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{¤ Placenta :

• It is a disc shaped structure which is embedded in the uterine wall of females.

• It develops during gestation period. 

• It contains villi on the embryo's side of the tissue. 
On the mother's side are blood spaces, which surround the villi. 
This provides a large surface area for glucose and oxygen to pass from the mother to the embryo.

• It is mainly for providing nutrition to the growing embryo.. 

• It is also helpful in excretion as the waste generated by the developing embryo can be removed by passing or transferring them into mother's blood through placenta.

STRUCTURE :-

Placenta is a structure that establishes firm connection between the foetus and the mother.

From the outer surface of the chorion a number of finger like projections known as chorionic villi grow into the tissue of the uterus. These villi penetrate the tissue of the uterine wall of the mother and form placenta.The placenta is a connection between foetal membrane and the inner uterine wall. Thus, placenta is partly maternal and partly embryonic. By means of placenta the developing embryo obtains nutrients and oxygen from the mother and gives off carbon dioxide and nitrogenous waste.

In the placenta, the foetal blood comes very close to the maternal blood, and this permits the exchange of materials between the two. Food (glucose, amino acids, lipids), water, mineral salts, vitamins, hormones, antibodies and oxygen pass from the maternal blood into the foetal blood, and foetal metabolic wastes, such as carbon dioxide, urea and warn pass into the maternal blood.

The placenta, thus, serves as the nutritive, respiratory and excretory organ of the foetus. The blood of the mother and foetus do not mix at all in the placenta or at any other place. The blood of the foetus in the capillaries of the chorionic villi comes in close contact with the mother’s blood in the tissue between the villi, Inn they are always separated by a membrane, through which substances must diffuse or lie transported by some active, energy requiring process.

The type of placenta in man is of described as deciduate (intimate contact between loetal and maternal tissue), discoidal (villi occur in the form of disc), haemo-chorial (chorionic epithelium in direct contact with maternal blood).

Functions :-

The placenta performs the following functions:

1. Nutrition:

Food materials pass from the mother’s blood into the foetal blood through the placenta.

2. Digestion:

The trophoblast ol the placenta digest protein before passing them into foetal blood.

3. Respiration:

Through the placenta oxygen passes from the maternal blood to the foetal blood, and carbon dioxide passes from foetal blood to maternal blood.

4. Excretion:

Nitrogenous wastes such as urea pass from foetal blood into maternal blood through placenta and are filtered out by the kidneys of the mother.