How does the hypothalamus send TRH to the pituitary gland?

Answer 1

The hypothalamus sends the TRH hormone via some capillaries. Now, these are very special capillaries, yes they connect to the circulation, as capillaries do. However, these capillaries are different in that they act as a portal. In fact, they have a name for them too, called the hypothalamo-pituitary portal vessels. Basically how they work is, blood coming from the heart first integrates into the hypothalamus, and upon the exocytosis type of release from the nuclei within the hypothalamus that contain the hormones (talking about in this way the nuclui that produce the homones release those hormones directly into capillaries via a similar manner as how neurotransmitters are released into a synapse). Once the hormones are released into the capillaries of the hypothalamus-pituitary vessels, they travel down and into the anterior pituitary. Where they are actively transported into the cells of the anterior pituitary (notice nothing about the posterior pituitary, because that functions in a different manner).