The placenta is a temporary organ required for the development of the embryo and foetus (see figure 3.3, below). It allows for the exchange of nutrients and oxygen from mother to foetus, and the transfer of foetal waste products back to the mother for disposal by her organs. Its functions are as follows:

a) Respiration: as the pulmonary exchange of gases does not take place in the uterus the foetus must obtain oxygen and excrete carbon dioxide through the placenta

b) Nutrition: food for the foetus derives from the mother's diet and has already been broken down into forms by the time it reaches the placenta site. The placenta can select those substances required by the foetus

c) Storage: the placenta metabolises glucose and can also store it in the form of glycogen and reconverts it to glucose as necessary. The placenta store iron and the fat soluble vitamins.

d) Excretion: the primary substance excreted from the foetus is carbon dioxide; bilirubin will also be excreted.

e) Protection: it provides a limited barrier to infection with the exception of the Treponema of syphilis, a virus such as the Rubella and HIV may pass

f) Endocrine: human chorionic gonadotrophin (HCG) is produced by the cytotrophoblastic layer of the chorionic villi. As the Corpus Luteum declines, the placenta takes over production of oestrogen and progesterone.

(The umbilical cord is the tube which serves for transfer of nutrients to the foetus and back waste from the foetus)

Fig. 3.3. The placenta with its umbilicus

Last modified: Sunday, 26 February 2017, 5:36 PM