissues in which allergic reaction has occurred → prevent the spread of the inflammatory process (detoxify substances and destroy Ag-Ab complexes).  Lymphocytes Lymphocytes are responsible for acquired immunity. They are present in lymph nodes and other lymphoid tissues throughout the body. B lymphocytes: Processed in bone marrow. When exposed to an Ag, they differentiate to plasma cells that produce antibodies (gamma globulins). This initiates the destruction of the antigen. T lymphocytes: Processed in thymus. They release chemicals that destroy target cells with which they make contact such as virus infected cells and cancer cells. 2nd Year Medicine- IBLS Module May 2008  White blood cell (leukocyte— neutrophil) Blood plasma Red blood cell (erythrocyte) Platelet White blood cell (leukocyte— monocyte) LM 400x (b) Blood smear 130 131 132  An increase in white blood cells in an infectious disease is leukocytosis An excessive increase in white blood cells for no apparent reason is leukemia Leukemia 134 Hemostasis and Blood Coagulation 135  The term hemostasis means prevention of blood loss. Whenever a vessel is severed or ruptured, hemostasis is achieved by several mechanisms: 1.vascular constriction; 2.formation of a platelet plug; 3.formation of a blood clot as a result of blood coagulation; 4.preventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently 136  (1) vascular constriction Immediately after a blood vessel has been cut or ruptured, the trauma to the vessel wall causes smooth muscle in the wall to contract; this instantaneously reduces the flow of blood from the ruptured vessel. 137  The contraction results from the following: (1) local myogenic spasm; (2)local autacoid factors from the traumatized tissues, vascular endothelium, and blood platelets; (3) nervous reflexes. 138  (1) local myogenic spasm; This reflex originates from the smooth muscle of the vessel wall And it is the contraction of the smooth muscle of the vessel in response to stimuli. 139  (2)local autacoids And that is the vasoconstrictor chemical compounds released from the damaged vessel. 140  The nervous reflexes are initiated by pain nerve impulses or other sensory impulses that originate from the traumatized vessel or nearby tissues. However, even more vasoconstriction probably results from local myogenic contraction of the blood vessels initiated by direct damage to the vascular wall. 141  for the smaller vessels, the platelets are responsible for much of the vasoconstriction by releasing a vasoconstrictor substance, thromboxane A2. The more severe the injury, the contraction of the vessel is greater. The spasm can last for many minutes or even hours, during which time the processes of platelet plugging and blood coagulation can take place. 142  stages of blood hemostasis Step 1: Vascular spasms Required factors: Endothelin Serotonin Step 2: Formation of a platelet plug Required factors: ADP Serotonin Thromboxane A2 von Willebrand factor 143  STEP 3: COAGULATION Phase 1: Formation of prothrombinase (also known as prothrombin activator) Phase 2: Conversion of prothrombin to thrombin Phase 3: Conversion of soluble fibrinogen into insoluble fibrin 144  Damage to wall of blood vessel Collagen Tissue factor exposed exposed Platelets adhere and Vasoconstriction release Coagulation platelet cascade factors Platelets aggregate Thrombin formation Converts fibrinogen Temporary Reinforced to fibrin hemostasis platelet plug (clot) Fibrin slowly Cell growth and dissolved by tissue repair plasmin Clot Figure 16-10 dissolves Intact blood vessel wall 145  Origin and structure Platelets The origin of the platelets is Megakaryocyte. Megakaryocytes diameter 35‐160 μm Platelet diameter 2‐3 μm Contain an irregular ring of lobed nuclei Platelets are formed within the cytoplasm of megakaryocytes and released into the circulation Platelet survival time 8‐12 days Destroyed mainly in spleen Blood count: 150,000-450,000 in cu/mm of blood  Structure of platelet Membrane structure: surface glycoproteins serve as receptors, facilitate platelet adhesion & contraction, and determine expression of specific platelet antigens and antigens shared with other formed elements Canalicular system: Dense tubular system : is the major site for storage of Ca2+ and the location of cyclooxygenase FORMATION OF PLATELETS 148 Physical and Chemical Characteristics of Platelets 1) actin and myosin molecules, another contractile protein, thrombosthenin, 2) the endoplasmic reticulum and the Golgi (3) mitochondria and enzyme systems (4) enzyme systems that synthesize prostaglandins, (5) an important protein called fibrin-stabilizing factor, (6) growth factor 150 Platelet Plug Formation Formation of a platelet plug in a severed blood vessel. Endothelial injury and exposure of the vascular extracellular matrix facilitates platelet adhesions and activation, which changes their shape and causes release of adenosine diphosphate (ADP), thromboxane A2 (TXA2), and platelet-activating factor (PAF). These platelet-secreted factors recruit additional platelets (aggregation) to form a hemostatic plug. Von Willebrand factor (vWF) serves as an adhesion bridge between subendothelial collagen and the glycoprotein platelet receptor. 