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The hypothalamus is a small, almond-shaped region located below the thalamus and forming part of the diencephalon. It serves as a critical interface between the nervous and endocrine systems, controlling many aspects of homeostasis and behavior. Through its connections with the pituitary gland and brainstem, the hypothalamus integrates autonomic, endocrine, and metabolic signals to coordinate physiological responses.

The hypothalamus regulates body temperature, appetite and energy balance, thirst, sleep–wake cycles, and sexual and reproductive behaviors. It receives input from limbic structures, sensory pathways, and circulating hormones, and conveys output through neural and hormonal pathways. A major route to the pituitary is the hypothalamic–pituitary axis: releasing and inhibiting hormones produced by hypothalamic neurons travel to the anterior pituitary to regulate hormones such as ACTH, TSH, LH/FSH, and growth hormone. Dopamine from hypothalamic neurons inhibits prolactin release. Posterior pituitary hormones, vasopressin (antidiuretic hormone) and oxytocin, are synthesized in the hypothalamus and released from nerve terminals there.

Key hypothalamic nuclei include the suprachiasmatic nucleus, which drives circadian rhythms; the arcuate nucleus, which influences appetite and metabolism; and the paraventricular, ventromedial, and lateral nuclei, which participate in autonomic control and endocrine output. The hypothalamus also interacts with the limbic system to influence emotions and motivated behaviors.

Clinical disorders arising from hypothalamic dysfunction include disturbances of temperature regulation, thirst and fluid balance, appetite and weight, sleep patterns, and pituitary hormone deficiencies or excesses, including central diabetes insipidus and secondary adrenal or thyroid disorders.