The placenta is the physiological connection between the mother and the foetus. In human, the placenta is referred to as chorioallantoic placenta. The placenta is formed of chronion (foetal part) and decidua basalis (maternal part). The chorion penetrates deep into the uterine wall with its chorionic villi. So the degree of intimacy between the maternal and foetus tissue is great. At the time of birth of uterine tissue is lost along with foetal membranes. This type of placenta is known as haemochorial placenta. The umbilical cord connects the foetus to the placeta.
Functions of Placenta1. It acts as a barrier between the foetus and the mother.
2. It acts as an ultrafilter.
3. Soluble inorganic and organic materials, nutrients, hormones, antibodies against diptheria, small pox, scarlet fever, measles etc, can pass through the placenta from mother to foetus.
4. It helps in the exchange of gases between the mother and the foetus.
5. It helps in the elimination of nitrogenous discharges and other wastes of the foetus.
6. It acts as an endocrine gland and produces hormones such as HCG(Human Chorionic Gonadotropin), chorionic thyrotropin, chorionic corticotropin, chorionic somatomammotropin, estrogens and progesterone. It also secretes progesterone until the end of pregnancy. At the time of parturition, the placenta secretes relaxin, which helps in the relaxation of pubic ligaments to enable birth of the child.