SECTION IV 

 PREGNANCY AND PARTURITION 



PREGNANCY 



FERTILISATION of the ovum takes place, as a rule, in the Fallopian 

 tube. Directly one spermatozoon has penetrated into the ovum, a 

 membrane is formed round the yolk, which prevents the entrance of 

 any other spermatozoa. The fusion of the male and female pro- 

 nuclei is followed immediately by division of the fertilised ovum, so 

 that, by the time it arrives in the uterus (about eight days after 

 fertilisation), it consists of a mass of cells known as the morula. At 

 this time the ovum has a diameter of about 0-2 mm. Pregnancy in the 

 human being lasts about nine months, birth generally taking place 

 280 days, i.e. ten periods after the last menstrual period. During 

 pregnancy menstruation is absent. 



With the arrival of the fertilised ovum in the uterus, extensive 

 changes begin in this and the neighbouring organs of generation. The 

 virgin uterus is pear-shaped, and its cavity amounts to about 2-5 c.c. 

 Just before birth the volume of the uterus is about 5000-7000 c.c., 

 and the walls of the organ are thickened in proportion. In the hyper- 

 trophy of the uterine wall all its elements are involved, but especially 

 the muscle-cells. It is doubtful whether there is an actual new forma- 

 tion of muscle fibres, but each fibre grows in length and thickness, 

 becoming finally between seven and eleven times as long and three to 

 five times as thick as in the unimpregnated uterus (Fig. 561). There 

 is at the same time a great growth of the blood-vessels, which have 

 to supply not only the growing wall of the uterus but also, by means 

 of a special organ the placenta, the nutritional needs of the 

 developing foetus. 



CHANGES IN THE UTERINE MUCOUS MEMBRANE. At the 

 moment of conception the uterine mucous membrane begins to undergo 

 hypertrophy. Within fourteen days it has attained a thickness of 

 ^ cm., and by the end of the second month, f cm. On section it shows 

 a compact layer, lining the cavity of the uterus, and beneath this, 

 abutting on the muscular tissue, is a spongy layer three times as thick 

 as the compact layer. The superficial epithelium becomes flattened, 

 loses its cilia, and degenerates. In the spongy layer the uterine glands 



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