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44 Cards in this Set

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What are the 2 primary systems that regulate plasma [Na] and osmolarity?
1. Osmoreceptor-ADH system
2. Thirst mechanism
What stimulates increased firing of osmoreceptor cells?
Shrinking due to hyperosmolarity of ECF
Where are osmoreceptor cells located?
In the ANTERIOR HYPOTHALAMUS - AV3V
What brain protection is missing near the AV3V?
Blood brain barrier
What happens when osmoreceptor cells firing rate increases?
They send an impulse to the preoptic nuclei to the posterior pituitary to release ADH
What happens when Posterior pituitary releases ADH?
It travels to the kidney via the bloodstream to increase water and urea reabsprotion.
Are osmoreceptors the only thing that stimulate the posterior pituitary to release ADH?
No; baroreceptors and cardiopulmonary receptors do too
Where do the baroreceptors and cardiopulmonary receptors project to and how?
Via projections from NTS to:
-Supraoptic nuclei
-Paraventricular nuclei
Where are the supraoptic and paraventricular nuclei?
In the hypothalamus
What exact cells in the kidney does ADH act on?
Principal cells
What happens if you drink lots of water to the osmoreceptor cells?
They swell and inhibit the release of ADH from the hypothalamus
What/where are the receptors that stimulate thirst and how do they work?
Osmoreceptors also in the AV3V; sense increased ECF osmolarity and then stimulate thirst.
What do the AV3V osmoreceptors recieve input from?
Baroreceptors/cardiopulmonary receptors via projections from NTS
Where is the thirst center located?
Anterolaterally in the preoptic nucleus in the hypothalamus
How does Ang II affect thirst?
It stimulates it
How does Ang II stimulate thirst?
By stimulating the
-subfornical organ
-organum vasculosum
What stimulates thirst other than Ang II?
-GI and pharyngeal distention
-dryness of mouth
5 factors that stimulate ADH to increase:
-Increased plasma osmolarity
-Decreased blood volume
-Decreased blood pressure
-Nausea
-Hypoxia
3 drugs that stimulate ADH to increase:
-Morphine
-Nicotine
-Cyclophosphamide
3 drugs that decrease ADH:
-Alcohol
-Clonidine (anti-HTN)
-Haloperidol
5 things that stimulate increased thirst:
-High plasma osmolarity
-Low blood volume
-Low blood pressure
-Increased Ang II
-Dryness of mouth
How does gastric distention affect thirst?
it DECREASES it
What causes plasma ADH to increase faster/more; plasma osmolarity or blood volume?
Plasma osmolarity!
Where in the kidney does ADH exert its effect?
In the late distal tubule and collecting duct.
How does ADH exert its effect?
By increasing the insertion of Aqp2 and UT1 in the lumenal membrane of the duct cells.
How much will plasma [Na] increase if you increase Na intake 5X (30 mEq/day - 150), if ADH and thirst systems are functioning normally?
Normally plasma sodium will only increase from about 142 to 143 mEq/L
How much will plasma [Na] increase if you increase Na intake 5X (30 mEq/day - 150), if ADH and thirst systems are BLOCKED?
Plasma sodium will increase from 142 to 150 mEq/L!
How do we define Hypernatremia?
Plasma sodium conc >150 mEq/L
How do we define Hyponatremia?
Plasma sodium conc <135 mEq/L
2 things that can cause hypernatremia:
1. Loss of ECF volume
2. Rise in ECF sodium
2 clinical conditions in which ECF volume would decrease:
-Diabetes insipidus (no ADH)
-Dehydration
Clinical condition where Na would be retained:
Aldosterone hypersecretion
2 things that can cause Hyponatremia:
-Excess retention/intake of H2O
-Excess excretion/decreased intake of sodium
What clinical condition causes excess retention or intake of water?
Excess secretion of ADH
What causes increased excretion or decreased sodium intake?
-Diarrhea
-Vomiting
-Overuse of diuretics
What does the Hickey Hare test look for?
a person's response to water deprivation
How will a person normally respond to water deprivation?
Their kidneys will excrete more concentrated urine due to water retention.
If you deprive a patient from water and there is no change in their urine osmolality, what do you suspect?
Diabetes inspidus - lack of ADH, or it's not working properly.
If you deprive a patient form water and then give exogenous ADH, and their urine concentration increases, what is the diagnosis?
Hypothalamic (central) diabetes insipidus
If you deprive a patient form water and then give exogenous ADH, and their urine conc still fails to increase, what is the diagnosis?
Nephrogenic Diabetes insipidus - they're making ADH but don't respond to it.
If you deprive a patient form water and their urine concentrates after a lagging period of time, what is it?
Partial hypothalamic diabetes insipidus.
So Central Diabetes insipidus is:
Failure to produce ADH
Nephrogenic Diabetes insipidus is:
Failure of the kidney to respond to ADH
What is SIADH?
Syndrome of inappropriate ADH - too much is produced so the ECF is dilute - hyponatremia.