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Autonomic Phys
Salt Appetite
34
Biology
Not Applicable
08/06/2010

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Cards

Term
Define behavioral salt appetite.
Definition

A natural preference for isotonic NaCl solutions

 

During Na deficiency, willingness to drink very concentrated NaCl solutions (normally not potable)

Term
What is the major ion in body fluids?
Definition
Sodium
Term
In terms of osmosis, what happens when sodium gets more concentrated?
Definition
Water will follow
Term
Hypovolemia is the loss of what?
Definition
Loss of both water and sodium.
Term
Explain the intake of sodium and water under conditions of hypovolemia.
Definition
Salt appetite develops after water intake, but there is a switch back and forth bewteen water and NaCl intake as body fluid composition is restored.
Term
Explain the relationship between salt intake and [sodium] in the ECF.
Definition

During hypovolemia, rats will drink both water and NaCl following volume loss if access to both are delayed.


Induced hyponatremia does not induce salt appetite.


Hyponatremia does boost salt in hypervolemic rats.


Hypernatremia does inhibit salt appetite.

Term
Does a change in plasma osmolarity initiate salt appetite?
Definition
No, but it does affect salt appetite once the behavior has started.
Term
Is there a neural sensor for salt appetite. If so, what is it?
Definition
Most likely no neural sensor because salt appetite appears to slowly.
Term
What is the relationship bewteen volume and salt appetite?
Definition
Hypovolemia initiates both an immediate thirst and a delayed salt appetite signal.
Term
Following hypovolemia, what are some hormones that are released to regulate salt appetite?
Definition

Renin-angiotensin system

 

Aldosterone

 

Oxytocin

Term
Which is the prominent Ang II cell surface receptor that regulates fluid balance and what is its mechanism?
Definition

AT1 and AT2 receptors: AT1 predominant in fluid balance

 

AT1: couples to Gq to stimulate PLC activating MAPK pathway

Term
What are the three target tissues of Ang II?
Definition

Brain

Kidney

Pituitary

Term
How does Ang II act on the brain to regulate salt appetite?
Definition
Ang II binds to receptors in the OVLT and SFO and increase salt appetite
Term
How does Ang II affect the pituitary?
Definition

Post. pituitary: binds AT1 receptors in CVO -> inc. release of vasopressin

 

Ant. pituitary: inc. release of ACTH -> inc. release of aldosterone from adrenal glands

Term
How does Ang II affect the kidneys?
Definition

Inhibits further release of renin from JG cells.

 

Binds to AT1 receptors -> inc. activity of Na+/H+ exchanger (antiporter allowing Na+ to enter cell from renal tubule and excrete H+)

Term
What part of the adrenal gland secretes aldosterone?
Definition
Adrenal cortex
Term
What is the broad function of aldosterone?
Definition
Maintain blood volume and BP
Term
How does aldosterone maintain blood volume and BP?
Definition

Promotes sodium reabsorption

 

Increases potassium excretion

 

Increases water reabsorption through osmosis

Term
Where, specifically, in the kidney does sodium reabsorption and what is a possible physiological consequence of increased reabsorption of water?
Definition
Occurs in the distal tubule and may result in hypertension.
Term
Aldosterone increases the transcription of what two things?
Definition

Acts on kidney tubular cells to inrease txn of sodium channels and Na+/K+ ATPases

 

Sodium channel: inc. Na+ reuptake from lumen of tubule

 

ATPase: inc. expression of Na+ pumps (active transport)

Term
What type of receptor does aldosterone bind to in the adrenal cortex?
Definition
Corticosteroid receptors, specifically type 1 mineralocorticoid receptors (expressed in cytoplasm of cells in late distal tubule and collecting duct)
Term
What are the effects of aldosterone binding to type 1 mineralocorticoid receptors?
Definition

Causes translocation of complex to the nucleus:

- affects gene txn

- inc. sodium reabsorption

- dec. reabsorption of potassium

Term
What other peripheral tissues does aldosterone act on?
Definition
Sweat glands, salivary glands, and colon to conserve sodium in the body
Term
What is the relationship bewteen Ang II and aldosterone?
Definition

Ang II inc. release of aldosterone from adrenal cortex.


Synergistic effect withothe signals that inc. aldosterone release:

- dec. sodium levels

- inc. postassium levels

- dec. blood flow to kidneys


Low or ineffective doses of Ang II will elicit salt appetite when administered with aldosterone

Term
What is a key site of salt appetite control that is effected by aldosterone?
Definition
Medial nucleus of amygdala
Term
What are the characteristics of oxytocin (release, synthesis, role)?
Definition

Produced my magnocellular cells of PVN and SON

 

Classic role for inducing childbirth and in lactation (milk letdown)

 

Role in control of salt appetite

Term
Describe the relationship between oxytocin and salt appetite.
Definition

Oxytocin is an inhibitory stimulus of salt appetite:

- inverse relationship between salt intake and plasma oxytocin

- inc. in plasma osmolality stimulate pituitary and central release of oxytocin

- i.c.v. oxytocin inhibits salt appetite but not water intake during hypovolemia

- normally, tonic inhibition of salt appetite by oxytocin

Term
Explain how oxytocin plays a role in the delayed salt appetite behavior after thirst?
Definition
Delayed salt appetite is due to decreasing oxytocin inhibition from the dilution of plasma osmolality.
Term
Where is salt satiety mainly sensed?
Definition

In the periphery

 

- Taste receptors in mouth do not contribute to satiety

- Receptors in liver help inhibit salt appetite

- Inc. blood volume sensed by atrial baroreceptors help inhibit salt appetite

Term
How do natriuretic peptides play a role in salt appetite?
Definition

Antagonize peripheral actions of angoitensin and aldosterone

 

Natriuresis: inc. sodium excretion

Diuresis: inc. fluid excretion

Term
What are the two natriuretic peptides and where are they found?
Definition

Atrial natriuretic peptide (ANP): produced by smooth muscle cells in the heart atria

 

B-type natriuretic peptide (BNP): produced by heart ventricles (esp. in left ventricle)

Term
How are natriuretic peptides synthesized and degraded?
Definition

Synthesized as pre-pro-hormone and then cleaved to form pro-hormone and then cleaved again to form active hormone

 

Endopeptidases degrade natriuretic peptides to inactivate them

Term
What stimulates the release of natriuretic peptide?
Definition

Ang II

Hypervolemia

SNS activation - mediated by beta adrenergic receptors

Term
What are the target tissue(s) of natriuretic peptides and what are their effects?
Definition

Vasculature: induce dilation


Kidney:

- inc. glomerular filtration rate

- inc. excretion of sodium

- dec. release of renin


Overall, ANP/BNP counter effects of Ang II/aldosterone.

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