Central Neural and Humoral Control of Blood pressure Flashcards by Stephen Schaffner

What is the over all effect of the sympathetic N.S. on TPR?

Increases

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Vasoconstrictor sympathetic fibers are widely dispersed, where are they most/least concentrated?

Most: Kidney and skin

Least: heart and brain

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•Norepinephrine:

Adrenoceptors on VSMC -> generalized vasoconstriction (pressor effect)

The exceptions include?

•Exceptions include skeletal and cardiac m. response can promote vasodilation (β2 )

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What is the primary neural influence on arteriolar smooth muscle?

Via what receptors and NT’s is this accomplished?

Sympathetic

Vasoconstriction:

α₁ receptors: Norepinephrine, epinephrine

Vasodilation
β₂ receptors preferentially bind epinephrine (expression: skeletal m., cardiac m., liver, & adrenal medulla

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What are the five components of the negative feedback loop involved in neural reflexes?

Receptor
Afferent path
integration center
efferent path
effector

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What are the receptors involved in MAP regulation?

Baroreceptors

Chemoreceptors

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What types of baroreceptors are there? What do they detect?

mechanoreceptors, detect stretch

–High-pressure receptors
–Low-pressure receptors

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What do chemoreceptors detect?

detect changes in blood PO2, Pco2, [H+]

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What is the primary integration center involved in MAP regulation?

medulla oblongata; cerebral cortex & hypothalamus

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What are the 4 effectors of MAP regulation?

–Cardiac myocytes (pacemaker & contractile)
–Arterial & venous vascular smooth muscle cells (VSMCs)
–Adrenal medulla
–Kidneys

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What six things provide feedback to the medulla oblongata?

–Baroreceptors
–Chemoreceptors
–Hypothalamus
–Cerebral cortex
–Skin
–Local CO2 and O2 concentrations

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What are the most important high-pressure baroreceptors?

Carotid sinus and aortic arch

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What does an increased receptor stretch due to increased pressure lead to regarding high pressure receptor firing rate?

Increases it.

(graded response with amplitude proportional to amount of stretch)

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Outline the 8 steps of the high-pressure baroreceptor reflex response to increased MAP.

(Important)

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Baroreceptors respond to increased MAP by causing vasodilation and decreased heart rate. Describe how this is accomplished beginning with the stretch sensation

TPR
–↑ Baroreceptor stretch
–↑ Baroreceptor firing rate
–Inhibition of vasomotor area
–↓ Sympathetic output
–↓ vasoconstriction
–↑ Vasodilation

–↑ Baroreceptor stretch
–↑ Baroreceptor firing rate
–Excitation of interneurons in cardioinhibitory area
–↑ Parasympathetic output
–↓ Heart Rate

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Which baroreceptors predominate?

What kind of pressure to these mostly respond to?

Carotid baroreceptors predominate over aortic
Greater response to pulsatile vs. steady pressure

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What are the low-pressure baroreceptors? Where are they found? What do they regulate?

Cardiopulmonary receptors:

In cardiac chambers and large pulmonary vessels
Involved in blood volume regulation

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What do the A and B fibers of the low pressure baroreceptors monitor respectively?

•A fibers: monitor HR (fire during atrial systole)
B fibers: monitor atrial volume

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What is the response of increased low pressure baroreceptor firing rate? (on heart rate and renal vessels)

Reflex Response:

•↑ HR•↓ Renal vasoconstriction

(Promotes renal vasodilation)

–↑ Renal blood flow
–↑ Urine output
–↓ Effective circulating volume

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What does the bainbridge reflex do?

Counterbalances the high-pressure baroreceptor reflex

↑stretch of high-pressure receptors → ↓ HR
↑stretch of low-pressure receptors → ↑ HR
High-pressure baroreceptors: generalized vasodilation
Low-pressure baroreceptors: renal vasodilation

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At what point in the cardiac cycle is the bainbridge reflex dominant?

During volume loading

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During which point of the cardiac cycle is the high pressure baroreceptor reflex dominant?

volume depletion

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At low blood volume, what impact does the baroreceptor reflex have on the slope of the starling relationship?

•Baroreceptor reflex

↑ sympathetic output ->↑ contractility & slope of Starling relationship

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At high blood volume what impact does the baroreceptor reflex have on the starling relationship?

