Here’s what you should know about Placenta of Animals!
What is a Placenta
The placenta is an organ of metabolic interchange between the conceptus and the Dam. The placenta is also an endocrine organ that secretes hormones
There are 7 types of Placenta as explained below.
- Diffuse Placenta
In some mammals (e.g., ungulates, pigs, sow, mare, horse, zebra, lemur, etc.) the chorionic villi remain scattered all over the surface of the chorion.
- Cotyledonary Placenta
In a cotyledonary placenta, the villi are found in groups or patches, while the rest of the chorion surface is smooth. The patches of villi are called cotyledons, and the placenta of this type is found in ruminants ungulates such as cattle, sheep Deer, and Antelope.
- Zonary
In a zonary placenta, the villi are developed in the form of a belt or girdle-like band around the middle of their blastocyst or chorionic sac, which is more or less elliptical. Such a placenta occurs in carnivores (e.g., cats, dogs, Big cats etc.). The raccoon has an incomplete zonary placenta. - Discoidal Placenta
It is characterized by having one or two distinct adjacent discs.
Discs contain chorionic villi that attach to the endometrium and provide the region for gas nutrients and metabolism exchange. In insectivores, bats, rodents (mouse, rat, rabbit, etc.) and bears, the villi are restricted to a circular disc or plate on the dorsal surface of a blastocyst.
Based on the degree of contact between chorionic villi and the maternal endometrium.
The placenta may be:
i. Non-deciduous
Ii. Deciduous
Iii. Contra-deciduous
i. Non-Deciduous placenta
At the time of birth, when parturition (the separation of the foetus and its membranes from the mother’s body) occurs, the chorionic villi are simply drawn out from the depressions in the wall of the uterus and, thus, maternal and foetal tissues are separated without further damage to the uterine wall and no bleeding occurs. This type of placenta is called non-deciduate or non- deciduous placenta and is found in pigs, cattle, horses etc.
ii. Deciduous placenta.
The wall of the uterus becomes eroded to various degrees through the action of the trophoblast and the embryonic tissues penetrate the uterine wall, establishing a more intimate contact and facilitating the passage of substances from the mother to the foetus and from the foetus to the mother. Here because the chorionic villi fuse with the eroded uterine mucosa, such placenta is called the true placenta.
iii. Contra-deciduous:
In Perameles and Talpa (mole), a somewhat modified type of deciduate placenta occurs, which is called the contra- deciduate placenta. In such a case, not only there is a loss of maternal tissue but also of the foetal portion of the placenta, both of which are absorbed by maternal leucocytes.
Conclusion
Placenta is an apposition of fetal membranes to the endometrium to permit physiological exchange between the fetus and the mother. It mediates the metabolic exchanges of the developing individual through an intimate association of embryonic tissues and of certain uterine tissues, serving the functions of nutrition, respiration, and excretion. It works as an endocrine gland. It will secretes lactogen, progesterone, etc. hormones. Placental hormones act to adapt maternal physiology to pregnancy and lactation
Contributor – Afnan Khaliq
