Lecture 1 Flashcards
Human embryonic development takes an average of ____________ and is composed of two stages __________
38 weeks.
- embryonic period
- Fetal period
First 8 weeks of embryonic development is called _______________
Embryonic Period
remaining 30 weeks of embryonic development is called___________________
Fetal Period.
_________ develops in ovary.
Oocyte
After ovulation, THE Oocyte IS transported to ______ by __________________
uterus, uterus by muscular contractions of the fallopian tube and the cilia lining the tube.
Oocyte is a _________ cell
haploid cell, containing only 1 copy of each chromosome
The Oocyte remains ______ within the fallopian tube for approximately 12 hours.
viable
The oocyte is surrounded by a ___________, a thick extracellular matrix called ___________
plasma membrane
zona pellucida
The additional layer of cells that surround the oocyte
the corona radiata.
Sperm are___________ and are attracted to the oocyte.
haploid cells
Sperm ______________ a pathway through these membranes to fertilize the oocyte.
enzymatically digest
Critical that only one sperm fertilizes the oocyte, and all others are inhibited______________ after the first sperm has entered
by chemical changes
induced in the zona pellucida
Unequal contribution of cytoplasm -
small amount of cytoplasm derived from the sperm compared
to the enormous amount derived from the oocyte.
Sperm and oocyte contribute
equal amounts of genetic material
Nuclear fusion takes ______________
approximately 12 hours
______________ the formation of a single diploid cell from the two haploid cells oocyte and sperm
nuclear fusion
24 hr after fertilization the __________ forms from _________
mammalian zygote, cleavage
___________ the series of mitotic divisions by
which the enormous volume of egg cytoplasm is divided into smaller cells.
cleavage,
Cells formed by cleavage divisions are called _____________
blastomeres.
As cleavage continues, more cells are formed. ______________ continues to surround the cells,
maintaining a constant diameter of the embryo.
The zona pellucida
At the 16-32 cell stage, the embryo is called __________
a morula.
During morula stage, Initially dividing cells are round, but then
become compacted with junctions between them.
• Embryo differentiates into ___________________
external and internal cells
Sphere of ________________ will become the embryonic contribution to the placenta.
external cells
Inside the sphere are a small number of__________ that give rise to the embryo.
internal cells
External cells differentiate into _________ and continue to divide and secrete fluid into the
middle of the morula to create the ___________
trophoblasts
blastocyst cavity.
Internal cells are compacted into the_____________
inner
cell mass.
As the blastocyst expands, the_______ degenerates, in preparation for ________________
zona pellucida
implantation
The __________ keeps developing embryo from attaching to fallopian tube lining until it reaches the uterus.
zona pellucida
Fertilization usually occurs in the ______________
lateral third of the fallopian tube.
By day 3, the embryo is a
compact ball of cells. By day 4, it contains about 60 cells and has reached the uterus. Fluid is secreted
into the middle of the morula forming a _________
blastocyst.
After the zona pellucida degenerates, trophoblast cells adhere to, and burrow into __________
the lining of the
uterus or endometrium.
Trophoblast cells proliferate and form two layers:
one maintains cellular membranes around the
embryo
the other fuses into a multinucleated mass,that invades the uterine lining.
the other fuses into a multinucleated mass ___________ that invades the uterine lining.
syncytium,
After the blastocyst is deeply embedded in the uterine lining, “holes” form in the outer trophoblast
layer and __________________
fill with maternal blood. Embryo is now in contact with its source of nourishment
Placenta is derived from both
embryonic trophoblast and maternal endometrial cells.
during the second week, inner cell mass grows and divides into 2 sheets of cells, forming a ________________
bilaminar disc.
Inner cell mass segregates into 2 layers:
epiblast (upper germ layer illustrated in blue) and
hypoblast (lower germ layer in yellow).
Extensions of these cell sheets form 2 fluid filled sacs:
epiblast forms the amniotic sac
hypoblast gives rise to the yolk sac.
________________ is filled with amniotic fluid that protects embryo from physical injury.
Amniotic sac
_____________ is not an important food source.
yolk sac
In order for the bilaminar disc to transform into a 3-layer structure, a raised groove called the
___________ forms in the epiblast.
primitive streak
The primitive streak ends in the ____________
primitive node.
________________ Changing from a 2 to a 3-layered disc
Mesoderm formation
Epiblast cells move inward at the primitive streak. Initially they displace the hypoblast and form_____________ ____________________________
endoderm but then they form the third germ layer, mesoderm.
