Embryology Flashcards
What is fertilisation?
Process by which the male gamete and female oocyte unite to form a zygote
How many chromosomes are in a diploid cell?
46 chromosomes
How many chromosomes are in a haploid cell?
23 chromosomes
What promotes ovulation?
Oestrogen
What is the process of ovulation?
Oestrogen promotes release of oocyte onto ovary surface.
Oocyte enters into the oviduct and is transported down the fallopian tube by peristaltic contractions.
Takes 4 days for the oocyte to reach the uterus.
What is the process of fertilisation?
- Sperm travels to oviduct to fertilise oocyte.
- Sperm attaches to zona pellucida
- Head bursts open releasing enzymes to loosen cell junctions
- Sperm drills through zona pellucida and merges with oocyte membrane.
- Membranes fuse forming pronuclei where the chromosomes of each gamete mix.
- Zygote is formed and cleavage starts.
What is the process of cleavage?
The zygote divides into smaller blastomeres (no growth of cells).
after 1 day the 2 cell blastomere is formed.
After 2 days the 4 cell blastomere is formed
After 3 days the 8 cell blastomere forms.
What happens at the 8 cell stage of the blastomere?
Compaction of the embryoblast cells begins.
When does the morula start to form?
Day 4.
Compaction of the cells in forms a 16-32 cell blastomere called a morula
How does the morula differentiate into the blastocyst?
Day 5 - 6:
- Outer embryoblast cells differentiate to form the trophoblast layer surrounding the inner cells.
- The epiblast cells compact to one end of the morula and form the inner cell mass (ICM).
- In doing so, a cavity is created called the blastoceol which is a fluid filled space.
- The zona pellucida starts to disintergrate and the blastocyst is formed by a process called hatching.
After how many days does implantation occur?
About day 7.
What is the process of implantation?
Day 7-10:
- Adhesion molecules on the endometrial epithelium and trophoblast cells of the blastocyst combine as the blastocyst attaches to the apical epithelial layer.
- Attachment of the blastocyst occurs above the ICM, this means that the trophoblast cells start proliferating and invade into the endometrial layer.
- The trophoblast cells form 2 layers; the cytotrophoblast, which lines the endometrial surface and the ICM and the syncitiotrophoblast cells which are multinucleated.
- The syncitiotrophoblast cells form overlying the ICM and eventually proliferate to surround the blastocyst entirely embedding it into the uterus lining by day 10.
How is the placenta formed?
Day 10:
- Vacuoles form in the syncitotrophoblast called lacunae which by day 12 form and interconnecting network for blood flow.
- Synctial lacuna fuse with maternal sinuosoids to allow maternal blood to enter the system.
- Cytotrophoblast cells penetrate into the surrounding syncitiotrophoblast and form primary villi which will contain the fetal capillaries.
- 21 days after fertilisation, teritary villi form and a network of capillaries linking maternal blood to the embryonic blood supply is formed. (the placenta)
What are the layers of the uterus lining?
External perimetrium
Medial Myometrium
Internal Endometrium.
What cycle conditions the endometrium?
Ovarian cycle
What are the stages of the ovarian cycle?
28 day menstrual cycle:
1. proliferative stage
2. Secretory stage
3, Menstrual / gravid phase (either no fertilisation or fertilisation)
What hormone is secreted by the syncitiotrophoblast?
hcG - Human chorionic gonadatropin.
What is the purpose of hcG?
Maintains pregnancy by maintaining the production of progesterone critical for the endometrium.
What do most abnormal implanations of the blastocyst occur?
95% in the ampulla
What can an abnormal implantation of an embryo lead to?
An extrauterine ectopic pregnancy.
What happens to the ICM at day 7?
ICM starts to differentiate into 2 layers:
Epiblast cells and hypoblast cells.
These form the bilayer embryoic disk
What cavity is formed with the differentiation of the ICM?
Amniotic cavity.
How does the amniotic cavity develop?
The epiblast cells have a cavity which is the amniotic cavity where the cells lining the cavity are termed the amnioblasts.