about placentation in mammals

1. Placentation in
Mammals
Presented by
Sharmila.S
Assistant Professor,
Department of Zoology ,
E.M.G.Yadava Womens Cllege,
Madurai

2. Introduction
• Placenta is a fetomaternal organ which is the primary site of nutrient and gas
exchange between the fetus and the mother.
• The term placenta derived from Greek (plakuos = flat cake) .
• named on the basis - organs appearance
• The placenta a mateno-fetal organ which begins developing at implantation of the
blastocyst and is delivered with the fetus at birth.
• At most recently have we start to understand the many different functions of this
organ carries out in addition to its role in embryonic nutrition.

3. • Generally placenta found in mammals
• It is a large organ that develops during pregnancy- internal development
• Embryo shows spl kind of tissue called placenta
• Formation of placenta – contribution of both embryonic and maternal
tissues.
• Process of placental development called as placentation.

4. Classification of placenta
• based on the type of Foetal Membranes Involved
• based on the Distribution of Villi
• based on the Nature of Contact
• based on the histological intimacy of foetal and maternal tisues

5. Based on the type of Foetal Membranes Involved
• Embryonic tissues which are involved in the formation of placenta, except
amnion other three membranes such as chorion , yolk sac and allantois are
plays important role in formation of placenta.
• Based on this placenta classified into two types
1. Yolk sac placenta
2. Chorio- allantoic placenta

6. 1.Chorio-vitelline placenta or yolk-sac palcenta (is formed by yolk sac and
chorion )
• In some marsupials, the allantois remains relatively small and never makes
contact with the chorionic sac, whereas the yolk sac becomes very large
and gets fused with chorion.
• The chorionic blood vessels are connected with the vitelline blood vessels
of the yolk sac. Hence,the yolk sac contributes the major share in the
formation of placenta. Eg. Didelphys, dasyurus

7. 2.Chorio-allantoic placenta (is formed on chorion and allntois)
• In some marsupials and all eutherian mammals, the yolk sac remains
rudimentary and the allantois becomes well developed and vascularised to
fuse with chorion. The chorio-allantoic villi constitute the plancenta. In
these animals yolk sac placenta is not seen.
• This type of placenta is called as chorio-vitelline placenta. The chorio-
allantoic villi grow out and get attached with the uterine wall. Eg.
Peramoles and eutherian mammals.

8. Based on the Nature of contact
• chorionic villi may be loosely /intimately connected with the uterine wall
• Based on this placenta is classified into two types
1. Indeciduate Placenta &
2. Deciduate Placenta

9. 1.Indeciduate Placenta
• Here the implantation is superficial type.
• The chorianic villi are simple projections, they lie in contact with uterus.
The villi are initially formed by the trophoblast but later on the blood
vessels and connective tissues are extended to them.
• They have a loose contact.
• There is no fusion.
• At the time of birth of embryo uterus is not damaged. No bleeding occurs
at the time of parturition.
• Ex. Ungulate (pig , cow) & Lemurs

10. • Deciduate type Placenta:
• Here the degree of intimacy between the maternal and foetal tissues is
great. The allanto-chorianic villi penetrate into uterine villi.
• They are intimately fused. Hence at the time of birth, the uterus is
damaged.
• Bleeding occurs, the uterine wall enters into formation of placenta is calle
• It d deciduas. Ex: Primates(monkey , human ) Rodentia (mice,rat) ..etc.
• It has three important parts

11. 1. Decidua capsularis [reflexa] –( portion of the uterine mucosa immediately
overlying the embryo) it covers the blastocyst except embryonic pole and
separates it from uterine cavity.
2. Decidua basalis – (beneath the embryo)
it is a part of decidua between blastocyst and
myometrium. It forms the fetal part of
placenta.
3. Decidua parietalis –( the remainder of the
uterine lining) it is the rest of the
endometrium that lines the rest of the
uterine cavity.

12. Based on the distribution of villi
• According to the distribution of villi six kinds of placenta are seen.
• 1.Diffused type placenta: Ex Horse, pig,
• The villi are uniformly distributed on the surface of blastocyst, except at
the extreme ends.
• 2.Cotyledonary placenta : Ex Sheep, Cow, Deer.
• The villi are arranged in groups. Each group is called cotyledon. Each
cotyledon fits into caruncla of uterus.

13. • 3.Intermediate type Placenta Ex : Giraffe & camel
• It is a rare type, it shows free villi on cotyledons. Hence it is called
intermediate type placenta
• In these three types of placenta during parturition the foetus will not
damage uterus.
• 4.Zonary placenta: Ex Cat, Dog, Carnivores.
• The villi are In the form of transverse zones. in dog a single girdle of vhf
will be present. In fox two girdles of villi are present. The villi penetrate
into uterine wall. Hence during parturition uterine wall is damaged.

14. • 5.Discoidal Placenta: ex Rat, Bat, Rabbit.
• On the entire surface of blastocyst the villi are in the form of discs. When
the embryo is growing.It moves away from uterus hence the with look
like a disc. These villi are intimately connected with uterus. Hence during
parturition much uterine tissue is damaged.
• 6.Metadiscoidal placenta: Ex. Man, monkey .
• The villi are at first uniformly distributed throughout the entire surface of
chorion .
• later they are restricted to one / more disc shaped areas on the ventral
side . It occurs in primates.
• Man has single disc of villi – monodiscoidal placenta
• Monkey has two discs of villi – bidiscoidal

15. Basede on the types of tisues involved
(histology)
• number of layers of cells present between foetus and
uterus blood supply the
placenta is classified into five types.
1.Epithelio chorial placenta : Ex Pig, Horse, (Ungulates Lemmures)
• The foetal chorion is in contact with epithelium of the uterus hence it is called
epithelio-chorial placenta. In between foetal, maternal parts six layers are
present. If all the six layers are present the placenta is called epithelio-chorial
placenta.

16. 2.Syndeumochorial placenta: Ex Sheep, Cow.
• The allanto-chorianic vith will pierce into the uterus of the mother, the chorion will
come in contact with syndesmose of mother’s uterus. Hence it is called
syndesmose chorial placenta.
3. Endotheliochorial placenta : Ex Dog, Carnivores.
• The chorion of the foetus will come in contact with the endothelim of mother ‘s uterus, hence it is called
endothelio-chorial placenta.
4. Hemochorial placenta: Ex: Bat, Man, Primates, Insectivores.
• The placental connections are more intimate. The chorion of foetus will float in the blood pools of
mother’s uterus. Hence it is called haemochorial placenta.
5.Hemo endothelial placenta Ex: Rat, Rabbit, Hence guinea-pig will float In mother’s blood.
• Hence it called hemo endothelial placenta.

17. • https://sites.google.com/site/virginiassonographysite/dms-132/placenta