Autonomic Control of Blood Pressure

Question 1

What do local intrinsic mechanisms for vascular regulation effect?

Answer 1

Primarily aimed at regulating regional blood flow (metabolic, myogenic)

Question 2

What do neural and hormonal mechanisms for vascular regulation effect?

Answer 2

They aim to regulate mean arterial pressure to maintain adequate tissue perfusion. MAP = CO x TPR

Question 3

Where is MAP monitored?

Answer 3

High-pressure arterial baroreceptors.
Renal juxtaglomerular apparatus.
low-pressure baroreceptors.

Question 4

What is single most important mechanism providing short-term regulation of arterial pressure?

Answer 4

Arterial baroreceptor reflex.

Question 5

How is acute regulation of blood pressure achieved?

Answer 5

Acute regulation of arterial pressure is primarily mediated by the high-[ressure baroreceptor reflex, with contributions by cardiopulmonary receptors (aka low-pressure baroreceptors or volume receptors) and chemoreceptors (primarily concerned with respiratory control)

Question 6

How is chronic regulation of arterial pressure achieved?

Answer 6

It is linked to volume control by the kidneys.

Question 7

Describe the baroreceptor system for controlling arterial pressure

Answer 7

This reflex is initiated but stretch receptors, called baroreceptors, located in the walls of several large systemic arteries (the carotid sinus and aortic arch). A rise in arterial pressure stretches the baroreceptors and causes them to transmit more APs to the CNS medullary control centers. “feedback”signals are then sent back through the ANS to the circulation to reduce arterial pressure downward toward the normal level. A fall in arterial pressure has the converse effecs on ANS efferent output.

Question 8

How are signals from the carotid baroreceptors transmitted?

Answer 8

They travel though small Hering’s nerves to the glossopharyngeal nerves (IX) in the high neck, and then to the nucleus tractis solitaries (NTS) in the medulla.

Question 9

How are signals from the aortic baroreceptors in the aortic arch transmitted?

Answer 9

They travel though the vagus nerve (X) to the nucleus tractis in the medulla.

Question 10

What effect does stretching a baroreceptor have on the body?

Answer 10

It results in vasodilation and bradycardia.

Question 11

Peripheral chemoreceptors located in the carotid and aortic bodies sense blood pressure how? When do they become activated?

Answer 11

When arterial pressure falls below a critical level the receptors become stimulated because diminished blood flow causes decreased oxygen. They are sensitive to low PO2. These receptors are less sensitive and not as powerful for arterial pressure control. Thus, they don’t work until BP falls below 80 mmHg.

Question 12

What do central chemoreceptors do? Where are they located?

Answer 12

In the medulla of the brain they are sensitive to decreases in brain pH (reflecting an increase in arterial PCO2) and cause and increase in SNS output.

Question 13

What are peripheral chemoreceptors sensitive to? What about central ones?

Answer 13

PO2 and PCO2. They act in concert to cause vasoconstriction.

Question 14

Baroreceptors ________ their firing rate in response to stretch (increased MAP) in a ________________ manner?

Answer 14

Increase. Frequency-dependent

Question 15

Do carotid sinus baroreceptors respond more rapidly to changing pressure or to stationary pressure?

Answer 15

To changing pressure. The baroreceptor reflex adapts to long-term changes in mean arterial pressure. For example, in hypertension, the curve is parallel and shifted to the right.

Question 16

Without baroreceptors what happens to MAP?

Answer 16

MAP fluctuates in the absence of baroreceptors. Baroreceptors reduce the minute-by-minnute variability in MAP to about one-third that which would occur if the baroreceptor system was not present.

Question 17

The innervation of the small arteries and arterioles allow sympathetic stimulation to have what effect?

Answer 17

To increase the resistance to blood flow and thereby to decrease rate of blood flow through the tissues.

Question 18

The inn nervation of the large vessels, particularly of the veins allows sympathetic stimulation to have what effect?

Answer 18

To decrease the volume of these vessels. Doing so pushes blood into the heart and can play a major role in regulation of CO.

Question 19

What is vasomotor tone? What happens if it is disrupted?

Answer 19

Partial state of contraction in the blood vessels. The SNS maintains this and if cut results in a drop in arterial pressure. Giving norepi can still increase the arterial pressure but as the drug quickly wears off pressure again drops.

Question 20

An adaptation to long-term changes in MAP like in hypertension has what effect on the set-point?

Answer 20

It raises it.

Question 21

The baroreceptor reflex when changing posture from a standing to a lying position leads to a reflex ______ in MAP

Answer 21

decrease. A change in posture from standing to lying down increases venous return and thus stroke volume which increases MAP.

Question 22

What is the carotid sinus massage used for?

Answer 22

It stimulates the baroreceptors and reflexly slows the heart in people with atrial tachycardia. Release from a Valsalva maneuver would do the same thing.

Question 23

What happens in someone with carotid sinus syndrome?

Answer 23

They have a hyper-sensitive baroreceptor such that even mild external pressure to the neck elicits a strong reflex, even stopping the heart for 5-10 seconds.

Question 24

The falling of arterial pressure upon standing causes what to happen? What effect does it have on HR, contractility, cardiac output, TPR, and veins?

Answer 24

An immediate reflex resulting in strong sympathetic discharge throughout the body. Increases HR, contractility and CO. Constriction of arterioles increases TPR. Constriction of veins decreases unstressed volume. This all minimizes the decrease in pressure in the head and upper body.

Question 25

The Valsalva maneuver can be used to test what? What is the response to the Valsalva maneuver?

Answer 25

Can be used to test the integrity of the baroreceptor reflex. This causes an increase in intrathoracic pressure and a decrease in venous return to the heart which decreases CO and MAP. Intact baroreceptors will sense the decrease in MAP and direct an increase in SNS and decrease in PNS outflow to the heart and vessels, the increase in HR is measured. A rebound decrease in HR is noted after release.

Question 26

What effect does a decrease in MAP have on the SNS and PNS activation?

Answer 26

It increases SNS and decreases PNS activation restoring MAP.