THE HORMONES IN HUMAN REPRODUCTION 



tional proliferation by which the early embryos are nourished 

 and implanted. 



From a count of the epithelial cells in sections of the uterus, 

 I estimate that a rabbit's uterus contains (in the two horns) 

 about 100,000,000 epithelial cells. This means that each of 

 the 180,000 epithelial cells in a corpus luteum can affect 

 about 500 epithelial cells. The corpus luteum cells are, how- 

 ever, about 25 to 50 times as large (in volume) as the epi- 

 thelial cells, and therefore each of the former takes care of 

 about 10 to 20 times its volume of the latter at the start of 

 progestational proliferation. The disproportion is not quite 

 so great if we calculate on the basis of the amount of corpus 

 luteum tissue to maintain pregnancy, not merely to induce 

 progestational proliferation. On this basis one corpus luteum 

 cell controls at first about 3 to 5 times its volume of epithelial 

 cells. By the time the effect is complete, the number of epi- 

 thelial cells has increased a great deal, and thereafter the 

 corpus luteum cell must maintain more of them. This means 

 that small amounts of progesterone stir up a proportionately 

 large effect in the uterus. That sort of trigger-like action 

 ("You push the button, we do the rest") is characteristic of 

 the internal secretions. It is necessary to suppose that some 

 sort of chemical reaction between the hormone and something 

 in the cells of the uterus starts a chain of secondary reactions 

 which profoundly change the physiology of the uterine lining. 

 We might have a better idea of what actually happens if we 

 could know how much progesterone actually reaches each 

 epithelial cell; but this cannot be calculated, because we do 

 not know what proportion of the hormone is diverted to other 

 receptors (the uterine muscle, the mammary gland cells, and 

 possibly other tissues). If all of it went to the epithelial cells 

 of the uterus, each such cell would receive daily about 1.3 x 

 10"* milligrams. This is almost 10^^ molecules. The actual 

 share received must be considerably smaller. 



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