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 sperma- 

 tozoa. The fusion of the male and female pronuclei 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 ajbout 5000-7000 c.c., and the walls of the organ 

 are thickened in proportion^ In the hypertrophy of the uterine wall all 

 its elements are involved, but especially the muscle-cells. It is doubtful 

 whether there is an actual new formation 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. 563). 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 f oetus. 



CHANGES IN THE UTERINE MUCOUS MEMBRANE. At the moment 

 of conception the uterine mucous membrane begins to undergo hyper- 

 trophy. 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 proliferate, the stroma cells are enlarged, 

 and the blood- capillaries are widely dilated. The stroma cells become con- 

 verted into the large decidual cells. By the time the fertilised ovum arrives 

 in the uterus the process of hypertrophy and loosening of the layers of the 



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