Coagula2on or blood clo;ng (secondary hemostasis)

Transcription

1 Blood coagulation

2 ! Arrest of bleeding! Events preven2ng excessive blood loss Vascular spasm Platelet plug forma2on Primary hemostasis Coagula2on or blood clo;ng (secondary hemostasis)

3 ! Vascular Constric.on: Immediate constric.on of blood vessel Vessel walls pressed together become s.cky / adherent to each other Minimize blood loss

4 Platelet Plug forma.on: PLATELETS a>ach to exposed collagen with the presence of von Willebrand factor (vwf) and Glycoprotein IbIX Aggrega2on of platelets causes release of chemical mediators (ADP, Serotonin, Thromboxane A 2 ) ADP a>racts more platelets Thromboxane A 2 (powerful vasoconstrictor) * promotes aggrega2on & more ADP Leads to forma.on of platelet plug!

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6 Blood Coagula.on (clot forma.on): Final Step in Hemostasis:! Transforma2on of blood from liquid to solid! Clot reinforces the plug! Mul2ple cascade steps in clot forma2on! Process requires plasma proteins, PLs and calcium. Thrombin! Soluble fibrinogen Insoluble fibrin

7 ! Stages of Coagula.on Ac2va2on of prothrombinase Conversion of prothrombin to thrombin Conversion of fibrinogen to fibrin! Pathways Extrinsic Intrinsic Ini2ally independent, then they converge on common pathway leading to the forma2on of a fibrin clot!

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9 PRIMARY AGGREGATION Platelet Aggrega.on CloUng SECONDARY COAGULATION Thrombin Fibrin Hemosta.c clot 0 min 10 min 5 min

10 ! A cascade is a mechanism in which enzymes ac2vate other enzymes sequen2ally usually leading to an amplifica2on of an ini2al signal.! Each of these pathways leads to the conversion of factor X (inac2ve) to factor Xa (ac2ve)

11 ! The intrinsic and extrinsic coagula2on pathways are a series of reac2ons involve coagula2on factors known as 1. Enzyme precursors (zymogens) 2. Non-enzyma2c (cofactors) 3. Calcium (Ca ++ ) 4. Phospholipids (PL)! All coagula2on factors normally are present in the plasma, with PL being provided by platelets.

12 ! Factors are designated by a roman numeral! Ac2ve forms are usually designated by the le>er a a[er the Roman numeral and may also have a different name (Ex. Ia/ Fibrin)! Cofactors are needed for many reac2ons in the cascade Ex. Calcium, platelet factor 3 (PF3)

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14 ! Zymogens: Factors II, VII, IX, X, XI, XII, and prekallikrein NO biologic ac2vity un2l converted by enzymes to ac2ve enzymes called serine proteases! Cofactors Factors V, VIII,.ssue factor, and HMWK

15 ! Extrinsic Release of biochemicals from broken blood vessels/damaged 2ssue.! Intrinsic No 2ssue damage, blood contacts damaged endothelial layer of blood vessel walls.

16 ! Intrinsic cloung all factors are found in circula2ng blood.! Extrinsic cloung Factor III (2ssue thromboplas2n) is found outside of blood.

17 ! A foreign surface such as collagen ac2vates factor XII (Hageman factor)! Ac2ng as catalysts are high MW Kininogen (HMWK) and kallikrein in the contact phase

18 ! XI, XII, HMWK, PK! Not Vitamin K dependent! The contact group is adsorbed by contact with a nega2vely charged surface such as collagen or the subendothelium in vivo.

19 ! Calcium is involved in three steps: the ac2va2on of FIX, X and FXI! Cofactor VIII interacts in the ac2va2on of factor X and cofactor V reacts with prothrombin.! The platelet PL surface acts as template in the ac2va2on of FX and prothrombin.

20 ! Is ini2ated by the release of 2ssue thromboplas2n (Factor III) which is exposed to the blood when there is damage to the blood vessel.! Factor VII which is a circula2on coagula2on factor, forms a complex with 2ssue thromboplas2n and Ca2+.! This complex rapidly converts Factor X to the enzyme form Factor Xa

21 ! Factor Xa catalyzes the prothrombin (Factor II) to thrombin (Factor IIa) reac2on which is needed to convert fibrinogen (Factor I) to fibrin.! XIIIa and Ca ++ stabilize fibrin clot! Forma2on of blood clot causes more clo;ng to occur posi2ve feedback.

