Physiology of blood system.

Blood system Blood system firstly was proposed by Lung in 1936. It consist of - blood circulated through the blood circulatory system - blood forming organs - blood destroying organs - regulatory apparatus.

Functions of blood Transport of cells and compounds Limit blood loss through damaged vessels Defend against pathogens, toxins

Amount of blood The amount of blood in the body has been measured in various ways. Naturally the volume of blood can be expected to vary with the size of the body. The blood volume of an adult human of average size is about 6-8 % in man – 52-83 mL/kg; woman – 50-75 mL/kg.

Blood Components Plasma (55%) water (90%), ions, proteins, gases, nutrients, wastes, hormones Cells (45%) RBCs, WBCs, platelets Develop from stem cells in bone marrow

Plasma Water – 90 % Solids – 10 % Proteins – 8 % Others – 1,1 % sodium, calcium, potassium, magnesium, chloride, bicarbonate, phosphate, sulfate Proteins – 8 % serum albumin, serum globulin, fibrinogen Others – 1,1 % Nonprotein nitrogenous substances: urea, uric acid, creatine, creatinine, ammonium salts, amino acids Nonnitrogenous substances: glucose, fats, cholesterol hormones Water – 90 % Solids – 10 % Inorganic chemicals – 0,9 % Organic chemicals – 9,1 % Gases oxygen, carbon dioxide, nitrogen

Proteins One liter of plasma has 65-85 gram of proteins. Concentration of albumins is 35-50 g/L; globulins is alpha-1-globulins – 1-4 g/L, alpha-2-globulins – 4-8 g/L, beta-globulins – 6-12 g/L, gamma-globulins – 8-16 g/L; fibrinogen – 2-4 g/L. Plasma which are not contain fibrinogen called serum (it is necessary for understanding the immunology, therapy etc.)

Albumins Albumins: on 80 % it provides oncotic pressure, contacts with bilirubin, fat acids, antibiotics, sulfanilamides. It connects with them and transports them. It produces in liver in average quantity of 17 gram per day.

Globulins Globulins produces in average quantity of 5 gram per day. in lymphatic nodes, in liver, in bone marrow Alpha-1-globulins connected with carbohydrates This is glycoproteins. (for example 2/3 of all glucose connected with alpha-1-globulins) Alpha-2-globulins connect 90 % of cupper. This is cerruloplasmin. Its may produced in hormones, for example, thyroxin, connected by vitamin B12. From this protein produce angiotensins (substances which are take place in increase of blood pressure). Beta-globulin carry out 75 % of fats, iron (for example, transferrin). Gamma-globulins has protective functions (for example, antibodies). two-thirds

Fibrinogen Fibrinogen is a protein which are produced by liver and take place in hemostasis system. Fibrinogen is dissolved form, which transform in insolved form – fibrin and provide coagulative hemostasis (plug production) and prevent bleeding. Daily production of fibrinogen is 2-4 g/L.

Quantity of cells, their changing Erythrocytes (In men – 4,0-5,1 Tera/L; in women – 3,7-4,7 Tera/L. ) The quantity of erythrocytes may be increase – in pregnancy, in physical training, mental work, in newborn or decrease. Leukocytes (Their number is 4-9 Giga/L. ) The number of leukocytes may increase – physical work, emotional load, in newborn, inflammation or decrease. Platelets (Their number is 180-320 Giga/L.)

Occurs in red bone marrow Blood Cell Formation Hematopoiesis: blood cell formation Hemopoiesis—The cellular pathways by which the formed elements are produced. Stem cells (hemocytoblasts)—Cells that divide and mature to produce all three classes of formed elements. skull, pelvis, ribs, s ternum, humerus, femur Occurs in red bone marrow

What are Red Blood Cells? Also called, erythrocytes or RBCs Make up about 45% of whole blood volume Make up 99.9% of the formed elements Red blood cells (RBCs) are the most numerous cells in the body. They circulate for about four months before being recycled; millions are produced each second.

Hematocrit—Percentage of whole blood volume taken up by formed elements (mostly RBCs). In clinical shorthand, it’s called, the “crit.”

What are the Properties of RBCs? Transport oxygen and carbon dioxide in blood stream Lack most organelles Makes more room for hemoglobin Degenerate after about 120 days The hemoglobin inside transports oxygen from the lungs to peripheral tissues and carbon dioxide from the tissues to the lungs.

