Circulatory Systen V

Question 1

What is the function of a platelet?

Answer 1

They’re essential for blood clotting and are the natural defence mechanism to prevent blood loss after vascular injury

Question 2

What is another name for platelets?

Answer 2

Thrombocytes

Question 3

Describe the characteristic of a thrombocyte?

Answer 3

• lifespan of 8-11 days
• small corpuscle cells
• made from large bone marrow cells (megakaryocyte)

Question 4

What happens to thrombocytes that are not used in haemostasis?

Answer 4

Destroyed by macrophages mainly in the spleen

Question 5

What is the function of thombopoetin?

Answer 5

Thrombopoetin is a hormone which regulates the production of platelets and is produced in the liver

Question 6

What is the physiological process of haemostasis?

Answer 6

• vasoconstriction- muscle contracts
• formation of platelet plug- clot
• blood coagulation - intrinsic and extrinsic pathway

Question 7

What is the process of vasoconstriction?

Answer 7

• thrombocytes meet damaged blood vessel
• their surface becomes sticky
• thrombocytes then adhere to damaged wall (fibrin helps reinforce and stick platelets)
• serotonin is released, constricting the vessel

Question 8

Describe the formation of a platelet plug?

Answer 8

• thrombocytes adhere to damaged tissue temp sealing break
• platelets adhere to collagen fibres in vessel wall, activates platelets
• activated platelets release factors to further stimulate ADP releases from platelet granules which activates more platelets
• quickly forms temp seal (platelet plug)

Question 9

what are the 3 critical functions of glycoprotein in primary haemostasis

Answer 9

• acts as bridging molecule at sites of vascular injury for normal platelet adhesion
• under sheer conditions promotes platelet aggregation
• important in fibrin formation

Question 10

what are the different clotting factors?

Answer 10

• thromboplastin
• prothrombin
• thrombin
• fibrinogen
• calcium

Question 11

describe thromboplastin?

Answer 11

• enzyme released by damaged tissue cells or platelets
• formation is dependent on other clotting factors e.g. factor V

Question 12

describe prothrombin?

Answer 12

• protein present in blood plasma
• made in liver
• Vit K dependent
• in presence of thromboplastin, prothrombin is converted to active thrombin

Question 13

what is the function of thrombin?

Answer 13

• is involved in coagulation cascade
• converts fibrinogen to fibrin

Question 14

what is fibrinogen?

Answer 14

• formed as plasma protein in liver
• in presence of thrombin changes from soluble to insoluble strands of fibrin

Question 15

what is the function of fibrin?

Answer 15

fibrin forms the network of clot, platelets trapped in fibrin threads, erythrocytes and leucocytes also collect in intersections

Question 16

what substance inhibits blood clotting?

Answer 16

heparin- natural anticoagulant

Question 17

what is fibrinolysis?

Answer 17

process of removing/breaking down the clot and healing of the vessel begins

Question 18

what is von Willebrand’s disease?

Answer 18

most common inherited bleeding disorder, those affected have low levels of VWF, a protein which helps blood clot

Question 19

what is haemophillia?

Answer 19

low levels or none of blood proteins important for clotting, causing an inability to clot

Question 20

what causes Type A haemophillia?

Answer 20

a deficiency in factor VIII

Question 21

what causes Type B haemophillia?

Answer 21

a deficiency in factor XI (christmas disease)

Question 22

what is thrombocytopenia?

Answer 22

relative decrease of platelets in the blood
- congenital absence of factor VIII