Steroid hormones

Abstract

Steroids are lipophilic molecules used as chemical messengers by organisms ranging in complexity from water mold to humans. In vertebrates, steroids act on a wide range of tissues and influence many aspects of biology including sexual differentiation, reproductive physiology, osmoregulation, and intermediate metabolism. Major sites of steroid synthesis and secretion include the ovaries, testes, adrenals, and placenta. Based on the distance of a target site from the site of synthesis and secretion, steroid hormones can be classified as either endocrine (distant target tissue), paracrine (neighboring cells), or autocrine (same cell) factors. When secreted into the environment, steroids can also act as pheromones by conveying information to other organisms. © 2005 Humana Press Inc.