The organ that develops in the uterus during pregnancy and that link the blood supplies of mother and baby. The placenta develops from the chorion.
It is firmly attached to the lining of the woman’s uterus and is connected to the baby by the umbilical cord. It is expelled shortly after the baby is born.
The thick, spongy, disc-like mass of tissue which connects the EMBRYO with the inner surface of the UTERUS, the embryo otherwise lying free in the amniotic ?uid (see AMNION). The placenta is mainly a new structure growing with the embryo, but, when it separates, a portion of the inner surface of the womb – called the maternal placenta – comes away with it. It is mainly composed of loops of veins belonging to the embryo, lying in blood-sinuses, in which circulates maternal blood. Thus, although no mixing of the blood of embryo and mother takes place, there is ample opportunity for the exchange of ?uids, gases, and the nutrients brought by the mother’s blood. The width of the full-sized placenta is about 20 cm (8 inches), its thickness 2·5 cm (1 inch). One surface is rough and studded with villi, which consist of the loops of fetal veins; the other is smooth, and has implanted in its centre the umbilical cord, or navel string, which is about as thick as a ?nger and 50 cm (20 inches) long. It contains two arteries and a vein, enters the fetus at the navel, and forms the sole connection between the bodies of mother and fetus. The name ‘afterbirth’ is given to the structure because it is expelled from the womb in the third stage of labour (see PREGNANCY AND LABOUR).
n. an organ within the uterus by means of which the embryo is attached to the wall of the uterus. Its primary function is to provide the embryo with nourishment, eliminate its wastes, and exchange respiratory gases. This is accomplished by the close proximity of the maternal and fetal blood systems within the placenta. It also functions as a gland, secreting *human chorionic gonadotrophin, *progesterone, and oestrogens, which regulate the maintenance of pregnancy. See also afterbirth. —placental adj.
Implantation of the PLACENTA in the bottom part of the UTERUS adjacent to or over the CERVIX. The condition may cause few problems during pregnancy or labour; it may, however, cause vaginal bleeding late in pregnancy or hinder vaginal delivery of the baby and this may necessitate obstetric intervention.... placenta praevia
(human chorionic somatomammotrophin) a protein hormone of 190 amino acids produced by the placenta during most but not all pregnancies. Despite its name it does not appear to have a role in lactation and its exact function remains obscure. It does, however, seem to contribute to the development of diabetes in some pregnancies.... human placental lactogen
a condition in which the placenta is abnormally strongly attached to the wall of the uterus with superficial penetration of chorionic *villi into the underlying *myometrium. Women with *placenta praevia and at least one previous Caesarean delivery are considered to be at high risk for placenta accreta. When placenta accreta is thought to be likely, consultant obstetric and anaesthetic input are vital in planning and conducting the delivery. Radiological input with temporary uterine balloon tamponade may be considered, and methotrexate has been used. The risk of haemorrhage, blood transfusion, and hysterectomy should be discussed. In placenta increta the chorionic villi extend into the myometrium; a placenta percreta occurs where the chorionic villi penetrate through the myometrial wall and can invade the bladder. An emergency hysterectomy is usually necessary in these rare cases.... placenta accreta
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