tropic hormone
Summary
A tropic hormone acts on another endocrine gland and stimulates it to make or release its own hormone. Classic examples are the anterior pituitary's TSH, ACTH, FSH and LH. Most testable: the end hormone usually feeds back negatively, so hormone levels show where an axis is broken.
Detail
Meaning: A tropic hormone acts on another endocrine gland and stimulates it to make or release its own hormone. The anterior pituitary is the classic source: TSH acts on the thyroid, ACTH on the adrenal cortex, and FSH and LH on the gonads. These form axes: hypothalamic releasing hormone → anterior pituitary tropic hormone → target gland → end hormone. Hypothalamic releasing hormones such as TRH, CRH and GnRH are tropic in this sense too. Direct hormones, such as prolactin, act on non-endocrine tissue.
On the MCAT: Passages describe a hormone axis and ask what happens when one step changes. The end hormone usually inhibits the hypothalamus and pituitary (negative feedback). If the target gland underproduces, the tropic hormone rises; if the pituitary fails, both the tropic and end hormones fall; if a tumor overproduces the end hormone, the tropic hormone falls.
Common confusion: Tropic is not trophic. Tropic here means acting on a gland; trophic means promoting growth or nourishment. They get mixed up because some tropic hormones, such as TSH, also enlarge their target gland. Also, tropic does not mean pituitary-only: releasing hormones from the hypothalamus count as well.
Sources
- Campbell Biology
- Principles of Anatomy and Physiology
- Human Physiology: An Integrated Approach
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.