CHAPTER I THE BEGINNING OF PREGNANCY
IMPREGNATION occurs as the result of the union of the ovum and spermatozoén. The former is the microscopic cell body which, being discharged from the ovary, passes through the Fallopian tube and seeks lodgment in the uterus. In its passage it is sought out by the male element or spermatozo6n.
In the unimpregnated state the ovum loses its vitality and is expelled from the uterus with the menstrual discharge. The lining membrane of the uterus, preceding the next recurring monthly flow, again becomes engorged with blood, and the freshly discharged ovum is cast off with the menstrual blood. The process is thus repeated. The periodic separation of the ovum from the ovary is called ovulation, while the return of the menstrual flow at each succeeding period is called menstruation— a term descriptive of the monthly recurrence of the flow.
Both ovulation and menstruation cease as soon as pregnancy takes place. The blood which ordinarily is discharged is retained and becomes the source of nourishment to the ovum.
In the early stage of pregnancy the local condition is not perceptible, as the slight enlargement of the uterus is not sufficient to displace the organ or to cause it to encroach upon its surroundings. In
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12 OBSTETRIC NURSING
general however, the absence of the monthly period and the instinctive impression which some
fay ina
Fig. 1.—Transverse section of uterus and Fallopian tube, showing the course which the ovum follows in its passage.
women have that conception has occurred are likely to call attention to the possibility of preg- nancy.
Fic. 2.—Showing attachment of ovum to uterine wall, also altered mucous membrane and enlarged blood-vessels.
While the signs of pregnancy in the early stage may not be evident, nevertheless the uterus is under- going changes which adapt it to the growth of the
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THE BEGINNING OF PREGNANCY 13
embryo or developing ovum. The cavity becomes enlarged and the lining or mucous membrane altered. The ovum, after passing through the Fallopian tube and entering the cavity of the uterus (Fig. 1), becomes attached to the wall of the latter at a point where the layers of the mucous membrane permit of its being embedded in them. At the same time the muscular tissue in the uterus becomes developed, causing a thickening of its wall and a general increase in volume (Fig. 2). The blood-vessels which carry the blood to and from the uterus undergo enlargement in order to supply the amount of blood necessary for the de- mands of the growing ovum.
These constitute the local changes which mark
the beginning of pregnancy.