#116 The development of the fetus

Credit: thomasreynoldsblog

The blastula develops into an embryo and some of the cells form a placenta, linking the embryo with the uterus lining. Organs such as the heart develops and, after 8 weeks, the embryo is called a fetus.

Growth of the fetus requires a good supply of nutrients and O₂. This is achieved through the link between the placenta and the mother’s blood supply in the uterus lining. The placenta is soft and dark res, and has finger-like projections called villi. The villi fit closely into the uterus wall. 

1. Umbilical cord 

• joins fetus to placenta; contains:
• 2 arteries: blood from fetus ---> placenta
• 1 vein: returns blood ---> fetus

2. Placenta 

Brings blood supply of fetus close to mother’s

• Blood from the fetus passes through the umbilical cord in the umbilical artery to the placenta. 
• Here it comes close to the mother's blood. 
• transport O₂ + nutrients (amino acids, glucose…) from mother ---> fetus
• transport CO₂ + wastes (urea… ) from fetus --->mother (through umbilical vein).

Prevents mixing 

This is really important because the fetus and mother may have different blood groups - any mixing could result in blood clotting, which could be fatal to both mother and fetus. 

3. An amnion protects the fetus

The fetus is surrounded by a strong membrane, called amnion. Inside the amnion is a liquid called amniotic fluid.

The fetus in the amniotic sac. Credit: preventdisease.com

Amniotic sac: membrane from embryo cells: encloses fetus, prevents entry of bacteria

Amniotic fluid:  supports, protects fetus from mechanical damage; absorbs urine released by fetus.

Try this 

Answer 

a) i) A, umbilical cord ; B, vagina

    

     ii) Tree functions from:

      - transfers O₂ from mother to fetus

      - transfers nutrients (of named nutrients) from mother to fetus

      - transfers CO₂ from fetus to mother

      - transfers wastes (or named wastes) from fetus to mother  

      - allows the transfer of antibodies from mother to fetus

      - prevents mixing of the blood of mother and fetus.

   

     iii) Helps prevent bacteria passing from mother to fetus, the blood group of mother and fetus may be different.