1 The phenotype may change constantly throughout the life of an individual because of environmental changes and the physiological and morphological changes associated with aging.
One special group of hormones is the tropic hormones that stimulate the hormone production of other endocrine glands. For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones. hormone (from Greek á½ÏÎ¼Î®, impetus) is any member of a class of signaling molecules produced by glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour.
TSH stimulated the thyroid gland to release thyroid hormone, which is a generic name for a pair of two hormones, triiodothryronine(T3) thyroxine(T4). T4 is much more (98%) prevalent in blood that T3 (2%). Hormone cascade pathways usually involve the mechanism of negative feedback. In the above-mentioned example, the thyroid hormone itself carries the negative feedback by inhibiting TSH release from the anterior pituitary gland, and TRH from the hypothalamus.