2. Haemostasis

Question 1

What is haemostasis?

Answer 1

The stopping of bleeding in a quick and localized manner when blood vessels are damaged to prevent haemorrhage.

Question 2

What are the methods utilised in haemostasis?

Answer 2

1. Vascular spasm
2. Platelet plug formation
3. Blood clotting

Question 3

Describe the process of the Vascular Spasms method of Haemostasis?
(Hint: there are 3 points)

Answer 3

1. Damages blood vessels initiates nervous and myogenic reflexes
2. Reflex contraction of smooth muscle of small blood vessels
3. Reduces blood loss until other mechanisms take over

Question 4

How do the platelets store their chemicals for Platelet Plug Formation?

Answer 4

As granules

Question 5

In Platelet Plug Formation, what do are the Alpha Granules?

Answer 5

Clotting factors and platelet-derived growth factor

Question 6

What is the function of the platelet-derived growth factor of the Alpha Granules?

Answer 6

Cause proliferation of endothelial cells, smooth muscle and fibroblasts to repair damaged vessels.

Question 7

In Platelet Plug Formation, what do are the Dense Granules?

Answer 7

Promote platelet aggregation and vasoconstriction through the production of thromboxane A2 (ADP, ATP, Ca^2+, seratonin, fibrin-stabilising factor and enzymes produce it)

Question 8

What is the normal platelet count?

Answer 8

150-400,000 (microlitres ^-1)

Question 9

Describe the characteristics of a thrombocyte (platelet)?

Answer 9

Disc shaped without a nucleus

Question 10

Platelets are essential to initiate blood clotting. What are the 3 steps to initiate blood clotting?

Answer 10

1. Platelet adhesion
2. Platelet release reaction
3. Platelet aggregation

Question 11

Describe what happens during the Platelet Adhesion step of the formation of a Platelet Plug for blood clotting?

Answer 11

Platelets stick to the exposed collagen underlining the endothelial cells in the vessel wall.

Question 12

Describe what happens during the Platelet Release Reaction step of the formation of a Platelet Plug for blood clotting?

Answer 12

The platelets are activated by adhesion and they make contact with each other. Thromboxane A2 and ADP are releases which activated other platelets. Thromboxane A2 and serotonin initiate vasoconstriction.

Question 13

Describe what happens during the Platelet Aggregation step of the formation of a Platelet Plug for blood clotting?

Answer 13

Activated platelets stick together and activate new platelets to form a Platelet Plug which becomes reinforced by fibrin threads.

Question 14

What is it called when clotting occurs in an unbroken vessel?

Answer 14

Thrombosis

Question 15

What is thrombosis?

Answer 15

When clotting occurs in an unbroken vessel.

Question 16

What are the substances required for blood clotting?

Answer 16

Ca^2+, enzymes synthesized by liver cells and substances released by platelets or damaged tissues.

Question 17

What is the first essential step in blood clotting?

Answer 17

Prothrombinase is formed in response to a ruptured vessel

Question 18

What is the second essential step in blood clotting?

Answer 18

Prothrombinase catalyses conversion of prothrombin to thrombin

Question 19

What is the third essential step in blood clotting?

Answer 19

Thrombin acts as catalyst to convert fibrinogen into fibrin threads which enmeshed platelets, blood cells and plasma proteins to make a bloodclot.

Question 23

What does prothombinase and Ca^2+ convert prothrombin into?

Answer 23

Thrombin

Question 24

What converts prothrombin into thrombin?

Answer 24

prothombinase and Ca^2+

Question 25

Thrombin converts ____________ into _____________?

Answer 25

Converts fibrinogen into fibrin threads

Question 26

What activates the clotting process?

Answer 26

Damaged to the vessel

Question 27

What activates the intrinsic pathway of blood clotting?

Answer 27

When blood comes into contact with injured vessel wall

Question 28

How is the extrinsic pathway activated during blood clotting?

Answer 28

When blood comes into contact with thromboplastin

Question 29

What does the intrinsic and extrinsic pathways lead to the formation of?

Answer 29

Factor X

Question 30

Describe the extrinsic pathway of blood clotting?

Answer 30

Blood leaks into surrounding tissues, tissue leaks thromboplastin into bloodstream, clotting factor X and factor V (in presence of Ca^2+) form prothrombinase

Question 31

Describe the intrinsic pathway of blood clotting?

Answer 31

Endothelium is damaged and platelets come into contact with collagen of blood vessel wall, platelets are damaged and release phospholipids

Question 32

On the final common pathway, what does that prothrombinase and Ca^2+ do?

Answer 32

Catalyse conversion of prothrombin and thrombin

Question 33

On the final common pathway, what does thrombin do?

Answer 33

In presence of Ca^2+ it converts fibrinogen into fibrin threads and activates fibrin stabilizing factor XIII

Question 34

Describe what happens during clot retraction and blood vessel repair?

Answer 34

Platelets pull on fibrin threads of clot, the edges of the damaged vessel pull together and fibroblasts and endothelial cells repair blood vessel

Question 35

What is intravascular clotting?

Answer 35

When clot/thrombus forms in an unbroken vessel, can happen of blood flows too slowly. Low doses of aspirin bc an block this from happening.

Question 36

What happens to small clots after vessel has been repaired?

Answer 36

It either becomes dissolute or invaded by fibroblasts as the tissues are being repaired.

Question 37

In the endothelial surface factor of the prevention of blood clotting, name the two chemicals capable of blocking platelet aggregation?

Answer 37

Nitric oxide and prostacyclin

Question 38

Other than chemicals, name another factor that can prevent blood clotting on the endothelial surface?

Answer 38

The smoothness of the endothelium itself

Question 39

Which alpha globulin blocks the formation of thrombin?

Answer 39

Antithrombin III

Question 40

Name two anticoagulants capable of preventing blood clotting?

Answer 40

Heparin (administrated during surgery) and warfarin

Question 41

Name at least two blood clotting deficiencies?

Answer 41

1. Haemophilia A (sex-linked gene, affects males only, lack of Fac. VIII) 2. Haemophilia B/Christmas Disease (genetic trait) 3. Vitamin K deficiency (vit K needed for synthesis of clotting factors) 4. Thrombocytopenia (low platelets in blood)