22 ! Prothrombin is soluble single chain glycoprotein (72kDa) synthesized in liver! Thrombin is produced by the enzyma2c cleavage of two sites on prothrombin by ac2vated Factor X (Xa) and generate ac2ve 2 chain thrombin molecule which is then released from platelet surface! The A and B chains of thrombin are held together by a dissulfide bond S S S S 1 2 A B A B Xa Xa Fragment 2-1 Fragment 2-1 Prethrombin Prothrombin (72kDa) Ac.ve thrombin (34 kda) Converts fibrinogen to fibrin

23 Thrombin in Hemostasis! The ac2va2on of prothrombin occurs on the surface of ac2vated platelets and requires assembly of prothrombinase complex consis2ng of platelet, anionic PLs, Ca2+, factor Xa and prothrombin! This complex is termed factor Va which is ac2vated by traces of thrombin! Factor Va is subsequently inac.vated by further ac2on of thrombin to limit ac2va2on of prothrombin to thrombin Factor Xa

24 Conversion of fibrinogen to fibrin " 340kDa (factor I) is soluble plasma glycoprotein that consists of 3 non iden.cal pairs of polypep.des chains (Aα, Bβ, γ) 2 covalently linked by disulfide bonds " The A and B por.ons of the Aα and Bβ chains, termed Fibrinopep.de A (FPA) and Fibrinopep.de B (FPB) Thrombin Release of FBs by thrombin generate fibrin monomer (weak) Aggregate spontaneously forming insoluble fibrin polymer (fibrin clot) (hard, insoluble)

25 Inhibitor Ac.on An.thrombin III Most important (75%) Inhibits IXa, Xa, XIa and XIIa factors Is enhanced and accelerated by the presence of Heparin Protein C Protein S Heparin Alpha 2- macroglobulins Alpha 1- an.trypsin Produced by liver; Vitamin K dependent Inhibits the cofactors VIIIa and Va Is enhanced by Protein S Needs to be ac2vated by Thrombin (IIa) Produced by liver; Vitamin K dependent Acts as a cofactor to Protein C to enhance its ability to degrade factors V and VIII Acts both in vivo and in vitro Rapid onset few minutes Increases the rate of forma2on of irreversible complexes between an2thrombin III and the serine protease clo;ng factors Contributes most of the remaining (25%) of an2thrombin ac2vity in plasma Its ac2vity normally increases markedly a[er injury to counteract excess elastase arising from s2mulated neutrophils

26 Inhibitor Vitamin K antagonists Ac.on Coumarin drug Dicumarol Citrate oxalate Used only in vivo Inhibit carboxyla2on of Glu residues in prothrombine and factors VII, IX, X Used only in vivo as an2coagulant to prevent thrombosis in pa2ents with a tendency to form blood clot Slow onset of ac2on 2-3 days but long dura2on 4-6 days Used only in vivo Defibrina.on of blood Removes Ca 2+ Break down of fibrin threads once formed by con2nuous shaking or by glass rod Heparin

27 ! Platelets (thrombocytes) have several func2ons in blood clo;ng: C Form platelet plug at the site of injury A Sites of ac2va2on of some clo;ng factors (II, X) B Provide the surface on which certain clo;ng factors bind (Va, Xa, II, Ca 2+ ) I Sources of some clo;ng factors (XIII, PL)

28 Role of platelets in blood cloung! Ac2vated platelets release: α-granules Fibrinogen ADP/ATP vwf Serotonin Dense core granules Factor V Ca2+ Factor VIII Platelet derived growth factor (PDGF) ~ promotes healing Platelet factor IV prevents forma2on of ac2ve thrombin inhibitor from heparin and an2-thrombin III.

