CHAPTER VIII 

 THE HORMONES IN PREGNANCY 



THE maintenance of pregnancy is a truly complex 

 afFair. A living creature is growing at a tremendous 

 rate inside a hollow chamber, the uterus. This organ 

 must at first tolerate, even support the newcomer. It must 

 grow in size and strength so that its enterprising tenant may 

 not overwhelm it (Fig. 28). All the other muscle-walled 

 organs of the body are built to keep things moving — the 

 heart, the intestines, the bladder for example — and so, ulti- 

 mately, is the uterus. For nine months, however, it must be 

 kept in check and not allowed to expel the infant prematurely. 

 Then all of a sudden its energies are released and it is called 

 upon to deliver its contents into the world, through the nar- 

 row bony canal of the pelvis, with sufficient force and speed 

 on one hand, and sufficient gentleness on the other, to avoid 

 wearing out the mother or crushing the baby. To use a cur- 

 rent expression of bewilderment, figure out all that if you 

 can ! Nature, indeed, has figured it out reasonably well ; but 

 when the physiologist attempts to discern the factors of this 

 multifarious process and to see how they are set in motion, 

 timed, and controlled, he finds he has yet a long research 

 ahead of him. 



In this book we can do no more than sketch the problems 

 involved. In outline, what has to be worked out is the growth 

 and function of a muscular organ, controlled in part by 

 the nervous system, in part by hormones. The latter are those 

 which come from the ovary, the pituitary and the adrenal, 

 together with the output of a new source, peculiar to preg- 

 nancy, the placenta. 



THE PLACENTA 



Once the embryo is safely lodged in the uterus and has 

 begun to grow, a new era of hormone activity begins. The 



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