Non-tropic hormone

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Non-tropic hormones are hormones that directly stimulate target cells to induce effects. This differs from the tropic hormones, which act on another endocrine gland. Non-tropic hormones are those that act directly on targeted tissues or cells, and not on other endocrine gland to stimulate release of other hormones. Many hormones act in a chain reaction. Tropic hormones usually act in the beginning of the reaction stimulating other endocrine gland to eventually release non-tropic hormones. These are the ones that act in the end of the chain reaction on other cells that are not part of other endocrine gland. The hypothalamic-pituitary-adrenal axis is a perfect example of this chain reaction. The reaction begins in the hypothalamus with a release of corticotropin-releasing hormone/factor (CRH/F; tropic). This stimulates the anterior pituitary and causes it to release adrenocorticotropic hormone (ACTH; tropic) to the adrenal glands. Lastly, cortisol (non-tropic) is secreted from the adrenal glands and goes into the bloodstream where it can have more widespread effects on organs and tissues. Since cortisol is what finally reaches other tissues in the body, it is a non-tropic hormone. CRH and ACTH are tropic hormones because they act on the anterior pituitary gland and adrenal glands, respectively, both of which are endocrine glands. [1] Non-tropic hormones are thus often the last piece of a larger process and chain of hormone secretion. Both tropic and non-tropic hormones are necessary for proper endocrine function. For example, if ACTH (Adrenocorticotropin hormone; a tropic hormone) is inhibited, cortisol can no longer be released because the chain reaction has been interrupted. [2] Some examples of non-tropic hormones are:

Contents

Most endocrine glands, such as the gonads, pancreas, and adrenal glands, produce non-tropic hormones. Those released from the pituitary gland in the brain include: [10]

See also

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<span class="mw-page-title-main">Hypothalamic–pituitary hormone</span>

Hypothalamic–pituitary hormones are hormones that are produced by the hypothalamus and pituitary gland. Although the organs in which they are produced are relatively small, the effects of these hormones cascade throughout the body. They can be classified as a hypothalamic–pituitary axis of which the adrenal, gonadal, thyroid, somatotropic, and prolactin axes are branches.

Pulsatile secretion is a biochemical phenomenon observed in a wide variety of cell and tissue types, in which chemical products are secreted in a regular temporal pattern. The most common cellular products observed to be released in this manner are intercellular signaling molecules such as hormones or neurotransmitters. Examples of hormones that are secreted pulsatilely include insulin, thyrotropin, TRH, gonadotropin-releasing hormone (GnRH) and growth hormone (GH). In the nervous system, pulsatility is observed in oscillatory activity from central pattern generators. In the heart, pacemakers are able to work and secrete in a pulsatile manner. A pulsatile secretion pattern is critical to the function of many hormones in order to maintain the delicate homeostatic balance necessary for essential life processes, such as development and reproduction. Variations of the concentration in a certain frequency can be critical to hormone function, as evidenced by the case of GnRH agonists, which cause functional inhibition of the receptor for GnRH due to profound downregulation in response to constant (tonic) stimulation. Pulsatility may function to sensitize target tissues to the hormone of interest and upregulate receptors, leading to improved responses. This heightened response may have served to improve the animal's fitness in its environment and promote its evolutionary retention.

References

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  2. ↑ Grinspoon, S.K.; B.M.K Biller (1994). "Laboratory assessment of adrenal insufficiency". Journal of Clinical Endocrinology and Metabolism. 79 (4): 923–931. doi:10.1210/jc.79.4.923.
  3. ↑ Stavisky, Ronda; Fillipo Aureli; Elizabeth Russel (1998). "Response of fecal cortisol to stress in captive chimpanzees (Pan troglodytes)". American Journal of Primatology. 44 (1): 57–69. doi:10.1002/(sici)1098-2345(1998)44:1<57::aid-ajp5>3.3.co;2-6. PMID   9444323.
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  7. ↑ Tremblay, Richard E. (1998). "Testosterone, Physical Aggression, Dominance, and Physical Development in Early Adolescence". International Journal of Behavioral Development. 22 (4): 753–777. doi:10.1080/016502598384153. S2CID   145436017.
  8. ↑ Husslein, P.; Fuchs, A.R.; Fuchs, F. (1981). "Oxytocin and the initiation of human parturition. I. Prostaglandin release during induction of labor by oxytocin". American Journal of Obstetrics and Gynecology. 141 (6): 688–693. doi:10.1016/s0002-9378(15)33312-3. PMID   6274193.
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  10. ↑ Cambell, Neil A.; Jane B. Reece (2007). Biology (6th ed.). Sinauer Associates. ISBN   978-0-321-27045-0.

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