Embedded Files
(SIADH)
Water homeostasis - maintained by hormones.
ADH - controls water retention in the body; (it also constricts blood vessels)
↑ ADH in the blood ⇒ ↑ fluid retention
↓ ADH in the blood ⇒ ↑ fluid excretion
ADH effects the principal cells of the distal convoluted tubules & collecting ducts in the nephron → expressing aquaporins II (active water transporters)
↑ ADH → ↑ aqp2 → ↑ fluid resorption → concentrated urine & diluted blood (= ↓ blood osmolality)
↓ ADH → ↓ aqp2 → ↑ fluid excretion → diluted urine & concentrated blood
Hypothalamus reacts to Δ's in plasma osmolality
↓ plasma osmolality (= diluted blood) ⇒ ↓ fluid retention (= ↓ ADH → ↓ aquaporins) ⇒ ↑ fluid excretion → ↑ blood concentration (↑ blood osmolality)
if excessive ↑ ADH despite ↓ plasma osmolality ⇒ ↑ fluid retention ⇒ ↓↓ plasma osm:
dilutional hyponatremia
↑ plasma vol. ⇒ ↓ aldosterone: causes sodium excretion into urine → water follows sodium gradient into urine
diluted urine w/ high sodium
↓ plasma sodium osmolarity = SIADH
Labs:
Blood - hyponatremia; ↓ osmolarity
Urine - ↑ osmolality; ↑ sodium
Tx:
Fluid restriction
↑ sodium intake; Hypertonic fluids
Page updated
Google Sites
Report abuse