Early Embryonic Development Flashcards
What is the basic overview of human development?
Fertilization
Single cell
Ball of cells
Cavities + two layered disc
Three layered disc with middle layer
Segments in middle layer
Where does fertilization occur?
In the ampulla of the uterine tube within two hours of ovulation
What is the hard shell that surrounds the egg?
Zona pellucida
How does the sperm break down the zone pellucida?
By releasing hyaluronic acid from its acrosome
How does the egg push away other sperm during fertilization?
Changing its polarity
What happens to the genetic material once fertilization has occurred?
The nuclear membrane breaks down to form pro nucleuses
All the sperms mitochondria and flagella also broken down through proteolysis
What happens in the first week of development?
The DNA replicates and undergoes normal somatic mitosis
What stages are repeated during the first week of development?
M and S phase because there is no cell growth ie G1 and G2
When is the initial cleavage of the first cell?
36 hours
What happens at the 8 cell stage?
Compaction- central cells are linked by gap junctions
What is 16 cells called?
Morula
Where does the morula travel?
Transported along the uterine tube and arrives at the uterus within 3-4 days after fertilisation
Approx 30-40 cells
After 4 days what happens to the morula?
Loses its zona pellucida and becomes a blastocyst
What are the different layers of the blastocyst?
Trophoblast
Blastocoel- cavity
Trophectoderm
What has to occur to allow the blastocyst to bind the epithelium wall?
Has to be a decrease of MUC-1 (ant-adhesion molecule)
Binding via selectins to glycol-components
Integrins, laminin and fibronectin have to initially penetrate
What are the main events that occur once the blastocyst has been implanted into the uterine wall?
Some of the invading trophoblast cells group together to form syncytiotrophoblasts
These invade via metalloproteases
What happens on day 8?
Trophoblasts become invasive through syncytiotrophoblasts and cytotrophoblasts
Two layers formed- epiblast and hypoblast
Amniotic cavity begins to forms as a space within the epiblast
What happens on day 9?
The hypoblast cells will migrate and coat the blastocyst cavity and once it has done this, it will be renamed to the primary yolk sac
Spaces develop within the syncytiotrophoblasts
Extraembryonic mesoderm will from deep to the trophoblasts
What happens on days 11 and 12?
The embryonic disk has two layers now
The blastocysts has fully buried into the endometrium
Syncytiotrophoblast cells erode through the walls of large maternal capillaries
What happens to the spaces developed in the syncytiotrophoblasts?
Invaded by capillaries which now provide the blastocyst with blood
What is the end result of 2 week development?
Trophoblast has two layers:; Syncytiotrophoblast and cytotrophoblast
Inner cell mass has the epiblast and hypoblast
2 cavities from the amniotic and chorionic cavity
What are the two layers of the inner mass cell going to develop to?
Epiblast- ectoderm
Hypoblast- endoderm
What is ectopic pregnancy?
The blastocyst doesn’t bury into the uterine wall
Most common in the ampulla
What are some examples of environmental causes of malformations?
Drugs or chemicals
Infectious agents
Ionizing radiation
What effect does alcohol have on foetal development?
Growth retardation
CNS damage
Effects on facial development
