hormonal control of BP Flashcards
what are the 3 rapidly acting control mechanisms of MAP? and how fast do these act?
-baroreceptors
-chemoreceptors
-CNS ischemic response
seconds to minutes to act
what are the intermediate control mechanisms of MAP? (3) and how fast do these acT?
-renin angiotension vasoconstritcor mechanism
-stress relaxation mechanism
-capillary fluid shift mechanism
minutes to hours
what is the long term control of MAP? and how fast does this act?
-volume control by the kidneys (renin-angiotensisin-aldosterone system)
days or longer
when does the CNS ischemic response occur?
when there begins to be ischemia in the CNS
at what BP is CNS ischemic response stimulated, and when does it receive its maximum degree of stimulation?
activated at BPs below 60 mmHg
receives greatest amount of stimulation of a BP at 15-20 mmHg
what is the cushing reaction?
type of CNS ischemic response that results from increased pressure of the CSF around the vrain in the cranial vault
relating to the arterial blood pressure, when does the cushing reaction occur?
when the CSF pressure equals that of the arterial blood pressure
do the baroreceptor reflexts compensate for the primary disturbance causing the decrease in MAP?
NO!
what mechanisms compensate for the primary disturbance causing the decreased MAP?
thrist
transcapillary refill
renal conservation of salt and water
what are the 4 major groups of receptors that compensate for the fall in MAP?
- high pressure baroreceptors
- low pressure baroreceptors
- peripheral chemoreceptors
- central chemoreceptors
what is the low pressure baroreceptor’s response to decreased MAP?
decrease firing rate due to decreased circulating volume. Leads to increase SNS mediated vasoconstriction, especially in renal bed. They also stimulate ADH release
what is the high pressure baroreceptor’s response to decreased MAP?
decrease their firing rate leading to increased HR, cardiac contractility and vasoconstriction
describe the function of peripheral chemoreceptors
respond to local hypoxia by increasing firing rate of chemoreceptor afferents leading to increased firing of SNS vasoconstriction fibers and changes in ventilation
describe the function of central chemoreceptors
respond to brain ischemia (fall in pH) leading to powerful SNS output (kidney can stop producing urine all together)
baroreceptors and chemoreceptors together result in what?
increased TPR enough to keep MAP near normal with moderate blood loss (10-20%) but CO remains depressed
how long does renin circulate in the system?
30-60 minutes
where is renin synthesized?
kidney in response to decreased MAP
what is the function of renin?
if cleaves angiotensinogen to make angiotensin I
what enzyme converts angio I to angio II?
ACE
where is ACR located
in the endothelium of the lung vessels
what is the function of ang II in the short term?
is is a short acting arterial vasoconstrictor
raises MAP by increasing TPR and promotes venous return to the heart by venoconstriction
what is the function of ang II in the long term?
- decreases renal excretetion of salt and water–slowly increases ECF volume and then artieral pressure
- also acts on adrenal glad to release aldosterone
- also promotes release of ADH/vasopression from posterior pituitary gland
what does unstressed volume refer to?
volume of blood that veins can hold. produces no pressure
what does stressed volume refer to?
the volume of blood that veins can hold
this produces pressure by stretching the elastic fibers in the walls of the vessels
increased salt intake does what to renin-angiotension activity?
decreases it
where is ADH synthesized?
hypothalamus in the supraopic nuclei. some in paraventricular nuclei
where is ADH stored and secreted from?
pituitary gland
what is the main function of ADH?
water balance
list some conditions that will increase the release of ADH
- increased body osmolarity
- decreased blood volume
- decreased BP
- increased levels of ang II
- pain/stress
- nausea/vomiting (because it causes dehyration)
what is the effect of atrial nautretic peptide on ADH?
it inhibits it
where does the greatest resistance to flow occur?
in the arterioles and small arteries which are regulated by the SNS
what is the effect of ANP on smooth muscle?
dilates it
what is endothelin?
potent vasoconstrictor derived from the endothelium
what types of substances will causes the endothelium to secrete N.O. and PG12
shear stress, acetylcholine and bradykinin
what do the low pressure baroreceptors in the heart and pulmonary circulation do?
they respond to changes in blood volume and modulate sympathetic activity and vasopression (ADH) release
if there is elevated blood volume in the atrium, what will it secrete?
atrial natiuretic peptide (ANP)
what are the effects of ANP?
it has direct effects on the kidney (natriuresis and diuresis) and also inhibits aldosterone release by the adrenal medulla
