Contra-deciduate placenta is a slightly modified kind of deciduate placenta seen in Parameles & Talpa (mole). Not only does this result in the loss of maternal tissue, but it also results in the loss of fetal tissue. Both the fetal and maternal portions of the placenta are absorbed in situ by the mother’s leucocytes.
The placenta is a mammalian organ that grows in the uterus during pregnancy. Its job is to supply oxygen and nourishment to the infant while also removing waste from the blood.
No part of the placenta is thrown out of the body in contra deciduous placenta. The fetal component of the placenta stays in the uterus for a while before breaking down and being absorbed by the mammalian body which helps with maternal leukocytes.
PLACENTA:
- The word “placentation” comes from Greek and means “flat cake.”
- The name comes from the human placenta, which is a flat, spherical mass that resembles a pan cake in shape.
- In its broadest sense, the term placenta makes reference to any region in a viviparous organism in which maternal as well as embryonic tissues of any kind are closely opposed and serve as a site for physiological exchange between parent and embryo or between parent and embryo.
- A transient organ created by the fetus’ EEM and maternal tissues that provides nutrients to the fetus (Eutherian).
- Placenta serves as the embryo’s temporary lung, intestine, kidney, and endocrine glands.
- It enables for the flow of chemicals between maternal and fetal blood.
- Highly selective actions let food, vitamins, oxygen, hormones, and antibodies in while allowing CO₂ & nitrogenous metabolic waste to depart. Placentation is the process of the placenta forming and fusing to the uterine wall.
ATTACHMENT AND ESTABLISHMENT IN IMPLANTATION:
The blastocyst must adhere to the uterus and establish the embryo’s food supply before significant growth may occur.
- Blastocyst pressed up against the lining of the uterus- Decidua= “to shed “
- The uterine capillaries & uterine wall within the immediate region of the embryo become more permeable, resulting in local stromal oedema.
- The endometrium surrounding the embryo soon shows the first signs of Decidual Cell Reaction (DCR):
The epithelium is disrupted, the stroma’s loosely packed fibroblast-like cells are converted into roundish glycogen-filled cells, the number of cells & vasculature of the area increases, and the decidual cells form an ” Implantation Chamber” around the embryo, likely serving a nutritious role before the placenta becomes functional.
- Trophoblast – Primary fetal membrane, which becomes Chorion – fetal component of placenta when mesoderm lines its hollow.
- Trophoblasts penetrate the endometrium, where they may damage the uterine epithelium & phagocytose the decidual cells to gain sustenance for the fetus.
PATTERNS OF IMPLANTATION:
- Most Ungulates (Pig), Carnivores (Dog), and Monkeys have a superficial or central blastocyst that remains unembedded in the uterine lumen.
- Blastocyst is entirely entrenched in the endometrium, as seen in hedgehogs, Guinea pigs, bats, apes, and humans.
- Eccentric- Blastocysts lie in a fold or pocket that separates from the main cavity for a period of time before becoming interstitial, as seen in beaver, rat, squirrel, and other rodents.
TYPES OF PLACENTA:
BASED ON VASCULAR SUPPLY:
Allantoic circulation provided by the allantois or Vitelline circulation of the yolk sac:
- Chorio-vitelline/ Yolk-sac placenta — Metatherian mammals, such as marsupials, Didelphis, and Macropus, have a highly vascular yolk sac that fuses with the chorion.
- Chorio-allantoic placenta: Allantois merges with the chorion via its blood arteries, as seen in some Marsupials as well as all Eutherian mammals.
DEGREE OF ASSOCIATION BETWEEN FETAL AND MATERNAL TISSUE:
- Non-deciduate placenta – Implantation is superficial; the fetal chorionic epithelium is in contact with the uterine epithelium, and the fetal villi are drawn out totally without tearing or injuring the uterine wall, and no bleeding occurs, as in pigs, cats, horses, and other ruminants.
- Deciduate (Deciduous) placenta – Implantation is more intimate; the uterine wall becomes eroded so that the fetal chorionic epithelium may come to lie either in the connective tissue or in the maternal blood; at the time of parturition, when the fetal part of the placenta separates from the uterine part of the placenta, there is more or less extensive bleeding or hemorrhage.
- Contra-Deciduate Placenta – although implantation or connection is close, maternal leukocytes absorb both fetal and maternal tissue in situ. Parameles and Talpa are two examples of this type of animal (mole).
USES OF CONTRA DECIDUATE PLACENTA:
- It serves as the fetus’s nutritive, respiratory and excretory organs.
- It allows selective diffusion, preventing harmful materials from the maternal blood from getting into the fetal blood.
- During pregnancy it serves as an important endocrine gland.
- Before the liver is formed it stores glycogen for the fetus.
- The trophoblast digests proteins before passing them onto the fetal blood.
CONCLUSION:
The placenta is a transitory organ generated by the fetal extraembryonic membranes and maternal tissues, through which the developing embryo or fetus of viviparous mammals receives sustenance from the maternal uterine tissue.
The placenta was defined simply by Balinsky (1981). The placenta is a transitory organ made up of maternal and fetal tissues that transports nutrients from the mother to the developing embryo.
The biological bridge for physiological material exchange is formed by the region of attachment between the embryonic tissue and the uterine wall. Placentation is the process of an embryo being implanted into the uterine wall.
Contra-deciduate placenta is a slightly modified kind of deciduate placenta seen in Parameles & Talpa (mole). There is indeed a loss of maternal tissue as well as the fetal section of the placenta in this situation, both of which are taken in situ via maternal leukocytes.