B11 Coagulation cascade

Question 1

description of platelets (4)

Answer 1

-cytoplasmic fragments from megakaryocytes of bone marrow/ lung which then enter the circulation

-rich in glycocalyx (important in making them negative so that they dont bind to the endothelial cells)

-7 to 14 days lifespan

-2 types of conditions: resting platelets (in circulation), and activated platelets (change shape to present pseudopods)

Question 2

structure of a platelet (7)

Answer 2

1. glycocalyx (-ve charge)
2. actin and myosin
3. electron dense granules (Ca and serotonin containing)
4. alpha granules (fibrinogen and fibronectin)
5. open canalicular systems (for substance release to extracellular space)
6. dense tubular system (Ca2+ storage)
7. filaments (give contractile ability)

Question 3

where do platelets originate from + where are they destroyed?

Answer 3

MEGAKARYOCYTES: production is induced by thrombopoietin (produced in kidney and liver)

DESTROYED: spleen and liver

Question 4

what changes occur as a platelet ages?

Answer 4

SENESCENCE: (stain blue)
-reduction in RNA content as they circulate, and lose glycocalyx sialic acid residues
-this activates pro-apoptotic signals that will lead to their death via phagocytosis (so they dont stick)

Question 5

describe the action of TPO

Answer 5

THROMBOPOIETIN:
-produced in liver and kidney
-regulates platelet production
-coded by the THPO gene, which is induced by an increased conc in senesent platelets –> diasylated platelets bind to the AMR receptor on hepatocytes and induce the transcription and translation of the gene –> feedback mechanism so that new platelets are made to replace the senecent ones

Question 6

components of platelet plasma membrane

Answer 6

-highly regulated Ca2+ channels (for uptake and release)

• PS (which is moved by flip flop enzymes for procoagulation)

-receptor complexes like GPIX and GPIbbeta (bind substances during coagulation cascade)

Question 7

general phases of hemostasis ()

Answer 7

1. vasoconstriction: minimise blood loss
2. primary hemostasis: platelet plug
3. secondary hemostasis: coagulation cascade
4. clot retraction and repair: stabilisationf of clot and repari of damaged vessel walls:
5. Fibrinolysis: breakdown of clot, via plasmin (disssolves it)