Hormonal Control of Blood Pressure Flashcards
what are the two main goals when there is severe hemorrhage?
respond rapidly to perfuse vital organs and gradually replenish blood volume
what are the rapid acting control mechanisms in response to acute change in blood pressure? what types of responses are these?
baroreceptors, chemoreceptors and CNS ischemic response.
these are nervous reflexes
what are the three intermediate controls of blood pressure?
renin-angiotensin vasoconstrictor mechanism, capillary fluid shift mechanism and the stress relaxation mechanism
what is the long term control of blood pressure?
volume control by the kindney, especially the renin-angiotensin-aldosterone system
what occurs when blood flow to the vasomotor center in the brain stem becomes decreased enough to cause cerebral ischemia?
the vasoconstrictor and cardioaccelerator neurons in that area become strongly excited and blood pressure compensates as much as it possibly can (up to 250 mmHg)
what is the specific cause of the CNS ischemic response?
buildup of local concentration of CO2 stimulates vasomotor control centers
what happens to urine production during the CNS ischemic response and why?
it slows dramatically and may even stop. this is because the vasoconstriction can be so great that some peripheral vessels become occluded
how far must the arterial pressure fall before the CNS ischemic response occurs? when it is optimal?
must be down to 60 mmHg but is optimal at 15-20 mmHg
what does the Cushing reaction respond to?
increased pressure of cerebrospinal fluid around the brain that cuts off blood flow to the brain
how does the cushing reaction respond to ischemia?
it initiates the CNS ischemic response so that the arterial pressure rises to a pressure above the intracranial pressure so there is blood flow
what are the four major groups of receptors that compensate for a large fall in mean arterial pressure?
high and low pressure baroreceptors, peripheral chemoreceptors and central chemoreceptors
what response do high pressure baroreceptors have to decreased pressure and what is the result?
decreased firing rate
increases heart rate, cardiac contractility and vasoconstriction
what do low pressure baroreceptors respond to and what does it mediate?
decrease firing rate responding to decreased circulating volume leads to SNS mediated vasoconstriction and ADH release
what do peripheral chemoreceptors respond to and what do they cause?
respond to hypoxia by increasing firing rate and increases vasoconstriction and changes ventilation
where can central chemoreceptors be found and what do they respond to? what effect does this have?
respond to brain ischemia (acidosis) and mediate the CNS ischemic response
the major compensations that are mediated with blood loss can keep MAP normal with what amounts of blood loss?
15-20% blood loss
where is renin secreted and what is its effect?
secreted by the kidneys and it cleaves the circulating protein angiotensinogen to angiotensin I
where is angiotensin I converted to angiotensin II and by what enzyme?
in the lungs by angiotensin converting enzyme (ACE)
what is the vascular effect of angiotensin II?
it is a powerful short acting arterial vasoconsrictor and causes venoconstriction to increase venous return as well
what effect does angiotensin II have on the kidney, brain and adrenal gland?
kidney- retains salt and water
brain-promotes release of ADH
adrenal gland- causes the release of aldosterone
what is the effect of aldosterone?
increases the salt and water reabsorption by the kidneys
what inactivates angiotensin II?
angiotensinases
how much does the renin-angiotensin vasoconstrictor response return mean arterial pressure after a drop from 100-50 mmHg?
can raise pressure back to about 83 mmHg (only raised to 60 mmHg without the response)
describe the capillary fluid shift mechanism of responding to a decrease in MAP.
decreased intravascular hydrostatic pressure increases fluid resorption in the capillaries and therefore increases blood volume
