24 Cardiovascular Reflexes and Regulation of Blood P & V

Question 1

What is the primary mechanism for short term regulation of BP?

Answer 1

baroreceptor reflex in carotid sinuses and aortic arch

Question 2

What are sensory nerve endings that detect and signal the CNS of changes in BP?

Answer 2

baroreceptors

Question 3

What are the 2 main outcomes of baroreceptor activity?

Answer 3

1. inhibit efferent sympathetc

2. activates parasympathetic pathway.

Question 4

What is the major function of the baroreflex?

Answer 4

buffer or oppose changes in BP

Question 5

What nerve innervates the carotid baroreceptors?

Answer 5

CNIX

Question 6

What nerve innervates the aortic baroreceptors?

Answer 6

CNX

Question 7

Afferent fibers of the baroreflex synapse where?

Answer 7

medulla oblongata–nucleus tractus solitarius

Question 8

Do baroreceptors fire more often in an expanded artery(i.e. High BP) or in a smaller artery (i.e.. low BP)?

Answer 8

Higher BP and stretch leads to malformation and increased firing of the AP to the brain.

Question 9

What are the 3 main determinants of baroreceptor activity?

Answer 9

1. Mean arterial BP
2. Rate of change in pressure
3. Large artery compliance

Question 10

What is the minimum pressure baroreceptors fire AP?

Answer 10

Pressure threshold- 40-60 mmHg

Question 11

Pressure above which the arterial baroreceptors no longer increase their firing?

Answer 11

Saturation Pressure – 180mmHg

Question 12

What are the main responses to increase of baroreceptor activity?

Answer 12

decrease SNA, increase paraSNA, and decrease AVP

Question 13

What are the main responses in a decrease of baroreceptor activity?

Answer 13

increase SNA, decrease paraSNA, increase AVP

Question 14

Does baroreceptor activity adapt to sustained increase?

Answer 14

yes an it does not take very long…10 minutes and leads to rapid resetting or (right shift) of pressure activity curve. [decrease is the opposite]

Question 15

what happens to baroreceptor sensitivity in chronic hypertension?

Answer 15

it decreases—leads to increased BP variability, arrhythmias, sudden cardiac death, promotes high SNA/ low paraSNA

Question 16

What type of nerve endings are found in the heart?

Answer 16

mechanosensitive (central blood volume) and chemosensitive (myocardial ischemia)

Question 17

What nerve is very important for normal reflex control of circulation?

Answer 17

vagus afferents

Question 18

When are SNA afferent fibers activated in the heart?

Answer 18

disease states (along with vagal afferents)

Question 19

Increased cardiac vagal afferent activity triggers what 2 responses?

Answer 19

decrease SNA, decrease AVP—–lower BP

Question 20

What reflex response would occur in mild-moderate hemorrhage or orthostatic stress?

Answer 20

increase SNA, vasoconstriction, and increase HR

Question 21

What reflex would you expect in severe hemorrhage or prolonged orthostatic stress?

Answer 21

increase paraSna, decrease HR, decrease SNA, decrease TPVR—-hypotension

Question 22

What results from paradoxical activation of vagal afferents innervating left ventricle stimulated by vigorous pumping of underfilled ventricles or chemicals released by myocardium?

Answer 22

vasovagal syncope (neurocardiogenic syncope)

Question 23

Can the CNS trigger syncope?

Answer 23

yes- perturbed cerebral blood flow or emotional stimuli (less understood)

Question 24

Hypoxia, apnea, hypovenitilation, respiratory disease and metabolic disorders cause abnormalities of arterial blood gases and pH. Where are these changes sensed in the blood?

Answer 24

carotid and aortic bodies

Question 25

glomus cells of carotid body are depolarized by what 3 signals?

Answer 25

decrease oxygen, increased carbon dioxide, decreased pH

Question 26

What are the reflex responses to carotid body (chemoreceptor stimulation)?

Answer 26

increase ventilation, increase SNA to periphery, increase paraSNA to the heart

Question 27

What is the outcome of the lung inflation reflex

Answer 27

1. inhibits paraSNA to heart—increases HR

2. inhibits SNA to vasculature—increased vasodilation

Question 28

What stimulates trigeminal afferents for cardiac reflex and what does it result in?

Answer 28

exposure of face to water—- 1. reflex apnea, 2.increase paraSNA to heart 3. increased SNA to vasculature

Question 29

what three things causes HR and BP variability?

Answer 29

behavioral changes, postural changes, regular oscillations

Question 30

high frequency HR variability synchronized to respiration reflects what type of cardiac autonomic modulation?

Answer 30

paraSNA

Question 31

low frequency HR variability is strongly dependent on what type of cardiac autonomic modulation?

Answer 31

SNA

Question 32

What is the bezold jarisch reflex?

Answer 32

fainting due to hypopnea (shallow rapid breathing) and bradycardia (low resting HR)