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Cards In This Set
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What is the definition of hypernatremia?
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Increased serum Na+ concentration; > 145 mEq/L
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What is the cause of hypernatremia?
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Decreased water compared to Na+
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What are the 3 causes of hypernatremia?
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1. Renal water loss2. Extrarenal water loss3. Iatrogenic
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In renal water loss, the urine volume is low/high.
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HIgh.
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In extrarenal water loss, the urine volume is low/high.
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Low.
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In renal water loss, the urine osmolality is low/high.
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Can be either low or high.
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In extrarenal water loss, the urine osmolality is low/high.
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HIgh. (concentrated urine)
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Name 2 causes of renal water loss.
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1) Diabetes insipidus2) Osmotic diuresis
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Name 4 causes of extrarenal water loss.
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1) Hyperventilation2) Diarrhea/GI3) Fever4) Diffuse sweating
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T/F. Diabetes causes only hyponatremia. It cannot cause hypernatremia.
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FALSE. Diabetes can also cause hypernatremia, when the glucose concentration gets so high that it is excreted in the urine. It causes osmotic diuresis, i.e. it acts as an osmole in the urine that pulls water out into the tubular lumen, causing osmotic diuresis.
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What is osmotic diuresis?
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Occurs when the urine osmolalilty > 300 mOsm/L. It creates a concentrated urine. Osmoles are in the urine and they pull water out into the tubular lumen.Some osmoles include glucose, mannitol, high protein feedings, high sodium. Anything that is excreted extra in the urine can increase the osmolality of the urine and thus pull water along w/ it.
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What is the caveat about glucose and mannitol?
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They may initially produce a hyponatremic state. This is when the levels are raised enough to pull fluid from ICF into the ECF, thus increasing the volume and giving a "pseudo" hyponatremia even though the Na+ content is the same. But, when they get too such high concentrations that they start being excreted in the urine, water will follow them there and be excreted with them, leading to decreased water in ECF and hypernatremia.
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What is the most common cause of osmotic diuresis?
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Diabetes with glucose in the urine.
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Diabetes inspidus causes _________. How?
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Renal water loss, leading to hypernatremia. Diabetes inspidus results from either inability to respond to ADH by the kidneys, or no ADH produced by the hypothalamus/posterior pituitary. If there's no ADH, then no aquaporins are inserted into the CCT and CD, then those segments of the nephron remain impermeable to water and you can't have reabosrption of water. More water is excreted/less is reabosrbed, and you get hypernatremia due to renal water loss.
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What are some causes of decreased ADH production?
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Post-surgical (pituitary), head trauma, infections (TB/meningitis/encephalitis), shistiocytosis X, idiopathic
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