Natriuretic Peptides and Vascular Function

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Questions and Answers

What is the primary purpose of natriuretic peptides (NPs)?

To enhance sodium reabsorption

To increase blood volume

To reduce blood pressure

To reduce volume by removing sodium (correct)

How do natriuretic peptides cause vasodilation?

By causing potassium efflux in vascular endothelial cells

By activating guanylate cyclase and increasing cGMP (correct)

By increasing calcium influx in vascular smooth muscle cells

Through nitric oxide production exclusively

What role does nitric oxide play in vascular smooth muscle cell (VSMC) dilation?

It decreases PKG activity in the VSMC.

It promotes the contraction of vascular smooth muscle cells.

It causes an increase in intracellular calcium levels.

It activates soluble guanylate cyclase leading to cGMP production. (correct)

What effect do natriuretic peptides have on sodium excretion in the kidneys?

They increase sodium excretion by antagonizing Na+ reabsorption pathways. Signup and view all the answers

What is a direct effect of PKG activation in vascular smooth muscle cells?

Decreased calcium influx and release. Signup and view all the answers

What effect do natriuretic peptides (NPs) have on the sympathetic nervous system (SNS)?

They reduce SNS activity. Signup and view all the answers

What is the primary physiological trigger for the production of natriuretic peptides (NPs)?

Myocardial stretch. Signup and view all the answers

Which of the following hormones is NOT inhibited by natriuretic peptides?

Epinephrine. Signup and view all the answers

In the case of high blood pressure, what is the primary role of the baroreceptor?

To modulate SNS and PNS activity. Signup and view all the answers

What mechanism do natriuretic peptides utilize to induce vasodilation?

Activation of guanylate cyclase domain receptors. Signup and view all the answers

What effect does the activation of alpha receptors in peripheral arteries primarily lead to?

Vasoconstriction Signup and view all the answers

How does angiotensin II primarily affect the kidneys?

Stimulates aldosterone production Signup and view all the answers

Which receptor activation decreases heart rate through the parasympathetic nervous system?

Muscarinic acetylcholine receptor (mAchR) Signup and view all the answers

What is the role of baroreceptors in blood pressure regulation?

They sense decreases in blood pressure and signal for increases Signup and view all the answers

What is one effect of anti-diuretic hormone (arginine-vasopressin) in the kidneys?

Increases fluid retention Signup and view all the answers

Which of the following is NOT a function of the sympathetic nervous system in blood pressure control?

Decreases cardiac contraction Signup and view all the answers

How does increased stimulation of beta-1 adrenergic receptors affect cardiac function?

Increases heart rate and contractility Signup and view all the answers

What role do natriuretic peptides play in blood pressure regulation?

Promote vasodilation and natriuresis Signup and view all the answers

What is the primary action of antidiuretic hormone (ADH) in the kidney?

Increases movement of AQP2 to the kidney lumen surface Signup and view all the answers

Which receptor does vasopressin primarily act on to cause vasoconstriction?

V1 receptor Signup and view all the answers

How does ADH influence blood pressure?

Increasing blood volume and resistance Signup and view all the answers

What triggers the production of atrial natriuretic peptide (ANP)?

Increased stretch of the heart Signup and view all the answers

Which mechanism does the RAAS system primarily utilize to regulate blood pressure?

Increased renin release leading to AngII and aldosterone production Signup and view all the answers

What is the role of AQP2 channels in the nephron?

Enhancing water reabsorption Signup and view all the answers

What type of receptor signaling is involved in vasopressin’s effect on increasing intracellular calcium?

IP3 signaling Signup and view all the answers

Which substance is primarily responsible for increasing sodium reabsorption in the collecting duct?

ADH Signup and view all the answers

What is the primary effect of SNS activity on the heart and blood vessels?

Increases heart rate and cardiac contractility Signup and view all the answers

Which mechanism is activated as part of the SNS response to low blood pressure?

Release of renin from juxtaglomerular cells Signup and view all the answers

What role does the baroreceptor system play in blood pressure regulation?

Balances SNS and PNS activity based on blood pressure changes Signup and view all the answers

What is the primary consequence of increased PNS activity on heart function?

Decreased heart rate and cardiac output Signup and view all the answers

Which of the following is NOT one of the systems that contribute to long-term blood pressure regulation?

Sympathetic Nervous System Signup and view all the answers

What effect does angiotensin II have in the body?

Stimulates aldosterone secretion and increases blood volume Signup and view all the answers

What is the function of juxtaglomerular cells in the kidney?

Synthesize and release renin in response to SNS activity Signup and view all the answers

How does the body respond to an increase in blood pressure as sensed by baroreceptors?

Increased PNS and decreased SNS activity Signup and view all the answers

What is the primary role of the baroreflex in the body?

To maintain blood pressure stability. Signup and view all the answers

Which adrenergic receptor is primarily responsible for vasoconstriction?

Alpha1 Signup and view all the answers

What condition is commonly caused by pharmacological interventions affecting the sympathetic nervous system?

Orthostatic Hypotension Signup and view all the answers

Which statement is true regarding Beta1 adrenergic receptors?

They stimulate renin release in kidneys. Signup and view all the answers

What is meant by sympathetic tone?

Continuous signaling of sympathetic nerves. Signup and view all the answers

What effect does norepinephrine infusion have on heart rate and vascular resistance?

Increases both heart rate and vascular resistance. Signup and view all the answers

Which of the following actions is NOT associated with Beta2 adrenergic receptors?

Contracts vascular smooth muscle. Signup and view all the answers

Which receptor type is responsible for mydriasis (pupil dilation)?

