Placentas and
Embryos
Animal Breeding
Pensacola Jr College
Trophoblast Formation
w Blastula splits à inner cell mass + trophoblast
w Inner cell mass à gastrulation, neurulation, becomes embryo
w Trophoblast à extraembryonic membranes
Trophoblast
Differentiation
w 3 extraembryonic membranes
form:
• Amnion = directly surrounds
and cushions embryo
• Allantois = vascular
membrane pouch connected to bladder of embryo, collects wastes
• Chorion = outer membrane, gas exchange
Platypus Egg
Mammal
Placentation
w Allantois and chorion fuse
in part (allanto-chorion) and attach to uterine endometrium à placenta
w Blood vessels of embryo and
mother come into contact
w Species differences:
• Delayed implantation
• Delayed development
Placental
functions
w Oxygen + nutrients from
maternal blood à placenta à embryonic circulation
w Carbon dioxide and waste
products from embryonic blood à placenta à maternal circulation
Comparative
Placentation
w Different orders and species
of mammals develop different placental types
w Classification based on:
• Structure of attachment =
how do the projections from the embryo physically attach
• Degree of attachment = how
close is maternal / fetal blood
Structure of
Attachment
w Diffuse
w Discoidal
w Cotyledonary
w Zonary
Structure of
Attachment
Diffuse
w Loose attachment
w Chorionic villi extend all
over into endometrial folds
w Horses, pigs
Structure of
Attachment
Red River Hog
placenta
Indian Rhino
placenta
Indian Rhino
placenta
Discoidal
w Chorionic villi extend into
endometrium within a circular plate
w Rodents, primates
Structure of Attachment
Golden Lion
Tamarin placentas
Porcupine placenta
Cotyledonary
w Chorionic villi extend into
caruncles (lumps of uterine endometrium)
w The spots of placenta formed
are cotyledons
w Cows, deer
Structure of
Attachment
Bongo placenta
Giraffe placenta
Zonary
w Chorionic villi extend into
endometrium in a ring around embryo
w Carnivores
Structure of
Attachment
Dog placenta
Dog placenta
Indochinese Tiger
placenta
Degree of
Attachment
w Epitheliochorial
w Endotheliochorial
w Hemochorial
w Hemoendothelial
Epitheliochorial
w No layers eroded
w Uterine epithelium opposes
epithelium of allanto-chorion
w Hoofstock
Red River Hog
placenta
Deer placenta
Elk placenta
Endotheliochorial
w Erosion of uterine
epithelium and connective tissue
w Uterine blood vessels oppose
epithelium of allanto-chorion
w Carnivores
Cat placenta
Hemochorial
w Erosion of all maternal
layers
w Maternal blood cells oppose
epithelium of allanto-chorion
w Primates
Orangutan placenta
Spider monkey
placenta
Hemoendothelial
w Erosion of maternal layers +
epithelium and connective tissue of allanto-chorion
w Maternal blood cells oppose
blood vessel walls of allanto-chorion
w Rodents
Porcupine placenta
Spring Hare
placenta
Embryo Development
Review
w Zygote
w Cleavage
w Morula
w Blastula / Blastocyst
w Gastrula
w Neurula
Differentiation
w Cells begin to specialize
for different purposes within different regions of the body
w Some parts of the genetic
material are “turned off” temporarily or permanently
w Totipotent = cells that
retain the ability to become any part of the body