Regional Circulation Flashcards
Discuss the effect of pressure on blood flow in the brain
A constant flow over a wide range of pressure
Neural control of blood in the brain
Relatively minor neural control as there are relatively few alpha1 adrenoceptors
Importance of hormones in blood flow to the brain
Minor importance
Local regulation of blood flow in brain
Good autoregulation
Important metabolic control during mental activity - (H+, K+, Adenoside, Hypercapnia, hypoxia cause vasodilation)
Endothelin
Important vasoconstrictor released in pathological states - e.g. subarrachnoid haemmorage to limit blood loss
Mechanical control of brain circulation
Constrained in rigid cranium influenced by CSF pressure
Special feature of brain circulation
Brain can sometimes steal blood from other regions due to its extreme importance
medullary ischaemic reflex
Ischaemia in medulla, brain detects this and sends signals to other body parts to send driving force to brain
Coronary sympathetic innervation
Not much innervation, but the effect of the innervation is chronotropy and inotropy, increasing metabolic activity in heart, releasing vasodilators (e.g. CO2, adenosine) and thus blood flow
Mechanical control of cardiac circulation
Major influence on flow during cardiac cycle - peak flow in early diastole; zero or negative flow at onset of systole
Why is the heart usually slowed in heart conditions
Heart spends longer in diastole so increased time for blood to be delivered
Special feature of cardiac circulation
Parallelism between metabolism and flow
AV anastomoses
Direct connections between arterioles and venules without having to go through capillaries
Neural control of skin vessels
Arterioles have relatively weak innervation, A-V anastomoses have a dense innervation though
What happens to arterioles and AV anastomoses as core temperature drops
Vasoconstriction in order to decrease skin blood flow and limit heat loss
Local control of skin circulation
Arterioles show some degree of myogenic autoregulation; endothelin may be involved in pathological states like raynauds
Hormones involved in skin circulation
Angiotensin, Vasopressin, Noradrenaline, Adrenaline all cause vasoconstriction
Special features of skin circulation
The primary funtion is thermoregulation
Sweat glands have sympathetic cholinergic innervation which may cause vasodilatation via release of e.g. bradykinin
Neural control of skeletal muscle circulation
Rest - important alpha vasoconstriction, some beta vasodilation
Exercise - Very little neural incluence, some beta vasodilation via mostly adrenaline, not nerve
Hyperaemia
Increased blood flow
Local control of skeletal muscle circulation
Rest - neural control over-ride autoregulatory mechanisms
Exercise - Local metabolites have major influence (K+, adenosine, lactate, etc.) all causing vasodilation
Hormones involved in skeletal muscle circulation
Adrenaline at low concentrations will vasodilate (beta adrenoceptors)
Special features of skeletal muscle circulation
Capacity to increase flow in exercise (20-fold) - active hyperaemia
Large increase in flow post-occlusion - reactive hyperaemia
(Increase above normal in blood flow if supply is temporarily cut off)
Describe the blood that reaches the liver
70% of blood in the liver is deoxygenated as it has passed through the digestive organs and is filtered before entering blood stream
30% enters as oxygenated via the hepatic artery
Neural control of intestinal circulation
Moderate alpha vasoconstriction
Neural control of hepatic circulation
Important venoconstriction
Local control of GI circulation
Poor autoregulation but importantly influenced by local peptides
Local control of hepatic circulation
Portal vein - No autoregulation
Hepatic artery - Good autoregulation
Hormones involved in GI circulation
GI hormones (gastrin, cholecystokinin) vasodilate, vasopressin, angiotensin constrict potently
Neural control of GI circulation
Minimal influence
Mechanical control of hepatic circulation
Minimal influence
Why is there pain sometimes if you exercise immediately after eating
There may be competition for blood supply between the GI tract and muscles
Special features of GI tract
Intestinal circulation exhibits functional hyperaemia following feeding; intense vasoconstriction can lead to damage and toxin release
Neural control of renal circulation
Important alpha vasoconstriction, some beta vasodilation
Discuss innervation of renin secreting cells
They have an important sympathetic innervation of beta adrenoceptors
Local control of renal circulation
Good autoregulation of flow over wide pressure range
Hormones involved in renal circulation
Noradrenaline, adrenaline, angoitensin can cause constriction
Vasopressin may cause vasodilation via PGI2/NO release
Dopamine causes vasodilation
Special features of renal circulation
Efferent constriction causes increase in BP upstream of that; thus the glomerulus
Neural control of pulmonary circulation
Relatively minor (alpha vasoconstriction)
Local control of pulmonary circulation (why is it different)
Unlike elsewhere, hypoxia causes vasoconstriction, augmented by hypercapnia (possibly mediated by endothelin)
NO causes vasodilation and may be therapeutic
Mechanical control of pulmonary circulation
Flow is affected by changes in aveolar pressure and lung volume; increase in flow (cardiac output) associated with recruitment and distentsion of mucrovessels and decrease in vascular resistance
What happens when alveolar pressure > intravascular pressure
Flow is reduced
Lung inflation reduces resistance in extra-alveolar vessles (traction) and increases resistance in intra-alveolar vessels (compression)
Special feature of pulmonary circulation
Thin walled vessels with low resistance & low vasoconstrictor capacity
Hydrostatic pressure < colloid osmotic pressure which favours reabsorption
