3. Posterior Pituitary (Neurohypophysis)

Embryology & Structure
  • Derived from a downward extension of the diencephalon (neuroectoderm).
  • Composed mainly of unmyelinated axons and pituicytes (glial-like cells).
  • Subdivisions:
    • Pars nervosa (main body)
    • Infundibular stalk (connects to hypothalamus)
    • Median eminence (interface with hypothalamus)


Hypothalamic Nuclei
  • Hormones of the posterior pituitary are synthesized in the hypothalamus and transported via the hypothalamo-hypophyseal tract (axonal transport)

    • Hormone

    Site of Synthesis

    Released From

    Main Functions

    ADH (Vasopressin)

    Supraoptic nucleus

    Posterior pituitary

    - Increases water reabsorption in collecting ducts (via V₂ receptors)
    - Vasoconstriction at high levels (V₁ receptors)

    Oxytocin

    Paraventricular nucleus

    Posterior pituitary

    - Uterine contraction during labor
    - Milk ejection (let-down reflex)
    - Emotional bonding, sexual behavior

  • Hormones are synthesized as pre-prohormones, packaged in vesicles, transported down axons, and stored in Herring bodies (axon terminals in posterior pituitary) until release.

Milk Ejection Reflex