fertilization happens where most of the time? And does not ever happen where?
The usual site of fertilization is the ampulla of the uterine tube, its longest and widest part. If the oocyte is not
fertilized here, it slowly passes along the tube to the uterus, where it degenerates and is resorbed. Although
fertilization may occur in other parts of the tube, it does not occur in the uterus.
1, 2, 3
the head, containing the nucleus and acrosome on the head tip
the acrisome contains what and does what?
the enzyme released from the acrisome called Acrosin digests the zona pellucida and membrane of the oocyte.
also the penetration of the corona radiata is done by releasing hyaluronidase from the acrosome to digest cumulus cells surrounding the oocyte
4 and 5
the mid connecting piece and it contains many large fused mitochondria
the tail is called what?
it's called the axial filament
what protein in the zona pellucida is responsible for binding the sperm?
zp3 bind the sperm, and is believed to only bind to human sperm. zp3 is also deactivated with the acrisome reaction
Part of the sperm's cell membrane then fuses with the egg cell's membrane, and the contents of the head sink into the egg. what happens next? what is this called?
slow block to polyspermy
after the fast block, the slow block to polyspermy is the Cortical Granule Response and release of enzymes that deactivate the ability for sperm to bind the zona pellucida
Part of the sperm's cell membrane then fuses with the egg cell's membrane, and the contents of the head sink into the egg. what happens next (immediately)? what is this called?
Fast block to polyspermy
Seconds after fertilization the membrane potential of the egg undergoes a large depolarization via a massive influx of Na+ ions. This depolarization is similar to a neuronal action potential in that it breaches voltage threshold, however, the egg’s depolarization takes about a minute to repolarize via K+ leakage. This is the fast block to polyspermy: sperm cannot fuse to a membrane that is not -70mV.
to avoid multiple sperm binding!!!
upon addition of the sperm dna, the egg is then called the _____.
once the egg begins to divide, the dividing cells are called ______.
the 2n egg is a zygote, and the dividing cells are called blastomeres.
after about 9 divisions, the blastomeres begin to undergo ______ for what reasons?
after around 12-30 divisions, the zygote is renamed what?
compaction, is probably mediated by cell surface
adhesion glycoproteins. Compaction permits greater cell-cell interaction
When there are 12-32 blastomeres, the developing human is called a morula. The morula forms 3 days after fertilization, and enters the uterus.
after entering the uterus, the morula begins to change. blastomere cells differentiate into what layers?
a fluid-filled space called the
blastocystic cavity appears inside the morula due apoptosis. The fluid passes from the uterine cavity through the zona pellucida to form this space. As fluid increases in the blastocystic cavity, it separates the blastomeres into 2 parts:
o Trophoblast (gives rise to embryonic part of placenta)
o Inner Cell Mass (Embryoblast) (gives rise to the embryo)
after blastogenesis, what happens to the blastocyst to allow further growth?
the blastocyst hatches from the zona pellucida (which is weak from the fertilization) and this allows rapid growth due to lack of the containing shell
after blastogenesis, two things happen. the cell mass differentiates and the trophoblasts differentiate
the Trophoblast starts to proliferate rapidly. It gradually differentiates into 2 layers:
Morphological changes occur in the embryoblast that result in the formation of a flat, almost circular bilaminar
plate of cells, called the embryonic disc, which consists of 2 layers:
o Epiblast – the thicker layer consisting of high columnar cells related to the amniotic cavity.
o Hypoblast – consisting of small cuboidal cells adjacent to the exocoelomic cavity.
The Syncytiotrophoblast are where and do what?
The Syncytiotrophoblast are on the outer layer of the blastocyte and produce enzymes that erode the maternal tissues, enabling the blastocyte to
burrow into the maternal endometrium.
the epiblast is important because it _____.
the epiblast cells give rise to the germ layers that form all the tissues and organs of the embryo.
1 and 5
Syncytiotrophoblast and Cytotrophoblast
9 and 8
amniotic cavity and exocoelomic (or yolk) sac/cavity
4 and 6
epiblast and hypoblast
cell layers noted by:
2 and 4
2. extra embryonic mesoderm
4. primary umbilical vesicle/yolk sack
closing plug of the endometrium
the extraembryonic mesoderm becomes two layers later down the line and one very important sac
The extraembryonic coelom splits the extraembryonic
mesoderm into two layers
- Extraembryonic somatic mesoderm, lining the trophoblast and covering the amnion
- Extraembryonic splanchnic mesoderm, surrounding the umbilical vesicle
The extraembryonic somatic mesoderm and the two
layers of trophoblast form the chorion. The chorion
forms the wall of the chorionic sac
in general what is gastrulation?
Gastrulation is the formative process by which the three germ layers and axial coordination
are established in embryos. During Gastrulation, the bilaminar embryonic disc is converted into a
trilaminar embryonic disc. Gastrulation is the beginning of morphogenesis (development of the
after implantation, where and from what cells do the pre-chordal plate form? what is the significants of the prechordal plate?
the prechordal plate are formed from hypoblastic cells in a
localized area near the head region (cranial) become columnar and form a thickened
circular area. this is the
this indicates the
future cranial region of the embryo and the future site of the mouth; the prechordal plate is also an
important organizer of the head region.
