Heme Lecture review

Primary hemostais

plt adhesion and aggregation to form a plt plug to temporary seal vascular breach

vascular contribution

: injured vessels will constrict and release biochemical mediators to aid in homeostasis

Plt functions

Plt adhere to damage endothelium, aggregate, and release granules content

→Plt recruitment

Secondary hemostasis

formation of stable fibrin clot, aggregated PLT surface is critical for 2ndary hemostasis

Inhibitory mechanisms

Blood flow dilution of plt agonist and endothelial inhibitors to regulate plt plug formation

Blood vessels and endothelial lining

initial response to injury is vasoconstriction to minimize blood loss and bring hemostatic components closer to the vessel wall

-maintains fluidity, prevents thrombotic events, stop injury

mechanisms of vasoconstriction

neurogenic factors

regulatory substances: serotonin, thromboxane A2, endothelin 1

endothelial cells synthesize PG1, N.O causes vasodilation and inhibit PLT activation

→ prevent thrombosis and maintain balance and maintain balance between clot formation and blood fluidity

resting endothelium

inhibits PLT activation and coag

activates fibrinolysis

damaged endothelium

activates PLT and coag

inhibits fibrinolysis

PLT structure and function

resting PLT: disc shaped

circulating PLT naturally repel

following injury PLT shape change and activate to for primary hemostatic plug

Peripheral zone composition

phospholipid membrane

Glycocalyx: surface coat (thicker on PLT with glycolipids)

PLT membrane:

→ dry laminar structure with phospholipids +integral proteins

organelle zone composition

• mitochondria

• glycogen

• dense granules

  • store non protein PLT mediators: ADP/ATP, nucleotide, phosphate, serotonin, calcium

  ADP and serotonin: activate more plt to form plug

coagulation factors and pathways

A. coagulation cascade: enzymes that activate other proteins → clot formation

B. Vitamin K: carboxylation and activation of coagulation factors

C. coagulation proteins into group:

1. Prothrombin

2. Fibrinogen

3. Contact

PLT adhesion

Glycoprotein 1b/IX for normal PLT adhesion

membranous zone: communicates with extracellular environment