Placenta is the intimate connection between the foetus and uterine wall of the mother to exchange the materials. The outer surface of the chorion in human develops a number of finger like projection, known as chorionic villi, which grows into the tissue of the uterus.
These villi , penetrate the tissue of the uterine wall in which they are embedded, make up the organ known as the placenta by means of which the developing embryo obtains nutrients and oxygen and gets rid of carbon dioxide and metabolic wastes. Because of the chorionic takes part in the formation of placenta, the human placenta is called the chorionic placenta.
It consist of foetal part, the chorion and a maternal part the decidua basalis. The foetal part of placenta grows to invade the uterine mucosa with its chorionic villi.
The degree of intimacy is so strong that the blood vessels of the chorionic villi are bathed in mother’s blood.This is due to erosion of the uterine mucosa, including its epithelium, connective tissue and the endothelial lining. This type of placenta which is based on the intimacy between foetal and maternal parts of the placenta, is referred to as haemochorial placenta.
The placenta is connected to embryo through an umbilical cord which helps in the transport of substance to and from the embryo. On the basis of the distribution of villi on chorion ‚human placenta is called Metadiscoidal Placenta.
The placenta performs the following functions:-
(i) Nutrition : All the nutritive elements from the maternal blood pass into the foetus through the placenta.
(ii) Respiration, Oxygen passes from the maternal blood to the foetal blood through the placenta, and carbon dioxide passes in the reverse direction.
(iii) Excretion, the foetal excretory products diffuse into the maternal blood through placenta and are excreted by the mother.
(iv) Storage, placenta stores glycogen, fat etc.
(v) As a barrier. Placenta soaps and efficient barriers and allow those material to pass into the fetal blood that are necessary. Teratogens are certain agent (virus or Chemicals )or drugs that cause abnormal development in developing embryo /foetus.
The most well-known synthetic Teratogen drug is thalidomide. this drug causes multiple different in the growing embryo.
(vi) Endocrine function. Placenta secretes hormones such as oestrogen, progesterone, human chronic gonadotropin(hCG), human chorionic somatomammotropin — (hCS). (It was formerly known as human placental lactogen HPL), chorionic thyrotropin, chorionic corticotropin and relaxing.
The hCG stimulates and maintains the corpus luteum to secrete progesterone until the end of pregnancy. The hCG stimulates the growth of the mammary glands during pregnancy. Relaxin facilitates parturition (act of birth) by softening the connective tissue of the pubic symphysis.
In addition, the levels of hormones like oestrogens, progesterone, cortisol, prolactin, thyroxine, etc. Are increased in the maternal blood during pregnancy. Increased production of these hormone is necessary for supporting the fetal growth ‚metabolic changes in the mother and maintenance of pregnancy.