Flashcards in Lecture 5: Blood Clotting Deck (89)
What gives rise to platelets?
___ are needed for blood clotting
How do megakaryocytes give rise to platelets?
Edges of megakaryocyte break off to form platelets (cell fragments)
giant cells with many copies of DNA in the nucleus
Half life of platelets?
____ increases platelet numbers by...
stimulating production of platelets
How is blood clotting regulated? (3 phases)
1. vascular phase
2. platelet phase
3. coagulation phase
Exposed collagen & tissue factors cause vasoconstriction of the damaged blood vessel. Vasoconstriction minimizes blood loss.
Vascular phase controlled by...
nervous system & muscles (neurogenic & myogenic control)
Vasoconstriction in vascular phase prolonged by...
3. Thromoboxane A2
1. Collagen exposed to blood stream; bind platelets passing by in the blood
2. Factors released from trapped platelets attract more platelets
3. Platelets aggregate to form plug
What makes von Willebrand factor?
What does von Willebrand factor bind to?
What are the factors released from platelets?
PAF (platelet activating factor)
When are factors released from platelets?
during platelet phase
What does serotonin and thromboxane cause?
What do activated platelets look like?
spiky outer surface
Purpose of activating platelets?
they can adhere to each other better
What do inactivated platelets look like?
disk-like cell fragments
What prevents platelet adhesion/activation during normal situations?
What releases NO and prostacyclin
Prostacyclin is made up of...
Prostaglandin I2, PGI2
Why is aspirin given after mild heart attacks?
Precursor for thromboxane is arachidonic acid.
Enzyme cyclooxygenase cleaves ADA -> PGH2 -> thromboxane.
Aspirin stops CO activity, so thromboxane can't be made.
Since thromboxane is used to vasoconstrict & aggregate platelets, these don't happen as easily.
Function of von Willebrand factor?
- link platelet with collagen
- draw platelet into exposed collagen area
- keep VII in circulation longer
What happens during vascular phase?
What happens during platelet phase?
Platelets are actively trying to stop bleeding (loose platelet plug)
What happens during coagulation phase?
- Proper blood clot forms via coagulation cascade
- Fibrinogen -> fibrin
Long strand of fibre that reinforces loose platelet plug
One piece of fibrinogen
Inactive form of fibrin