The Anatomy of Red Blood Cells

What is the Red Blood Cell Composition? Hemoglobin makes up 95% of RBC protein Globular protein composed of four subunits Each subunit contains: A globin protein chain A molecule of heme An atom of iron A binding site for one oxygen molecule

What are White Blood Cells (WBCs)? Also called, leukocytes Defend the body against: Pathogens Toxins Abnormal cells Damaged cells

What are the Three Types of Granulocytes? Neutrophils 50–70% of circulating WBCs Phagocytic Eosinophils Less common Attracted to foreign proteins Basophils Release histamine Promote inflammation

What are Two Types of Agranulocytes? Lymphocytes Found mostly in lymphatic system Provide specific defenses Attack foreign cells Produce antibodies Destroy abnormal (cancer) cells Monocytes Migrate into tissues Become macrophages Live as phagocytic amoeba

Platelets Produced in the bone marrow Cell fragments (irregularly- shaped bodies) Needed for clotting blood

HEMOSTASIS Hemostasis The process by which the body stops bleeding upon injury and maintains blood in the fluid state in the vascular compartment Process is rapid and localized

HEMOSTASIS The primary players in hemostasis include Blood vessels Platelets Plasma proteins Coagulation proteins – involved in clot formation Fibrinolysis – involved in clot dissolution Serine protease inhibitors Other minor players include Kinin system Complement system

HEMOSTASIS Defects In blood vessels, platelets or serum proteins can be corrected by utilization of the other 2 players In 2 of the 3 players results in pathologic bleeding Blood Vessels Plasma Proteins Platlets

HEMOSTASIS Hemostasis can be divided into two stages Primary hemostasis Response to vascular injury Formation of the “platelet plug” adhering to the endothelial wall Limits bleeding immediately Secondary Hemostasis Results in formation of a stable clot Involves the enzymatic activation of coagulation proteins that function to produce fibrin as a reinforcement of the platelet plug Gradually the stable plug will be dissolved by fibrinolysis

FORMATION OF A STABLE PLUG

VASCULAR SYSTEM Smooth and continuous endothelial lining is designed to facilitate blood flow Intact endothelial cells inhibit platelet adherence and blood coagulation Injury to endothelial cells promotes localized clot formation Vasoconstriction Narrows the lumen of the vessel to minimize the loss of blood Brings the hemostatic components of the blood (platelets and plasma proteins) into closer proximity to the vessel wall Enhances contact activation of platelets Von Willebrand factor Collagen fibers Platelet membrane glycoprotein Ib Activated platelets enhance activation of coagulation proteins

PRIMARY HEMOSTASIS Platelets Interact with injured vessel wall Interact with each other Produce the primary hemostatic plug Primary platelet plug Fragile Can easily be dislodged from the vessel wall

PLATELETS Platelets Small, anucleated cytoplasmic fragments Released from megakaryocytes in the BM Megakaryocyte proliferation is stimulated by thrombopoietin (TPO) Humoral factor Produced primarily by liver, kidney, spleen, BM Produced at a relatively constant rate Normal platelet count is 150-400 x 109/L Survive 9-12 days Nonviable or aged platelets removed by spleen & liver 2/3 of platelets circulate in the peripheral blood 1/3 are sequestered in the spleen These 2 pools are in equilibrium and constantly exchanging Spontaneous hemorrhaging occurs when platelet count gets below 10 x 109/L

PLATLETS

MATURE MEGAKARYOCYTE

PLATELET RELEASE

PLATELET FUNCTION Platelets function to Provide negatively charged surface for factor X and prothrombin activation Release substances that mediate vasoconstriction, platelet aggregation, coagulation, and vascular repair Provide surface membrane proteins to attach to other platelets, bind collagen, and subendothelium

PLATELETS Are the primary defense against bleeding Circulate in resting state Have minimal interaction with other blood components or the vessel wall Morphology of resting platelet is smooth, discoid When stimulated by endothelial damage, platelets become activated and they Become round and ‘sticky’ Build a hemostatic plug Provide reaction surface for proteins that make fibrin Aid in wound healing Platelet activation and plug formation involves Adhesion Shape change Secretion Aggregation

ADHESION Damage to endothelium exposes blood to the subepithelial tissue matrix with adhesive molecules Platelet receptor GPIb binds to subendothelium collagen fibers through von Willebrand’s factor (vWF) Platelet adherence stops the initial bleeding

SHAPE CHANGE Following vessel injury and platelet exposure to external stimuli, platelets change their shape from circulating discs to spheres with pseudopods Shape change is mediated by an increase in cytosolic calcium Exposure of platelet membrane phospholipids promotes the assembly of vitamin-K dependent factors on the platelet membrane surface Activated platelets adhere to exposed collagen

CHANGE IN PLATELET SHAPE

AGGREGATION Platelet-to-platelet interaction Begins 10-20 seconds after vascular injury and platelet adhesion Requires dense granule release from the adhering platelets Requires Ca++ and ATP Requires fibrinogen and fibrinogen receptors GPIIb and IIIa Mechanism: ADP released from platelet cytoplasm upon adherence induces exposure of fibrinogen receptors GPIIb and IIIa Fibrinogen binds to the exposed GPIIb and IIIa Extracellular Ca++-dependent fibrinogen bridges form between adjacent platelets, thereby promoting platelet aggregation This is primary or reversible aggregation Secondary aggregation begins with the release of dense granules Secondary aggregation is considered irreversible

SECRETION Secondary aggregation begins with platelet secretion of dense granules Dense granules contain large amounts of ADP ADP binds to the platelet membrane triggering the synthesis and release of TXA2 The release of large amounts of ADP combined with TXA2 amplifies the initial aggregation of platelets into a large platelet mass

