Development of Embryo Flashcards
What is the structure of the blastocyst?
Inner cell mass - embryoblast (subsequently forms the embryo).
Outer layer of cells - trophoblast (will form the placenta.
A week after fertilisation, the implanted blastocyst starts to differentiate into various types of cell.
What do the cells of the embryoblast develop into?
The cells of the embryoblast split into two: the yolk sak on one side and the amniotic cavity on the other.
What sits between the yolk sac and the amniotic cavity?
The embryonic disc.
What do the cells of the embryonic disc develop into?
The foetal pole, and eventually into the foetus.
What are some intrinsic factors affecting foetal growth?
Maternal:
- height & weight
- parity
- ethnic group
Fetal:
- sex
- genes/inherited conditions
- multiple pregnancy
How does parity affect foetal growth?
Higher parity is positively associated with macrosomia.
What are some extrinsic factors affecting foetal growth?
Maternal:
- social class
- nutritional status
- environment: altitude
- pre-existing disease: cardiac/renal/respiratory/vascular
- pregnancy-related disease: HTN, diabetes
Foetal:
- nutrition: placental
- teratogenic: tobacco, narcotics, alcohol, medication
- infective: rubella, CMV, listeria, syphilis
How does altitude affect foetal growth?
High altitude exposure increases the incidence of pregnancy complications and neonatal morbidity, such as intrauterine growth restriction (IUGR).
Chronic hypoxia slows fetal growth and reduces the pregnancy-associated rise in uterine artery blood flow.
What surrounds the complex of the developing embryo?
The chorion
What are the 2 layers of the chorion?
The cytotrophoblast (inner layer) and the syncytiotrophoblast (outer layer).
What is the syncytiotrophoblast embedded in?
The endometrium
Over a short time, what forms around the yolk sac, embryonic disc and amniotic sac?
A space called the chorionic cavity
How are these structures (yolk sac, embryonic disc and amniotic sac) suspended from the chorion?
By the connecting stalk
What does the connecting stalk go on to form?
The umbilical cord
At around 5 weeks gestation, what does the embryonic disc develop into?
The foetal pole
The foetal pole contains 3 layers. What are they?
1) Ectoderm (outer layer)
2) Mesoderm (middle)
3) Endoderm (inner)
These three layers go on to become all the different tissues of the body.
What does the endoderm go on to form?
- GI tract
- Lungs
- Liver
- Pancreas
- Thyroid
- Reproductive system
What does the mesoderm go onto form?
- Heart
- Muscle
- Bone
- Connective tissue
- Blood
- Kidneys
What does the ectoderm go onto form?
- Skin
- Hair
- Nails
- Teeth
- CNS
When does the foetal heart begin to form/beat?
Around 6 weeks gestation
When do the spinal cord and muscles begin to develop?
Around 6 weeks gestation
At how many weeks gestation have all major organs started to develop?
Around 8 weeks gestation
During what phase of the menstrual cycle does the endometrium thicken and get ready for a fertilised egg to arrive?
Follicular phase
What makes the endometrial tissue highly vascular?
The myometrium sends off artery branches into the endometrium.
Initially, these arteries grow straight outwards like plant shoots.
As they continue to grow, they coil into a spiral. These thick-walled and coiled arteries are bunched together, making the endometrial tissue highly vascular.
These are known as the spiral arteries.