•↓ sympathetic output -> ↓ contractility & plateau of Starling relationship

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What are the peripheral chemoreceptors? Where are they located?

•Carotid body (carotid a. bifurcation) Aortic bodies (aortic arch)

What do peripheral chemoreceptors do?

Detect changes in arterial blood

What does the chemoreceptor reflex do?

–Primarily regulates respiration (increased rate and depth) –Some influence on cardiovascular system (vascular tone and HR)

What is the chemoreceptor integrated physiologic response?

Vasoconstriction and tachycardia

If ↓ MAP and ↑ Pco2 ↓ pH ↑ [H+] occur simultaneously, what happens?

•↑ stimulation of chemoreceptors and ↓ stimulation of baroreceptors -\> ↑ vasoconstriction

If ↑ Pco2 ↓ pH ↑ [H+] occurs along with ↑ MAP

•↑ stimulation of chemoreceptors and ↑ stimulation of baroreceptors -\> (ex: high carotid sinus pressure and low Pao2) -\> baroreceptor-mediated inhibition of vasoconstriction dominates

What are the major hormones that control vascular resistance? 4

- Epinephrine - Angiotensin II (ANG II) - Atrial natriuretic peptide (ANP) - Anti-diuretic hormone (ADH) = Arginine Vasopressin (AVP, Vasopressin)

What are the hormones that control blood volume? 3

Anti-diuretic hormone (ADH) = Arginine Vasopressin (AVP, Vasopressin) - Aldosterone - Atrial natriuretic peptide (ANP)

What hormone controls heart rate and stroke volume?

Epinephrine

Where is epinephrine produced? What does it do when binding alpha 1 and beta 2 receptors respectively?

adrenal gland - Vasoconstriction via α₁, vasodilation via β₂ receptors

What is ANG I converted to ANG II by? What does it do? What is it stimulated by? Where is it released?

Converted from ANG I by ACE (mainly in lungs; ACE is secreted by pulmonary and renal endothelial cells) - Vasoconstriction - Ex: released during blood loss or exercise - ↓renal BP à stimulates renin release

What is the effect of ADH/AVP that is released by the posterior pituitary? When is it released?

Vasoconstriction - Ex: released during hemorrhagic shock

Histamine is released in response to tissue trauma, what is the result of this?

Vasodilation (arteriolar), Venoconstriction

Atrial myocytes release ANP, what does this lead to?

Vasodilation

Characterize the response time of endocrine control of blood volume

Long-term

What is the key effector organ for long term blood volume regulation? How does it regulate this?

Kidney –Regulation of Na+ and H2O excretion in urine

What are the 3 humoral regulators of blood pressure?

1. Renin Angiotensin Aldosterone System (RAAS) 2. Antidiuretic Hormone (ADH)/Vasopressin (AVP) 3. Atrial Natriuretic Hormone (ANH/ANP)

Review the renin-angiotensin-aldosterone system on slide 70. Draw it.

What are the major effects of angiotensin II? (6)

1. Vasoconstriction 2. Stimulates adrenal gland aldosterone production 3. Stimulates ADH/AVP 4. Stimulates thirst 5. Stimulates renal Na+ reabsorption 6. Stimulates SNS activity

What triggers secretion of aldosterone by the adrenal cortex? What does it promote? What does this do to MAP?

ANG II * Promotes renal Na+ reabsorption * H2O follows by osmosis * ↑ Effective Circulating Volume•↑ MAP

If the hypothalamus detects increased osmolarity, what does it do?

Stimulate fluid retention by increased release of vasopressin (and ANGII) by the posterior pituitary gland. Leads to increased MAP

What system does the atrial natriuretic peptide/hormone oppose?

renin-angiotensin-aldosterone system

•Cardiac atrial cells (low-pressure baroreceptors) detect: ↑ wall stretch (↑ blood volume), what do they do in response? What is the impact on MAP?

* Secrete ANP (vasodilator AND natriuretic) * Results in ↓ renal Na+ reabsorption ↑ Na+ excretion = natriuresis ↑ H2O follows in urine •↓ ECF volume, ↓ ECV, ↓ MAP

Identify the neural and hormonal responses shown in the graph

Understand the integrated response to a decreased effective circulating volume/MAP Slide 80

What is the dominant reflex responding to orthostatic changes? What is the ANS response? This leads to what regarding the muscle pump?

