Haemostasis

Question 1

What is haemostasis

Answer 1

Balance between bleeding & hypercoagulability

Question 2

What are some platelet features

Answer 2

Small

No nucleus

Lifespan = 10 days

Stored in spleen

Question 3

What are platelet granules

Answer 3

Alpha granules:
Contains:
Von Willebrand factor & coagulation factor 4 for blood clotting
Platelet derived growth factor

Dense granules:
Contains:
ADP
Calcium

Question 4

Describe the haemostasis mechanism

Answer 4

1. Vascular constriction
   Smooth muscles in wall of injured blood vessel contract to narrow vessel & reduce blood flow to site
2. Platelet plug formation
   a. Platelet adhesion
   Von Willebrand factor (vWF) released from damaged endothelial cells & alpha granules bind to platelet receptors to promote platelet adhesion

b. Platelet activation
Platelets become activated, releasing ADP & serotonin & express surface receptors
Leads to platelet aggregation with platelets binding to each other through glycoprotein IIB & IIIa

c. Platelet aggregation
Platelet plug formed
Facilitated by ADP, thromboxane A2 & collagen

3. Coagulation cascade
   a. Activation
   Intrinsic pathway initiated by collagen
   Extrinsic pathway initiated by release of tissue factor from damaged cells
   Pathways converge to formed factor X

b. Prothrombin activation
Factor X & calcium form thrombin

c. Fibrin formation
Thrombin cleaves fibrinogen into fibrin which forms clot

4. Fibrinolysis
   Fibrin clot broken down by plasmin

Question 5

What is thrombocytopenia

Answer 5

low platelet count

Question 6

What is thrombocytopathy

Answer 6

abnormal platelet function

Question 7

What is buccal mucosal bleeding time

Answer 7

Time taken for bleeding to stop after making small incision

Healthy dog: 1.7-4.2 min

Healthy cat: 1.0-2.4 min

Question 8

How are platelets counted

Answer 8

Counts should be performed as soon as possible to avoid clumping

3 methods can be used:
Haemocytometer
Automated cell count
Blood smear