The hypothalamus is a part of the brain whose function is to help maintain homeostasis (balance) in many body systems.
The hypothalamus is located below the thalamus and is physically connected to the posterior pituitary by neurons and connected by blood vessels to the anterior pituitary. It weighs only a fraction of an ounce and is a little larger than the tip of a person's thumb. The hypothalamus is one of the regulators of the autonomic nervous system. It controls involuntary activities such as heart rate and temperature. It also regulates survival-driven behaviors related to eating and drinking, sexual behavior, and sleeping.
The hypothalamus exerts its control by releasing hormones that stimulate the pituitary gland, to which it is connected, to release other hormones into the bloodstream. These pituitary hormones act on distant organs in the body to maintain homeostasis, stimulate growth and maturation, and respond to changing body conditions. The pituitary hormones help regulate many automatic body functions such as fluid balance, temperature, heart rate, and sleep cycles, as well as normal growth, sex drive, sexual maturation, contractions during pregnancy, and milk production in women who have given birth.
The suprachiasmatic nuclei (SCN), another part of the hypothalamus, is the site of a person's internal clock that regulates biological rhythms according to a circadian cycle of roughly 24 hours. From the SCN, signals reach areas of the hindbrain that regulate sleep and wakefulness and determine the periods of greatest alertness—whether one is a morning person or a night person. Pathways from the SCN to the eyes allow the SCN to respond to changes in light and dark.
The hypothalamus, along with the limbic system, has also been implicated in regulating mood and emotions. It produces the neurotransmitter dopamine, which may play a role in regulating mood.
Damage to the hypothalamus can occur due to birth defects, head trauma, malnutrition, anorexia nervosa or bulimia, or infection. This damage can have devastating effects on the body. Symptoms of hypothalamic failure can include delayed growth, delayed sexual maturation, changes in menstrual cycle, impotence, depression, intolerance to cold, and fatigue.
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National Endocrine and Metabolic Diseases Information Service, 6 Information Way, Bethesda, MD, 208923569, (888) 828-0904; TTY (866) 569-1162, firstname.lastname@example.org, http://www.endocrine.niddk.nih.gov .