Gastrulation begins with what?
formation of the primitive streak on the surface of the Epiblast of the embryonic disc.
1, 2, 3
explain the arrows
1. Primitive groove
2. Primitive pit
3. Primitive node
1+2+3 = primitive streak
epiblast cells migrate towards the primative streak caudally and then submerge and migrate back cranially.
the cells first displace the hypoblast and form the endoderm, then the cells left in the space between the ectoderm and endoderm form the mesoderm.
4 and 5
4.the pre-chordal plate that gives rise to the endoderm of the oropharyngeal membrane, located at the future site of the oral cavity
5.Cardiogenic plate, future heart
6, 7, 8
6. Sectional edge of amniotic membrane
Future cloacal membrane
Caudal to the primitive streak there is a circular area—
the cloacal membrane, which indicates the future site of
the notocord and notocordal process is formed how?
- The notochordal process elongates by invagination of cells from the primitive pit.
- The primitive pit extends into the notochordal process, forming a hollow notochordal canal
- The notochordal process is now a cellular tube that extends cranially from the primitive node to the prechordal plate.
how does completion of the notocord happen?
- The floor of the notochordal process (The fused layers with the underlying embryonic endoderm) gradually undergo degeneration
- the interior cells grow
- Beginning at the cranial end of the embryo, the notochordal cells proliferate and the notochordal
plate infolds to form the notochord
plate infolds to form the notochord
what is the significance of the notocord?
The notochord functions as the primary inductor (signaling center) in the early embryo.
- l Defines the primordial longitudinal axis of the embryo and gives it some rigidity
- induces the development of axial musculoskeletal structures and the central nervous system (CNS)
- Contributes to the intervertebral discs
neurulation is what?
The process involved in the formation of the neural plate and neural folds and closure of the folds
to form the neural tube constitutes Neurulation
what is the primary step of neurulation and what induces it?
As the notochord develops, the embryonic ectoderm over it thickens to form an elongated, slipperlike
plate of thickened epithelial cells, the neural plate.
o Neural Plate formation is induced by the notochord.
what are the steps involved in neurulation?
the neural plate thickens and expands beyond the notocord and eventually extending cranially as far as
the oropharyngeal membrane.
the cells are growing and eventually cause a groove to form due to their growth and lack placed to expand.
they begin to expand downward into the mesoderm right above the notocord and form a deeper groove.
finally the groove becomes as tube as the top of the grooves seal together like a zipper and the neural tube pinches off from the ectoderm layer.
what are neural crest cells and what are their significance?
neural plate cells from the ectoderm that were dislodged and did not form part of the neural tube or remain on the ectoderm.
Neural Crest cells give rise to spinal ganglia (DRT) and ANS ganglia (peripheral nervous system).
significance of the neural tube?
Neural tube differentiates to form Brain and Spinal Cord, eventually forming the central nervous system (CNS).
what are the somites? when do they begin to differentiate?
the somites are the paraxial mesoderm differentiates that begins to divide into paired cuboidal bodies (paraxial mesoderm that becomes segmented),
these begin to form at the same time as the notochord and neural tube form. the intraembryonic mesoderm on each side of them
proliferates to form a thick, longitudinal column of paraxial mesoderm
the somites develope are prominent around what time? where do they begin developement and in what direction do they grow?
The somites first appear in the occipital region of the embryo (week 3-5). They soon develop craniocaudally
and give rise to most of the axial skeleton and associated musculature, as well as to the adjacent
dermis of the skin.
what are the most important things formed by the intermediate mesoderm?
ovaries and testis
Lateral mesoderm is where and is responsible for what? what are the three parts?
Lateral mesoderm is continuous with the extraembryonic mesoderm covering the yolk sac and amnion. There are two thick layers and a cavity on each side of the notocord that is known as the lateral mesoderm.
the cavity is the intraembryonic coelom (the coelom represents the future serous cavity of the
trunk: peritoneal, pleural and pericardiac cavities).
The somatopleure, which is close to the ectoderm, is involved in the formation of the lateral and ventral walls of the embryo.
The splanchnopleure, which lies on the endoblast, takes part in The formation of the wall of the digestive tube
amniotic cavity with amniotic fluid
5, 6, 7
they become what?
digestive system, pancreas, liver, inner layers of the lungs
circulatory system, out layer of lungs, skeletal system, genitourinary, muscles
skin, hair, nails, CNS,
vestigial structure and may regress, yet the homologous blood vessels persist as the umbilical arteries and veins connecting the embryo with the placenta
maternal blood pool
in the placenta, what are chorionic villi? primary, secondary and tertiary?
projections of synciotiotrophoblast (exterior) and cytotrophoblast (interior) layers that hold the fetal vein and arteries and allow diffussion through the materanl blood pool
Shortly after primary chorionic villi appear at the end of
the second week, they begin to branch.
Early in the third week, mesenchyme grows into these primary villi, forming a core of mesenchymal tissue. The villi at this stage—secondary chorionic villi—cover the entire surface of thechorionic sac (Fig. 4-14A and B).
cells in the villi soon differentiate into capillaries and
blood cells. Villi are called tertiary
chorionic villi when blood vessels are visible in them.