Circulation 1

Question 1

Describe the origin of platelets in terms of anatomical site, precursor cell type, and method of production

Answer 1

Produced in bone marrow
From megakaryocyte - Large cell with many nuclei
Platelets bud off as fragments from cytoplasmic extensions

Question 2

Explain the role of platelets in forming a thrombus in relation to trauma or tissue damage

Answer 2

Trauma to vessel increases exposure of platelets to interstitial collagen
Platelets adhere to collagen to close gap

Question 3

What is coagulation

Answer 3

solidification of blood
2 types:
Thrombus formation
Clot formation

Question 4

describe thrombus formation

Answer 4

Occurs in flowing blood
pure thrombus is pale cream coloured
Consists of platelets and mesh network of fibrin strands

Question 5

Why does a thrombus of platelets and fibrin occur in flowing blood

Answer 5

Molecules on platelet surfaces allow adherence to interstitial collagen
Clotting cascade deposits Factor VIII which enhances this further

Question 6

What is clot formation

Answer 6

Blood leaks out vessel and becomes stagnant
Next to interstitial collagen, clotting cascade activated
Network of fibrin strands and RBCs form clot

Question 7

What happens if clot formation does not work perfectly and the wound may continue to bleed

Answer 7

Vessel vasoconstricts to decrease blood loss
Platelet and fibrin thrombus forms to close gap between adjacent vessel ends

Question 8

how is thrombus removed

Answer 8

Plasminogen (blood protein) converts to plasmin, cuts fibrin into smaller fragments, removing fibrin (in clots and thrombi)

In thrombus called thrombolysis

Question 9

What are the 3 main causes of thrombosis

Answer 9

Change in intimal surface of vessel (when trauma occurs)
Changes in pattern of blood flow
Changes in blood constituents

Question 10

Describe cloting factors

Answer 10

Mainly produced in liver (also endothelial cells)
Amplification system
Thrombin production
Thrombin converts soluble fibrinogen to insoluble fibrin
Endpoint of cascade is production of mesh network

Question 11

How does the clotting system work

Answer 11

Clotting cascade is amplification system – many more molecules of fibrin are produced compared to TF

Damage activates diff proteins
Prothrombin to thrombin
Fibronogen and thrombin to fibrin
Fibrin to crosslinked fibrin

Question 12

How do clotting factors become active

Answer 12

Many are serine proteases - have serine amino acid and cleave other clotting factors to form active molecule