Vascular system

Question 1

Cerebral Blood Flow

Answer 1

• Internal carotid artery and vertebral arteries form circle of Willis; allows for perfusion of blood if part is blocked
• 5-10 secs without blood; loss of consciousness
• 3 mins; irreversible damage

Question 2

Theories on auto-regulation of cerebral blood flow

Answer 2

• METABOLIC THEORY; increased blood flow washes away vasodilators metabolites, leads to vasoconstriction
• MYOGENIC THEORY; increased BP, stretch receptors causes reflex vasoconstriction

Question 3

Local variations in cerebral blood flow

Answer 3

• CBF is generally stable but there are variable regions
• dependent on requirements
• mediators; K+, adenosine, nitric oxide from vascular endothelium

Question 4

Neural control of cerebral blood flow

Answer 4

• sympathetic nerves provide for the large arteries
• protects smaller vessels; when large changes occur, reflex vasoconstriction
• CNS Ischaemic response

Question 5

CNS Ischaemic Response

Answer 5

• preserves blood flow to the brain
• when mean arterial pressure (MAP) drops during haemorrhage, hypoxia occurs, metabolites build up, stimulates the medullary cardiovascular centre
• sympathetic nerve activity maintains BP

Question 6

Cushing’s Reflex

Answer 6

• related to intracranial pressure
• raise in ICP will constrict blood vessels
• leads to CNS ischaemic
• systemic vasoconstriction occurs; BP is elevated due to increased TPR but HR is low
• increased BP leads to increased perfusion
• CBF maintained
• low HR high BP; BAD prognosis

Question 7

Coronary circulation

Answer 7

• Arteries arise from the aorta close to aortic valve
• Blood returns to the right atrium via coronary sinuses/anterior coronary veins
• Collateral coronary circulations; divert from occluded to non-occluded
• ## coronary vessels have sympathetic innervation; alpha and beta- 1 adenoreceptors

Question 8

Examples of vasodilator metabolites

Answer 8

• high CO2
• H+
• K+
• lactate
• adenosine
• hypoxia

Question 9

Splanchnic Circulation

Answer 9

• composed of gastric, small intestine, colonic, pancreatic, hepatic and splenic circulations
• arranged in parallel to each other
• 3x major arteries; celiac, inferior and superior mesenteric
• portal system; direct blood from GIT to the liver
• ## substances absorbed in SI travel to liver for processing before the heart

Question 10

Regulation of splanchnic circulation

Answer 10

• In fight/flight; sympathetic, vasoconstriction of splanchnic arteries diverts blood to skeletal muscles and cardiac muscle
• damages microvilli
• necrosis of hepatocytes
• reduced GFR of kidney, necrosis of nephrons