Chapter 37 Hemostasis And Blood Coagulation

Question 1

How is hemostasis achieved with 4 mechanism?

Answer 1

1. Vascular constriction
2. Formation of a platelet plug
3. Formation of a blood clot as a result of blood coagulation
4. Eventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently

Question 2

Immediately after a blood vessel has ruptured, the trauma to the vessel wall causes smooth muscle in the wall to contract. Which factors do the contraction result from?

Answer 2

1. Local myogenic spasm
2. Local autacoid factors from the traumatised tissues, vascular endothelium and blood platelets
3. Nervous reflexes

For the smaller vessels, the platelets are responsible for much of the vasoconstriction by releasing a vasoconstrictor substance - thromboxane A2

Question 3

What can be found in the thrombocytes cytoplasm?

Answer 3

1. Actin and myosin filaments which are contractile filaments and trombostenin that can cause platelets to contract
2. Residuals of the endoplasmic reticulum and Golgi apparatus that synthesise enzymes and store large quantities of calcium ions
3. Mitochondria and enzyme systems that are capable of forming ATP and ADP
4. Enzyme systems that synthesise prostaglandins
5. Fibrin-stabilising factor
6. A growth factor that causes vascular endothelial cells, vascular smooth muscle cells and fibroblasts to multiply and grow causing cellular growth that helps repair damaged vascular cells.

Question 4

What does the glycoproteins on the thrombocyte membrane surface do?

Answer 4

Repulses adherence to normal endothelium and yet causes adherence to injured endothelial cells and even more so to any exposed collagen from deep within the vessels wall

Question 5

What is the half life of platelets?

Answer 5

8-12 days

Question 6

How are platelets eliminated from the circulation?

Answer 6

Mainly by the tissue macrophage system. More than half of the platelets are removed by macrophages in the spleen.

Question 7

Describe the formation of a platelet plug in a severed blood vessel?

Answer 7

Question 8

How fast is a blood clot formed?

Answer 8

15-20 seconds when there is severe trauma to the vascular wall
1-2 minutes if the trauma is minor

Question 9

What courses can follow once a blood clot has formed?

Answer 9

1. It can be invaded by fibroblasts which form connective tissue all through the clot
2. It can dissolve

The usual corse is invasion by fibroblasts beginning within a few hours after the clot is formed which is promoted at least partially by growth factor secreted by platelets. This process continues to complete organisation of the clot into fibrous tissue within 1-2 weeks.

Question 10

What are clotting factors in blood and their synonyms?

Answer 10

Question 11

Describe the three essential steps of clotting?

Answer 11

Question 12

Describe the conversion of prothrombin to thrombin.

Answer 12

Question 13

Describe the schema for conversion of phrotrombin to thrombin and polymerisation of fibrinogen to form fibrin fibers.

Answer 13

Question 14

Describe the schema of coagulation cascade after vascular injury.

Answer 14

Question 15

What is prothrombin and where is it made? What does it do?
What is required by the liver for normal activation of prothrombin?

Answer 15

Question 16

What is fibrinogen and where is it formed?

Answer 16

Question 17

How does thrombin act on fibrinogen to form fibrin?

Answer 17

Question 18

In the early stages, fibrin clot is weak. What is the process that strengthens the fibrin reticulum?

Answer 18

Question 19

What is the blod clot composed of? How does the clot retract?

Answer 19

Question 20

How are platelets necessary for clot retraction to occur?

Answer 20

Question 21

What is the positive feedback of clot formation?

Answer 21

Question 22

Initiation of coagulation. What causes formation of prothrombin factor?

Answer 22

Question 23

Describe the extrinsic pathway for initiating blood clotting.

Answer 23

Question 24

Describe the intrinsic pathway for initiating blood clotting.

Answer 24

Question 25

What is the role of calcium ions in the intrinsic and extrinsic pathways?

Answer 25

Question 26

What is the interaction between extrinsic and intrinsic pathway and what is an especially important difference between them?

Answer 26

Question 27

What are the most important factors for preventing clotting in the normal vascular?

Answer 27

Question 28

What substances that inhibit platelet aggregation and initiation of blood clotting does intact endothelial cells produce?

Answer 28

Prostacyclin
Nitric oxide

Question 29

What is prostacyclin?

Answer 29

Also called prostaglandin I2
A member of the eicosanoid family of lipids and is a vasodilator as well as an inhibitor of platelet aggregation.

Question 30

What is NO?

Answer 30

Powerful vasodilator released from healthy vascular endothelial cells throughout the body and is an important inhibitor of platelet aggregation.

Question 31

What happens to the production of NO and prostacyclin when endothelial cells are damaged?

Answer 31

It’s greatly diminished

Question 32

What are the most important anticoagulants in the blood?

Answer 32

Question 33

How does heparin act as a powerful anticoagulant as a pharmacological agent?

Answer 33

Question 34

Where is heparin produced and why?

Answer 34

Question 35

What does plasmin do and what is it made from?

Answer 35

Question 36

Describe the activation of plasminogen to form plasmin, the clot lysis.

Answer 36

Forts. Efter Bild
After the clot has stopped the bleeding, t-PA eventually converts plasminogen to plasmin which in turn removes the remaining unnecessary blood clot.