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
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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
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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
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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
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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
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6
Q

central chemoreceptors

A

-in medulla are sensitive to decreases in brain pH and cause and increase in SNS output

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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
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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
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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
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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
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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
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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
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13
Q

standing to lying down

A

-increases MAP-baroreceptor relex

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14
Q

carotid massage or release from valsalva

A

-stimulates receptors and slows heart

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15
Q

carotid sinus syndrome

A
  • hypersensitive receptors

- mild external pressure elicits strong response

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16
Q

nerves

A
  • SNS and PNS in SA and AV
  • SNS in heart muscle
  • atreries and veins SNS
  • PNS in genitals and lower GI
17
Q

standing up

A
  • blood pools in veins
  • decreases MAP
  • baroreceptors slow down AP
  • SNS increases
  • increases HR, contractility, CO
  • constricts arterioles and increases TPR
  • constriction of veins decreases unstressed volume
  • MAP increases toward normal
18
Q

valsalva

A
  • increases intrathoracic pressure
  • decreases venous return to heart
  • decreases CO and MAP
  • intact baroreceptors will sense decrease and decrease AP, increase SNS and decrease PNS, increase in HR
19
Q

medullary control centers

A
  • most afferent fibers from high P baroreceptors to NTS
  • inhibitory interneurons from NTS to vasomotor-rise in P inhibits C1 neurons and results in vasodilation
  • excitatory interneurons from NTS to cardioinhibitory area-nucleus ambiguous and dorsal motor nucleus
  • leads to bradycardia
  • some inhibitory neurons in cardioaccelatory area- regulates increased HR and contractility