Renal VI: Hormonal Regulation of Body Water Flashcards
Where does ADH originate?
It is synthesized as a peptide prohormone in the neurons of the hypothalamus, travels down the axons, and terminates in the posterior pituitary. It is released in the circulation in response to EC hyperosmolality and volume depletion.
Which sensors stimulate vs. inhibit ADH release?
- stimulate: hypothalamic osmoreceptors
- inhibit: aortic arch and carotid baroreceptors
What does ADH target in the kidney?
extracellular ADH receptors in the distal tubules and collecting duct
Does angiotensin II stimulate or inhibit ADH release?
stimulate
Does atrial natriuretic peptide (ANP) stimulate or inhibit ADH release?
inhibit (because ANP acts to reduce BP and ADH acts to increase BP)
What is our thirst threshold?
It is near 298 mOsm/kg H2O (the plasma osmolality at which we begin feeling thirsty)
How much change in blood volume/pressure is required before AVP secretion is stimulated?
5-10% decrease
What are some ADH disorders?
- central (pituitary) diabetes insipidus: inadequate ADH release, often due to hypothalamic damage
- nephrogenic diabetes insipidus: ADH has trouble exerting effects due to mutation in V2 receptor
- syndrome of inappropriate ADH secretion (SIADH): too much ADH secretion
Total body water is about what percentage of body weight?
60%
What is the extracellular fluid composed of?
interstitial fluid and plasma
Does ICF or ECF make up more of total body water?
ICF (2/3 of TBW, whereas ECF is 1/3 of TBW)
What are the major cations and anions of the ICF and ECF?
- ICF cations: K+ and Mg2+
- ICF anions: proteins and inorganic phosphates
- ECF cations: Na+
- ECF anions: Cl- and HCO3-
The anion gap represents the difference between what?
measured cations and measured anions in plasma or urine [Na+ - (Cl- + HCO3-)]
How are fluid volumes measured by the dilution method (what is the equation)?
V space = (Amt. given - Amt. lost) / equilibrium in space
What is ADH released in response to?
hyperosmolality and volume depletion
How do we measure the different fluid volumes?
- TBW: w/ D2O
- ECF water: w/ radiosodium or radiosulfate
- Plasma water: w/ Evans Blue
- IC water: TBW - EC water
- IS water: EC water - Plasma water
Example of isosmotic volume contraction?
diarrhea
Example of hyperosmotic volume contraction?
water deprivation
Example of hyposmotic volume contraction?
adrenal insufficiency (insufficient aldosterone, which normally increases sodium reabsorption)
Example of isosmotic volume expansion?
infusion of physiologic saline (isotonic NaCl)
Example of hyperosmotic volume expansion?
high NaCl intake, like gulping sea water
Example of hyposmotic volume expansion?
syndrome of inappropriate ADH (SIADH)
What is the major way in which the anion gap is used in clinical practice?
to identify the cause of metabolic acidosis (low blood pH)
What is the anion gap mainly composed of?
albumin (but also can contain phosphate, sulfate, and other anions)
