Describe the post –zygotic events leading to implantation and placenta formation in humans. Mention any two functions of placenta.
Dear student ,,,,After the formation of the zygote in the ampulla of the ovarian duct, it starts moving towards the uterus through the isthmus. On its path it undergoes its first mitotic division in the isthmus region known as clevage, thua forming 2 cells. This cells then again divide to form 4,8,16 cells. The 2,4,8, and 16 daughter cells are known as the blastomers. The 8 - 16 celled stage is known as the morula which keeps on dividing. This rapid division ultimately leads to the formation of the blastocyst. The blastomer in the blastocyat is arranged into 2 types of cells- a) the outer layer of the blastocyst known as the trophoblast b) the inner cell mass. The trophoblast layer then gets attached to the uterine wall- endometrium and the inner cell mass differentiates into the embryo. Immediately after attachment, the uterine wall undergoes rapid mitotic division and surrounds the trophoblast within itself. This leads to the embedding of the trophoblast in the uterine wall and is known as implantation which leads to pregnancy. After implantation finger like projections appear on the trophoblast known as the chorionic villi which are surrounded by the uterine tissue nad maternal blood. The chorionic villi and the uterine tissue become integrated to form the placenta. ......... FUNCTIONS OF PLACENTA- a) facilitates the supply of oxygen and nutrients to the embryo and removal of wates. b) acts as an endocrine tissue and produces several hormone: i) human chorionic gonadotrophin ii) human placental lactogen iii) estrogen iv) progestogen v) relaxin.......hope this helps,Regards.