High pressure baroreceptor reflex responding to volume depletion. •↑ Sympathetic; ↓ parasympathetic Increased muscle pumping for increased venous return

What is the vasovagal (vasopressor) syncope a common response to?

•sudden emotional stress, acute pain, sight of blood, etc.

The vasovagal syncope response follows this pathway: •(Vagal afferents) -\> Higher CNS -\> medulla oblongata: –Dramatic ↑ parasympathetic output – ↓ sympathetic output What physiological changes result from this path?

•Bradycardia and hypotension –↓ TPR, ↓ CO, ↓ MAP Loss of consciousness: ↓ cerebral perfusion pressure

In vasovagal syncope MAP decreases due to diminished TPR and CO, due to failure of activation of what response?

Baroreceptor Response

What are the peripheral receptors and reflexes involved in the fight or flight response?

No peripheral receptors or reflexes

How is blood flow to skeletal muscle increased in response to the fight or flight response?

•Adrenal medulla: epinephrine –β2 adrenoceptor activation –Vasodilation and ↑blood flow: skeletal m. –If exercising: metabolite production also promotes vasodilation and ↑ flow via autoregulation

During fight/flight, there is general vaso- and venoconstriction, how is this accomplished?

•Sympathetic output: norepinephrine & epinephrine –α1 adrenoceptor activation –↓ Renal and Splanchnic blood flow

During F/F response how is cardiac output increased?

–↑ sympathetic and ↓ parasympathetic output –↑ HR and ↑ SV (↑ contractility)

During F/F response, how is blood volume maintained?

–↑ ADH/AVP -\> ↓ urine output

In F/F what causes the net increase in MAP?

–↑ CO –Increase/decrease in TPR •Depends on balance between vasodilation and vasoconstriction

What are the central command changes in response to exercise? How about local responses? (Important)

Slide 95

What organizes the early neural response in ANTICIPATION of exercise?

Hypothalamus

What are the delayed responses to exercise?

•Mechanical response: –Muscle pump –Increased VR •Chemical response: –Autoregulation of exercising skeletal m. –Metabolites -\> vasodilation –↓ TPR

During exercise, what do muscle afferents and reflexes reinforce?

Sympathetic output

What is the impact of exercising muscle on capillary hydrostatic pressure?

•Increased capillary hydrostatic pressure –Arteriolar dilation –Net fluid filtration –↑ interstitial fluid hydrostatic pressure •↑ lymphatic flow

What is the increased O2 delivery during exercise due to?

•oxyhemoglobin dissociation relationship –↓ pH •Due to ↑ CO2 and lactic acid –↑ temperature –↓ Hb affinity for O2 , promotes “off-loading”

By what factor can O₂ consumption increase during exercise?

60x

What are the 6 components of the integrated CV response during exercise?

1. Exercise pressor reflex 2. Sensitivity of baroreflexes 3. Skeletal m. vasodilation 4. Circulating epinephrine 5. Venous return 6. Temperature regulation

Where does the exercise pressor reflex originate? What receptors mediate?

–Reflex originates within the exercising muscle -\> Neural drive •Stretch receptors: muscle tension •Chemoreceptors: metabolites

During exercise, we have continued sympathetic output despite increased MAP. How is this possible?

Arterial baroreflexes –Re-set of arterial baroreflex sensitivity by central command

Metabolites released locally dilate resistance vessels during exercise, to what degree is this possible?

20x

Venous return increases during exercise, what causes this? What factors contribute to this balance?

–Muscle pump: ↑ VR à ↑ SV (Starling’s law) à ↑ CO –Balance of SV, HR, Contractility, Relaxation rate

What fibers maintain temperature regulation during exercise? How do they do it?

–Sympathetic cholinergic fibers activate to sweat glands –Inhibition of sympathetic vasoconstriction to skin (constricted in early response) à↑ cutaneous flow

How is stroke volume maintained in exercise induced tachycardia?

What is the major cardiovascular component that decreases with exercise? What does this serve to offset?

MAP: General Increase SBP \> DBP ↑ PP * Due to increased CO * Offset by overall decrease in TPR