29 ! If platelets are not lysed, blood does not clot! The hormone Thrombopoiten (produced by liver) increases the rate of megakaryocytes in the bone marrow, s2mula2ng them to produce more platelets! Platelets deficiency can be due to many agents (drugs, some infec2ons, ionizing radia2on)! Individuals with thrombocytopenia (low platelets), bleed for a long 2me

30 ! Clot is slowly dissolved by the fibrin spli;ng called Plasmin! Plasmin gets trapped in clot and slowly dissolves it by breaking down the fibrin meshwork at various places, leading to the produc2on of circula2ng fragments that are cleaved by other proteases or by the kidney and liver

31 ! Plasminogen is the inac2ve pre-cursor that is ac2vated by ac2vators in plasma: 1. Tissue plasminogen ac.vator (t-pa) 2. Urokinase (to lesser extend)! Is produced as a precursor prourokinase by epithelial cells! Its main ac2on is probably in the degrada2on of extracellular matrix

32 ! Inac2ve t-pa is released from vascular endothelial cells following injury! It binds to fibrin and is consequently ac2vated! Ac2ve t-pa converts plasminogen into plasmin Dissolves the clot

33 ! Inherited bleeding disorders! Acquired bleeding disorders Hemophilia A and B Von Willebrand disease Other factor deficiencies Liver disease Vitamin K deficiency

34 1- Hemophilia A and B Are the best-known coagula2on factor disorders Hemophilia A Hemophilia B Coagula.on factor deficiency Factor VIII Factor IX Inheritance X-linked X-linked recessive recessive Incidence 1/10,000 males 1/50,000 males

35 2- von Willebrand Disease! It is the most common hereditary bleeding disorder and is characterized as being inherited autosomal recessive or dominant! In this disease there is a defect in von Willebrand factor (vwf) which: 1. acts as a carrier for factor VIII 2. mediates the binding of glycoprotein Ib (GPIb) to collagen

36 " This binding helps the ac2va2on of platelets and forma2on of primary hemostasis " vwd is characterized by excessive bleeding in infants because platelets fail to form hemosta2c plug

37 Source of vitamin K Green vegetables Synthesized by intes.nal flora Required for synthesis Factors II, VII, IX,X contribute to bleeding disorders Causes of deficiency Malnutri.on Biliary obstruc.on Malabsorp.on An.bio.c therapy

38 1. Forma.on of carboxyglutamate! Vitamin K is essen2al for the func2oning of several proteins involved in blood clo;ng (II, VII, IX and X)! These proteins contain a unique modified glutamate residue, called carboxyglutamate (Gla).! These proteins are synthesized as inac2ve precursors that are ac2vated by the vitamin K-dependent carboxylase which converts glutamate in these proteins to carboxyglutamate forming mature clo;ng factors.

39 1. Forma.on of carboxyglutamate (mature) - (Gla residue) Dicumarol, Warfarin

40 2. Interac.on of prothombin with platelets! The Gla residue of prothrombin is a natural high affinity binder (chelator) of posi2vely calcium ions, hence the designa2on of calcium as a co-factor (factor IV) in the schema2c.! The prothrombin-calcium complex is then able to bind to PLs essen2al for blood clo;ng on the surface of platelets.

41 Intrinsic system (surface contact) Extrinsic system (.ssue damage) XII XIIa Tissue factor XI XIa IX IXa VIIa VII VIII VIIIa X V Va Xa II Fibrinogen IIa (Thrombin) Fibrin Vitamin K dependant factors

42 Leukocytes (WBC s)

43 Two major components of blood: liquid phase and formed elements

44 ! All new WBCs except for lymphocytes are produced in the bone marrow (that also give rise to erythrocytes and platelets). Most new lymphocytes are produced by colonies of cells in lymphoid.ssues, such as lymph nodes Bone Marrow Circula.on

45 Mobile units of body s defense system:! Seek and Destroy Func.ons: Destroy invading microorganisms Destroy abnormal cells (ie: cancer )! Clean up cellular debris (phagocytosis) Assist in injury repair! Each WBC has a specific func.on

46 Leukocytes (WBC s) (Cont )

47 ! Five Types! Classified according to the presence or absence of granules and the staining characteris2cs of their cytoplasm.! Leukocytes appear brightly colored in stained prepara2ons, they have a nuclei and are generally larger in size than RBC s.

