Fertilization And Gastrulation Flashcards
What are the two different calendars for human development and what is the difference?
- Obstetrical/gestational calendar: starts of the first day of the last menstrual period
- Ovulatory Calendar: starts at fertilization
There is typically a 2 week difference between the calendars.
What is the corona radiata?
Follicular cells that surround the oocyte.
What is the zone pellucida?
It is the layer after the corona radiata, composed of a glycoprotein network.
What is the perivitelline space?
Between the zona pellucida and the egg, releases granules with enzymes including esterase, acrosin, neuraminidase
What specialized organelle in the sperm is crucial for fertilization?
The acrosome at the head.
Full of enzymes: hyaluronidase
Why do sperm have so many mitochondria?
Because they need lots of ATP to swim
What events happen during week 1 of human development?
- Fertilization
- Cleavage
- Formation of the blastocyst
- Formation of the inner cell mass
- Implantation
Where does fertilization occur?
In the ampulla: the distal third of the tube
What is capacitation?
Where does it take place?
How long does it take?
- The removal of the glycoprotein coat and the seminal plasma protein.
- Happens in uterus
- Takes 7 hours
*Sperm cannot fertilize without going through capacitation.
What is the zona reaction
It is a block to polyspermy.
Conformational change in the zona, becomes more rigid, traps and blocks sperm
What happens after the block to polyspermy?
The membrane of the winning sperm and of the oocyte fuse
After the fusion of sperm and egg…..
There is the completion of second meiotic division, formation of the male pronucleus, and the fusion of male and female pronuclei
What is the gist of cleavage?
When does it start?
Zygote divides, making a bunch of tiny cells, but there is no time to grow them.
Starts 30 hours after fertilization
How many cells is a morula?
What day does it form?
12-32 cells
When does the blastocyst enter the uterus, and what happens there?
Enters day 3-4.
Fluid diffuses in and creates the blasocytic cavity on day 5
What part of the blastocyst gives rise to the embryo?
The inner cell mass
When does hatching occur?
What is it?
Starts day 5, done by day 7.
Degeneration of the zona pellucida
What are 3 assisted reproductive technologies?
- In vitro fertilization and embryo transfer
- Cryopreserevation of embryos
- Intracytoplasmic sperm injection
Describe the trophoblast.
- What does it secrete
- What does it give rise to.
- What do those things do?
- Secretes early pregnancy factor: an immunosuppressant that protects the embryo from destruction. Produced during first 10 days.
- Trophoblast becomes cytotrophoblast (mitotically active stem cell layer) and the Syncytiotrophoblast (secrete proteolytic enzymes, hCG, responsible for implantation and initial sign of pregnancy.
Two kinds of hyadtidiform mole, describe them
- Complete: empty oocyte fertilized by one sperm that duplicates its DNA, or by two separate sperms
- Partial: normal oocyte fertilized by two sperm.
- clinical features include vag bleed, pelvic pain, enlarged uterus, hyperemesis gravidarium
What is choriocarcinoma?
Malignant tumor which develops from hydatidiform mole
Mets include liver, lungs, vagina, intestine, bone, and brain
What happens during week 2 of development
Formation of bilaminar disk and further implantation
The inner cell mass becomes 2 things during week 2, describe them.
Epiblast: will give rise to ectoderm, amnion, and amniotic cavity
Hypoblast: is temporary and will only be present in week 2
What does the hypoblast give rise to?
It actually holds the place for the endoderm which will become the following:
- The prechordal plate
- Primary and secondary yolk sac
- Extraembryonic mesoderm
What is the function of the prechordal plate
Fuses to the epiblast and is the future location of the mouth and organizational center for the head
What is the difference between the primary and secondary yolk sac?
Time.
The primary yolk sac becomes the secondary yolk after pinching off and becoming smaller.
Where does extraembryonic mesoderm come from
Arise from parietal endoderm
Describe the extraembryonic somatic mesoderm:
Lining covering the trophoblast and covering the amnion (next to the ectoderm)
Describe extraembryonic splanchnic mesoderm:
Lining the yolk sac/umbilical vesicle (next to the endoderm)
Describe the connecting stalk
- this becomes the umbilical chord
- this point is not fixed, moves
- extraembryonic somatic mesoderm
Where does primitive blood develop?
In the extraembryonic splanchnic mesoderm
In the walls of the yolk sac
What is the chorion?
- Becomes a layer of the placenta.
- Arise from the somatic mesoderm
Where does implantation occur?
At the posterior wall of the uterus.
implantation outside of the uterus is referred to as what?
Ectopic pregnancy.
Some can be viable, but become dangerous to the mother
Describe placenta previa
Occurs when implantation occurs over the internal cervical os.
Can be marginal, partial, or total.
Placenta can sometimes move superiorly and correct the mistake.
What must you do before examination if you suspect placenta previa?
ULTRA SOUND.
A digital exam could rupture the placenta and mom could bleed to death
What is Gastrulation and when does it occur?
Gastrulation is the formation of all 3 germ layers (which give rise to all tissue types)
Happens in week 3
What happens in week 3
Gastrulation, Neurulation, and heart formation
What are the three layers of Gastrulation, and what do they become?
Ectoderm: skin, hair, nails, brain, spinal cord
Mesoderm: muscle, bone, blood, heart, spleen (connective tissues)
Endoderm: lungs, GI, bladder, glands (tonsils, parathyroid, thyroid)
Describe the primitive streak
There is a proliferation and migration of cells.
- the number of cells causes an envagination.
- the cells that envaginate first become true endoderm.
- cell that envaginate further come true mesoderm
*as the cells envaginate, they receive molecular signals that determine their fate (endo or mesoderm)
**all of these cells replace the hypoblast
Describe the notochord
- midline mesodermal structure
- extend from primitive node to prechordal plate
- longitudinal axis for embryo
- provide template for vertebral column
- induce formation of neural plate
In what direction does the notochord migrate
From primative pit towards the head
Describe notochord formation
- between ectoderm and endoderm
- form tube called notochordal process
- notochordal process fuses with the endoderm»notochordal plate
- notochordal plate allows amniotic cavity and primary yolk sac to communicate
- notochordal cells round back up and form the proper notochord
Describe chordomas
- rare and slow growing neoplasm of bone
- arise from remnants of notochord
- occur in axial skeleton
What is the allantois?
- at posterior midline
- pouch from wall of yolk sac
- endodermic structure
- template for umbilical arteries and veins
- becomes urachus (important when forming the bladder)
Three bits of mesoderm, what are they and what do they become?
- Paraxial»Somites
- muscle (myotome)
- vertebral skeleton (scleratome)
- dermis (Dermatome) - Intermediate»Urogenital
- kidneys
- gonads - Lateral plate (somatic layer is dorsal, near ectoderm. Splanchnic layer is ventral, near endoderm.)»Connective tissues
- blood
- lymph
- Mesenteries
- cardiovascular
