Hemostasis Physiology

Question 1

What is hemostasis?

Answer 1

Steps taken by the body to prevent blood loss. These include 4 steps- vascular spasm, primary plug, formation of the blood clot (fibrin), and the repair of damage

Question 2

How are platelets produced?

Answer 2

Platelets are produced from a lineage called megakaryocytes and from the release of TPO enzyme. This causes the megakaryocyte to develop and break pieces of platelets off from the vascular surface.

Question 3

What are the differences between TPO and EPO?

Answer 3

TPO is non-specific for Megakaryocyte development and platelet formation and all other HSC lineages; THIS MAKES SENSE BECAUSE WHEN THE TPO is released it is due to loss of BLOOD SO IT NEEDS TO STIMULATE RBCS to replenish LOST BLOOD!!!!!!!

EPO is specific to only RBC lineages

***The enzyme itself has similar N- terminals for both EPO and TPO but not for the C-terminals

Question 4

How does metabolic cascade of the Megakaryocyte proceed from the binding of the TPO to the megakaryocyte?

Answer 4

TPO will cause the binding to megakaryocytes which causes the differentiation and activation of the JACK/STAT 5 cascade via binding to c-mpl/cd-110 receptors on the megakaryocytes.

Question 5

Describe the initiation and the functioning of the vascular spasm

Answer 5

Vascular Spasm is shown by neural reflex, myogenic response

Platelet Factors Release: serotonin, thrombaxane A2 (cyclooxygenase via AA–> TXA2)

Endothelial Cell Release: VW factor, serotonin, ADP, Ca2+ (granules)

Question 6

To produce the blood clot layer, what is necessary?

Answer 6

Conversion of fibrinogen into fibrin by thrombin.

Ca2+ helps convert prothrombin into thrombin. Thrombin needs Vitamin K to convert fibrinogen into fibrin which produces cross-linked fibrin fibers.

This produces the blood clot

Question 7

Once the secondary blood clot has formed, what is secreted from the platelets to help reseal the damaged smooth muscle?

Answer 7

The platelets will secrete:

platelet-derived growth factor hormone- this will help the smooth muscle cells grow back

Question 8

Now, once the platelets have rebuilt the smooth muscles underneath the cell, then how can the cells get rid of the blood clot?

Answer 8

The molecule plasmin is needed to break apart the built fibrin fibers. This is done by the activation of the TPA (Tissue Plasminogen Activator).

***There is a platelet protein called Protein C that binds to Thrombin molecule that causes the de-activation of TPA inhibitor which leads to the activation of the TPA molecule.

This allows for the the fibrin fibers to break apart