Circulatory responses Flashcards
Hyperaemia
blood flow increases in relation to metabolic activity of a tissue/organ
CO2 increase
pH decrease
lactate production
Factors regulating blood flow
sympathetic vasoconstriction
metabolic vasodilation
endothelial derived relaxing factors - nitric oxide/prostaglandins
Redistribution blood flow during exercise
increase to working skeletal muscles
80-85%
decrease to less active organs
e.g., liver/kidney
Redistribution of local blood flow during exercise
skeletal muscle vasodilation (decrease vascular resistance)
autoregulation
due to changes in local factors (increase nitric oxide, prostaglandins, ATP, adenosine)
inactive muscle vasoconstriction (increase vascular resistance) - reduced to 20-30%
Cardiac output redistribution during exercise
skeletal muscles 90% CO
skin
coronary circulation
Circulation special regions during exercise
sympathetic vasoconstriction inactive organs (resting muscles, skin)
metabolic vasoconstriction in active organs
thermoregulatory vasodilation in skin
Splanchnic circulation duirng exercise
liver, GI tract, pancrease, spleen
oxygen consumption stay same
oxygen extraction increase to compensate
blood flow decrease through symapthetic vasoconstriction
constriction = +blood volume into circulation back to heart = increase SV
more during heat = more CO for skin
Skin circulation
rest = 1-3 L.min-1 m2 body surface
max = 7-8
Sympathetic neutral control of skin blood vessels
adrenergic vasoconstrictor (noradrenaline) - non-hairy skin
cholinergic vasodilator (acetylcholine) - hairy skin
Cold stress
vasoconstriction
sympathetic constrictor activity increases (adrenergic)
Heat stress
vasodilation
sympathetic dilator activity increase (cholinergic)
Exercise onset
initial vasocontriction
followed by vasodilation
Dynamic exercise
vasodilation occur at high threshold than during heating at rest
to lose heat
vasoconstriction during prolonged to maintain central blood volume and venous return
sympathetic cholinergic nerves
nitric oxide
Blood pressure regulation
heat = blood shifted from core to surface
muscle pump to aid venous return
filling heart reduced
=vasoconstriction occur to maintain BP
Renal blood flow during exercise
flow decrease
oxygen extraction increase
as renal blood flow increase HR decrease
Endothelial derived relaxing factors
endothelial cells = release nitric oxide
made from l-arginine (amino acid)
into vascular smooth muscle
release CGMP = vasodilation
Prostaglandins
arachidonic acid –> PGs
PGs released from tissues during inflammation or infection
Sympathetic vasoconstriction
conduit artery
EDRFs
NO/PGs
feed artery
Metabolic vasodilation
arterioles
Adrenergic vasoconstrictor
non hairy
neurotransmitter = noradrenaline
Cholinergic vasodilator
hairy skin
neurotransmitter = acetylcholine
Blood flow to skin during rest
100-300 ml.min-1.m2 of body surface
Blood flow to skin during exercise
7-8L.min.m2 of body surface
