Hematology- platelets

Question 1

characteristics of platelets

Answer 1

NOT CELLS

• small fragments of megakaryocytes
• formation regulated by thrombopoietin
• blue staining outer region, purple granules
• granules contain serotonin, CA2+, enzymes, ADP, and platelet derived growth factor (PDGF)

Question 2

all formed elements…

Answer 2

come from hemocytoblasts

hemocytoblasts -> megakaryocyte -> platelets

Question 3

circulating platelets

Answer 3

• form a temporary plug to help seal leaks in blood vessels
• circulating platelets are kept inactive but mobile by NO and prostacyclin from endothelial cells of blood vessels

Question 4

hemostasis (clotting)

Answer 4

fast series of cascade rxns to stop bleeding. rxn started by platelets and results in activated prothrombin and then fibrinogen

1. vascular spasm
2. platelet plug formation
3. coagulation (clotting)

Question 5

vascular spasm

Answer 5

• vasoconstriction of damaged blood vessel
• caused by:
  direct injury
  chemicals released by endothelial cells and platelets
  pain reflex

Question 6

platelet plug formation

Answer 6

positive feedback loop
at site of blood vessel injury, platelets:
1. stick to exposed collagen fibers with the help of von willebrand factor (plasma protein)
2. swell, become sticky and spiked and release chemicals
- ADP, causes more platelets to stick and release their contents
- serotonin and thromboxane enhance vascular spasm and coagulation

Question 7

coagulation

Answer 7

• transformed from liquid to gel
• reinforces the platelet plug with fibrin threads

OCCURS IN THREE PHASES:
1. make prothrombin activator (intrinsic and extrinsic pathways)
2. prothrombin –> thrombin
3. thrombin causes fibrinogen to form into fibrin

Question 8

intrinsic pathway

Answer 8

• HAPPENS WHEN EXPOSED TO NEGATIVE CHARGE
• blood clots in its own

Question 9

extrinsic pathway

Answer 9

secretion of tissue factor to bypass steps to clot QUICKER

Question 10

clot retraction

Answer 10

*pull sides of wound tight… causes creation of prothrombin activator
*happens after coagulation

• actin and myosin in platelets contract within 30-60 minutes
• platelets pull on fibrin strands, squeezing serum from the clot

Question 11

serum

Answer 11

plasma WITHOUT clotting factors

Question 12

clot repair

Answer 12

clot forms in 3-5 minutes

• platelet derived growth factor (PDGF) stimulates cells to come out of quiescence (G0). stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall
• vascular endothelial growth factor (VEGF) stimulates endothelial cells to multiply and restore endothelial lining

Question 13

fibrinolysis

Answer 13

*get clot outta the way to get rid of it

• begins within 2 days
• plasminogen in clot -> into plasmin
• plasmin is a fibrin digesting enzyme
• mesh goes away and cells divide to fill that space

Question 14

factors limiting clots

Answer 14

2 ways:
- removal and dilution of clotting factors
- inhibition of activated clotting factors (NO)

Question 15

inhibition of clotting factors

Answer 15

• most thrombin is bound to fibrin, and prevented from spreading
• heparin, anticoagulent, inhibits thrombin activity

Question 16

platelets sticking is prevented by…

Answer 16

1. smooth endothelial lining of blood vessels
2. antithrombic substances NO (nitric oxide) and prostacyclin secreted by endothelial cells