Sex hormones are hormones that affect the reproductive system. They are a type of steroid. A hormone (from Greek horman - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... A sex organ, or primary sexual characteristic, narrowly defined, is any of those parts of the body (which are not always bodily organs according to the strict definition) which are involved in sexual reproduction and constitute the reproductive system in an complex organism; namely: Male: penis (notably the glans penis... A steroid is a lipid characterized by a carbon skeleton with four fused rings. ...
See also: Estrogens (or oestrogens) are a group of steroid compounds that function as the primary female sex hormone. ... Progesterone is a steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. ... Androgen is the generic term for any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of masculine characteristics in vertebrates by binding to androgen receptors. ... Testosterone is a steroid hormone from the androgen group. ...
Natural sexsteroids are made by the gonads (ovaries or testes), by adrenal glands, or by conversion from other sexsteroids in other tissues such as liver or fat.
The development of both primary and secondary sexual characteristics is controlled by sexhormones after the initial fetal stage where the presence or absence of the Y-chromosome and/or the SRY gene determine development.
Hormone molecules are secreted (released) directly into the bloodstream; some hormones, called ectohormones, aren't secreted into the blood stream, they move by circulation or diffusion to their target cells, which may be nearby cells (paracrine action) in the same tissue or cells of a distant organ of the body.
The function of hormones is to serve as a signal to the target cells; the action of hormones is determined by the pattern of secretion and the signal transduction of the receiving tissue.
A recently-identified class of hormones is that of the "Hunger Hormones" - ghrelin, orexin and PYY 3-36 - and "Satiety hormones" - e.g., leptin, obestatin.
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