The outputs of the hypothalamus can be divided into two categories: neural projections, and endocrine hormones.
Neural projections
Most fiber systems of the hypothalamus run in two ways (bidirectional).
- Projections to areas caudal to the hypothalamus go through the medial forebrain bundle, the mammillotegmental tract and the dorsal longitudinal fasciculus.
- Projections to areas rostral to the hypothalamus are carried by the mammillothalamic tract, the fornix and terminal stria.
- Projections to areas of the sympathetic motor system (lateral horn spinal segments T1-L2/L3 of the) are carried by the hypothalamospinal tract and they activate the sympathetic motor pathway
Endocrine hormones
The hypothalamus affects the endocrine system and governs emotional behavior, such as anger and sexual activity. Most of the hypothalamic hormones generated are distributed to the pituitary via the hypophyseal portal system. The hypothalamus maintains homeostasis; this includes a regulation of blood pressure, heart rate, and temperature.
| Secreted hormone | Abbreviation | Produced by | Effect |
|---|
Thyrotropin-releasing hormone
(Prolactin-releasing hormone) | TRH, TRF, or PRH | Parvocellular neurosecretory neurons | Stimulate thyroid-stimulating hormone (TSH) release from anterior pituitary (primarily)
Stimulate prolactin release from anterior pituitary |
|---|
Dopamine
(Prolactin-inhibiting hormone) | DA or PIH | Dopamine neurons of the arcuate nucleus | Inhibit prolactin release from anterior pituitary |
|---|
| Growth hormone-releasing hormone | GHRH | Neuroendocrine neurons of the Arcuate nucleus | Stimulate Growth hormone (GH) release from anterior pituitary |
|---|
Somatostatin
(growth hormone-inhibiting hormone) | SS, GHIH, or SRIF | Neuroendocrine cells of the Periventricular nucleus | Inhibit Growth hormone (GH) release from anterior pituitary
Inhibit thyroid-stimulating hormone (TSH) release from anterior pituitary |
|---|
| Gonadotropin-releasing hormone | GnRH or LHRH | Neuroendocrine cells of the Preoptic area | Stimulate follicle-stimulating hormone (FSH) release from anterior pituitary
Stimulate luteinizing hormone (LH) release from anterior pituitary |
|---|
| Corticotropin-releasing hormone | CRH or CRF | Parvocellular neurosecretory neurons | Stimulate adrenocorticotropic hormone (ACTH) release from anterior pituitary |
|---|
| Oxytocin | | Magnocellular neurosecretory cells | Uterine contraction
Lactation (letdown reflex) |
|---|
Vasopressin
(antidiuretic hormone) | ADH or AVP | Magnocellular neurosecretory neurons | Increases water permeability in the distal convoluted tubule and collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume |
|---|
Further Reading
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"Hypothalamus"
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