Fluid homeostasis

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  • Fluid homeostasis
    • Systems needed to maintain fluid physiology
      • renal, vascular, respiratory and GI
    • normal ECF osmolarity = 280-300mOsmoles/L
    • Stimulations that trigger hypothalamic thirst centre
      • decrease in plasma volume
      • increase in plasma osmolarity
      • baroreceptor input
    • Osmolarity values
      • At bottom of Loop of Henle = 1200mOsm/L
      • In blood = 300 mOsm/L
      • In urine = 50-1200mOsm/L
    • Hormone used
      • Vasopressin - activates aquaporins, secreted frm posterior pituitary
    • Primary brain osmoreceptor lies outside BBB
    • What happens if dehydration occurs
      • 1. Increase in osmolarity directly inhibits aldosterone secretion by zona glomerulosa in adrenal cortex
      • 2.Decrease aldosterone
      • 4. Decrease in osmolarity
      • 3. Decrease sodium ion reabsorption
    • Hyperhydration - temporary excess of water
    • Hyponatremia - deficient sodium in blood
      • Symptoms: vomiting, headache, muscle weakness, fatigue, confusion
      • Treatment - Diuretics

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