Autonomic Control of BP Flashcards
1
Q
MAP
A
- local intrinsic mechanisms for vascular regulation are primarily aimed at regulating regional blood flow
- neural and hormonal mechanisms are often aimed at regulating MAP
- MAP=COxTPR
- monitored at high pressure arterial baroreceptors, renal juxtaglomerular apparatus, low pressure baroreceptors
- adjustments are made via the ANS, release of specific hormones
2
Q
arterial baroreceptor reflex
A
- single most important mechanism for short term regulation
- high pressure baroreceptors, contributions by cardiopulmonary receptors (low pressure) and chemoreceptors
- chronic regulation linked to volume control by kidneys
3
Q
baroreceptor reflex 2
A
- initiated by stretch receptors (baroreceptors)
- receptors in several large vessels
- carotid sinus and aortic arch
- rise in pressure causes more AP to be fired to the CNS
- feedback through ANS to reduce pressure
- signals from carotid baroreceptors transmitted through small Herings nerves to IX and to nucleus tractus solitarius
- signals from aortic receptors through vagus nerve and to NTS
4
Q
high pressure baroreceptors
A
- mechanoreceptors located at strategic high pressure sites
- carotid sinus and aortic arch
- stretching at either site leads to vasodilation and bradycardia
5
Q
peripheral chemoreceptors
A
- carotid and aortic bodies
- close contact with blood
- when pressure falls, receptors activated due to decreased oxygen and excess buildup of carbon dioxide and hydrogen ions
- signals from chemoreceptors pass through Herings nerves and vagus into vasomotor center to elevate pressure
- only when arterial pressure falls below 80 mm Hg
6
Q
central chemoreceptors
A
-in medulla are sensitive to decreases in brain pH and cause and increase in SNS output
7
Q
rate of AP
A
- increases with baroreceptor activation due to increased MAP
- stretch causes increase in transmural pressure which produces an inward current that depolarizes the receptor and generates a receptor potential
- large initial depol followed by more modest steady depol
- graded response, amp is proportional to degree of stretch
8
Q
baroreceptor response
A
- most sensitive in normal operating range
- carotid not stimulated from 0 to 50/60, reach maximum at 180
- aortic work 30 mmHg higher
- in normal range of 100, slight change in pressure causes a strong reflex to readjust
- can change it rapidly, AP increase in systole and decrease in diastole
- respond to changing pressure better than stationary pressure
- reflex adapts to long term change, in HTN curve is shifted to right
9
Q
absence of baroreceptors
A
- MAP fluctuates greatly
- should stay relatively constant throughout the day
- normal stays around 100 (85-115), without has much wider range (50 to >160)
- referred to as pressure buffer/buffer nerves, reduces minute by minute variation
10
Q
sympathetic innervation of the systemic circulation
A
- in most tissues, sympathetic innervates everything except the capillaries
- precap sphincters and metarterioles are innervated in some tissues, but not as dense (mesenteric BV)
- innervation of small arteries and arterioles allows sympathetic stimulation to increase resistance to blood flow and decrease rate
- innervation of large veins allows SNS to decrease volume of these vessels, putting blood back in the heart and increase CO
11
Q
SNS and vasomotor tone
A
- BV partially constricted
- slow firing of SNS fibers for constriction at .5-2 impulses per second
- maintain partial contraction
- total spine anesthesia blocks SNS, arterial pressure falls from 100 to 50
- injecting norepi few minutes later vessels constrict, pressure rises even more for 1-3 minutes until norepi metabolized
12
Q
increase in MAP
A
- activates baroreceptors by stretch
- afferent pathways to NTS in medulla
- efferent pathways to effector
- decreases heart rate and vasodilates vessels
13
Q
standing to lying down
A
-increases MAP-baroreceptor relex
14
Q
carotid massage or release from valsalva
A
-stimulates receptors and slows heart
15
Q
carotid sinus syndrome
A
- hypersensitive receptors
- mild external pressure elicits strong response