Extraembryonic Membranes and Placentation Flashcards
vertebrates are characterized by having and extra embryonic membrane called
the amnion
what vertebrates have the amnion
reptiles, birds, mammals
how many extraembryonic membranes develop?
4
what is the first membrane to form
yolk sac
yolk sac derived from
extraembryonic endoderm
yolk sac is continuous with what
the primitive embryonic gut (midgut of GI tract);
what is the connection between the yolk sac and gut
yolk stalk or vitelline duct
the mesoderm that associates with the endoerm of yolk sac is the
splanchnic mesoderm
complete wall of the yolk sac is composed of
endoderm and splanchnic mesoderm
endoderm and splanchnic mesoderm is called
splanchnopleure
flat disc
C shaped embryo with mid-ventral opening
flat disc expands in what direction
cranially, caudally, and lateroventrally
what extends through the opening in the flat disc
yolk sac
what is the amnion
membrane that surrounds the embryo and separates it from immediate contact with environment
the amnion is derived from and continuous with the
ectoderm
amnion eventually forms what
outer layer of umbilical cord
mesoderm associated with ectoderm of amnion is
somatic mesoderm
complete wall of amniotic sac is composed of
ectoderm and somatic mesoderm
ectoderm and somatic mesoderm are called
somatopleure
what is the amniotic cavity
space between embryo and amnion
what is the function of the amniotic fluid that fills the amniotic cavity
keeps embryo/fetus moist; protects from dessication
protect and cushion of embryo/fetus from physical forces
prevents adhesion of embryo/fetus to surroundings
what are the sources of amniotic fluid
fetal urination
(continuously recycled: fetus urinates, swallos, abosred by fetal GI, and returned to maternal circulation via umblical vessels and placental exchange)
maternal plasma
chorion membrane forms where
outside the amnion
chorion is derived from
fetal ectoderm and trophoblasts
what mesoderm associates with ectoderm of chorion
somatic mesoderm
complete wall of chorion is composed of
ectoderm and somatic mesoderm
ectoderm and somatic mesoderm is
somatopleure
what is the mesoderm lined space between the amnion and chorion
extraembryonic coelom;
the body cavity associated with embryo body
intraembryonic coelom
what is the last membrane to develop
allantois
allantois is derived from
endoderm with splanchnic mesoderm
what is the complete wall of allantois called
splanchnopleure
diverticulum of hindgut enlarges into
space between amnion and chorion (extraembryonic coelom)
diverticulum of hindgut attached to
allantoic stalk
diverticulum of hindgut ____ system
extensive blood vessel system
what is also produced during allantois development
storage area for excretory substances produced during development
ovary of a bird ovulates ____ ova
yolk-rich
what makes up a majority of the avian reproductive tract
the oviduct
in the oviduct, there are secretions of ______ that surrounds the ova/zygote
albumen and fibrous membranes
what creates the hard shell of the egg
shell gland
where and when does fertilization occur in the avian
in the oviduct; before albumen and shell are added
can chickens lay unfertilized eggs?
yes
following gastrulation, extraembryonic germ layers (splanchnic mesoderm and endoderm or splanchnopleure) do what
expand over the yolk
avian yolk stalk formed connecting yolk sac with
embryonic/fetal gut
yolk is absorbed from sac
endothelial blood vessels, connect with blood vessels in splanchnic mesoderm and pass to embryo
yolk sac decreases in size as
embyro uses yolk (nutrition)
yolk eventually drawn into abdominal cavity and
incorporated into small intestine
when is the last of the yolk absorbed
shortly after hatching
avian amnion and chorion
“paired” folds; ectoderm, extraembyronic mesoderm, and trophoblasts (somatopleure) form
elevates
chorioamniotic folds
chorioamniotic folds expand ____
dorsally
chorioamniotic folds meet and fuse over _____ of embryo creating ______
dorsal midline; 2 layers of somatopleure (inner layer is amnion, outer layer is chorion)
avian allantoic splanchnic mesoderm fuses with
yolk sac splanchnic mesoderm
amnion somatic mesoderm
chorion somatic mesoderm of apposed to inner membrane of shel
vascularization of chorioallantoic membrane allows
o2/co2 exchange across shell
what happens to albumin during incubation
albumen loses water (increases in viscosity) and decreases in volume
expanding chorioallantoic membranes surrounds =
albumen sac
communication develops between albumen and amniotic cavity; how does embryo get nutrients?
