Disorders of Water balance Flashcards
Hyponatremia
Normal plasma sodium
Hypernatremia
Hyponatremia: <135mmol/L (too much water)
Normal: 140 mmol/L
Hypernatremia: >145mmol/L (too little water)
What hormones are turned on when we are hyponatremic? Hypernatremic?
Hyponatremic: Too much water
ADH is turned OFF
Hypernatremic: Not enough water
ADH is turned ON
What hormones are turned on when we are volume depleted? Volume overloaded?
Volume depleted: Not enough water and salt
ADH and RAAS are ON (reabsorbs salt and water)
Volume overloaded:
ADH and RAAS are OFF
ANP is ON (excretes salt, followed by water)
Plasma sodium concentration is regulated by…
changes in WATER balance, not by changes in sodium or volume balance.
Hypernatremia and hyponatremia are due to too little or too much water. Serum [Na] is either too high or too low.
When you have too much or too little sodium in the body, serum [Na] is usually…
… within normal range.
High sodium intake will trigger water retention to maintain normal Na concentration (edema).
High sodium intake will NOT trigger hypernatremia!
Low sodium intake will trigger water loss to maintain normal Na concentration (volume depletion).
Low sodium intake will NOT trigger hyponatremia!
Explain what can cause cerebral edema
Severe hyponatremia (low serum [Na]) will make water shift from the ECF to the ICF, causing cells to swell.
Brain cells are especially vulnerable: hyponatremia can therefore cause cerebral edema (leads to coma & death)
SIADH
Syndrome of inappropriate ADH secretion
Patient is euvolemic and hypo-osmolar, but ADH is secreted anyway.
Major causes of SIADH
- Tumours producing ADH-like hormone (small cell lung cancer, duodenum, pancreas)
- Chest disorders (pneumonia, empyema)
- CNS disorder (abscess, meningitis)
- Drugs
*( Pain, nausea - appropriate)
Nausea is a potent stimulus for…
ADH secretion
When is hyponatremia symptoma
