What Is It, Location, Function, and More
Authors:Maria Emfietzoglou, MD ,Ian Mannarino, MD, MBA
Editors:Alyssa Haag,Kelsey LaFayette, DNP, RN
Copyeditor:David G. Walker
What is the hypothalamus?
The hypothalamus is a small part of the brain that plays an important role in homeostasis (the bodily state where conditions are optimal for internal processes, such as blood pressure, thermoregulation, and sleep-wake cycle) to function properly. The hypothalamus is made up of several nuclei, which are clusters of neurons with various roles, including secretion of hormones.
Where is the hypothalamus located?
The hypothalamus is located deep in the brain, hidden between the cerebral hemispheres. On a mid-sagittal section through the brain, the central part of the brain is occupied by the diencephalon (i.e., the thalamus and hypothalamus) surrounding the cavity of the third ventricle. The hypothalamus creates the floor and the inferolateral walls of the third ventricle. Superior to, or on top of, the hypothalamus is the thalamus (i.e., an egg-shaped structure that relays sensory and motor signals to the cerebral cortex), which is separated from the hypothalamus by the hypothalamic sulcus. Finally, anterior to, or in front of, the hypothalamus resides the optic chiasm (i.e., the point where the two optic nerves cross over each other).
What is the function of the hypothalamus?
The hypothalamus regulates a number of bodily processes, including thirst and water intake, hunger and food intake, the autonomic nervous system (i.e., the part of the peripheral nervous system that controls organs and glands), biological circadian rhythms (such as the sleep-wake cycle), body temperature, blood pressure, breastfeeding, learning and memory, sexual drive, and emotional expression. The hypothalamus can send direct signals to the brain as well as other parts of the body to regulate internal processes (e.g., thermoregulation, circadian rhythms). Additionally, the hypothalamus produces hormones that act on their various target organs, such as the pituitary, to perform essential functions of the body.
What hormones does the hypothalamus produce?
A variety of hormones are produced by the hypothalamus, including thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), growth hormone-releasing hormone (GHRH), somatostatin, and dopamine. The hypothalamus also produces vasopressin, also known as antidiuretic hormone (ADH), and oxytocin. These hormones either act on the anterior pituitary gland (i.e., a pea-sized endocrine organ that controls vital functions of the skin, brain, reproductive organs, and vision) to secrete pituitary hormones or are stored in the posterior pituitary to be released later (e.g., specifically, vasopressin and oxytocin).TRH leads to the production and release of thyroid stimulating hormone (TSH) from the pituitary, which then acts on the thyroid to increase the production of thyroid hormones. CRH causes the pituitary to produce adrenocorticotropic hormone (ACTH), which later acts on the adrenal gland to stimulate secretion of cortisol (i.e., a steroid hormone that helps regulate the metabolic and immune pathways of our body). GnRH causes the pituitary to secrete gonadotropins, such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH). GHRH acts on the anterior pituitary to stimulate secretion of growth hormone (GH), which is a hormone that stimulates the growth of long bones and other tissues in our body. Somatostatin causes the pituitary to decrease GH secretion. Dopamine reduces the production of prolactin (i.e., a hormone produced in the pituitary gland that is involved in breastfeeding) and is also involved in the body’s reward system. ADH causes water retention and vasoconstriction that ultimately increases blood pressure. Finally, oxytocin dilates the cervix and stimulates uterine contractions during childbirth and aids in breast muscle contraction to eject the milk during breastfeeding.
What are hypothalamic disorders?
Hypothalamic disorders are typically caused by hypothalamic dysfunction that may be secondary to a genetic condition or damage to the hypothalamus from brain injury, surgery, tumor, or autoimmune destruction. Examples of genetic conditions that may cause hypothalamic disorders include Kallman syndrome, which is a genetic condition characterized by delayed puberty and anosmia (absence of sense of smell), and Prader Willi syndrome, characterized by poor feeding, low muscle tone, overeating, intellectual disability, and low sex hormones. Damage to the hypothalamus may result in hypothalamic obesity, characterized by excessive appetite and weight gain; functional hypothalamic amenorrhea in which there is absence of menstruation; and diabetes insipidus, characterized by lack of ADH, causing excessive urination and thirst. Finally, hypothalamic disease can result in a condition called syndrome of inappropriate antidiuretic hormone (SIADH) where the body produces excessive levels of ADH, leading to decreased blood osmolality, muscle weakness, and altered mental status (e.g., restlessness, irritability, and confusion).
What are the most important facts to know about the hypothalamus?
The hypothalamus is a small but complex brain structure that plays an important role in homeostasis and hormone regulation. Anatomically, it is located between the two cerebral hemispheres and is part of the diencephalon, a brain structure that also includes the thalamus. The hypothalamus can either send signals directly to the brain and other parts of the body to regulate processes, such as thermoregulation and circadian rhythms, or produce hormones that act on various target organs, including the pituitary and the thyroid gland. Dysfunction of the hypothalamus can result in several hypothalamus disorders, including Kallman syndrome, Prader Willi syndrome, hypothalamic obesity, functional hypothalamic amenorrhea, central diabetes insipidus, and SIADH.
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Anatomy of the diencephalon
Resources for research and reference
Gould, D. J. (2014). Neuroanatomy (5th ed.). Lippincott Williams & Wilkins.
Le, T. B., & Vikas, B. (2020). First aid for the USMLE step 1 (30th ed.). McGraw Hill.
Splittgerber, R., & Snell, R. S. (2019). Snell’s clinical neuroanatomy (8th ed.). Wolters Kluwer.