During the reproductive cycle of a human female when, where and how does, placenta develop ? What is the function of placenta during pergnancy and embryo development ?

Explanation

Placenta is an organ that connects the developing foetus to the uterine wall of mother for supporting pregnancy.
After implantation finger-like projections appear on the trophoblast called chorionic villi, which are surrounded by the uterine tissue and maternal blood. The chorionic villi and the uterine tissue become interdigitated with each other and jointly form a structural and functional unit between foetus and maternal body, i.e. placenta.
Functions of Placenta
(i) It facilitates the supply of oxygen and nutrients to the embryo.
(ii) It also facilitates the removal of carbon dioxide and waste materials produced by the foetus.
(iii) The placenta is connected to the embryo through the umbilical cord, which helps in the transport of substances to and from the embryo.
(iv) Placenta also acts as an endocrine tissue and produces several hormones like human Chorionic Gonadotropin (hCG), human Placental Lactogen (HPL), oestrogen, progesterone, etc. The production of thesehormones is necessary to support foetal growth, metabolic changes in the mother and maintenance of pregnancy.