Fertilization and Gastrulation Flashcards
Step one in fertilization- capacitation
Glycoprotein coat and seminal plasma proteins removed from plasma membrane of sperm
Passage of sperm through corona radiata with help of hyaluronidase
Step two in fertilization- penetration
Penetration of zona pellucida helped by releasing esterases, acrosin* and neuraminidase
Zona reaction helps to block polyspermy
Step three fertilization
Fusion of plasma membranes of oocyte and sperm
Head and tail of sperm enter oocyte cytoplasm
Step four fertilization
Completion of second meiotic division
Formation of male pronucleus
Fusion of male and female pronuclei
Features of cleavage
Increase in cell number, decrease in cell size
Embryo size unchanged
Starts about 30 hours after fertilization
Morula development occurs at about day 3
Blastocyst forms when
Days 5-7, and that is when implantation of the blastocyst into the uterus ocurs
What type of stem cells are in inner cell mass
Embryonic stem cells- pluripotent
Trophoblast
Gives rise to cytotrophoblast -Stem cell layer for placenta
Mitotically active
Releases early pregnancy factor so female body does not reject the cell as foregin
Syncytiotrophoblast
Formed from cytotrophoblast
Release proteolytic enzymes
Chorionic gonadotropin hCG which is responsible for implantation and initial signal of pregnancy
Hydatidiform mole and choriocarcinomas
Abnormal trophoblastic proliferation, excessive amounts of hCG produced
Complete mole results from fertilization of empty oocyte followed by duplication of sperm, or fertilization of empty oocyte by two sperm
Partial mole results from feralization of normal oocyte by two sperm
Can develop into malignant tumor
Week 2 inner cell mass
Inner cell mass gives rise to:
Epiblast -gives rise to ectoderm, amnion and amniotic cavity
Hypoblast- gives rise to extraembryonic endoderm, prechordal plate, primary/secondary yolk sac, extraembryonic mesoderm
Extraembryonic somatic mesoderm and extraembryonic splanchnic mesoderm
Somatic mesoderm lines the trophoblast/amnion (also forms connecting stalk (umbilical cord)When and chorion)
Splanchnic mesoderm lines the yolk sac (umbilical vesicle)- also forms primitive blood
Placenta previa
Vaginal bleeding beyond 20 weeks gestation
Should prompt sonographic evaluation before digital vaginal examination
Week 1-3: main events each week
Week 1- formation of inner cell mass
Week 2- formation of epiblast and hypoblast
Week 3- gastrulation (formation of 3 primary germ layer- ectoderm, mesoderm, endoderm), neurulation, formation of heart and circulatory system
Notochord
Midline between ectoderm/endoderm. Comes from mesoderm
Extends from primitive node/knot at the top of the primitive streak anterior to prechordal plate
Template for vertebral column
Induces neural plate formation by releasing SHH
This all happens in the epiblast
Formation of notochord plate
Cells forming notochord migrate from primitive pit in a cephalic direction
Lie between ectoderm and endoderm and form notochordal process
Notochordal process fuses with endoderm forming notochordal plate *amniotic cavity and primary yolk sac are in communication at this time
Notochordal cells round up and form notochord proper
Chordomas
Rare slow growing aggressive neoplasms of bone
Arise from remnants of notochord
Occur in axial skeleton in spheno-occipital region of skull and sacral regions
Allantois
Posterior midline Diverticulum from wall of yolk sac Endodermal structure Template for umbilical arteries and vein Becomes urachus which is attached to bladder
Mesoderm derivatives
Paraxial–> Somites: muscle, skeleton, dermis
Intermediate–>Urogenital: kidneys, gonads
Lateral plate–> Connective tissue: blood, lymph, mesenteries, cardiovascular
Embryonic ectoderm forms the
Neural crest
Epiblast cells form
The actual embryo
Fertilization occurs where
Ampulla of uterine tube which is the distal 2/3rds of the tube
What is the corona radiata
Follicular cells from the ovary that surround the human ovum
What is expelled at the end of fertilization
The second polar body
When does cleavage occur
About 30 hours after fertilization
When does formation of morula occur
About day 3, and at day 4 it enters the body of the uterus
When does implantation occur
Starts about day 6
Sacrococcegreal teratoma
Persistence of the primitive plate (in the caudal region)
Oropharyngeal teratoma
Primordial germ cells have abnormal migration and migrate to oral region
