Question

How do releasing or inhibiting hormones secreted by the hypothalamus reach the adenohypophysis?

A. They travel along axons

B. They travel along dendrites

C. They diffuse through the interstitial fluid between the hypothalamus and adenohypophysis

D. They are delivered by a portal system

E. They are delivered through active transport mechanisms

Answer 1

The anterior pituitary is the gland that secretes the hormones produced by the hypothalamus into the circulation. The anterior pituitary is also known as adenohypophysis. Posterior pituitary is called the neurohypophysis. Hypothalamus secretes the hypothalamic releasing and inhibiting hormones, (e.g. GnRH, TRH) which control the release of other hormones in anterior pituitary. The hypothalamic-hypophyseal portal veins carry these hormones from hypothalamus to the anterior pituitary. The primary capillary plexus is involved in transport of the hormones to these portal veins. Release of hormones in anterior pituitary is via the specific hormone receptors on anterior pituitary. The anterior pituitary releases their subsequent hormones into a secondary capillary plexus into blood circulation.

The neurons on the hypothalamus secrete these releasing and stimulating hormones. The action potential that triggers the hormone release travels via the dendrites to axons. The synaptic vesicles containing the hormones fuse with axonal membrane (nerve endings) to release the hormones. The hypothalamus and anterior pituitary are not in contact with each other for active transport to work. Interstitial fluid is the fluid surrounding the cell and in contact with blood circulation. The interstitial fluid has to transfer the hormones to blood and not directly to anterior pituitary.

Right choice: D. They are delivered by a portal system.