Brain
Hypothalamus
Master regulator of the body
Overview
The hypothalamus is a small but vital structure below the thalamus that serves as the brain's master regulator of homeostasis. It manages hunger, thirst, body temperature, sleep-wake cycles, and stress responses through direct control of the pituitary gland and the autonomic nervous system.
Function
- Regulates hunger, thirst, and satiety
- Controls body temperature (thermoregulation)
- Governs circadian rhythm via suprachiasmatic nucleus
- Releases hormones controlling pituitary gland output
- Directs fight-or-flight and rest-and-digest responses
Key Facts
- The hypothalamus is only about 4 grams in weight
- It contains the suprachiasmatic nucleus—the brain's master clock
- Leptin from fat cells signals satiety directly to the hypothalamus
- Lesions can cause hyperphagia (extreme overeating) or adipsia (no thirst)
Key Substructures
- Suprachiasmatic nucleus (SCN): master circadian clock, synchronized by retinal light input
- Arcuate nucleus: integrates hunger and satiety signals; leptin and ghrelin receptor site
- Paraventricular nucleus (PVN): produces oxytocin and vasopressin; coordinates stress response
- Lateral hypothalamic area: hunger center — lesions suppress eating
- Ventromedial nucleus: satiety center — lesions cause hyperphagia and obesity
Clinical Notes
- Damage causes sleep and circadian rhythm disorders, body temperature dysregulation
- Lesions may cause diabetes insipidus (loss of ADH → excessive urination and thirst)
- Hypothalamic tumors (craniopharyngioma) can disrupt growth, puberty, and metabolism
- Severe damage to lateral area causes adipsia (no thirst) and near-total anorexia