Alpha1 Signup and view all the answers

Study Notes

ANS Control of Blood Pressure

The autonomic nervous system (ANS) regulates blood pressure through both the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system (SNS) increases blood pressure.
The parasympathetic nervous system (PNS) decreases blood pressure.

SNS stimulation causes vasoconstriction in most peripheral arteries, increasing resistance.
In muscle and lung arteries, primarily epinephrine and norepinephrine released from the adrenal glands have an effect.
Beta receptors cause vasodilation
Alpha receptors predominate in veins, lowering venous capacitance and increasing preload/CO.
There is very little PNS innervation of most blood vessels.

Baroreceptors and Blood Pressure

Baroreceptors sense changes in blood pressure and send signals to the brain.
A decrease in blood pressure results in increased SNS activity.
An increase in blood pressure results in increased PNS activity.

Long-Term Blood Pressure Regulation

Several physiological mechanisms regulate long-term blood pressure, aiming to control blood volume.
Three major systems include RAAS (renin-angiotensin-aldosterone system), ADH (antidiuretic hormone, vasopressin), and natriuretic peptides (NP).

Short-Term and Long-Term Response to Low Blood Pressure/Volume

Short-term response to a decrease in blood pressure or volume includes sympathetic activation via norepinephrine and epinephrine and release from adrenal glands, causing increased cardiac output and peripheral vasoconstriction.
Corresponding long-term response to the decrease includes stimulation of the kidneys for renin and erythropoietin production and subsequent aldosterone release, increasing blood volume.

RAAS System

The renin-angiotensin-aldosterone system (RAAS) is a crucial long-term mechanism for blood pressure regulation.
Renin, produced by the kidneys, initiates the cascade.
Angiotensinogen is cleaved to angiotensin I, then to angiotensin II by ACE.
Angiotensin II affects various functions, including thirst stimulation, cardiac and vascular hypertrophy, vasoconstriction, and aldosterone release.
Aldosterone causes Na+ retention in the kidney.

The sympathetic nervous system (SNS) plays a vital role in activating the renin-angiotensin-aldosterone system (RAAS).
SNS efferent signals to the kidneys stimulate the release of renin by juxtaglomerular cells.

Juxtaglomerular Cells and Renin Release

The cells of the juxtaglomerular apparatus express beta-1 adrenergic receptors.
Activation of these receptors triggers renin release.
This response is pivotal to the SNS-RAAS feedback loop.

Angiotensin II Effects on the Kidney

Angiotensin II directly affects the kidneys, increasing Na+ reabsorption in the proximal tubule.
Angiotensin II increases the activity of the ENaC (Epithelial Na+ Channel).
This increases Na+ reabsorption in the cortical collecting duct.

Angiotensin II and Vasoconstriction

Angiotensin II is a potent vasoconstrictor.
It activates AT1R receptors, leading to an increase in intracellular calcium, and causing an increase in MLC phosphorylation.
Causing myosin contraction.
This powerful vasoconstriction, in high doses, can lead to significant increases in blood pressure.

Aldosterone and Blood Pressure

Aldosterone, released by the adrenal cortex, plays a crucial role in maintaining blood pressure by increasing Na+ retention.
Aldosterone acts on the mineralocorticoid receptor (MR) in the distal tubule.
Aldosterone also stimulates expression and movement of ENaC and Na/K ATPase to the membrane.

ADH (Vasopressin) and Blood Pressure

ADH, released by the posterior pituitary, acts on the collecting ducts of the kidneys to increase H2O reabsorption.
It causes fluid retention, increasing blood volume in the event of low blood pressure.
ADH also exhibits vasoconstriction effects mediated by V1 receptors.

Natriuretic Peptides (NPs) and Blood Pressure

Natriuretic peptides are hormones that decrease blood volume and pressure.
NPs are produced in response to stretching of the heart, most in the atria and ventricles and also in blood vessels.
The most notable effect of NPs is natriuresis, which increases sodium excretion.

NPR Receptors and Vessels

Natriuretic peptide receptors (NPRs) are involved in vasodilation, which counters vasoconstriction effects of other peptide hormones.
Natriuretic receptors NPR-A & NPR-B have an in-built guanylate cyclase domain and activate PKG.

Molecular Basis of VSMC Dilation

In endothelial cells, receptor-activated signaling cascades activate nitric oxide synthase (eNOS).
NO diffuses to VSMC causing an activation of soluble guanylate cyclase (SGC).
SGC makes cyclic-GMP (cGMP)
cGMP activates PKG.
PKG counteracts smooth muscle contraction via mechanisms, increasing K+ efflux

NP Effects on Kidney

NPs cause dilation of afferent arterioles (increasing glomerular filtration rate).
NPs counteract effects of RAAS and ADH.
Increases in blood flow through the kidney also result in increased Na+ excretion.
NPs decrease blood pressure.

NPs antagonize RAAS and SNS responses in the kidney, affecting blood vessels.
NPs reduce SNS signaling and have a negative feedback effect on RAAS.
NPs also cause dilation of blood vessels.

BP Regulation: Responses if BP Low / High

Acute responses occur rapidly to adjust blood pressure in response to decreased or increased pressure.
Chronic responses impact hormones and activity of various systems.

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Description

This quiz explores the functions and effects of natriuretic peptides (NPs) on vasodilation, sodium excretion, and the sympathetic nervous system. It assesses your understanding of their physiological roles and mechanisms, including the interaction with nitric oxide and baroreceptors. Test your knowledge on how NPs contribute to vascular health and blood pressure regulation.