Embryology Flashcards
How long is the spermatogenesis cycle?
Approx 53 days
When does oogenesis begin?
28th-30th week of gestation
Then arrest in prophase until puberty
Where does fertilisation typically occur?
Ampulla
What do sperm and oocyte form when they fuse?
Zygote
What is a zygote?
Single cell diploid embryo
What is the process of fertilisation?
Sperm binds to zona pellucida glycoprotein 3 and releases acrosomal enzymes
Egg and sperm membranes fuse and sperm contents enter the egg
Oocyte completes meiosis II
Release of cortical granules by oocyte makes zona pellucid impenetrable to other sperm
When is cleavage?
Day 1-3
What is cleavage?
Rapid mitotic division without increase in size as it is confined within the zona pellucida
What is a morula?
16+ cells
What is a blastocyte?
200-300 cells
What is the trophoblast?
The outer layer of cells held together by gap junctions
Where does an embryo implant?
Endometrial lining on the posterior or anterior uterine wall
What is ectopic pregnancy?
Embryo implants somewhere other than uterine wall
What are the two layers of a bilaminar embryo?
Epiblast
Hypoblast
What does the trophoblast divide into?
Cytotrophoblast
Synctiotrophoblast
What do the epiblast and hypoblast turn into next?
Epiblast - amniotic cavity
Hypoblast - primitive yolk sac
How does uteroplacental circulation form?
Vacuoles appear and unite in the synctiotrophoblast to form lacunae
Maternal blood flows into lacunae and diffuses into embryoblast
How is the chorionic cavity formed?
Extraembryonic mesoderm forms and degenerates to form chorionic cavity
What is gastrulation?
Process by which epiblast cells move through the primitive streak between epiblasts and definitive endoderm to form 3 primary germ layers
When does gastrulation take place?
Week 3
What are the three primary germ layers?
Ectoderm
Mesoderm
Endoderm
How do the three germ layers form?
In the caudal end of the bilaminal embryo a pit forms and extends to form a groove (primitive streak)
During invagination epiblast cells are displaced and move through this groove into a layer under the embryo, displacing hypoblast cells to form a definitive endoderm
Some epiblasts remain in the layer between the epiblast (ectoderm) and the new definitive endoderm forming a 3rd layer - the mesoderm
What structures does the ectoderm form?
Skin epidermis
Nervous system
What structures does the mesoderm form?
Skeleton
Smooth muscles
Visceral and parietal linings
What structures does the endoderm form?
Gut
Respiratory tract
Bladder
Urethral lining
What is superior in embryological terms?
Cranial
What is inferior in embryological terms?
Caudal
What is anterior in embryological terms?
Ventral
What is posterior in embryological terms?
Dorsal