152  Importance of Platelet Mechanism for Closing Vascular Holes. The platelet-plugging mechanism is extremely important for closing minute ruptures in very small blood vessels that occur many thousands of times daily. Indeed, multiple small holes through the endothelial cells themselves are often closed by platelets actually fusing with the endothelial cells to form additional endothelial cell membranes. 153  thousands of small hemorrhagic areas develop each day under the skin (petechiae, which appear as purple or red dots on the skin) and throughout the internal tissues of a person who has few blood platelets. This phenomenon does not occur in persons with normal numbers of platelets. 154 Suggested sequence of events in hemostasis: Platelet adherence to collagen in damaged vessels wall ATP is converted to ADP by ATPase ADP is released and promotes aggregation of passing platelets : formation of platelet plug Release of tissue factor from damaged vessels & phospholipids from platelets will promote thrombin formation Firm clot seals the vessel permanently  Blood coagulation BLOOD COAGULATION IN THE RUPTURED VESSEL The third mechanism for hemostasis is formation of the blood clot. The clot begins to develop in 15 to 20 seconds if the trauma to the vascular wall is severe and in 1 to 2 minutes if the trauma is minor. 157  Activator substances from the traumatized vascular wall, from platelets, and from blood proteins adhering to the traumatized vascular wall initiate the clotting process. 158 Within 3 to 6 minutes after rupture of a vessel, the entire opening or broken end of the vessel is filled with clot if the vessel opening is not too large. After 20 to 60 minutes, the clot retracts, which closes the vessel still further. Platelets also play an important role in this clot retraction. 159  MECHANISM OF BLOOD COAGULATION More than 50 important substances that cause or affect blood coagulation have been found in the blood and in the tissues—some that promote coagulation, called procoagulants, and others that inhibit coagulation, called anticoagulants. 160 Whether blood will coagulate depends on the balance between these two groups of substances. In the blood stream, the anticoagulants normally predominate, so the blood does not coagulate while it is circulating in the blood vessels. However, when a vessel is ruptured, procoagulants from the area of tissue damage become activated and override the anticoagulants, and then a clot does develop. 161 162 163  Coagulation A set of reactions in which blood is transformed from a liquid to a gel. Coagulation follows intrinsic and extrinsic pathways The final three steps of this series of reactions are: – Prothrombin activator is formed – Prothrombin is converted into thrombin – Thrombin catalyzes the joining of fibrinogen into a fibrin mesh 165 1.Prothrombin activator is formed as a result of rupture of a blood vessel or as a result of damage to special substances in the blood. 2. Prothrombin activator, in the presence of sufficient amounts of ionic calcium (Ca2+), causes conversion of prothrombin to thrombin 3. Thrombin causes polymerization of fibrinogen molecules into fibrin fibers within another 10 to 15 seconds. 166 Prothrombin activator is generally considered to be formed in two ways, although, in reality, the two ways interact constantly with each other: (1) by the extrinsic pathway that begins with trauma to the vascular wall and surrounding tissues; (2) by the intrinsic pathway that begins when a blood cell is damaged 167  In both the extrinsic and the intrinsic pathways, a series of different plasma proteins called blood-clotting factors plays a major role. Most of these proteins are inactive forms of proteolytic enzymes. When converted to the active forms, their enzymatic actions cause the successive, cascading reactions of the clotting process. 168  Extrinsic Pathway for Initiating Clotting The extrinsic pathway for initiating the formation of prothrombin activator begins with a traumatized vascular wall or traumatized extravascular tissues that come in contact with the blood. 