Term
| Define behavioral salt appetite. |
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Definition
A natural preference for isotonic NaCl solutions
During Na deficiency, willingness to drink very concentrated NaCl solutions (normally not potable) |
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Term
| What is the major ion in body fluids? |
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Definition
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Term
| In terms of osmosis, what happens when sodium gets more concentrated? |
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Definition
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Term
| Hypovolemia is the loss of what? |
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Definition
| Loss of both water and sodium. |
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Term
| Explain the intake of sodium and water under conditions of hypovolemia. |
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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. |
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Term
| Explain the relationship between salt intake and [sodium] in the ECF. |
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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.
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Term
| Does a change in plasma osmolarity initiate salt appetite? |
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Definition
| No, but it does affect salt appetite once the behavior has started. |
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Term
| Is there a neural sensor for salt appetite. If so, what is it? |
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Definition
| Most likely no neural sensor because salt appetite appears to slowly. |
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Term
| What is the relationship bewteen volume and salt appetite? |
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Definition
| Hypovolemia initiates both an immediate thirst and a delayed salt appetite signal. |
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Term
| Following hypovolemia, what are some hormones that are released to regulate salt appetite? |
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Definition
Renin-angiotensin system
Aldosterone
Oxytocin |
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Term
| Which is the prominent Ang II cell surface receptor that regulates fluid balance and what is its mechanism? |
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Definition
AT1 and AT2 receptors: AT1 predominant in fluid balance
AT1: couples to Gq to stimulate PLC activating MAPK pathway |
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Term
| What are the three target tissues of Ang II? |
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Definition
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Term
| How does Ang II act on the brain to regulate salt appetite? |
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Definition
| Ang II binds to receptors in the OVLT and SFO and increase salt appetite |
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Term
| How does Ang II affect the pituitary? |
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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 |
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Term
| How does Ang II affect the kidneys? |
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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+) |
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Term
| What part of the adrenal gland secretes aldosterone? |
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Definition
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Term
| What is the broad function of aldosterone? |
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Definition
| Maintain blood volume and BP |
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Term
| How does aldosterone maintain blood volume and BP? |
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Definition
Promotes sodium reabsorption
Increases potassium excretion
Increases water reabsorption through osmosis |
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Term
| Where, specifically, in the kidney does sodium reabsorption and what is a possible physiological consequence of increased reabsorption of water? |
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Definition
| Occurs in the distal tubule and may result in hypertension. |
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Term
| Aldosterone increases the transcription of what two things? |
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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) |
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Term
| What type of receptor does aldosterone bind to in the adrenal cortex? |
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Definition
| Corticosteroid receptors, specifically type 1 mineralocorticoid receptors (expressed in cytoplasm of cells in late distal tubule and collecting duct) |
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Term
| What are the effects of aldosterone binding to type 1 mineralocorticoid receptors? |
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Definition
Causes translocation of complex to the nucleus:
- affects gene txn
- inc. sodium reabsorption
- dec. reabsorption of potassium |
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Term
| What other peripheral tissues does aldosterone act on? |
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Definition
| Sweat glands, salivary glands, and colon to conserve sodium in the body |
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Term
| What is the relationship bewteen Ang II and aldosterone? |
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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
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Term
| What is a key site of salt appetite control that is effected by aldosterone? |
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Definition
| Medial nucleus of amygdala |
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Term
| What are the characteristics of oxytocin (release, synthesis, role)? |
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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 |
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Term
| Describe the relationship between oxytocin and salt appetite. |
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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
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Term
| Explain how oxytocin plays a role in the delayed salt appetite behavior after thirst? |
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Definition
| Delayed salt appetite is due to decreasing oxytocin inhibition from the dilution of plasma osmolality. |
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Term
| Where is salt satiety mainly sensed? |
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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 |
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Term
| How do natriuretic peptides play a role in salt appetite? |
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Definition
Antagonize peripheral actions of angoitensin and aldosterone
Natriuresis: inc. sodium excretion
Diuresis: inc. fluid excretion |
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Term
| What are the two natriuretic peptides and where are they found? |
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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) |
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Term
| How are natriuretic peptides synthesized and degraded? |
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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 |
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Term
| What stimulates the release of natriuretic peptide? |
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Definition
Ang II
Hypervolemia
SNS activation - mediated by beta adrenergic receptors |
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Term
| What are the target tissue(s) of natriuretic peptides and what are their effects? |
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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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