dev bio basics extraembryonic membranes and placenta types

1. S.Y.B.Sc ZOOLOGY
COURSE 10 UNIT 1
COMPARATIVE EMBRYOLOGY
SUB TOPIC: EXTRA-EMBRYONICMEMBRANES
Date : 21-01-2022

6. Somatopleure: Amnion & Chorion
Splanchnopleure: Yolk Sac & Allantois

9. ENDOGENOUS YOLK SAC IN TELEOST FISHES
ENDOGENOUS YOLK
SAC IN TELEOST
FROG

10. EXOGENOUS YOLK SAC IN SHARK

14. AMNION
• Formed from Somatopleure
• Definition: Protective membrane that surrounds embryo forming a sac of fluid
• Formed from : somatic mesoderm and ectoderm
• Cavity is called amniotic cavity & filled with amniotic fluid
• Amniotic fluid is viscous : Provides Free flotation of embryo for its even growth
• Efficient shock absorber (to protect from mechanical injury)
• Protects embryo from dessication
• Amnion is connected to embryo at ventral hollow stalk called somatic umbillicus

16. CHORION
• The outermost layer of extra-embryonic membrane
• Involved in respiration in birds
• The wall of the chorion is made of two layers: Outer
Ectoderm & Inner somatic mesoderm

17. ALLANTOIS

19. Placenta
• Characteristic feature of viviparous vertebrates
• Not seen in egg laying animals (Yolk reserve)
• Foeto-maternal Association (To accomplish Nourishment)
• Placenta in mammals
• Egg laying mammals: Lactate (but no placenta)
• Marsupials /Therians (Kangaroo) : Morphological & histological
basis
• Intimacy of foeto-maternal association
• Extra embryonic membrane comes in contact with
reproductive tract of mother and forms close association
Why placenta is form?/Functions
Carbon dioxide, oxygen , hormones, toxicants are exchanged at
placenta through network of capillaries

20. Chorio-Vitelline Placenta
• Marsupial Mammals
• Rudimentary , short lived placenta
• Milk (from Pouch) Nourishment : Nourishment from placenta negligible
• Allantois small
• Yolk sac + Chorion = Yolk Sac placenta /chorio vitelline placenta
• Blood supply though vitelline blood vessels
• Chorion does not form Villi

21. Yolk sac placenta

23. Chrio-allantoic or allantochorionic placenta
• Yolk sac rudimentary
• Chorion + Allantois fuse together
• Chorion developes villi to get more closely associated with maternal mucosa
• Seen in Marsupials & Eutherians

28. Chorionic Placenta
• When allantois and chorion association is insignificant or
absent Based on type of embryo implantation in uterine wall
and attachment with embryo
• Central/Superficial Implantation
• Eccentric Implantation
• Interstitial Implantation

29. Central/Superficial Implantation
Embryo remains In centre of uterine lumen & extra-embryonic
membrane make superficialcontact with
Uterine mucosa
Eg. Lower mammals : marsupials , eutherians (Dogs, sheep, cat ,
cow, rabbit)
Eccentric implantation : Embryo lies on one side of endometrial
wall
Embryo is not entirely covered entirely by uterine epithellium
Eg. Mouse & rat
Interstitial implantation
Embryo is completely buried inside the uterine mucosa
Embryo is completely covered by endometrial tissue
Eg. Human , chimpanzee , guinea pig

36. TYPE OF PLACENTAE
Based on implantation
• Central/Superficial
Implantation
• Eccentric Implantation
• Interstitial Implantation
Based On Morphological
characteristic features
• Diffused
• Cotyledonary
• Zonary
• Disocoidal
• Intermediate
Based on intimacy of foeto-
maternal tissue
• Non-deciduous placenta
• Deciduous placenta
• Contra-deciduous placenta
Based on Histological
characteristics
• Epithelio-chorial placenta
• Syndesmo-chorial placenta
• Endothelio-chorial placenta
• Hemo-chorial placenta
• Haemo—endothellial placneta

37. Based On Morphological
characteristic features
• Diffused
• Cotyledonary
• Zonary
• Disocoidal
• Intermediate

38. • DIFFUSED PLACENTA
Villi are distributed uniformly on the surface of the chorion except
terminal ends
It is seen in: Mare, pig etc
• COTYLEDONARY PLACENTA
• Villi are developed in patches on chorionic surface while remaining
part of chorion is smooth
• These patches are called as cotyledons
Sheep, goat, cattle
Based On Morphological characteristic features

39. • INTERMEDIATE PLACENTA
Combination of diffused & cotyledonary placenta.
There are some isolated villi present between cotyledonary patches
Eg. Camel &Giraffe
• ZONARY PLACENTA
• Villi are developed along a equatorial belt on blastocyst.
• This belt is usually elliptical in shape
Eg. Carnivores like dog, fox, lion, tiger, mongoose
• DISCOIDAL PLACENTA
• Villi are confined in a disc like area, eccentrically on blastocyst.
• Eg. Rat , Bat, Rabbit , Bare, monkeys

57. THANK YOU
COMPARATIVE EMNBRYOLOGY
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