Homeostasis

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Homeostasis:

= a set of fast, controlled, localised responses that prevent significant blood loss when there is a breach in the vessel wall

3 stages - Vascular spasm

- Platelet plug formation

- Coagulation

Vascular spasm

- VC of the blood vessels to minimise blood loss

- 20-30mins

- buys time for platelet plug formation

- Triggered by: - damage to the vascular smooth muscle

- chemicals released from the damaged endothelium

- pain reflexes

Platelet plug formation

- Platelets aggregate and attach to each other and the exposed collagen from the vessel wall

- They become sticky, swollen and spikey.

- They then release chemicals: SEROTONIN - enhances vascular spasm

ADP - attracts platelets

THROMBOXANE A2 - both

- Platelets release these chemicals, attracting more platelets which release more chemicals - postive feedback cycle.

Coagulation

- Changing from a liquid state to a gel-like state

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