1. What happens to total body water following Na+ infusion?
    It shifts (water moves from the ICF to the ECF)
  2. What happens to compartmental water balance following infusion of pure water?
    The water redistributes equally to both ICF and ECF (water is freely permeant across membranes)
  3. Why is it important to maintain a relatively constant serum osmolarity?
    The brain cannot tolerate small changes in osmolarity (it will swell or shrink)
  4. Consequences of brain shrinkage
    Pulls apart from meninges → hemorrhage, meningeal tears, neuronal/glial tears
  5. Consequences of brain swelling
    Herniation beyond the tentorium → compression of the brainstem
  6. Why can the brain tolerate minor changes in serum osmolarity?
    Blood-brain barrier
  7. Most dysnatremias are [mild, moderate, or severe] and SNa is in the range [#]-[#] mM
    Mild; 125-155 nM
  8. What kinds of patients most often have dysnatremias?
    Hospitalized, institutionalized, or “polypharmacied” patients
  9. T/F: Dysnatremias are often emergencies and require aggressive treatment
    False – most are non-emergent and require only a “tweak” in treatment
  10. Define osmoregulation
    Maintenance of constant Sosm (serum osmolarity)
  11. What areas of the brain sense changes in Sosm?
    • Supraoptic nucleus (SON)
    • Hypothalamic thirst nucleus
  12. Hypothalamic cells can sense Sosm
    changes of [%] once the level is about [#] mOsm
    1%; 285-290 mOsm
  13. How do these nuclei respond to increased Sosm?
    Hypothalamic thirst nucleus
    • ADH secretion
    • Increase thirst drive
  14. How do stimuli from the baroreceptor and brainstem nuclei affect ADH release?
    Lower the threshold for ADH release
  15. Stimuli that can lower the threshold for ADH release from the SON
    • Decreased PO2
    • Decreased BP
    • Decreased ECFV
    • Pain/stress
    • Nausea
    • Drugs
  16. ADH is released from the [anterior or posterior] pituitary
  17. Operational definition of euvolemia
    Intravascular volume required to maintain the least preload for optimizing stroke volume
  18. How is preload measured?
    Swan-Ganz catheter
  19. Practical definition of euvolemia
    Intravascular volume that maintains stable BP and HR (lying or standing), without peripheral pitting edema or pulmonary vascular congestion
  20. Diuretics lead to which one?
    A. Too much water for the amount of salt
    B. Too little salt for the amount of water
    C. Too much salt and water, but more water than salt
    B. Too little salt for the amount of water
  21. Cirrhosis leads to which one?
    A. Too much water for the amount of salt
    B. Too little salt for the amount of water
    C. Too much salt and water, but more water than salt
    C. Too much salt and water, but more water than salt
  22. Molecular mechanism for SON response, leading to decreased ADH release
    Decreased Sosm → SON cell swelling → closure of stretch-inactivated cation channels → less depolarization → fewer APs → decreased Ca2+ entry at terminal → decreased ADH release
  23. Molecular mechanism for decreased ADH resulting in decreased urine osmolarity
    Decreased ADH binding at V2 receptors in collecting duct → less exocytosis of aquaporins into apical membrane → decreased water permeability → decreased urine osmolarity (urine is more dilute)
  24. Increased renal free water clearance → [increase or decrease] in Sosm
  25. 4 major causes of hyponatremia
    • Stimulus for inappropriate thirst
    • Stimulus for massive ADH release
    • Salt wasting with water replacement
    • Overactivation of CVMP
  26. Osmolarity of the most dilute urine possible
    50 mOsm/L
  27. ADH release is inappropriate if Sosm falls below [#]
    280 mOsm
  28. CVMP is a [non-osmolar or osmolar] drive for ADH secretion
  29. Methods for determining a patient’s volume status
    • Weight
    • Recent photograph
    • Orthostatic BP changes
    • Central venous pressure
  30. How can cancer cause hyponatremia?
    Paraneoplastic secretion of an ADH-like substance
  31. How can CNS inflammation or injury cause hyponatremia?
    Cytokine stimulation of SON neurons → ADH release
  32. How can affective disorders cause hyponatremia?
    • Psychotic thirst
    • Antidepressants → non-osmotic induction of ADH release
  33. The urine of a hyponatremic patient should be below [#] mOsm
    100 mOsm
  34. How can you measure renal function?
    Serum creatinine
  35. The urine of a hyponatremic patient should have UNa below [#] mEq/L
    20 mEq/L
  36. A hyponatremic patient should be hyper-osmolar, with Sosm < [#] mOsm
    285-290 mOsm
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