structure and function of Placenta
Placenta is defined as a temporary intimate mechanical and physiological connection between foetal and maternal tissues for the nutrition, respiration and excretion of the foetus.
Structure of Placenta.
Human placenta consist of chorion only. Hence, it is called a chorionic placenta. Allantois remains small. The allantoic blood vessels, however, extend to vascularize it. A large number of branching villi from the vascular chorion penetrate the corresponding pits, the crypts, formed in the uterine wall. The latter becomes very thick and highly vascular to receive the villi. The intimate connection established between the foetal membrane and the uterine wall is known as the placenta. The placenta has two parts : the part contributed by the foetus, i.e., chorionic villi, is called the foetal placenta; and the part shared by the mother, i.e., part of uterine wall, is termed the maternal placenta. The chorionic villi receive blood from the embryo by umbilical artery and return it by umbilical vein. These blood vessels are derived from the allantois and run between the foetus and the uterine wall in the tough umbilical cord covered with cells derived from the amnion and chorion. The choroinic villi come to lie in uterine lacunae that receive blood from the uterine arteriole and return it by uterine venule. The cells forming the wall of chorionic villi bear microvilli which increase their surface area for quick and adequate exchange of materials by diffusion, active transport and pinocytosis.For more details about the Biology you can refer Botany class 12 Notes prepared by academic team of Physics Wallah.