Embryology : Early human development Flashcards Preview

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Flashcards in Embryology : Early human development Deck (43)
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Describe the phases of fertilisation.

1. Penetration of the corona radiata
2. Penetration of the zona pellucida
3. Fusion oocyte and sperm cell membrane + Secondary oocyte in 2nd meiotic division


Name and describe features of the sperm molecule.

-Acrosome- sack which carries enzymes to allow fertilisation to take place
Midpeice – engine of sperm
Flagellum- beats for movement of sperm


Does corona radiata and zona pellucida provide a barrier to sperm?

Corona radiata- does not provide barrier for sperm
Zona pellucida- does provide a barrier


what is a zygote?

single cell embryo


what does sperm entry trigger?

Sperm entry triggers cortical granule release in egg cortex triggering formation of fertilisation membrane, which is impenetrable to sperm


what does fusion of the male and female pronuclei restore?

restores the diploid number of chromosomes = zygote, day 0 of development


How long does the zona pellucida remain during development?

first few days


what is cleavage?

Period of rapid cell division (no size increase)


is there an increase in cell size during cleavage?

No because the cell size is limited by zona pellucida


what happens to the morula under pressure?

changes into the blastocyst


Describe the structure of the blastocyst.

-outer wall- trophoblast
-inner cell mass- embyoblast
-blastocyst cavity


Describe the blastocyst hatching.

-Inner Cell Mass gives rise to the embryo, remaining cells form the trophoblast which contributes to the placenta

-Embryonic Stem (ES) cells are derived from the ICM

- Following hatching from the zona pellucida the embryo now interacts directly with the endometrial lining of the uterus


where does the blastocyst normally implant?

dorsal wall of uterus


where are abnormal implantation sites?

2. ampula
3. uterine tube
5. internal os of uterus


what is the maternal response after implantation?

new blood vessels form -maternal response


What happens during implantation?

-blastocyst makes contact with uterine epithelium
-Trophoblast sends projections into epithelium – breakdown connecting cells and crawl in
- trophoblast is now differentiated
-leading edge - syncytiotrophoblast
-Cytotrophoblast –remaining part of trophoblast


what ways does the cell face ?

-Emybroblast – 2 cells: one facing into cavity of blastocyst and one adjacent to trophoblast (epiblast)
- epiblast are proliferating – producing early cells of amnioablast


what happens to the implanted embryo at 9-12 days.

-The syncytiotrophoblast has extended and by erosion contacts maternal blood supply.

- The amniotic cavity is present above the bilayered embryonic disc and the definitive yolk sac below

-The chorionic cavity has developed and encircles the entire embryo


what is gastrulation?

formation of the germ layers


what are the 3 germ layers?

-Ectoderm : nervous system and skin
-Mesoderm: Muscle, bone and internal organs
-Endoderm: gut


where do cells migrate through?

primitive streak


Describe the process of gastrulation.

-Surface of epiblast is not uniform surface – impression at one end –buccopharyngeal membrane (cranial end) and primitve streak at one end – -drives prosess of gastrulation for 3 germ layers
Primitive streak sends signal – some epiblasts will come towards primitive streak and go deep into it and some go into hypoblast and some fill space (3 germ layers)


what is neurulation?

formation of the neural tube


what is the first step of neurulation?

An area of the ectoderm is induced to form Neural Tissue


when does neurulation start?

once gastrulation finishes


how is the brain formed during neurulation

In response to signals from mesoderm, some ectodermal cells differentiate and become neural
Then neural plate expands –produces brain - the different areas of brain i.e dicephalon


what happens at day 19/20 of neurulation?

-Creates hinge point along midline-pulling edges of neural tube upwards – pulls ectoderm with them as they are connnected
-The groove gets deeper over time
-Midpoint of embyro- make contact with one another – the neural edges fuse with one another and pulling ectoderm with them so will fuse with each other over the top and so neural tube is hidden
-Fiusion contines in both direction to enclose the entire neural tube


what happens during neural tube formation at day 23?

Anterior part close first


Neural crest

Undergo Epithelial to Mesenchymal transition and leave the neuroectoderm to enter the mesoderm


Name neural crest derivatives.

-Schwann cells and Meninges
-Dorsal root ganglia
-Autonomic ganglia
-Bones and connective tissue of craniofacial structures
-Chromaffin cells (adrenal medulla)