Unit 1: Beginnings of life Flashcards
What is the surface of the oocyte called ?
The zona pellucida
When the sperm enters the oocyte what happens ?
- The zona pellucida becomes impenetrable
- This is to resist more than 1 sperm entering
What is polyspermy ?
- When more than 1 sperm fertilises the ovum
- This means too much genetic material which leads to abnormal development and can be fatal
Once the diploid status is achieved what happens ?
Cell division (of nucleus) is initiated
What is each cell in the fertilised oocyte called ?
Blastomere
What is a blastomere (2) ?
- Solid mass of cells
- In contact with the zona pellucida
What are the 4 stages of fertilisation ?
1) Zygotic stage
2) Cleavage stage
3) Morula stage
4) Blastocyst stage
What happens at the morula stage (3) ?
- Cells divide but do not grow therefore size of embryo does not increase
- Difficult to count at this stage
- Appear smaller due to less space
What happens at the blastocyst stage (4) ?
- Cell on inside to blastocyst clumps forming a condensed inner cell mass (ICM)
- Cells on outside pump fluid into embryo to form blastocyst cavity
- Trophoblasts form on inside of cells
- Blastocyst ‘hatches’ (Breaks out of zona pellucida and grows)
What happens in normal pregnancies (2) ?
- Embryo develops as it moves along oviduct
- Implantation should occur outside oviduct and should occur in uterus
What happens in ectopic pregnancies ?
- Implantation occurs in oviduct or outside of the uterus
- This leads to rupture of oviduct and embryo dies
- Life threatening to mother
Where does the hatched blastocyst implant (2) ?
- Into the uterine wall (buried in endometrium)
- This gives it access to nutrition and allows it to secrete waste
What 2 layers are formed by the ICM ?
1) Epiblast
2) Hypoblast
What happens to totipotency as the embryo develops ?
As embryo develops, totipotency decreases
What does epiblast give rise to ?
It gives rise to all embryonic tissues
