HORMONES 



295 



difficulty has been completely overcome in many cases by the clinical 

 use of progesterone. 



After about the third month of pregnancy the placenta also begins to 

 function as an endocrine organ and partially takes over the production 

 of progesterone. It also secretes hormones with FSH and LH action, 

 and probably others. The urinary excretion of various hormones during 

 pregnancy is shown in Fig. 11-3. Toward the later months estradiol is 

 again produced in increasing amounts. This renders the muscles of 

 the uterus more responsive to the oxytocic hormone of the pituitary (a 

 "contracting" hormone, see p. 303) and eventually brings about the onset 

 of labor. Delivery is facilitated by still another hormone, relaxin. This 

 substance has been studied mainly in animals, where it appears to be 

 produced by the placenta under the influence of estradiol and progesterone. 

 As the name implies, relaxin loosens the pelvic ligaments and thus facili- 

 tates birth. Chemically it appears to be a peptide. 



The final hormone cooperating in the reproductive process in the female 

 is the lactogenic hormone, which is produced immediately following de- 

 livery (Tig. 11-3) and stimulates milk production. It is probable that 

 the luteotropic hormone is, in fact, the same substance as the lactogenic 

 hormone. 



4 5 6 



Lunar Months of Pregnancy 

 Reproduced by courtesy of Parke, Davis & Company's Therapeutic Notes. 

 Fig. 11-3. Hormone production during pregnancy. 



In addition to the roles described above, the female sex hormones exert 

 a profound inffuence on the development of the secondary sex character- 

 istics such as body shape, body hair distribution, and voice tone, and on 

 the growth of the reproductive organs. 



The male sex hormones, testosterone and androsterone, control the 

 development of the male genital organs, the production of spermatozoa, 



