hypothalamus, an important supervisory center in the brain, rich in ganglia, nerve fibers, and synaptic connections. It is composed of several sections called nuclei, each of which controls a specific function. The hypothalamus regulates body temperature, blood pressure, heartbeat, metabolism of fats and carbohydrates, and sugar levels in the blood. Through direct attachment to the pituitary gland, the hypothalamus also meters secretions controlling water balance and milk production in the female. The role of the hypothalamus in awareness of pleasure and pain has been well established in the laboratory. It is thought to be involved in the expression of emotions, such as fear and rage, and in sexual behaviors. Despite its numerous vital functions, the hypothalamus in humans accounts for only 1/300 of total brain weight, and is about the size of an almond. Structurally, it is joined to the thalamus; the two work together to monitor the sleep-wake cycle.

Region of the brain containing a control centre for many autonomic-nervous-system functions. Its complex interaction with the pituitary gland makes it an important part of the endocrine system. As a critical link between the body's two control systems, the hypothalamus regulates homeostasis. Nervous and hormonal pathways connect it with the pituitary, which it stimulates to release various hormones. The hypothalamus influences food intake, weight regulation, fluid intake and balance, thirst, body heat, and the sleep cycle. Disorders can produce pituitary dysfunction, diabetes insipidus, insomnia, and temperature fluctuations.

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