23- Regulation of Arterial BP & CPR Endocrinology

Question 1

What is the equation for MAP (Mean Arterial Pressure)?

Answer 1

MAP = CO x TPR

***Can also be MAP = HR x SV x TPR

Question 2

What is a normal MAP?

Answer 2

93.3 mmHg

***Usually about 100 mmHg

Question 3

MAP is composed of 2/3 ______ and 1/3 ______.

Answer 3

DBP

SBP

Question 4

What are the 3 major systems that regulate the MAP?

Answer 4

– Baroreceptor reflex (rapid)

– Endocrinologically via Renin-Angiotensin-Aldosterone System (RAAS) (slower)

– Some input from ADH (vasopressin) and ANP (slower)

Question 5

The MAP uses the baroreceptor reflex, which uses a classical reflex arc. Describe this.

Answer 5

1) Detector – detects deviation from set point
2) Afferent neural pathway
3) Coordinator center – brainstem
4) Efferent neural pathway
5) Effectors – correct deviation from set point

Question 6

What are the locations of the Baroreceptors for the MAP, and what nerves do they utilize?

Answer 6

Carotid Sinus – Glossopharyngeal N. and Sinus nerve of Hering

Aortic Sinus – Vagus N. and Aortic N.

Question 7

Baroreceptors are a type of ___________ that respond to changes in arterial pressure to return to “normal”. __________ are also present and responds to PO2, PCO2, and pH.

Answer 7

Mechanoreceptors

Chemoreceptors

Question 8

Baroreceptors can make changes in pressure through stretch receptors on vessel walls. They can (INCREASE/DECREASE) firing rate to increased stretch, and (INCREASE/DECREASE) firing rate when pressure falls. They can act within seconds and these changes can last indefinitely.

Answer 8

Increase
Decrease

***Most responsive to change in pressure, not just magnitude of change

Question 9

This can be reset for Baroreceptors to create a new “normal”, especially for hypertensive patients.

Answer 9

Basal set point

Question 10

Baroreceptors send signals to the ________ ________ in the medulla.

Answer 10

Vasomotor Center

Question 11

If there is decreased stretch of Baroreceptors, there is decreased firing rate of _________ neurons (i.e., TRP channels).

Answer 11

Afferent

Question 12

For Baroreceptors, Efferents are both __________ and _________. Efferents travel into the Cerebral Cortex and _________.

Answer 12

Parasympathetic
Sympathetic
Hypothalamus

Question 13

This area of the brain/brainstem receives and coordinates peripheral signals, specifically for Baroreceptors in this case.

Answer 13

Nucleus of Tractus Solitarius (NTS)

Question 14

This area of the brain/brainstem consists of Parasympathetic activity associated with CV function.

Answer 14

Dorsal Motor Nucleus of the Vagus

Nucleus Ambiguus

Question 15

This area of the brain/brainstem consists of Sympathetic activity associated with CV function.

Answer 15

Rostral Ventrolateral Medulla

Question 16

The Baroreceptors from the Carotid Sinus and Aortic Sinus lead to what?

Answer 16

Nucleus Tractus Solitarius (NTS)

***Via Afferent Neurons – use Glutamate

Question 17

Briefly explain how the Carotid Sinus baroreceptors can decrease BP.

Answer 17

Carotid Sinus baroreceptors — Travel to NTS via CN IX — Activate Cardiac Decelerator — SA Node is inhibited/slowed

***This is Parasympathetic!

Question 18

Briefly explain how the Aortic Sinus baroreceptors can decrease BP.

Answer 18

Aortic Sinus baroreceptors — Travel to NTS via CN X — Inhibit Cardiac Accelerator and Vasoconstrictor

• **This is Parasympathetic!
• **Cardiac Accelerator and Vasoconstrictor are components of Sympathetics (so they have to be inhibited)

Question 19

For Baroreceptors, (AORTIC/CAROTID) has a higher threshold for activation and continues to respond above saturation. It’s less sensitive to rate and less effected by decreases.

Answer 19

Aortic

Question 20

The Sympathetic nervous system is stimulated by an (INCREASED/DECREASED) baroreceptor firing rate.

Answer 20

Decreased

Question 21

For Sympathetics, the preganglionic fibers are below T1, and it influences heart muscles and the SA Node directly, as well as vessels and Adrenal Gland via Splanchnic N. What do the Sympathetics do for these?

Answer 21

– Constriction of arterioles and veins (alpha-receptors)

– Increases HR and contractility (B1 receptors)

– Fluid retention by kidney due to afferent arteriole constriction and renin secretion

Question 22

The Parasympathetic nervous system is stimulated by an (INCREASED/DECREASED) baroreceptor firing rate.

Answer 22

Increased

Question 23

What influence does Parasympathetics have?

Answer 23

– Decreased HR - Muscarinic receptors (via Vagus N. signal to SA Node)

– Indirect vasodilation on blood vessels (i.e., stimulate NO release)

Question 24

Briefly explain what happens when there is decreased MAP and you need to increase it?

