HypothalamusHypophyseGonaden

The hypothalamus is a small but essential brain region located below the thalamus, forming the ventral part of the diencephalon. It is connected to the pituitary gland by the infundibulum and to autonomic and brainstem centers through neural and hormonal pathways. The hypothalamus integrates visceral signals, emotional context, and environmental information to regulate homeostasis and coordinate endocrine, autonomic, and behavioral responses.

Anatomy and nuclei: The hypothalamus contains multiple nuclei, including the paraventricular and supraoptic nuclei (releasing substances and neurohypophyseal hormones), the arcuate and ventromedial nuclei (energy balance and neuroendocrine control), the lateral hypothalamic area (feeding and arousal), the dorsomedial and preoptic regions (temperature, reproduction, autonomic function), and the suprachiasmatic nucleus (circadian rhythms). The mammillary bodies are also considered part of this region and play a role in memory. A network of connections links the hypothalamus to the pituitary via the hypothalamic-pituitary portal vascular system and to brainstem and limbic structures.

Functions: Endocrine control is achieved through releasing and inhibiting hormones that regulate anterior pituitary secretion, along with the production of oxytocin and vasopressin released from the posterior pituitary. Autonomic regulation modulates sympathetic and parasympathetic outputs. Core homeostatic roles include thermoregulation, thirst, hunger and energy balance, sleep-wake cycles, circadian timing, and reproductive behavior.

Clinical relevance: Hypothalamic dysfunction can cause diabetes insipidus, obesity or weight disturbances, sleep and temperature dysregulation, and broader endocrine abnormalities. Lesions or tumors in this region, such as hypothalamic hamartomas, can produce seizures and behavioral or metabolic changes.