The hypothalamic osmoreceptors that regulate ADH secretion are located in which specific nucleus and are activated by what mechanism?
- A Paraventricular nucleus; activated by stretch-activated channels sensing increased plasma volume
- B Supraoptic and paraventricular nuclei; intrinsically osmosensitive neurons expressing TRPV1/TRPV4 channels that detect cell shrinkage from hyperosmolality ✓
- C Organum vasculosum of the lamina terminalis (OVLT) exclusively; responds to angiotensin II only
- D Arcuate nucleus; activated by leptin signaling from adipose tissue
Explanation
Magnocellular neurons of the supraoptic (SON) and paraventricular nuclei (PVN) are intrinsically osmosensitive. Increased plasma osmolality (above ~280 mOsm/kg) causes water efflux from these neurons, cell shrinkage, and activation of mechanosensitive TRPV1/TRPV4 channels on the cell membrane, generating depolarizing currents that increase action potential firing → ADH release from posterior pituitary. The OVLT (circumventricular organ lacking BBB) also projects to SON/PVN and contributes to osmosensing but is not the sole mediator. Low-volume high-osmolality states maximally stimulate ADH; high-volume low-osmolality states suppress it via baroreceptor pathways.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.