Answer 24

Decreased MAP — Decreased Baroreceptor Firing — Increased SNS Activity and Decreased PSNS Activity — Leads to Increased CO and the Decreased PSNS will cause increased TPR

***This leads to increased arterial pressure!

Question 25

Briefly explain what happens where there is increased MAP and you need to decrease it?

Answer 25

Increased MAP — Increased Baroreceptor Firing — Decreased SNS Activity and Increased PSNS Activity — Leads to Decreased CO and the Increase PSNS will cause decreased TPR

***This leads to decreased arterial pressure!

Question 26

_________ resets baroreceptors to regulate pressure at a higher set point. That way the heart isn’t working quite so hard.

Answer 26

Hypertension

Question 27

Baroreceptor reflex occurs within seconds and attenuates somewhat with time. For long term adjustments, a hormonal response is invoked and begins within minutes and can build over a period of days or longer if needed. This creates vascular and body fluid dynamic changes. What are examples of these hormones?

Answer 27

RAAS (Renin-Angiotensin II-Aldosterone System)
ADH/Vasopressin
ANP

Question 28

This controls blood pressure by regulating blood volume and TPR. It overlaps with the Sympathetic nervous system.

Answer 28

RAAS

Question 29

_______ is an enzyme secreted by the kidneys into the bloodstream in response to a drop in BP. Vice versa, if BP goes higher than normal, less is secreted.

Answer 29

Renin

Question 30

Renin release is stimulated by __________ receptor activation. This causes a decrease of ________ at the Macula Densa. Secretion of Renin is also stimulated by Sympathetics.

Answer 30

B1-Adrenergic

NaCl

Question 31

Renin causes __________ to be converted to __________ (inactive) in the blood.

Answer 31

Angiotensinogen

Angiotensin I

Question 32

Angiotensin I is converted to __________ (active) in the lungs (and kidneys) to begin the compensation mechanism.

Answer 32

Angiotensin II

Question 33

Renin is secreted by ____________ cells in the walls of renal afferent arterioles in response to low BP and in response to Sympathetic stimulation.

Answer 33

Juxtaglomerular

Question 34

What does Angiotensin II cause?

Answer 34

• • Secretion of Aldosterone from Adrenal Cortex
• • Stimulates secretion of ADH
• • Causes global vasoconstriction of arterioles by binding to specific receptors (AT1 receptors)

Question 35

Secretion of Aldosterone from the Adrenal Cortex leads to ________ and ________ retention by the kidney. This causes increased blood volume, preload/stroke volume, CO, and therefore BP.

Answer 35

Na+

Water

Question 36

Secretion of ADH reduces _________ production (fluid retention).

Answer 36

Urine

Question 37

When Angiotensin II causes global vasoconstriction of arterioles by binding to specific receptors (AT1 receptors) this leads to increased _______ and BP.

Answer 37

TPR

Question 38

ADH (Vasopressin) is secreted via the Posterior Pituitary. It acts on ______ receptors to smooth muscle, increasing TPR, and acts on _______ receptors to collecting ducts, increasing water retention and blood volume. These result in increased BP.

Answer 38

V1

V2

Question 39

________ _______ have increased secretion by excessive Preload of Atria and Ventricles. They protect against overdilation or overstitching of cardiac chambers (lower BP).

Answer 39

Natriuretic Peptides

Question 40

What are the 3 types of Natriuretic Peptides?

Answer 40

Atrial (ANP)
Brain (BNP)
C-type (CNP)

Question 41

What do Natriuretic Peptides do?

Answer 41

• • Arteriolar dilation (decrease TPR)
• • Increase fluid loss (decrease Preload)
• • Inhibit Renin (decrease both TPR and Preload)

Question 42

What can happen when there is decreased blood volume?

Answer 42

Hemorrhage
Dehydration
Loss of body fluids

• **Decreased venous return, preload, SV, CO, and MAP
• **Vascular function curve shifts left

Question 43

What is the compensatory response to decreased blood volume hemorrhage?

Answer 43

• • Decreased Carotid Sinus nerve firing
• • Increased HR, Contractility, CO
• • Decrease unstressed volume
• • Increased TPR
• • Increased Epinephrine, ADH, Renin, Angiotensin II, Aldosterone

Question 44

For exercise, where is there vasoconstriction and where is there vasodilation?

Answer 44

Vasoconstriction – Skin, Splanchnic regions, Kidney, inactive muscle

Vasodilation – Active muscle and Coronary circulation

Question 45

Normally, upright movement initiates muscle pumps which push blood upward towards the heart past valves in the limbs. If there is no movement, then what happens?

Answer 45

Venous return accumulates in lower limbs, increasing venous and capillary hydrostatic pressure. Venous pooling can result in edema and/or hypotension. Reflexes will attempt to bring BP back to normal.

***Hormonal reflex will also be initiated, but probably too slow to make a difference.

Question 46

When you’re standing for too long _________ _________ can occur. MAP will decrease, no change in HR and TPR, and SV and CO will decrease (from decreased venous return). Central venous pressure will also be decreased because the blood is pooling in the LE. To compensate, the body will initiate Baroreceptor reflex to increase all of these and go back to normal.

Answer 46

Orthostatic Hypotension