For about nine months a developing fetus lives in the uterus with no lungs in use and no food of its own. The placenta, the umbilical cord and the amniotic sac keep it supplied and protected. How substances cross the placenta, and what harmful things can cross too, are Extended content.
The placenta is attached to the wall of the uterus and the umbilical cord joins it to the fetus; the amniotic sac encloses the fetus in amniotic fluid, which protects it. Extended: in the placenta the blood of the mother and the blood of the fetus come very close but do not mix; dissolved nutrients and oxygen diffuse to the fetus and carbon dioxide and urea diffuse to the mother. Some pathogens and toxins can also cross the placenta and affect the fetus.
In the fetus tab the front of the uterus is see-through. Click each structure that supports the fetus, or pick it from the list, and read its function.
| Structure | Function |
|---|---|
| Placenta | attached to the uterus wall; exchange of substances between the mother's blood and the fetus's blood, without the bloods mixing |
| Umbilical cord | joins the fetus to the placenta; contains blood vessels that carry the fetus's blood to and from the placenta |
| Amniotic sac | membrane that encloses the fetus and the amniotic fluid |
| Amniotic fluid | supports the fetus and protects it from bumps and shocks |
The umbilical cord carries the fetus's blood, not the mother's. The mother's blood stays in her own vessels in the placenta.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the fetus tab, what is the function of the amniotic fluid?
According to the fetus tab, what does the umbilical cord carry?
Extended: in the placenta tab, which substance moves from the fetus to the mother?
Extended: what does ticking Mother smokes show in the placenta tab?
Extended. Watch the coloured particles in the placenta tab. Then tick Mother smokes (nicotine) and Rubella virus to see what else can cross.
| Mother → fetus | Fetus → mother |
|---|---|
| oxygen; dissolved nutrients such as glucose and amino acids (also water and mineral ions) | carbon dioxide and urea (excretory products), removed by the mother's lungs and kidneys |
Do not write that the mother's blood flows into the fetus. Substances diffuse across the placenta; the two bloods never mix.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Which structure encloses the fetus and the fluid around it?
Extended: which pair shows substances that pass from the fetus's blood to the mother's blood?
Extended: by what process do oxygen and glucose cross the placenta?
Extended: why are pregnant women advised not to smoke?
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