Hypothalamus–Pituitary Axis - Anatomy and Physiology
- What structure connects the hypothalamus to the posterior pituitary?
- The hypothalamo-hypophyseal tract, a bundle of axons from hypothalamic neurons that end in the posterior pituitary.
- Which hypothalamic hormone stimulates the anterior pituitary to release TSH?
- Thyrotropin-releasing hormone (TRH).
- Which hypothalamic signal mainly inhibits prolactin secretion?
- Dopamine (prolactin-inhibiting hormone). Prolactin is unusual in being held mostly under inhibitory hypothalamic control.
- A patient has low cortisol, low ACTH and high CRH. Which gland in the axis is most likely failing?
- The anterior pituitary. High CRH shows the hypothalamus is signaling, but the pituitary is not responding with ACTH (secondary adrenal insufficiency).
- Which two hormones are released by the posterior pituitary?
- ADH (vasopressin) and oxytocin. Both are made by neurons in the supraoptic and paraventricular nuclei of the hypothalamus.
- Which hypothalamic hormone stimulates the anterior pituitary to release ACTH?
- Corticotropin-releasing hormone (CRH).
- Which hypothalamic hormone inhibits growth hormone secretion from the anterior pituitary?
- Somatostatin (growth hormone-inhibiting hormone). GHRH has the opposite, stimulating effect.
- What is the other name for the anterior pituitary, reflecting its glandular tissue?
- Adenohypophysis. The posterior pituitary, made of neural tissue, is the neurohypophysis.
- GnRH from the hypothalamus stimulates release of which two anterior pituitary hormones?
- FSH and LH, the gonadotropins that act on the ovaries and testes.
- In the stress response, put CRH, cortisol and ACTH in their order of release.
- CRH, then ACTH, then cortisol. CRH from the hypothalamus triggers ACTH from the anterior pituitary, which triggers cortisol from the adrenal cortex.
- How are hypothalamic releasing hormones delivered to the anterior pituitary?
- Through the hypophyseal portal system, a set of blood vessels linking hypothalamic capillaries directly to anterior pituitary capillaries.
- Why is the posterior pituitary not considered a true endocrine gland?
- It synthesizes no hormones. It is neural tissue that stores and releases hormones made by hypothalamic neurons.