What Causes Hyponatremia?

Discussion Normal kidneys regulate water balance to maintain a plasma osmolality of 275-290 mOsm/kg normally. Thirst and arginine vasopressin or antidiuretic hormone (ADH) are the primary regulators of plasma osmolality. ADH is made in the hypothalamus and released by the posterior pituitary gland. ADH acts on the kidney’s distal collecting duct to increase water reabsorption. ADH is appropriately released in hypovolemic states, such as dehydration caused by gastroenteritis. ADH has an ~10 minute half-life and therefore can respond to rapid changes in volume status. Sodium balance is regulated by aldosterone (as part of the renin-angiotensin system) causing sodium to be reabsorbed from the distal kidney tubules and secreting potassium and hydrogen. Atrial naturitic peptide is released from the atrium in hypervolemic states causing the kidney to excrete sodium and excessive water. In normal states, urine sodium is < 20 mmol/L. Hyponatremia occurs when the body has a relative excess of free water relative to sodium. Rapid shifts in water can cause cellular damage particularly in the central nervous system (CNS). Normally, water and solutes pass through the cellular membrane to maintain homeostasis, but solutes generally pass slower than free water. Therefore with hyponatremia there is a relatively low amount of sodium and higher amount of water in the plasma with the opposite true for the cell. Therefore water will try to move into the cell to balance the intracellula...
Source: PediatricEducation.org - Category: Pediatrics Authors: Tags: Uncategorized Source Type: news