48 Types of WBC s Are classified in 3 main classes Agranulocytes Granulocytes

49 ! Granulocytes (Polymorphonuclear leukocytes): have 2 types of granules in their cytoplasm: the specific granules (specific func2ons) and azurophilic granules (lysosomes) Neutrophils Eosinophils Basophils

50 ! Agranulocytes: do not have specific granules, but they do contain azurophilic granules in their cytoplasm Lymphocytes Monocytes

51 1. Neutrophils (cond )! Cons2tute 60-70% of circula2ng WBC s! Have an average diameter of µm! Several lobes in nucleus (2-5 segments) linked by fine threads chroma2n! Also contain glycogen (source of energy)! Stain light purple with neutral dyes

52 1. Neutrophils (cond )! Granules are small and numerous! Highly mobile/very ac2ve! Diapedesis: Can leave blood vessels and enter 2ssue space! Short lived cells: life span of 6-7h in blood and 1-4 days in connec2ve 2ssues! Func.on: Phagocytosis (contain several lysosomes) and play a major role of acute inflamma2on

53 2. Eosinophils! 2-4% in normal blood! Large, numerous granules! Typical bilobed nuclei! Are about µm in size, pale blue colour! Found in lining of respiratory and diges2ve tracts

54 2. Eosinophils (cont )! Persist in the circula2on for 8 12 hours! Func.ons: o Important func2ons involve protec2ons against infec2ons caused by parasi2c worms and involvement in allergic reac2ons o Secrete an2-inflammatory substances in allergic reac2ons

55 3. Basophils! Least numerous, less than 1% of blood WBC s! They are about µm diameter! They contain many large, rounded, dark purplish black granules! Their nucleus is divided into irregular lobes

56 3. Basophils (cont )! Diapedesis! Contain histamine and heparin (inflammatory chemical)! Func.on: Like eosinophils, basophils play a role in both parasi2c infec2ons and allergies

57 1. Lymphocytes! Cons2tute 28% of WBC s! Small lymphocytes (6-8 µm); medium-sized lymphocytes (small number) and large lymphocytes (18 µm)! Large nuclei/small amount of cytoplasm! Color pale-blue

58 1. Lymphocytes (cont )! Only type of WBC s that return from the 2ssue back to blood a[er diapedesis! Vary in life span: some live only a few days (~3days), others survive in circula2ng blood for many years (4-5 years)

59 1. Lymphocytes (cont )! Func.on: immune responses and memory, mainly found in lymph 2ssue! Two types: T lymphocytes a>ack an infect or cancerous cell B lymphocytes produce an2bodies against specific an2gens (foreign body)

60 Agranulocytes (cont ) 2. Monocytes! Largest of WBCs (12-20µm)! Dark kidney bean shaped nuclei! Cytoplasm is basophilic and frequently contain very fine azurophilic granules! In 2ssues differen2ate into macrophages

61 Agranulocytes (cont ) 2. Monocytes (cont )! Func.on: phagocytosis evident in chronic infec2ons Tuberculosis defense vs. viruses and certain bacteria ac2vate lymphocytes

62 ! Doctors look at WBC numbers.! Clinics will count the number of WBC s in a blood sample, this is called differen2al count! A decrease in the number of white blood cells is leukopenia! An increase in the number of white blood cells is leukocytosis

63 ! They have aerobic glycolysis and ac2ve pentose phosphate pathway (NADPH)! During phagocytosis of bacteria, there is an increase of O 2 consump2on (respiratory burst: the rapid release of reac2ve oxygen species) and superoxide radical O - 2 (involved in killing the bacteria) is formed.

64 ! Phagocy2c leukocytes use NADPH as a substrate for the NADPH-oxidase enzyme, which contributes to the killing of ingested microorganisms NADPH NADPH +A +O 2 NADP + + AH + O - oxidase 2 2H + Acidic ph + 2O - 2 2H 2 O 2 + AH + O - 2 SOD Helps to kill microorganisms

65 ! Ac2ve leukocytes release O 2 - ions and H 2 O 2 to surrounding 2ssues in areas of inflamma2ons! Superoxide dismutase, catalase and glutathione peroxidase are normal an2oxidant enzymes that help to protect the body against the toxic effect of O 2 ions and H 2 O 2