Question

What does the neural innervation of the hypothalamus indicate about the effect it has on the pituitary? How does this relate to the fact that the pituitary is sometimes called a "double organ"?

Answer 1

Answer :~ For understanding this question first we have to understand about the pituitary gland and its relationship to the hypothalamus

The pituitary gland also called the hypophysis is a small gland about 1cm in diameter and 0.5 to 1 gm in weight that lies in the sella turcica, a bony cavity at the base of the brain, and is connected to the hypothalamus by the pituitary stalks.The pituitary is divisible into two distinct portion

1. Anterior pituitary (adenohyophysis)

2. Posterior pituitary (neurohypophysis)

Neural innovation of the hypothalamus indicates about the effect it has on pituitary

Almost all the secretion by the pituitary is controlled by either hormonal or nervous signal from the hypothalamus. Secretion from the Posterior pituitary is controlled by nerve signals that originate in the hypothalamus and terminate in the Posterior pituitary.

In contrast, secretion by the Anterior pituitary is controlled by hormones called hypothalamic releasing and hypothalamic inhibitory hormones secreted within the hypothalamus and then conducted as shown in below figure to the Anterior pituitary through minute blood vessels called hypothalamic - hypophysis portal vessels. In the Anterior pituitary, these releasing and inhibitory hormones act on glandular cells to control their secretion.

The hypothalamus receives signals from many sources in the nervous system and is collecting center for information concerning the internal well being of the body, and much of this information is used to control secretions of many globally important pituitary hormones.

The neurons originated various parts of the hypothalamus and sent their nerve fibers to the median eminence and tuber cinereum, an extension of hypothalamic tissue into pituitary stalk.

The ending of these fibres are different from most endings in the CNS, in that their function is not to transmit signals from one neuron to another but rather to secrete the hypothalamic releasing and inhibitory hormones into the tissue fluids. These hormones are immediately absorbed into the hypothalamic-hypophysial portal system and carried directly to the sinuses of the Anterior pituitary gland.

You understand all the theories by this diagram "hypothalamic - hypophysial portal system

Pituitary is sometimes called a DOUBLE ORGAN

This is because the secretion of Anterior and solid epithelial portion discharge into the blood sinuses which traverse this part of gland whereas the hyaline substance from the epithelium of the Posterior pituitary enters the pars nerves.