Peripheral Vascular Blood Flow Regulation Flashcards
cerebral circulation
brain is the most actively metablizing organ, constant intravascular volume
total flow remains relatively constant but regional distribution changes dramatically and rapidly with neuronal activity
effect of aterial CO2 on cerebral blood flow
factors affecting cerebral blood flow
vasoconstrictor influences - HCO3
vasodilator influences - low O2 (below 50mmHg), adenosine, NO, low pH, K+
cerebral spinal fluid pressure
cushing reflex
a reflex increase in arterial pressure (via smpathetic systemic vasoconstriction) in response to increased intracranial pressure (tumor, hemorrhage, etc.) that results in ischemia in the vasomotor areas of the brainstem
the net result is that cerebral blood flow is maintained short term
splanchnic bed
major blood reservoir, holds 20% of the total blood volume
control of the splanchnic circulation
neural control primarily NE - vasoconstrictor tone is present due to normal sympathetic activity
reflex control - target organs for all reflexes that change sympathetic activity
local control - locally released hormones, metabolism
control of splancnic veins
large venous reservoir
sympathetic tone
mechanical influences
effect of sympathetic nerve activity in the GI tract
potent vasoconstriction
shunting blood to other beds and reducing venous capacitance during exercise or hemorrhage
Why does an obstruction of the portal vein lead to ascites?
70% of blood flow from the aorta that goes to the liver goes through the portal vein, so obstrucction leads to increased pressrues and edema in the peritoneal cavity
innervation of skeletal muscle
sympathetic adrenergic innervation - vasoconstriction and reduced flow
symapthetic cholinergic innervation - vasodilation
tonic activity on these nervse contributes to the high basal tone of muscle vessels needed to limit flow at rest
reflex controls of skeletal muscle
baroreceptors
chemoreceptors
other
exercise
local control of skeletal muscles
oxygen
adenosine
others
**these are metabolic byproducts
cerebral circulation
750 ml/min
14% of resting CO
50-60 ml/min/100gm
splanchnic circulation
1500 ml/min
25-30% of CO
skeletal muscle circulation
at rest 800-1200 ml/min
15% of CO
3 ml/min/100g of muscle
cutaneous circulation
at normothermia:
200-500 ml/min
10% of CO
10 ml/min/100 gm skin
cutaneous and venous plexuses
found near the surface of the skin and are important sites of heat loss due to large volume and slow blood velicty
thermoregulation of the skin
temperature sensors in the skin and muscle
blood-sensitive neurons in CNS
high environmental temperatures lead to increase flow and significant vasodilation -> flow diverted form the splanchnic and renal beds
this leads to 60% of CO
low temperatures sympathetic vasoconstriction happens to decrease flow, venous return is directed through deeper veins
pulmonary circulation
5000 ml/min, 100% of CO -> total flow is not strongly regulated by lungs
functional characteristics of the pulmonary circulation
low pressure (MAP 14mmHg)
high flow (5L/min)
low resistance (1/7th TPR)
hydrostatic pressure
reservoir
recruitment of closed capillaries
results in an increased flow with a small increase in pulmonary arterial presure
effect of inhalation on pulmonary circulation
intrathoracic pressure decreases -> decreased external pressure on large pumonary blood vessels
lung inflates -> increased stretch on small pulmonary vessels
small increase in ascular resistance
effect of expiration on pulmonary circulation
opposite effects of inspiration
small net increase in vascular resistance
circulatory changes at birth
presence of oxygen in lungs reelaxes pulmonary precapillary vessels - causes fall in pulmonary vascular resistance and pulmonary arterial pressure
increase in pulmonary blood flow
increased blood flow through lungs causes increased left atrial pressure
when left atrial pressure exceeds the right atrial pressure, the foramen closes
when the umbilical cord is tied off, venous return and arterial pressrues decreases
when the pulmonary artery pressure falls below aortic pressure, flow is reversed in the ductus arteriosus which causes a temporary increase in both pulmonary blood flow and pressure
