Embryology I and II Flashcards
ovulation
the release of a maturing egg (ovum) from an ovarian follicle at the surfaces of the ovary
How long is the developing zygote a blastocyst?
weeks 1-2
How long is a zygote an embryo?
weeks 3-8
How long is a zygote a fetus?
weeks 8-term
Which period generates most birth defects?
weeks 3-8 during the embryo stage
fimbriae
a structure of the uterine tube that covers the ovary and guides the ovum into the uterine tube
Where does conception usually take place?
the distal third of the uterine tube
morula
a tight ball of cells that is formed shortly after fertilization
forms by day 4
components of the blastocyst
outer shell, trophoblast, inner cell mass, amnion, and yolk sac (umbilical vesicle)
forms by day 5
implantation
the blastocyst normally sinks into the upper posterior uterine wall (endometrium or decidus)
two components of the trophoblast
outer syncytiotrophoblast (syntrophoblast) and inner cytotrophoblast
chorion
consists of the syntophoblast, cytotrophoblast, and extra-embryonic mesoderm
amnion
consists of ectoderm and its extra-embryonic mesodermal coat
yolk sac (umbilical vesicle)
consists of endoderm and extra-embryonic mesoderm
What happens 10 days post-fertilization?
syncytiotrophoblast layers differentiate
yolk sac forms
extraembryonic mesoderm appears
What happens days 11-13 post-fertilization?
extraembryonic mesoderm cavitates
implantation nears completion
What structures do the extraembryonic mesoderm (mesenchyme) form?
connective tissue core of the villi and the blood vessels
What happens to the cytotrophoblast?
disappears midway through pregnancy
sites of ectopic pregnancies
tubal, abdominal, ovarian, cervical
origin of the syncytiotrophoblast
forms from the outer part of the trophoblast
origin of the hypoblast (future endoderm)
differentiates from inner cell mass
which cells of the trophoblast generates the embryo
epiblast + hypoblast
main event sof the second week of development
implantation and extra-embryonic membrane formation
three layers of the chorion
syncytiotrophoblast, cytotrophoblast, and mesoderm forming the connective tissue core of the villus
extraembryonic coelom
forms as the extraembryonic mesoderm becomes hollow
smooth corion
covers the amnion
villous chorion
conists of the placental villi, the primary components of the placenta, both are derived fromt he trophoblast
decidua basalis
the maternal component of the placenta
decidua capsularis
the “bag” with chorion and amnion
decidua parietalis
the uninvolved uterine mucosa
anchoring villi
extend through the thickness of the placenta to connect with the decidua basalis
free villi
branch from the anchoring villi for many generations, bathed directly in maternal blood as the site of metabolic exchange
cytotrophoblastic shell
at the interface between the villous chorion and decidua basalis, firmly attach the placenta to the endometrium
at birth the shell and villous chorion separate from the decidua basalis and are expelled with the fetal membranes as “afterbirth”
cotyledons
circular, convex structures on the placental surface that are formed from the decidua basalis as the connective tissue septa extend into the villous chorion
primitive not (or node)
forms a midline cord of mesoderm, the notochord
primitive streak
ectoderm behind the primitive knot that ofrms all the rest of the intraembryonic mesoderm
notochord
induces the neural plate, only remains as the nucleus pulposis of intervertebral discs
paraxial columns
form segmental somites bone, muscle and dermis of skin
intermediate columns
contribute to the urogenital system
lateral plates
forms pleura, peritoneum, and connective tissue of organs and body wall
development of monozygotic vs. dizygotic twins
dizygotic twins - two chorions, two placentas, two amnions
monozygotic twins - one chorion and one placenta, but two amnions
What happens in week 3 of development?
gastrulation - creates a third germ layer, elongation of the embryonic disc
neural tube
forms as the ectoderm in front of the receding primitive streak, induced by the notochord to form a thickened, ectodermal, neural plate, which will invaginate and sink into the embryo as the neural tube
neural crest
cells from here pinch off during tube formation and play an important role in forming peripheral nerves and many tissues in the head and neck
prechordal plate
the future oropharyngeal membrane
intra-embryonic mesoderm
primitive streak and node give off cells which made up this third embryonic germ layer
four structures formed by condensation of the intra-embryonic mesoderm
notochord
paraxial mesoderm
intermediate mesoderm
lateral plate
connecting stalk
the only physical connection between the embryo and placenta, shifts toward the tail-end of the embryo and will form the umbilical cord
oral and cloacal membranes
sites of the future mouth and anus, respectively, where ectoderm remains in firtm contact with the endoderm
cardiogenic plate
mesoderm in front of the oral membrane (derived from the primitive streak) that will form the heart
the heart starts functioning by day 21
allantois
a vestigial membrane in humans consisting of an endodermal evagination of the yolk sac into the mesoderm of the connecting stalk
the fourth and final extra-embryonic membrane
will shift from the yolk sac (umbilical vesicle) to the hindgut of the GI tract within the embryo
notochord
disc nucleus pulposis
induces neurulation
paraxial mesoderm
future somites for bone, muscle, C.T.
intermediate mesoderm
future UG system including kidneys and gonads
lateral plate
future body wall and cavities
gut wall
function of yolk sac
nourishes embryo early on, but later there is no yolk
later becomes the first source of embryonic blood cells
shaping the gastrula
the aminon begins to tuck around the side of the tri-laminar disc to form a cylinder
it also tucks around the head and tail
somatopleure
surface ectoderm plus mesoderm from the lateral plate
forms the basis of the lateral and ventral body wall
eventually forms the skin of the limbs and all of the connective tissue components
splanchnopleure
ectoderm plus mesoderm from the lateral plate
will form the visceral structures such as walls of the gut tube and the mesenteries that support it
myotomes
somite mytotomes migrate into the somatopleure
parietal pleura and peritoneum
line their respective body cavities and develop from somatopleure
form the innermost layer of the body wall
mesenteries
two sheets of visceral peritoneum (with some fat and connective tissue) that suspend the gut tube from the body wall and provide a route for vessels and nerves to supply the gastro-intestinal organs
visceral peritoneum and pleura
develop from splanchnopleure and form the mesenteries and the coverings of the visceral organs
septum transversum
a transverse condensation of primitive streak mesenchyme that separates the thoracic (pleural) and abdominal (peritoneal) cavities just caudal to the developing heart
it will form part of the diaphragm and the connective tissue framework (stroma) of the liver
splanchnopleure
the source of most GI organs, buds off of the gut tube
GI tube itself will form the pharynx, esophagus, stomach, small an d large intestines, and the rectum
somites
form skeletal muscles, bones, and dermis of the skin in the back
