Haemostasis

Question 1

What is the average blood volume?

Answer 1

4-6 litres

Question 2

What is the name given to when you lose more than 20% of your blood?

Answer 2

Hypovolaemic shock

Question 3

Define haemostasis

Answer 3

The cessation of blood loss from damaged vessels

Question 4

What does haemostasis require?

Answer 4

Cell-cell communication

Question 5

How many cells per mm3 of peripheral blood do Erythrocytes make up?

Answer 5

5 million cells per cm^3

Question 6

What is the lifespan of an erythrocyte? What is the significance that they are anucleate when they are damaged?

Answer 6

• 120 days

- They cannot repair themselves as they have no nucleus for transcription

Question 7

What are the 3 phases of haemostasis?

Answer 7

1. Vascular phase
2. Platelet phase
3. Coagulation phase

Question 8

What occurs during the vascular phase?

Answer 8

Vasoconstriction
Endothelial cells contract
Endothelial adhesion increases

Question 9

In the vascular phase of haemostasis, what does the contraction of endothelial cells result in?

Answer 9

• Exposes basal lamina to blood

- Releases factors; ADP, tissue factor, endothelins

Question 10

In the vascular phase of haemostasis, what does the release of ADP result in?

Answer 10

ADP - platelet aggregation

Question 11

What are endothelins?

Answer 11

Peptide hormones which stimulate contraction of smooth muscle and promote mitosis of damaged tissue in vessels

Question 12

During the vascular phase of Haemostasis, what are 4 examples of factors that endothelial cells release? What do each of these factors contribute to?

Answer 12

1. ADP - platelet aggregation
2. Prostacyclin - reduces spread of platelet aggregation 3. Tissue Factor - involved in extrinsic pathway of coagulation
3. Endothelins - stimulate contraction of smooth muscle

Question 13

In smaller vessels how can endothelial adhesion help haemostasis?

Answer 13

• Endothelial cells can stick together to cover damaged vessels
• Can also provide attachments for platelets

Question 14

How and where are platelets formed? How long is the life span of a platelet?

Answer 14

• Megakaryocytes have structures that project into marrow sinuses in the bone marrow - These pockets of cytoplasm them pinch off to form platelets -
  Life span of a platelet is 10 days

Question 15

What are the 3 stages of the platelet phase?

Answer 15

1. Adhesion
2. Activation
3. Aggregation

Question 16

What is the platelet phase dependent on?

Answer 16

Temperature

Question 17

During platelet adhesion, what do the platelets adhere to? What factor is important for this?

Answer 17

• They adhere to the endothelium and basal lamina

- von Willebrand factor (for activation and aggregation of platelets)

Question 18

What occurs during the activation stage in the platelet phase?

Answer 18

• They swell and form spike extensions

- Granulolysis

Question 19

During platelet activation, what are 5 examples of substances released by granulolysis? What do they each do?

Answer 19

1. ADP - platelet aggregation
2. Serotonin - stimulates smooth muscle contraction
3. Thrombaxane A2 - stimulates smooth muscle contraction
4. Clotting factors - promote clot formation
5. Ca2+ - platelet aggregation and coagulation

Question 20

What is the aggregation stage of the platelet phase stimulated by?

Answer 20

ADP, thromboxane A2 and calcium ions

Question 21

What are 3 examples of substances that inhibit platelet activation?

Answer 21

1. Prostacyclin
2. Nitrous Oxide (produced by intact endothelial cells)
3. Aspirin

Question 22

What does prostacyclin do?

Answer 22

Inhibit platelet activation and vasodilator

Question 23

What are the 2 pathways involved in the coagulation phase of haemostasis?

Answer 23

1. Intrinsic Pathway

2. Extrinsic Pathway

Question 24

Which vitamin is essential for formation of clotting factors in the liver?

Answer 24

Vitamin K

Question 25

What is essential for the formation of clotting factors in the liver?

Answer 25

Vitamin K

Question 26

As well as catalysing the conversion of fibrinogen into fibrin, what is another function of thrombin?

Answer 26

It causes release of more tissue factor and clotting factors

Question 27

Why is clot restriction important?

Answer 27

Prevents the formation of a thrombus

Question 28

What are 3 substances that inhibit coagulation?

Answer 28

1. Thrombin stimulates anti-thrombin III to slow down coagulation 2. Natural anticoagulants e.g. heparin and prostacyclin 3. Thrombolytics e.g. warfarin and aspirin

Question 29

Describe the pathway for fibrinolysis of a clot

Answer 29

Clot removal by plasmin Plasminogen activated by thrombin and t-PA (tissue plasminogen activator) Plasminogen is converted to plasmin which digests the fibrin strands in the clot

Question 30

Give 4 examples of disorders related to abnormal haemostasis

Answer 30

- Haemophilia - Deep vein thrombosis - Liver function - von Willebrand's disease

Question 31

What are the 3 types of haemophilia? What clotting factors are absent in each type?

Answer 31

- A - factor VIII, X-linked recessive - B - factor IV, X-linked recessive - C, factor VI, autosomal recessive

Question 32

Haemophilia B is associated with which clotting factor?

Answer 32

Factor IV

Question 33

Clotting factor VIII is associated with which type of haemophilia?

Answer 33

Haemophlia A

Question 34

Clotting factor VI is associated with which type of haemophilia?

Answer 34

Haemophilia C

Question 35

What kind of disease is acquired haemophilia?

Answer 35

An autoimmune disease

Question 36

What is the cause of deep vein thrombosis?

Answer 36

Clotting factor accumulation

Question 37

What is von Willebrand's disease?

Answer 37

vWF deficiency | vWF factor links platelets to endothelium by activating and aggregating them