Physiology of Finfish and Shellfish (2+1)

5.2.2.1 Hypothalamus

The Hypothalamus (from Greek ὑπό = under and θάλαμος = room, chamber) is a portion of the diencephalon that lies inferior ( below) to the thalamus and contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus drives the endocrine system.

(The brain is made of three main parts: the fore brain, mid brain, and hind brain. The forebrain consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system). The mid brain consists of the tectum and tegmentum. The hind brain is made of the cerebellum, pons and medulla. Often the mid brain, pons, and medulla are referred to together as the brainstem.

The thalamus is the largest structure in the diencephalon, the part of the brain situated between the mid brain (mesencephalon) and fore brain (telencephalon).

Function of thalamus:

• Motor Control
• Receives Auditory, Somatosensory and Visual Sensory Signals
• Relays Sensory Signals to the Cerebral Cortex

It synthesizes and secretes certain neurohormones, often called hypothalamic-releasing hormones that travel in blood vessels to the anterior pituitary and these in turn stimulate or inhibit the secretion of pituitary hormones . The blood vessel that carries hypothalamic-releasing hormones from the hypothalamus to the pituitary is called a portal vein because it connects two capillary beds. One capillary bed is in the hypothalamus and the other is in the anterior pituitary. Release-inhibiting hormones produced by the hypothalamus inhibit the pituitary from secreting its hormones.

The hypothalamus is responsible for certain metabolic processes and other activities like maintaining homeostasis (constant internal conditions) by regulating the internal environment (examples: heart rate, body temperature, water balance, hunger, thirst, fatigue, Sleep, circadian cycles and the secretions of the pituitary gland).

Hypothalamo-hypophyseal system: Pertaining to the hypothalamus and pituitary complex. A neuroendocrine system of neurones, fibre tracts, endocrine tissue and blood vessels which produces and releases pituitary hormones into the systemic circulation.