169 170  Intrinsic Pathway for Initiating Clotting The second mechanism for initiating formation of prothrombin activator, and therefore for initiating clotting, begins with trauma to the blood or exposure of the blood to collagen from a traumatized blood vessel wall. For example, when you put a drop of blood on a slide Or you pour the blood into the test tube 171 172  Common Pathways to the Fibrin Mesh Thrombin catalyzes the polymerization of fibrinogen into fibrin Insoluble. fibrin strands form the structural basis of a clot Fibrin causes plasma to become a gel-like trap Fibrin in the presence of calcium ions activates factor XIII that: – Cross-links fibrin – Strengthens and stabilizes the clot Fibrinogen Fibrin  Thrombin Fibrinogen Fibrin  Prothrombin Xa Va Thrombin Fibrinogen Fibrin  Extrinsic Pathway TF Prothrombin VIIa Xa Va Thrombin Fibrinogen Fibrin Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIIIa Xa Va Thrombin Fibrinogen Fibrin Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIIIa Xa Va Soft clot Thrombin Fibrinogen Fibrin XIIIa Hard clot Fibrin Intrinsic pathway XIIa Extrinsic Pathway XIa TF Prothrombin IXa VIIa VIII VIIIa Xa Va V Soft clot Thrombin Fibrinogen Fibrin XIIIa Hard clot Fibrin  Platelet Red blood cell (a) Early stage Fibrin threads (b) Intermediate stage 181  Factors II, VII, IX, X, protein C & protein S are formed in the liver  Vitamin K is necessary for some post translational modifications in these factors.  In vitamin K defficiency or inhibition by oral anticoagulant ,Warfarin the plasma levels of these factors are low 182 183  Ethylenediaminetetraacetic acid (EDTA) : It inhibits clotting by removing or chelating calcium from the blood Sodium oxalate: like citrates, can be used to remove calcium ions (Ca2+) from blood plasma Heparin : natural anticoagulant produced by basophils and mast cells that inhibits thrombin by enhancing the activity of antithrombin III 184  Intravascular Anticoagulants Prevent Blood Clotting in the Normal Vascular System Endothelial Surface Factors: (1) the smoothness of the endothelial cell surface, (2) a layer of glycocalyx on the endothelium (3) a protein bound with the endothelial membrane, thrombomodulin, which binds thrombin. thrombomodulin-thrombin complex also activates a plasma protein, protein C, that acts as an anticoagulant by inactivating activated Factors V and VIII. 185  When the endothelial wall is damaged, its smoothness and glycocalyx-thrombomodulin layer are lost, Which activates both factor XII and the platelets, thus setting off the intrinsic pathway of clotting. 186  Intact endothelial cells also produce other substances such a prostacyclin and nitric oxide (NO) that inhibit platelet aggregation and initiation of blood clotting. Prostacyclinis a vasodilator, as well as an inhibitor of platelet aggregation. NO is a powerful vasodilator and it is an important inhibitor of platelet aggregation. When endothelial cells are damaged, their production of prostacyclin and NO is greatly diminished. 187  Antithrombin Action of Fibrin and Antithrombin III. Among the most important anticoagulants in the blood are those that remove thrombin from the blood. The most powerful of these are the following: (1) the fibrin fibers that are formed during the process of clotting; (2) an α globulin called antithrombin III or antithrombinheparin cofactor. 188 The complex of heparin and antithrombin III removes several other activated coagulation factors in addition to thrombin,  The others include activated Factors XII, XI, X, and IX. 189  Clot retraction Clot retraction occurs by shortening of fibrin fibers produced by contraction of attached platelet pseudopodia, which contain actomyosin like protein. 190  PLASMIN CAUSES LYSIS OF BLOOD CLOTS The plasma proteins contain a euglobulin called plasminogen (or profibrinolysin) that, when activated, becomes a substance called plasmin (or fibrinolysin). Plasmin digests fibrin fibers and some other protein coagulants such as: fibrinogen, Factor V, Factor VIII, prothrombin, and Factor XII. 191 Coagulation and Fibrinolysis 192  Factors Effecting Clot Formation Normal coagulation:  Normal platelets  ALL clotting factors  Vitamin K  Calcium ions  TF 193  Conditions that cause excessive bleeding in humans can result from a deficiency of any one of the many blood-clotting factors. For example: Vitamin K is an essential factor (1) vitamin K deficiency, for five of the important (2) hemophilia, clotting factors activation: (3) thrombocytopenia prothrombin, (platelet deficiency). Factor VII, Factor IX, Factor X, protein C 194  Effects of Drugs on Clotting Aspirin = antiprostaglandin that inhibits thromboxane A2 Heparin = natural anticoagulant that inhibits thrombin by enhancing the activity of antithrombin III Warfarin = interfers with the action of vitamin K 195