embryo swallows
as embryo grows, _____ decrease in size
albuen sac
remaining albumen sac incorporated into
yolk sac (fuses with vitelline-allantoic membrane)
2 fibrous membranes are added around albumen
inner and outer
inner membrane eventually contacts with _____
chorion
outer membrane contacts
eggshell
what forms between the two membranes
air sac or air cell for gas exchange
what is an eggshell
a mineralized (calcium carbonate) or protein matrix
how does gas exchange occur
has pores to allow for gas exchange (allows air in and out of air sac)
when the egg is laid, the embryo is a ____
blastocyst
____ are just beginning to form
fetal membranes
the egg itself is mostly
yolk and ablumen with the embryo only a small disc sitting on the yolk
as the embryo grows, it will fill the eggshell, it and fetal membranes expand as albumen
decreases
yolk sac of mammalian extraembryonic membranes
develops even though there is no yolk
may belarge in early embryo before placenta established
yolk sac placenta also known as
choriovitelline placenta
yolk sac placenta has extensive contact with
chorion
yolk sac becomes highly vascularized and absorbs
nutrients and oxygen
yolk sac placenta is definitive placenta of
most marsupials
yolk sac placenta is temporary placenta for
many mammals (excluding humans)- does not establish extensive, intimate contact with endometrium
amnion and chorion initial development is much like avian including
body folds (head fold, tail fold, lateral body fold) and chorioamniotic folds
chorion becomes
integral part of placneta
amnion expansion forms
umbilical cord encompassing umbilical vessels and allantoic stalk; grows as development proceeds
allantois fuses with
chorion to become part of the placenta (chorioallantoic) to establish extensive contact with endometrium
some marsupials develop ____ for the short intra-uterine development
primitive allantoic placenta
what is a placenta
an organ composed of maternal and fetal components
what are the functions of the placenta
O2/CO2, nutrient and waste exchange
acts as an endocrine organ (progensterone or chorionic gonadotropin in mares);
regulated barrier betwen fetal and maternal circulation
what is the placental labrynth
interdigitating folds, increased surface area for exchange
what determines the gross characteristics of the placenta
chorionic villi and relationship with endometrium
what animals have diffuse
horse and pig
what is diffuse
entire chorioallantois
what animals have cotyledonary
ruminants
what is cotyledonary
small areas of chorioallantois (cotyledons) attach to caruncles (maternal); together called placentome
what animals have zonary
carnivores
what is zonary
circumferential area of mid-chorioallantoic
discoid occurs in what animals
primates and rodents
what is discoid
disc-shaped area of chorioallantois
placenta is a ___ structure
layered
fetal layers include
fetal endothelium/fetal capillaries (deepest layer) fetal CT fetal epithelium (chorionic feal membrane ectoderm/trophoblasts)
maternal layers include
uterine epithelium
uterine CT
maternal vascular endothelium of capillaries
what animals have epitheliochorial placenta
horse, donkey, pigs
what is epitheliochorial
endometiral epithelium with chorionic epithelium; endometrial epithelium remains intact
syndesmochorial placenta is found in
ruminants
what is syndesmochorial layers
uterine connective tissue with chorionic epithelium; removal of uterine epithelium; single epithelial layer (contains epithelial cell of fetal and maternal origin)
adhered only at cotyledons
endotheliochorial occurs in
dogs and cats
endotheliochorial layers
endometrial capillaries with chorionic epithelium
uterine epithelium and uterine connective tissue removed
hemochorial occurs in
rodents and primates
hemochorial laers
maternal blood and chorionic epithelium; uterine epithleium, uterine connective tissue, and endometiral capillary endothelium removed
canine/dog degree of implantation
conjoined/deciduate
feline degree of implantation
conjoined, deciduate
ruminants, equine, and porcine degree of implantation
apposed, nondeciduate
endometrial cups are unique in the
horse
what are endometrial cups
ulcer like structures (2mm to 5 cm) developed at chorionic girdle
how do these endometrail cups develop
fetal epithelial cell migrate into endometrial stroma and burry themselves; causing discrete, pale raised plaques in endometrium; triggers an immune response necessary for survival of pregnancy
endometrial cups are a source of
chorionic gonadotropin
endometrial cups develop at day
35 of gestation
endometrial cups regress at day
120 of gestation
once endometrial cups are formed, will termination of pregnancy alter course?
no; pregnancy serum will test positive until cups regress; and estruss will not resume until cups have regressed
