The placenta is a foetal organ that develops from the blastocyst shortly after implantation. It also acts as an endocrine gland that produces several hormones. The main function of placenta is to regulate the exchange of nutrition, gas, and waste between the maternal and foetal circulations. The umbilical cord serves as the passage between the placenta and the foetus.
Explore: Difference between Anterior and Posterior Placenta
Histologically, there are at least six membranes or tissues (known as barriers) that separate the maternal and foetal bloodstreams. Endothelium of the maternal blood vessel, endometrial connective tissue, uterine epithelium, chorionic epithelium, chorionic connective tissue, and endothelium of the foetal blood vessel are these membranes in the order of their sequence from the mother to the foetus. The following varieties of the placenta are created depending on whether these tissues are present or absent.
- Epitheliochorial placenta
- Endotheliochorial placenta
- Syndesmochorial placenta
- Haemochorial placenta
- Haemoendothelial placenta
Haemoendothelial Placenta
The haemoendothelial placenta is a specific type of placenta in which the outer covering, the trophoblast, becomes so thin that the maternal blood seems to be divided from the foetal blood only by a single layer of embryonic chorion cells. The chorionic villi lose their endothelial and mesenchymal layer to the point where, in most locations, the endothelial lining of their blood vessels is basically bare, separating the foetus’ blood from the mother’s sinuses. Rats, guinea pigs, mice and rabbits typically have this type of placenta.
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