Topic: Human Foetal Development

The embryo begins to form from an inner cell mass within the blastocyst. Some parts of the blastocyst will form the extra embryonic membranes.
What is extra embryonic membrane?
The supportive structures to the embryo in foetal development.
Examples: placenta, chorion, amniotic fluid, allantois
What is a placenta?
A thin membrane forms from the foetus/chorion and maternal tissue.
1. Numerous chorionic villi: increase its surface area
2. Allows diffusion of materials between mother & foetus without 2 blood mixing, thus:
– Prevent blood agglutination (foetal blood maybe incompatible with mother’s)
– Prevent entrance of pathogens/toxins/maternal hormones into foetus
– Prevent harm by mother’s higher blood pressure
3. Umbilical cord connects the embryo to mother, thus:
– Oxygen, water, amino acids, glucose, essential minerals are transferred
(from maternal blood) to the foetus via umbilical vein
– Carbon dioxide, urea and other waste products from the foetus are transferred
to the maternal blood via umbilical artery
4. Placenta secretes oestrogen & progestrone
– These hormones maintain the thickness and development of endometrial lining to prevent miscarriages.
What is chorion?
The outermost membrane, arises from the trophoblasts.
It’s also the foetal portion of placenta, which houses umbilical cords.
1. Thousands of fingerlike projections–chorionic villi
– Provides large surface area for exchange of substances between mother and foetus.
2. Maternal blood pool
– Walls of maternal blood vessels near chorionic villi break open, so that the maternal blood bathes the outer surface of villi.
What is amniotic fluid?
It is contained inside a cavity, enclosed by a layer of membrane called amnion.
Amnion completely surrounds the foetus.
What is its role?
To protect the developing embryo by:
– Antibacterial, thus protecting foetus from pathogenic infections
– Prevents foetal tissue from drying out
– Keeps the embryo at constant temperature
What is allantois?
A membrane formed from the mesoderm tissue of embryo.
It fuses with chorionic villi.
It moves toward the endometrial lining to become umbilical cord.