B4.004 Cardiovascular Control Mechanisms Flashcards
how do veins differ from arteries?
more distensible
more compliant
ability to store blood
which vessels do sympathetic axon varicosities act upon?
BOTH arterioles and venules
sympathetic action on arteries
noradrenergic- a1
decreases diameter by smooth muscle contraction
increased resistance = increased MAP
sympathetic action on veins
noradrenergic- a1
decreases diameter by smooth muscle contraction
decreased capacitance = increased venous return = increased cardiac output
which vessels do parasympathetic nitrergic axon varicosities act upon?
arterioles
parasympathetic action on arterioles
NO- guanylate cyclase -increased diameter Epinephrine- b2 (non-neural) -decreased resistance -increased flow
difference between sympathetic and parasympathetic effects on vasculature
parasympathetic = very discrete, local control mechanism within limited vessels sympathetic = overall function regulation
3 ranges for changing blood vessel diameter
- to change local blood flow
- to change total peripheral resistance (TPR)
- to change cardiac output (CO)
purpose of changing local blood flow
important for discrete reflexes (genital erection, GI vasodilation during a meal)
local resistance is decreases so local flow increases
no significant change in TPR or MAP
why does TPR need to be adjusted?
if MAP decreases (blood loss, pooling while standing, etc) this will reduce brain perfusion because the brain is at the top of the hydrostatic column
leads to syncope
compensated for by changing TPR
how is TPR determined
by arterial blood vessel diameters in vascular beds (renal, GI, skeletal)
TPR increased by arterial vascular constriction
-renal and GI by a1 receptors
-skeletal by b2 receptors
effects of TPR on MAP
increased TPR increases MAP
increased TPR normally will not significantly decrease CO
process of changing cardiac output
venules/veins store 2/3 of total blood volume
venous smooth muscle contraction forces blood back to the heart (increased venous return)
increased venous return = increased CO
increased CO = increased MAP
what is tone
level of activity of nerves and targets
high nerve discharge rate or contractile state = high tone
vascular tone
determined by balance between vasoconstrictors influences (mainly sympathetic a1) and vasodilatory factors
cardiac tone
determined by concurrent discharge of excitatory sympathetic and inhibitory parasympathetic nerves
HR increased by increasing symp or decreasing parasym discharge
describe the process of changing from supine to upright posture and the effect on MAP
increased hydrostatic pressure causes venous distention in lower body and venous pooling of about 700 mL of blood
decreased venous return > decreased CO > decreased MAP
process of increasing cardiac tone
increasing cardiac sympathetic tone and decreasing vagal parasympathetic tone increased HR and force of contraction
makes heart a more effective pump
this can help restore cardiac output
