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What is the physiologic response of the body to changes in osmolarity?
- ADH secretion from posterior pituitary activates V2 receptors on renal collecting tubular cells, aquaporin-2 molecules inserted into luminal membrane, results in water retention
- thirst - stimulated by hyperosmolality and decreased circulating volume
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Causes of hypernatremia:
Hypertonic saline, sodium bicarbonate, enema (NaP), Seawater, beef jerky, salt-flour dough mixtures
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What is the short and long term adaptation to hypernatremia:
- Short: NaCl moves from CSF into cerebral tissue
- Long: organic solutes accumulate (inositol, glutamine, glutamate)
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Causes of hyponatremia:
- Decreased circulating volume: compensation with ADH release, CHF, GI and urinary losses, effusions, edema
- Addison's disease: decrease Na retention
- Diuretics & Renal failure: induction of hypovolemia, HypoK+ causing intracellular shift, inability to dilute urine
- SIADH: excess ADH
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Causes of pseudohyponatremia:
- hyperglycemia
- hyperlipemia
- hyperproteinemia
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What is the body's response to hyperkalemia
- increased colon excretion
- increased in K+ uptake from muscle and liver cells (insulin and catecholamines)
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What is the body's adaptation to hypokalemia
- Decrease in aldosterone secretion
- Suppression of K+ secretion (distal nephron)
- Increased K+ absorption @ inner medullary collecting ducts
- Decreased colonic secretion
- Decreased K+ concentration in muscles
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