. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Endocrine Mechanisms 743 structures functionally important in the female. The progestins function pri- marily in providing adequately for the intimate relationship between the parent and developing young. The principal naturally occurring substance in each class is: (1) androgen—testosterone; (2) estrogen—estradiol; and (3) progestin—progesterone, which have the chemical structures shown. CH, OH OH C=0. c/V\/ Testosterone Estradiol Progesterone Just as these three classes of hormones show a basic similarity to o
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. Endocrine Mechanisms 743 structures functionally important in the female. The progestins function pri- marily in providing adequately for the intimate relationship between the parent and developing young. The principal naturally occurring substance in each class is: (1) androgen—testosterone; (2) estrogen—estradiol; and (3) progestin—progesterone, which have the chemical structures shown. CH, OH OH C=0. c/V\/ Testosterone Estradiol Progesterone Just as these three classes of hormones show a basic similarity to one an- other in their chemical organization, so is there also considerable functional overlapping, and, in many instances, a ready conversion within the body from one tvpe to another. These facts have made the acquisition of knowl- edge of their normal function somewhat difficult. ANDROGENS. Androgen is a term used to describe all those compounds whose biological actions resemble in general those of testosterone. The pri- mary function of androgens is to stimulate the development and activity of the male accessory reproductive organs. They are also responsible in part for differences in the conformation of the male body, the lower pitch of the human male voice, the characteristic distribution of hair, male pugnacious assertiveness, and many special male secondary sex characteristics such as the swollen clasping digits of the male frog, the comb of the cock, the crest of the newt, and the nuptial coloration and gonopodal appendages of cer- tain viviparus fishes. Many of these are characters the presence of which is largely restricted to the breeding season. The various androgens differ from one another in their overall potency and their relative effects on the numerous individual characters within the body and these differences in turn may vary from species to species. This complicates greatly the problem of the roles of androgens within the body. The testes comprise the p
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