Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary.:719 The hypothalamus secretes tropic hormones that target the anterior pituitary, and the thyroid gland secretes thyroxine, which targets the hypothalamus and therefore can be considered a tropic hormone.
The term tropic is from Ancient Greek τροπικός (tropikós), in the sense "of or pertaining to a turn or change", meaning "causing a change, affecting"; this is the same origin as tropic and trope. This should not be confused with trophic, as in similar-sounding trophic hormone – the words and concepts are both unrelated. Tropic hormones are contrasted with non-tropic hormones, which directly stimulate target cells.
Tropic hormones from the anterior pituitary include:
- Thyroid-stimulating hormone (TSH or thyrotropin) – stimulates the thyroid gland to make and release thyroid hormone.:718
- Adrenocorticotropic hormone (ACTH or corticotropin) – stimulates the adrenal cortex to release glucocorticoids.:718
- Luteinizing hormone (LH) – stimulates the release of steroid hormones in gonads—the ovary and testes.:718
- Follicle-stimulating hormone (FSH) – stimulates the maturation of eggs and production of sperm.:718
In turn, the hypothalamus controls the release of hormones from the anterior pituitary by secreting a class of hypothalamic neurohormones called releasing and release-inhibiting hormones—which are released to the hypothalamo-hypophyseal portal system and act on the anterior pituitary.:720–721
- Purves, William K.; David Sadava; Gordon H. Orians; H. Craig Heller (2001). Life: The Science of Biology (6th ed.). Massachusetts: Sinauer Associates. ISBN 0-7167-3873-2.
- Cambell, Neil A.; Jane B. Reece. Biology (6th ed.). Sinauer Associates. ISBN 0-321-27045-2.
- Steinberg, Werner (1952). "Trophic Vs. Tropic". Journal of the American Medical Association. 149: 82. doi:10.1001/jama.1952.02930180084027.