Fertilization and Gastrulation Flashcards
What are the structural features of a human ovum?
Corona radiate= follicular cells from the uterus
Zona pellucida= cellular amorphous proteoglycan meshwork
Nucleus= haploid 23 X chromosomes
Perivitelline space
Plasma Membrane
What are the structural features of the mature sperm?
Head made of the acrosome on the anterior 2/3 which contains enzymes and a nucleus with 23 X or 23 Y chromosomes
Neck
Tail with flagella and mitochondrial sheath for energy
What events take place during fertilization? What are their timing?
- Capacitation= glycoprotein (acrosome lid) and seminal plasma proteins removed and sperm passes through the corona radiata via Hyaluronidase, movement of sperm, and tubal mucosal proteins
- takes 7 hours as going through uteran tube - Penetration of the zone pellucida via esterases, actosin, and neuramindiase, zona reaction to block polyspermy
- Fusion of plasma membranes of oocyte and sperm, head and tail of sperm enter oocyte cytoplasm
- Completion of second meiotic division, formation of male pronucleus, fusion of male and female pronuclei
Can take up to 24 hours to complete
What are the parts of the blastocyst? How does it differ between Day 5 and Day 7
Inner cell mass, Blastocyst cavity, Trophboblast
There is degeneration of the zona pellucida- embryo hatched so cells can get bigger because implantation occurs at Day 6
What is the difference between the trophoblast and inner cell mass (embryoblast)?
The trophoblast is the stem cells for the placenta whereas the inner cell mass aka embryoblast is the stem cells for the embryo
What are the events of cleavage? What is the timing of these?
Increase in cell number and decrease in cell size
- 2 cell –> 4 cell –> 8 cell and development of morula –> early blastocyst –> late blastocyst
Occurs about 30 hours after fertilization, happens as traveling into the uterus
What are the derivatives of the trophoblast?What are their functions?
Cytrotrophoblast= stem cell layer of placenta, miotically active
Gives rise to Syncytiotophoblast= proteolytic enzymes, hCG aka initial signal for pregnancy and immunosuppressant so don’t reject cells, multi nuclear, have lost cell walls
What are the early derivatives of the inner cell mass (embryoblast)?
In week two derivives into the epiblast which gives rise to the ectoderm, amnion, and amniotic cavity
What is the difference between the hypoblast and embryonic endoderm?
The hypoblast is just the places holder for the endoderm during week 2
How does the prechordal plate develop?
Develops from hypoblast during week 2, columnar cells that are the future mouth
From endoderm along with primary and secondary yolk sacs
How does the extraembryonic mesoderm develop? What are its parts?
Hypoblast –> endoderm –> extraembryonic mesoderm
Extraembryonic coelom= cavity outside of embryo
Extraembryonic somatic mesoderm= lining the trophoblast and covering the amnion
Extraembryonic Splanchnic Mesoderm= lining the yolk sac (umbilical vesicle)
What are patient signs and symptoms that can be used to diagnose placenta previa? What are the 3 types?
vaginal bleeding beyond 20 weeks
antepartum bleeding should prompt sonographic evaluation before digital because palpation can cause severe hemorrhage
Marginal
Partial
Total/ central= totally covering the cervix
What are the 3 germ layers?
- ectoderm from epiblast (“ec”tratctive tings that make up your appearance)
- mesoderm (m for muscle)
- endoderm from hypoblast –> GI, lungs, bladder, pharynx, thyroid tonsils
How do teratomas form?
A sacrocoxcegeal forms due to persistence of the primitive streak in the caudal region
Oropharyngeal forms due to primordial germ cells not being sequestered early so they abnormally migrate
How does the notochord form? What is its role?
Comes from the mesoderm
Extends from the primitive node anterior to the prechordal plate
Template (DOES NOT BECOME) for the vertebral column
Induces neural phase via Sonic Hedgehog
What are the major classes of the mesoderm and what are their derivatives?
Paraxial= somites –> muscle, skeleton, dermis
Intermediate= urogenital –> kidneys and gonads
Lateral plate= connective tissue –> blood, lymph, mesnteries, cardiovasculat
- has 2 layers somatic which is adjacent to the ectoderm and the splanchnopleure adjacent to the endoderm
- supports viscera and organs
What happens during the second week of human development?
Formation of epiblast and hypoblast
What happens during the third week of human development?
Gastrulation
What are the derivatives of the extraembryonic mesoderm?
Connecting stalk= Somatic mesoderm
- forms embryonic pole, precursor to umbilical cord, position can change
Primitive Blood= sphlanic mesoderm
- forms in wall of yolk sac
Chorion= somatic mesoderm
- cytrotrophoblast and syncytiotrophoblasts aka layers of the placenta
What are chordomas?
Slow growing agressive neoplasms of bone
Arise from remnants of the notochord
Occur in axial skeleton in the spheno-occipital region
What are chordomas?
Slow growing agressive neoplasms of bone
Arise from remnants of the notochord
Occur in axial skeleton in the spheno-occipital region
What is the allantois?
Residual piece of endoderm
posterior midline
Diverticulum from wall of yolk sac
Template for umbilical arteries and vein
Becomes urachus attached to bladder
What is the allantois?
Residual piece of endoderm
posterior midline
Diverticulum from wall of yolk sac
Template for umbilical arteries and vein
Becomes urachus attached to bladder
What is the process of gastrulation?
Formation of primitive streak= cut in epiblast caudal end to head end
- the cells of primitive streak going from the epiblast and moving down so they end up between the original epiblast layer and the hypoblast
- layer closest to hypoblast aka deepest is endoderm then mesoderm then ectoderm
What is the process of the formation of the notochord?
The cells forming the notochord migrate from the primitive pit in a cephalic direction
• Lie between ectoderm and endoderm they form a tube called the notochordal process
• Notochordal process will fuse with the endoderm forming the notochordal plate
– At the time the amniotic cavity and the
primary yolk sac are in communication
• Notochordal cells will round up and form the
notochord proper
What secretes hCG to maintain pregnancy?
Syncytiotophoblasts
also responsible for degradation of endometrial epithelium during implantation
What cells are mitotically active during implantation?
Cytotophoblast cells
Where is ectopic pregnancy most commonly found?
proximal uterine tube
What is the primitive streak?
Identifies site where the formation of the embryonic mesoderm is initiated, where cells of embryonic mesoderm invaginate
Site of formation of the notochord
Determines body axis of the embryo
What is the cloacal membrane?
Located between notochord and primitive streak, immediately caudal to the primitive knot
composed of meso, ecto, and endo derm
What population of mesodermal masses contributes to the body wall?
Somatic layer of lateral mesoderm plate
