Early Embryology Flashcards
What occurred in the 1st week of fertilization?
- Capacitation
- Acrosome reaction
- Fusion of the plasma membranes of sperm and oocyte
What is a capacitation ?
- removal of seminal proteins from the surface
- penetration through corona radiata
What is the acrosome reaction?
- release of acrosomal enzymes (acrosin etc.)
- penetration of sperm through zona pellucida
What occurs in the fusion of the plasma membranes of sperm and oocyte?
-changes in zona pellucida inactivates sperm receptors and prevents polyspermy
What transformation the corona radiata undergo in the 1st week fertilizat?
Corona radiata—> zona pellucida —> plasma membrane of secondary oocyte—> cytoplasm of secondary oocyte
Describe week 1 fertilization
Normal site
-ampulla of Fallopian tube
Fertilization stimulates completion of the 2nd meiotic division to form the mature oocyte (nucleus = female pronucleus)
-sperm nucleus forms the male pro nucleus
Fusion of pronuclei:
-Restores the normal diploid number in the new organism forming the zygote
-Embryonic sex is determined
DNA replication
Mitotic division and cleavage begins
What occurs for cleavage to occur?
Repeated mitotic division of the zygote to produce trp identical daughter cells or blastomeres
- zygote is subdivided without increase in size
- After 16-32 blastomeres: Morula (day 3)
Explain blastocyst formation
After the morula enters the uterus a fluid-filled space , the boastocystic cavity, appears inside the morula. The fluid passes from the uterine cavity through the zona pellucida to form this space.
As fluid increases in the blastocystic cavity, it separates the blastomeres into 2 parts:
- Inner blast cells-> embryoblast—> embryo(located at embryonic pole)
- Outer blast cells—> peripheral cells /trophoblast —> fetal component of the placenta
Where 8s the normal site for implantation?
-Posterior wall of body of uterus close to the fundus
Explain implantation week 1-2
Approximately 6 days after fertilization, the blastocyst attaches to the epithelium of the endometrium (inner lining of the uterus), us7ally adjacent to the embryonic pole.
- As soon as the blastocyst attaches to thr endometrial epithelium, the trophoblast proliferates rapidly and differentiates into two layers.
- An inner layer of cytotrophoblast
- An outer layer of synchtiotrophoblast
How long does implantation take?
6-10 days
What are the two distinct layers of the trophoblast?
Inner cytotrophoblast- makes cells
- mitotically active
- forms new cytotrophoblast and synchtiotrophoblast
Outer synchtiotrophoblast-secretes and invades
- secrete human chorionic gonadotropin (hCG)- early pregnancy tests
- mass of cells or synctium at the embryonic pole erode endometrial ciponnectivr tissue enabling the blastocyst to “burrowing”binginthevendometrium
What are the constituents of the bilaminar disc?
Once the embryo has implanted, morphological changes occur in the embryoblast that result in the formation of a flat, circular bilaminar plate of cells, the embryonic disc, consisting of two layers:
- epiblast- the thicker layer, consisting of high columnar cells. Eventually forms the three definitive germ layers
- hypoblasr- consisting of small cuboidal cells. Becomes part of the yolk sac
Explain the intro to gastrulation
The process by which three germ layers, which are the precursors of all embryonic tissues are formed
- The bilaminar disc (epiblast) develops into a trilaminar disc with three definitive layers:
- primitive mesoderm
- Intraembryonic mesoderm
- paraxial
- intermediate
- lateral
-Ectoderm
What are the adult derivatives of the endoderm?
- Epithelial lining of gut and associated glands (liver, pancreas, gall bladder)
- Epithelial lining of the respiratory organs (trachea, bronchus, lungs), tonsils, middle ear and pharyngotympanic tube
- Parathyroid and thyroid gland
- Epithelial lining of bladder, most of urethra and lower vaginal canal
