Introduction to Hemostasis

hemostasis

the process by which the body spontaneously stops bleeding and maintains blood in the fluid state within the vascular compartment

four systems of hemostasis

• vascular system

• platelets

• coagulation system (fibrin forming)

• fibrinolytic system (fibrin lysis)

hemostasis related systems

• kinin system - semi related (inflammatory) cofactors in coag

• serine protease inhibitors - cleave peptide bonds

• complement

hemostasis vs. coagulation

• hemostasis is overall process

• coagulation is fibrin clot formation

primary vs secondary hemostasis

primary - platelets

secondary - coagulation factors

timeline of clotting with vessel injury

1. collagen is exposed

2. platelets adhere to injury site

3. coagulation factors activated an thrombin is formed while platelets aggregate

collagen initiates the—

intrinsic pathway

tissue thromboplastin initiates —

the extrinsic pathway

tissue plasminogen activator at the same time as the initiation of intrinsic/extrinsic pathway begins —

fibrinolysis

endothelial cells release _____ which—

ADP; induces platelet aggregation and releases granules

purpura

patches of purplish discoloration usually indicating platelet or vascular defect

• two types: ecchymoses and petechiae

ecchymoses

general bruising - blood escapes into larger areas of skin

petechiae

pinpoint spots of bruising - capillary bleeding

hematoma

swelling, mass of blood confined to an organ, tissue, or space caused by blood vessel break

epistaxis

nose bleed

menorrhagia

excessive menstrual bleeding

hemarthrosis

bleeding in the joints

melena

blood in stool

hematuria

blood in urine

hemoptysis

coughing up blood

why do we not test the vascular system?

it is hard to test

• rule out other two systems - platelets and coagulation factors

vasoconstriction

contraction of vessel to cut off blood flow

vascular intima

collagen or tissue factor (factor 3 or thromboplastin) found under the endothelial lining

• activates 7 (extrinsic)

endothelial vitamin C

maintains blood’s fluidity and vascular integrity

endothelial cell secretions

prostacyclin, tissue factor inhibitor, tissue plasminogen activator (injury), ADP (injury)

prostacyclin

vasodilator and inhibitor of platelets

non wettable surface of endothelial cells

blood flows freely without adherence to surface

quantitative platelet testing

platelet count

qualitative platelet testing

platelet function testing

purpose of platelets

primary hemostasis at site of clot formation

• interacts with fibrin to form stable platelet fibrin clot complex

platelet life span

7-10 days

platelet functions

• adhesion

• aggregation

• promotion of coagulation (of phospholipid surface)

• release of biochemicals (alpha-granules and dense bodies)

• clot retraction

adhesion

platelets adhere to site

aggregation

platelets adhere to other platelets

fibrinogen group

1, 5, 8, 13

• used up in coagulation

• present in plasma

• 5, 8 are heat labile

• all are found on platelets

• acute phase reactant

• increase in pregnancy and oral BC

prothrombin group

2, 7, 9, 10, protein C, protein S

• vitamin K dependant

• not consumed during coagulation (except 2 in plasma only)

• in serum and plasma

contact group

12, 11, prekallikrein (cofactor), high MW kininogen (cofactor)

• in serum and plasma

• initial phase of intrinsic

• not vitamin K dependent

factor 4

calcium - must be present for all steps and is not a protein

• minute amounts necessary

• serves as a catalyst

• no bleeding disorders for decrease

factor 3

tissue factor - not present in normal untreated plasma

• found in tissue

• liberated with tissue damage

• aka thromboplastin

intrinsic system is activated by—

SEC - subendothelial collagen exposure

• activates 12→11→9→8→10

• aPTT test

extrinsic system

requires tissue factor

• activates 7→10

• PT test

common pathway

10→5→2→1

function of thrombin (factor 2)

• converts fibrinogen to fibrin

• activates 13

• enhances 5 and 8

• aggregates more platelets

• generates plasmin