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