Steroid hormones (Greek) stereos – solid and eidos – kind; Greek hormao – I set in motion, I encourage] – a group of physiologically active substances (sex hormones, corticosteroids, the hormonal form of vitamin D) that regulate the vital processes in animals and humans. In vertebrates, steroid hormones are synthesized from cholesterol) in the adrenal cortex, Leydig cells of the testes, in the follicles and corpus luteum of the ovaries, as well as in the placenta. Steroid hormones are contained in the free form of lipid drops in the cytoplasm. Due to their high lipophilicity, steroid hormones diffuse relatively easily through plasma membranes into the blood, and then penetrate into target cells. The human body contains six steroid hormones: progesterone, cortisol, aldosterone, testosterone, estradiol and calcitriol (the obsolete name is calciferol). With the exception of calcitriol, these compounds have a very short side chain of two carbon atoms or not at all. Steroid hormones that perform a signaling function are also found in plants.
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