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Progestogens (also sometimes spelled progestagens or gestagens) are a class of steroid hormones that bind to and activate the progesterone receptor (PR). The most important progestogen in the body is progesterone (P4). Other endogenous progestogens include 17α-hydroxyprogesterone, 20α-dihydroprogesterone, 5α-dihydroprogesterone, 11-deoxycorticosterone, and 5α-dihydrodeoxycorticosterone. Synthetic progestogens are generally referred to as ''progestins''.〔 However, the terms ''progesterone'', ''progestogen'', and ''progestin'' are frequently used interchangeably both in the scientific literature and in clinical settings.〔 The progestogens are one of the five major classes of steroid hormones, in addition to the androgens, estrogens, glucocorticoids, and mineralocorticoids, as well as the neurosteroids. All progestogens are characterized by their basic 21-carbon skeleton, called a pregnane skeleton (C21). In similar manner, the estrogens possess an estrane skeleton (C18), and androgens, an andrane skeleton (C19). The progestogens are named for their function in maintaining pregnancy (i.e., ''progestational''), although they are also present at other phases of the estrous and menstrual cycles.〔〔 ==Functions== In the first step in the steroidogenic pathway, cholesterol is converted into pregnenolone (P5), which serves as the precursor to the progestogens progesterone and 17-hydroxyprogesterone. These progestogens, along with another steroid, 17-hydroxypregnenolone, are the precursors of all other endogenous steroids, including the androgens, estrogens, glucocorticoids, mineralocorticoids, and neurosteroids. Thus, many tissues producing steroids, including the adrenal glands, testes, and ovaries, produce progestogens. In some tissues, the enzymes required for the final product are not all located in a single cell. For example, in ovarian follicles, cholesterol is converted to androstenedione, an androgen, in the theca cells, which is then further converted into estrogen in the granulosa cells. Fetal adrenal glands also produce pregnenolone in some species, which is converted into progesterone and estrogens by the placenta (see below). In the human, the fetal adrenals produce dehydroepiandrosterone (DHEA) via the pregnenolone pathway. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「progestogen」の詳細全文を読む スポンサード リンク
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