1. Hypothalamic-pituitary Axis

• The Hypothalamus is the main link between the Nervous System and the Endocrine System
• The Pituitary Gland is connected to the Hypothalamus by a stalk-like structure
  • The Pituitary Gland consists of two distinct lobes, the larger Anterior Lobe and the smaller Posterior Lobe
• The Hypothalamus and the Pituitary Gland secrete a multitude of hormones
  • Major regulators of growth, development, metabolism and homeostasis

Pituitary Gland

Posterior Lobe - Neurohypophysis

• Acts as a neural extension of the Hypothalamus
• Hormones are synthesised in the cell bodies of Hypothalamic Neurons
  • Axons of these neurons pass down to and terminate in the Posterior Pituitary Gland
  • Synthesised hormone is packaged into vesicles and moves down to the neuron terminals where it is stored
• Upon stimulation of the neuron, APs will travel down the axons and the hormones will be released into the blood stream
  • through which they reach their target tissues
• Posterior Pituitary Gland releases 2 hormones that are delivered by separate neurosecretory cells with cell bodies in the different parts of the Hypothalamus
  • Oxytocin
    • Delivery of milk by breast, stimulated by nursing
    • Contraction of Uterine smooth muscles, stimulated by labour
  • Vasopressin (ADH)
    • Acting on smooth muscles, constricts blood vessels and thus increases BP$\uparrow$
    • Acts within the kidney to reduce water loss$\downarrow$ through the urine and thus maintains blood volume
    • Impact on social behaviour

Anterior Lobe - Adenohypophysis

• Neurosecretory cells from specific nuclei in Hypothalamus end in the Median Eminence where the Hypothalamo-pituitary Portal blood supply originates
  • Neurons secrete Hypophysiotropic Hormones into the Hypothalamo-pituitary Portal
  • Blood flows from the Median Eminence towards Anterior Pituitary where the hormones stimulate secretion of Anterior Pituitary Hormones

<aside> 💡 Hypophysiotropic Hormone $\to$ Anterior Pituitary Gland Hormone

$\to$ Hormone from other endocrine gland $\to$ Target Cell

</aside>

2. Anterior Pituitary Gland

Hypophysiotropic Hormone

<aside> 💡 Tropic Hormones are hormones that target other endocrine glands

</aside>

• Hypophysiotropic Hormones act on the Anterior Pituitary Gland and are Tropic Hormones
  • Can be either Stimulating or Inhibiting

• GnRH - Gonadotropin-releasing Hormone