_____________ gives rise to sheets of tightly joined cells on outside of the body (skin).
Ectoderm
_____________ gives rise to sheets of tightly joined cells inside the body (digestive & respiratory tracts).
Endoderm
_____________ gives rise to everything else. Mesodermal cells migrate widely and give rise to tissues
such as muscle and bone.
Mesoderm
Epiblast cells invaginate at the primitive node and migrate anteriorly to form __________
dorsal mesoderm.
_________________ forming at the large arrow will become the notochord, a transient structure found in the
midline that divides the body into right and left halves.
Mesoderm
____________ has an important developmental function - it induces the formation of the nervous
system.
Notochord
The primitive streak is later reduced to a strip of __________________
epidermis over the coccyx.
______________ part of the embryonic disc corresponds to the top of the future head.
Dorsal-most
Events by which the notochord induces ectoderm cells to form the nervous system are called
____________
neurolation
Ectoderm in the dorsal midline thickens - called the ______________________
the neural plate.
Edges of the neural plate begin to fold toward each other called the ___________
neural folds.
Neural tube develops into ____________________
the
central nervous system (i.e., brain and spinal cord).
Neural crest cells migrate
throughout the body developing_________________
into the peripheral nervous system.
Ectoderm that will become ___________ is shown in dark blue -
neural crest
Ectoderm that will become the__________ is shown in light blue -
neural tube
Ectoderm that forms ____________ is shown in medium blue and forms the skin covering the spine
epidermis
• The neural plate ____________ as the embryo grows.
•
enlarges dorsally
The neural groove forms and neural
folds meet in the midline to form the ____________
neural tube. Somites (~40 pairs) are adjacent to neural tube.
Neural tube closes first near the middle of the embryo and then proceeds both______________
rostrally and caudally.
If closure is incomplete caudally, ,________________________
closure is incomplete
rostrally___________________
the child is born with spinal bifida.
, the brain will not develop.
Animation shows how the embryo’s body changes from a flat disc into _____________
a 3-dimensional cylinder
Main force responsible for embryo folding is differential growth of tissues - ____________
ectoderm expands more
than endoderm.
Cross-section of an embryo illustrates the neural tube and derivatives of mesoderm: __________________
notochord,
somites, intermediate mesoderm and lateral mesoderm.
The ectoderm grows more vigorously than yolk sac, becoming convex in shape. Ectoderm then
grows together ventrally, forming the ventral midline of the body.
Middle stage ~ Day 25
Ectoderm then
grows together ventrally, forming the _____________________
ventral midline of the body.
The mesoderm differentiates – the medial part of the somite forms _________ whereas the
lateral mesoderm divides into ________________
the sclerotome
somatic mesoderm and splanchnic mesoderm.
Most of the yolk sac is folded inside the embryo, forming
•
the gut tube.
Somites divide into 3 parts:
1) Sclerotome forms the vertebral column and ribs.
2) Myotome forms the limb and trunk muscles.
3) Dermatome gives rise to the dermis.
___________ forms the vertebral column and ribs.
Sclerotome
__________ forms the limb and trunk muscles.
Myotome
____________ gives rise to the dermis.
Dermatome
_______________ gives rise to kidneys and gonads.
Intermediate mesoderm
_________________ forms membranes that surround viscera & gives rise to heart
and blood vessels.
Splanchnic (visceral) mesoderm
_________________forms membranes that line the body cavity. The coelom, or ventral
body cavity, is surrounded by lateral mesoderm
- Somatic (body) mesoderm
Animation that presents embryo folding from the
sagittal perspective Heart Development
Condensations of mesoderm at the rostral end of the embryonic disc give rise to ____________
the heart.
• Condensations form a pair of tubes that fuse,________________________
giving rise to the primitive heart tube.
• Primitive heart tube folds up and twists around to form the ________________
four-chambered heart.
• Embryonic heart is beating and pumping blood by _______________________
1 month in utero.
Endoderm attached to the yolk sac folds inward, forming ___________________
the major divisions of the gut (foregut,
midgut, and hindgut).
• Tissues derived from endoderm differentiate into
linings of respiratory, gastrointestinal, and
urogenital systems:
___________ differentiates into the mouth, pharynx, esophagus, lung buds, stomach, and part of the
small intestine.
Foregut
__________ differentiates into the remainder of the small intestine and two-thirds of the large intestine.
Midgut
____________ differentiates into the remainder of the large intestine, rectum and urogenital system.
Hindgut
• There is a common pattern to all vertebrate development.
__________ forms skin and the nervous system.
- Ectoderm
_______ forms connective tissue, blood cells, heart, bone, and muscle.
mesoderm
______________ forms the lining of respiratory and digestive tubes.
Endoderm
