Hemostasis

Question 1

How do the platelets react to an injury?

Answer 1

1. Platelets come in contact with collagen fibres from the damaged vascular wall, which makes them sticky.
2. This makes them attach to collagen fibres from endothelial tissues and von Willebrand factor that leaks in from plasma.
3. This causes the platelet to swell.
4. Platelet extends pseudopods that release granules like ADP, seratonin and thrombaxin A2.

Question 2

What is the use of ADP, thrombaxin A 2 and seratonin?

Answer 2

1. ADP makes the platelets stickier for aggregation.
2. ADP, thrombaxin A2 and seratonin activate other platelets.
3. Thrombaxin A2 and seratonin are vasoconstrictors that decrease the blood flow to the damaged area.

Question 3

What is the von Willebrand factor?

Answer 3

It is a large adhesive protein that is found in the plasma and produced in the endothelial cells and megakaryocytes.

Question 4

What causes the formation of prothrombin activator?

Answer 4

1. Trauma to blood or vascular wall and adjacent tissues.
2. Contact of blood with collagen.
3. Contact of blood with damaged endothelial cells.

Question 5

What is prothrombin?

Answer 5

Prothrombin is an alpha 2 globulin. It is also called Clotting Factor I.

Question 6

Where is prothrombin formed?

Answer 6

Liver

Question 7

Why do people with liver diseases have bleeding tendencies?

Answer 7

Liver diseases affect the synthesis of prothrombin.

Question 8

Why do people with steatorrhea have a bleeding tendency?

Answer 8

Vitamin K, a fat soluble vitamin is found to be deficient in people with steatorrhea. Vitamin K is esential for the synthesis of prothrombin.

Question 9

What is the plasma concetration of fibrinogen?

Answer 9

100- 700 mg/dL

Question 10

Where is fibrinogen formed?

Answer 10

Liver

Question 11

What role does thrombin play in activating fibrinogen?

Answer 11

1. Thrombin is a proteolytic enzyme that removes 4 low-molecular-weight peptides to gives fibrin monomers.
2. Fibrin monomers polymerise with weak non-covalent hydrogen bonds.
3. Thrombin activates the Fibrin stabilsing factor that creates covalent bonds between the fibrin fibres, leading to the fomation of cross linkages.

Question 12

What is a bood clot?

Answer 12

It is a meshwork of cross linked fibrin fibres entrapping platelets, RBCs and plasma.

Question 13

How does clot retraction take place?

Answer 13

1. Platelets contain contractile proteins that cause it to clot the same way as muscle.
2. The platelets contract pulling the fibrin fibres together.
3. Serum is squeezed out.
4. The clot is compacted drawing the ruptured edges of the blood vessels together.

Question 14

How does fibrinolysis take place?

Answer 14

1. Plasminogen present is plasma is trapped in the clot.
2. Injured tissues and vascular endothelium release tissue plasminogen activator very slowly that converts plasminogen to plasmin.
3. Plasmin is a proteolytic enzymes that digests fibrin, fibrinogen, prothrombin, factor V, VIII, XII.

Question 15

How does repair of injured tissues take place?

Answer 15

Platelet derived growth fact stimulste fibroblasts and smooth muscle cells to divide and rebuild the wall.