Embryology: Fertilisation To Trilaminar Flashcards
What is fertilisation
union of gametes - fusion of sperm and oocyte to form a zygote
Where does fertilisation take place
ampulla of the uterine tube
Fertilisation (1/4)
Sperm binds to zona pellucida glycoprotein
Fertilisation (2/4)
Acrosomal enzymes released from sperm head; sperm digests its way into egg
Fertilisation (3/4)
Egg and sperm plasma membranes fuse and sperm contents enters the egg
Fertilisation (4/4)
Sperm entry triggers completion of meiosis 2 and release of cortical granules by oocyte (make ZP impenetrable to other sperm)
What is cleavage
Zygote undergoes series of mitotic divisions that divide fertilised egg into blastomeres
What is a blastomere
one of the cells that are produced during cleavage of a zygote and that form the morula
Up to what stage are blastomeres thought to be totipotent
8 cell stage
What is a totipotent cell
Cells that can differentiate into any cell type including embryonic and placental cells
Mosaicism
Individuals with 2 or more cell line with different chromosome complements
When can mitotic nondisjunction occur
Early division of zygote
mitotic nondisjunction
The failure in mitosis for the two members of a chromosome pair to separate (to disjoin) normally, which causes both chromosomes to go to one daughter cell while none go to the other daughter cell
How many blastomeres in morula
16+
What does the inner cell mass of a blastocyst form
Embryo
What does the trophoblast of a blastocyst form
Feral placenta
Blastocyst hatching
developing embryo (at around five days after fertilization) that is hatching out of the zona pellucida (ZP(Protective coating))
On what day (number) does implantation typically occur
Day 6
Where does implantation occur
Posterior or anterior uterine wall
Ectopic pregnancy
implantation outside the uterus
Placenta previa
placenta lies low in uterus and partially/completely covers cervix
Development of the bilaminar embryo - day 7.5
Trophoblast divides into cytotrophoblast (individual cells) and syncytioblast (single multinucleated cell which produces hCG)
Embryobast divides into epiblast (dorsal surface) and hypoblast (ventral surface)
Amniotic cavity begins to form
Development of the bilaminar embryo - day 9
amniotic cavity (epiblast) and primitive yolk sac (hypoblast) are formed
-Implantation complete
Development of the bilaminar embryo - day 12
Uteroplacental circulation established
chorionic cavity is formed (Extraembryonic mesoderm develops then degenerates)
Development of the bilaminar embryo - day 13
- Further development of chorionic cavity
- Presence of existing stalk (later umbilical cord)
- Second wave of hypoblast cells migrate to form definitive yolk sac
Development of the bilaminar embryo - Implanted embryo
Uteroplacental circulation forms
Amniotic cavity present above embryonic disc
Chorionic cavity developed and encircles embryo
Implantation + location
Embryo implants into endometrial lining on posterior or anterior uterine wall
Primitive streak features
-Primitive streak appears in midline at caudal end of epiblast
- Cranial end of Primitive streak = Primitive Pit and Node
Gastrulation
Invagination of the epiblast cells through the primitive stream to form the 3 primary germ layers
What layers is the trilaminar embryo composed of
ectoderm, mesoderm, endoderm
Fate of Epidermis
- Epidermis of skin, hair, nails
- Nervous system
Fate of mesoderm
Paraxial mesoderm: axial skeleton, skeletal muscle
- Intermediate mesoderm: urogenital systems
- Lateral plate mesoderm
- Somatic layer: dermis, lining of body wall, parts of limbs
- Visceral layer: cardiovascular system, mesothelial covering of organs, smooth muscle
Fate of endoderm
- Lining of gut tube
- Lining of respiratory tract
- Lining of bladder and urethra
