Birth
As the time of birth draws near, the foetus is positioned within the uterus with its head downwards.
- After about 280 days have passed, the development of the foetus is complete.
- Then, by the contraction of the muscles of the uterus, the baby is pushed out along the vagina. This is called birth.
- By the uterus contracting further, the placenta and the other tissues connected with it are removed. This is called the afterbirth.
- Afterwards, the umbilical cord that connected the placenta and the foetus is cut and tied.
Why head downwards
The head is the largest and least compressible part of the baby. Leading with it means that once the head has passed, the rest follows easily — which is why this position is settled well before labour begins.
Assignment 14.4
- What are the substances that diffuse across the placenta from the mother's blood into the blood of the foetus?
- Likewise, what are the substances that diffuse from the blood of the foetus into the mother's blood?