FORMATION OF PRIMARY HEMOSTATIC PLUG

PLATELETS AND SECONDARY HEMOSTASIS Primary platelet plug is Unstable and easily dislodged Secondary hemostasis Fibrin formation stabilizes the platelet plug Proteins interact to form fibrin assemble on negatively charged membrane phospholipids of activated platelets

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

Coagulation

Detailed Events of Coagulation

Coagulation Phase 1: Two Pathways to Prothrombin Activator May be initiated by either the intrinsic or extrinsic pathway Triggered by tissue-damaging events Involves a series of procoagulants Each pathway cascades toward factor X Once factor X has been activated, it complexes with calcium ions, PF3, and factor V to form prothrombin activator

Coagulation Phase 2: Pathway to Thrombin Prothrombin activator catalyzes the transformation of prothrombin to the active enzyme thrombin

Coagulation Phase 3: 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

The intrinsic pathway begins with the contact factors, factor XII, HMWK, and prekallikrein, which activates factor XI. Activated factor XI can then activate factor IX, which then acts with its cofactor, factor VIII, to form tenase complex on a phospholipid surface to activate factor X. Activated factor X then combines with its cofactor, factor V, to form the prothrombinase complex on a phospholipid surface, converting prothrombin to thrombin.

(Tissue Factor Pathway) Extrinsic pathway (Tissue Factor Pathway) IX TF Prothrombin (II) IXa VIIa Xa Thrombin (IIa) NB: production of IXa Interaction of intrinsic and extrinsic pathways

Tissue Factor Pathway Inhibitor Kunitz-type protease inhibitor (kringles) 34 and 41 kD forms in plasma (C-term truncation) Directly inhibits Xa Inhibits VIIa-TF complex in a [Xa]-dependent manner Bound to LDL, HDL and Lp (a) ~10% present in platelets (endothelium also)

Tissue Factor Pathway Inhibitor IX TF Prothrombin (II) IXa VIIa Xa TFPI TFI Thrombin (IIa) NB: Inhibition of Xa and VIIa

Net result: Tissue Factor Pathway Production of IXa Production of small amounts of thrombin (IIa) NB: no/little fibrin formed!

Tissue Factor Pathway VIIa forms as usual via binding of VII to TF VIIa activates some XXa Xa converts a small amt of prothrombin to thrombin; this thrombin is used to produce small amts of VIIIa and Va As the conc of TF-VIIa-Xa-thrombin increases, Tissue Factor Pathway Inhibitor inactivates this complex stopping further production of thrombin. New: VIIa also activates IXIXa (Key to new scheme) IXa, with VIIIa (produced as above), produces Xa; this Xa with Va (produced as above) produces new thrombin; this thrombin produces more VIIIa and Va and now we get lots of thrombin and fibrin!

V VIII Thrombin (IIa) Va VIIIa

Tissue Factor Pathway NB: activation of IX by VIIa IX TF Prothrombin IXa VIIa VIII VIIIa Xa Va V Soft clot Thrombin Fibrinogen Fibrin XIIIa Hard clot Fibrin

Coagulative (secondary) hemostasis. Characteristics of clotting factors There are 12 clotting factors: I – fibrinogen; II – prothrombine; III – thromboplastin of tissue; IV – ions of calcium; V – proaccelerin; VII – proconvertin; VIII – antihemophylic factor A; IX – Christmas factor or antihemofilic factor B; X – Stuart-Prower factor or prothrombinase; XI – plasma thromboplastin antecedent; XII – Hageman factor; XIII – fibrin stabilizing factor. Coagulative (secondary) hemostasis.

Anticoagulative mechanisms. Fibrinolysis. The tendency of blood to clot is balanced by a number of limiting reactions that tend to prevent clotting inside the blood vessels and to break down any clots that do form.

The primary anticoagulants are antithrombin III heparin (It is the most important anticoagulant in the blood); heparin (This substance was originally found in the liver, by large basophilic cells (mast cells) in tissues of various organs. Heparin reduces the ability of the blood to clot by blocking the change of prothrombin to thrombin. It can also be used to aid in reducing clots in cases in which internal clotting has already occurred. Heparin form complex with antithrombin-III. Activate nonenzyme fibrinolysis.);

alpha-2-macroglobulin, Alpha-2-macroglobulin is a similar to antithrombin-heparin cofactor in that it combines with the proteolytic coagulation factors. Its activity is not accelerated by heparin. Its function is mainly to act as a binding agent for the coagulation factors and prevent their proteolytic action until they can be destroyed in various ways. It a faint inhibitor of thrombin, connect with plasmin. alpha-1-antitripsin, Alpha-1-antitripsin inhibits thrombin activity, IXa, XIa, XIIa factors, plasmin and kallilrein. protein C Protein C inhibits VIIIa, Va factors. Its activity depends on thrombin and vitamin K concentration.

Functioning of secondary anticlotting substances Primary anticoagulants are produced and present all time in plasma and secondary anticoagulants form in a case of blood clotting. They are antithrombin-I or fibrin and products of fibrinolysis or products of fibrinogen degradation. Fibrin sorbs and inactivates thrombin and Xa factor. Products of fibrinolysis inactivate ending stage of clotting, IXa factor, platelets' agregation.

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