Which portal vessel characteristic is unique to the hypothalamo-hypophyseal portal system compared to other portal systems in the body?
- A It connects two capillary beds, both located within the same organ
- B It carries oxygenated blood from the hypothalamus directly to adenohypophysis
- C It drains venous blood from the hypothalamus into pituitary capillaries, allowing high local concentrations of releasing hormones ✓
- D It bypasses the systemic circulation and delivers hormones directly to target organs
Correct answer: C. It drains venous blood from the hypothalamus into pituitary capillaries, allowing high local concentrations of releasing hormones
Explanation
The hypothalamo-hypophyseal portal system is unique in that it allows hypophysiotropic hormones secreted by hypothalamic neurosecretory cells to reach the anterior pituitary at concentrations 1000-fold higher than systemic levels, enabling precise regulation with tiny amounts of releasing/inhibiting hormones. Blood flows from primary capillary plexus in the median eminence through portal veins to secondary capillary plexus in the adenohypophysis — connecting two organs, not within the same organ.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.