Describe the relationship between the hypothalamus and the anterior pituitary gland.  Why is the anterior pituitary gland called the master gland?  What is negative feedback?

The hypothalamus is located at the floor of the third ventricle between the mamillary body and the optic chasm. Just inferior to the hypothalamus is an area called the "median eminence" (ME) which tapers into the hypophysial stalk. The hypophysial stalk then flares out into the pituitary gland.

In the hypothalamus there are neuron bodies which have axon terminals in the ME that secrete neuro-- transmitters into a bed of capillaries. These capillaries empty into a vein that supplies blood flow to another capillary bed (portal blood flow) in the anterior pituitary gland. The cells in the anterior pituitary are the target cells of the neuro – transmitters secreted by the hypothalamic neurons (neuro – endocrine) which have a stimulatory or inhibitory effect on the anterior pituitary cells.

This hypothalamic – pituitary portal system acts as a one way chemical messenger system between the hypothalamus and anterior pituitary gland.

The anterior pituitary then react to these chemical signals by either increasing or decreasing the release of hormones that effect other cells in the body.

The anterior pituitary is called the "Master Gland" because the hormones that it releases effect every other cell in the body such as human growth hormone.

The regulation of the communication between the anterior pituitary and the hypothalamus seems to be controlled by negative loop -- back mechanisms that have their controllers in the hypothalamus. Negative loop -- back is a system similar to a home thermostat where there is a variable condition that is compared to a set point. When the variable differs from the set point a response is stimulated that attempts to bring the variable condition closer to the set point.