A reference hand-book for nurses

by Amanda K. Beck

OBSTETRICS.

Puberty.—This is the period of transformation from childhood to adolescence. There is a marked development of the throat and chest, the breasts become fuller, more rounded, and there is also an enlargement of the pelvis. These outward signs are combined with certain internal changes, affecting especially the ovaries and the uterus, that are described under the terms of ovulation and menstruation.

Ovulation.—The ovaries produce ova that are retained in cavities termed ovisacs (Graafian follicles), which are scattered throughout the ovary. Sometimes an ovisac contains more than one ovum, but usually each ovisac contains but one. When the ovary becomes functionally active, some of the ovisacs in the deeper part of the organ increase in size and develop toward the surface. From time to time one of these ovisacs, having continued to increase in size so as to form a projection on the surface of the ovary, actually bursts and sets free an ovum. This frequently occurs in association with menstruation, but may take place at other periods. While this development of the ovisac has been taking place there is a special flow of blood to the pelvic contents, and the fringe-like processes of the Fallopian tube become more closely applied, so that a cup is formed by the fimbriated extremity of the Fallopian tube, into which the ovum drops. Eventually the ovum reaches the cavity of the uterus, and, unless it becomes fertilized or impregnated, it is in due course cast off from the uterus in the menstrual discharge and perishes.

When the uterus has become the seat of a fertilized ovum there is no further ripening of ovisacs. After the escape of an ovum from the ovisac the follicle is filled with blood, and this takes part in the formation of a structure known as the corpus luteum, which is formed within the burst ovisac. The corpus luteum varies in its development according as the ovum becomes fertilized or not. If pregnancy takes place it remains to its close, but if the ovum is not fertilized it disappears in about three months. The ruptured ovisac always contains the elements of a corpus luteum, but its development depends on the fate of the ovum. Ovulation has been said to commence before menstruation; ovisacs may sometimes ripen and burst in childhood. Conception may take place before menstruation has set in.

Menstruation.—The blood is derived from the mucous membrane of the uterus (endometrium) and not from that of the cervix. The endometrium becomes swollen and thickened prior to the commencement of the flow, and the blood-vessels are distended. With the beginning of the flow this swelling gradually diminishes. A few superficial cells of the endometrium are usually cast off during menstruation, and this is regenerated during the interval between the periods. The mucous membrane of the uterus is thus never at rest until menstruation ceases for good.

Conception.—Fertilization of the ovum may occur anywhere in its course from the ovisac to the uterus, but ordinarily it takes place in the uterus. Certain changes take place in the uterus preparatory to the arrival of the fertilized ovum. The whole organ enlarges, it contains more blood than before; the mucous membrane becomes soft, spongy, thickens greatly, and is thrown into folds which are called the decidua vera.

Decidua Vera.—The part of the decidua vera to which the ovum becomes attached and where the placenta afterward forms is called the decidua serotina. The presence of the ovum acts as an irritant to the spot where it lodges, and active growth takes place. At the same time the ovum burrows into the mucosa and gradually becomes embedded. The vera closes over the ovum. The decidua vera is a mold of the interior of the uterus. The external surface is rough where it has been torn from the underlying tissues of the uterus, and the internal aspect which is in contact with the ovum is smooth. It is thickest at the third month; after this time the membrane becomes thinner and thinner, until by the end of pregnancy it is very thin. It is to a considerable extent expelled at labor and forms part of the membranes.

Ovum.—As the ovum develops the decidua reflexa expands until it fills the decidua vera at the end of the second month, and by the end of the third month it has intimately united with the decidua vera to form one membrane. Until these two membranes have coalesced the ovum is not free in the uterine cavity, but is enclosed in the decidua reflexa.

Pregnant Uterus.—As pregnancy proceeds the uterus ceases to be a pelvic organ; it becomes rounded, and after the sixth month gradually assumes an ovoid shape. At the end of the third month it has reached to the brim of the pelvis. By the sixth month it is level with the umbilicus, and by the ninth it has reached to the tip of the sternum. During the last fortnight the organ sinks a little, and this relieves to some extent the shortness of breath which has been caused by the pressure on the diaphragm.

Fetal Membranes.—Inside of the decidual membranes we find the chorion and amnion. Whereas the deciduæ are maternal structures, the chorion and the amnion are derived from the ovum. The chorion is the more external of the two fetal membranes; it early surrounds the ovum and throws out processes (villi) toward the decidua reflexa and serotina. These processes are at first formed equally all over the chorion, but those which lie in connection with the decidua serotina grow more rapidly in size and complexity, and remain to form the main part of the placenta. The membrane in which the fetus lies is the amnion. Contained within the amnion is more or less fluid, the liquor amnii, in which the fetus rests as in a water-bed. It permits free movements on the part of the fetus and protects it from violence from the outside; it equalizes the pressure on the uterine walls, preventing pressure on the cord and placenta; and during labor it assists in the dilation of the os uteri and lubricates the maternal passages. From it also the fetus derives its supply of water. Occasionally water may form between the three membranes, and during labor the chorion may rupture and not the amnion, and the waters between them be discharged. In like manner, water which has formed between the decidua and the chorion may come away. These, then, are two sources of fluid which may be discharged from the vagina in labor when the amnion is intact.