Fertilization to Trilaminar Flashcards
What are the steps to fertilization?
- Sperm binds in a human specific interaction with the zona pellucida glycoprotein
- Acrosomal enzymes released from sperm head to digest ZP and allow sperm head entry into egg
- Egg and sperm plasma membranes fuse and sperm contents enter egg
- Sperm entrance triggers egg compltetion of meiosis 2 and release of cortical granules that harden ZP to prevent further sperm entry
What occurs during cleavage?
Zygote undergos mitosis to create many identical daughter cells called blastomeres. Up to cell 8, blastomeres are totipotent.
What is compaction?
Cells are confined within ZP and so when they divide the cell mass does not expand
What forms when the cells become closer together during compaction?
They begin to form cell junctions. The outer cells which are in contact with the ZP form extensive gap junctions, but fluid can still enter the cell to form the inner cell mass.
What is the names of the cells that form extensive gap junctions at the peripheral of the cell?
Trophoblasts
What will the trophoblast finally become?
Embryonic part of the placenta
What will the inner cell mass become?
Embryo proper (amnion and yolk sac)
What will happen when the cell has multiplied to its capacity within the ZP
The blastocyst will hatch
Where are the implantation sites
Normal - Middle or upper dorsal uterine wall
Abnormal - ovary, ampulla, uterine tube, lower part of uterus, cervix, peritoneum
What drives implantation?
Trophoblast
What does the trophoblast divide into?
Cytotrophoblast - made of individulal cells
Syncytiotrophoblast - Single multinucleated cell
What are the layers that the embryo divides into?
Epiblast - dorsal surface of embryo
Hypoblast - ventral surface of embryo
Amniotic cavity forms
What has begun to form by the end of week 2
The primitive streak
Where does the primitive streak form?
Midline at the caudal end of the epiblast. The cranial end of the primitive streak contains the primitive pit and node
What can occur after the formation of the primitive streak?
Gastrulation - formtation of endoderm, ectoderm and mesoderm
Where will the cells migrate through to form gastrulate?
Primitive streak
What will the hypoblast form?
Difinitive endoderm
Where is the intraembryonic mesoderm layer formed?
Between the endoderm and epiblast
What will the epiblast form?
Ectoderm
What will the endoderm form?
Skin and nervous system
What will the mesoderm form?
Paraxial - axial skeleton, voluntary muscle and dermis
Intermediate - Urogenital systems
Lateral plate:
Somatic mesoderm - lining of body wall, most of dermis and limbs
Visceral mesoderm - CV system, mesothelial covering of organs, smooth muscle
What will the endoderm form?
Lining of gut tube
Lining of respiratory tract
Lining of bladder and urethra
