Topic 4 - Embryology Flashcards
Where is the oocyte fertilised by the sperm?
- in the ampulla of the Fallopian tube
What name is given to a fertilised oocyte?
- Zygote
Which site is ideal for implantation?
- Posterior uterine wall
Explain cleavage.
- the splitting by first mitotic division of the zygote into 2 blastomeres of equal size
What is the name of the glycoprotein shell that surrounds the pre-embryo before hatching occurs and how is it involved in fertilisation?
- Zona pellucida
- A Sperm cell must break through it using enzymes to fertilise the egg
In the morula, pre compaction, each cell could be said to be…?
- Totipotent (they could become any cell in the body), embryonic stem cells
Compaction leads to the formation of the first cavity, what names are given to the inner and outer cell masses in this blastocyst?
Outer - trophoblast
Inner - embryoblast
Briefly describe hatching.
- the blastocyst breaks free from the zona pellucida cell, its no longer constrained and can enlarge freely and interact with uterine surface for implantation.
What are the jobs of the tropho and embryoblasts?
Trophoblast - gives supporting tissue
Embryoblast - forms embryonic tissue
The epiblast and hypoblast form a structure called the…?
- bilaminar disc
Why is implantation interstitial?
- To get close to the mothers tissues to receive support
What is ectopic pregnancy?
- implantation in the Fallopian tube instead of the uterine body (wrong place)
What is placenta praevia?
- implantation in the lower uterine segment (wrong place), can cause large haemorrhaging at birth as placenta is highly vascular and can form a block across the gap
Why is Caesarean section indicated for placenta praevia?
- to bypass the placenta covering the opening, avoiding massive haemorrhaging (placenta is highly vascular)
Totipotent week 1 embryonic stem cells can be removed from the…?
- Morula
Explain the process of compaction.
- the cells become two distinct groups, inner cell mass and outer cell mass and a cavity forms as a result.
- inner cell mass = embryoblast, outer cell mass = trophoblast
- the structure is now a blastocyst instead of a morula
In week 2, what are the two types of cells that come from the outer cell mass (trophoblasts)?
- syncytiotrophoblasts and cytotrophoblasts
Which cells, in week 2, are formed from the inner cell mass (embryoblasts)?
- epiblasts (give the embryo itself!)
- hypoblasts
- together they form the bilaminar disc
What is the name of the breakaway yolk sac from the primitive one of the embryo?
- Secondary/definitive
List, in order, the 5 main processes that occur within the first 4 weeks.
- fertilisation and implantation
- gastrulation
- neurulation
- segmentation
- folding
Pre - gastrulation, what forms on the dorsal surface of the epiblast?
- the primitive streak and node
Explain what occurs during gastrulation.
- epiblast cells pile up at the primitive streak, and burrow down into the bilaminar disc
- bilaminar disc becomes the trilaminar disc, endoderm, mesoderm and ectoderm, these are all formed from the epiblast layer, the hypoblast layer degenerates as it is no longer needed.
What are the derivatives of the layers of the trilaminar disc?
Endoderm - internal structures e.g. epithelial lining of GI tract, respiratory tract
Mesoderm - supporting tissues e.g. muscle, cartilage, bone, vascular system
Ectoderm - structures to make contact with the outside e.g. nervous system, epidermis.
How is the necessary asymmetry of the body achieved in an embryo?
- by action of ciliated cells at the primitive node that “waft” molecules where they need to be
- an example of a pathology is situs inversus where the viscera are reversed due to defective cilia
