W5 LECT1: intro to hemostasis

Question 1

how are platelets activated?

Answer 1

1. Shape change from discoid to spiny
2. Flip flop of membrane lipids resulting in a
   change of the external surface from neutral
   to charged
3. Release of storage granules
4. Conformational change of GPIIb/IIIa
   allowing for the binding of fibrinogen

Question 2

what is hemostasis?

Answer 2

Haemostasis is the process that stops bleeding at the site of an injury by forming a blood clot

Question 3

What are the main stages of haemostasis?

Answer 3

-vascular spasm
-platelet plug formation
- and coagulation.

Question 4

What triggers platelet adhesion during haemostasis?

Answer 4

Platelet adhesion is triggered by exposure to collagen in the blood vessel wall and is mediated by von Willebrand factor (vWF) binding to glycoprotein Ib/IX/V on the platelet surface.

Question 5

What are the consequences of platelet activation?

Answer 5

Platelet activation leads to shape change, membrane flip flop exposing charged phospholipids, release of granule contents, and conformational change of GPIIb/IIIa allowing for fibrinogen binding.

Question 6

Name some physiological agonists of platelet activation.

Answer 6

Thrombin, collagen, adrenaline, ADP, and thromboxane A2 (TXA2)

Question 7

what are the consequences of plt activation?

Answer 7

1. Shape change leads to a huge increase in surface area
2. Membrane flip flop exposes charged phospholipids to support coagulation
3. Release of granule contents
   - Increased concentration of certain clotting factors
   - Further activation of other platelets – dense granule ADP release
   There is a resultant cycle of aggregation leading to the formation of a large mass
   or plug of platelets over the layer of platelets covering the breach in the
   endothelium
   This plug is friable but supports the generation of a stronger fibrin clot

Question 8

What is the primary function of platelets in haemostasis?

Answer 8

Platelets adhere to the site of blood vessel injury, aggregate to form a temporary plug, and release factors that help in the coagulation process

Question 9

How does the shape of platelets change upon activation?

Answer 9

Upon activation, platelets change from a discoid shape to a spiny shape, increasing their surface area.

Question 10

What role do glycoproteins play on the surface of platelets

Answer 10

Glycoproteins on the platelet surface mediate adhesion and aggregation by binding to other platelets, collagen, and other proteins

Question 11

What is the function of von Willebrand factor (vWF) in platelet adhesion?

Answer 11

von Willebrand factor (vWF) acts as a bridge between platelets and collagen in the blood vessel wall, facilitating platelet adhesion.

Question 12

Describe the role of ADP in platelet activation.

Answer 12

ADP is released from activated platelets and further stimulates platelet activation and aggregation.

Question 13

where does iniation of coagulation occur?

Answer 13

occurs on the tissues factor bearing cell

Question 14

what are the steps in coagulation cascade?

Answer 14

• initiation of coagulation:This occurs on the tissue factor-bearing cell
• Amplification: the site of the reaction moves to the platelet and thrombin
  activates V, VIII and XI
  Propagation: the formation of the bulk of the fibrin clot

Question 15

What is the role of tissue factor (TF) in the coagulation cascade?

Answer 15

Tissue factor (TF) initiates the coagulation cascade by forming a complex with Factor VIIa, which then activates Factor X and IX.

Question 16

What is the propagation phase of the coagulation cascade?

Answer 16

The propagation phase involves the amplification of the coagulation response, leading to the formation of a stable fibrin clot through the activation of additional clotting factors on the surface of platelets

Question 17

Which factor stabilizes fibrin fibers?

Answer 17

Factor XIIIa stabilizes fibrin fibers by cross-linking them.

Question 18

What is the coagulation cascade?

Answer 18

The coagulation cascade is a series of enzymatic reactions that lead to the formation of a fibrin clot.

Question 19

What initiates the extrinsic pathway of coagulation?

Answer 19

The extrinsic pathway is initiated by tissue factor (TF) released from damaged tissue

Question 20

What is the role of Factor X in coagulation?

Answer 20

A9: Factor X, once activated to Factor Xa, converts prothrombin to thrombin in the presence of Factor Va, calcium, and phospholipids

Question 21

What is the intrinsic pathway of coagulation

Answer 21

A10: The intrinsic pathway is initiated by the activation of Factor XII on negatively charged surfaces and involves a series of reactions leading to the activation of Factor X.

Question 22

How is thrombin generated in the coagulation cascade?

Answer 22

Thrombin is generated by the cleavage of prothrombin by Factor Xa in the prothrombinase complex

Question 23

What is the final product of the coagulation cascade?
A.

Answer 23

12: The final product is fibrin, which forms a stable clot by cross-linking with the help of Factor XIIIa