How does blood pass across the placenta?

Blood passes across the placenta through a process known as placental circulation. Here is a detailed explanation:

1. Maternal Blood Circulation:

- Oxygenated maternal blood from the mother's heart enters the placenta through the uterine arteries.

- These uterine arteries branch into smaller vessels, called spiral arteries, within the placenta.

2. Placental Barrier:

- The maternal blood does not directly mix with the fetal blood within the placenta.

- There is a placental barrier consisting of several layers that allow the exchange of nutrients and waste products between the maternal and fetal circulatory systems while preventing the mixing of blood.

3. Exchange of Substances:

- As maternal blood flows through the placenta, it comes into close proximity with the fetal blood vessels, which are located within tiny finger-like projections called chorionic villi.

- Oxygen, nutrients (such as glucose, amino acids, and vitamins), and hormones (e.g., estrogen and progesterone) from the maternal blood pass through the placental barrier into the fetal bloodstream by the process of diffusion.

- At the same time, carbon dioxide and waste products from the fetus diffuse from the fetal blood into the maternal blood.

4. Fetal Blood Circulation:

- The fetal blood that receives oxygen and nutrients from the placenta travels back to the fetus through a single umbilical vein.

- The umbilical vein carries oxygenated blood from the placenta to the fetal heart and then throughout the fetal body.

5. Return to Maternal Circulation:

- Deoxygenated maternal blood, now carrying carbon dioxide and fetal waste products, exits the placenta via the uterine veins and returns to the mother's circulatory system to be reoxygenated in the lungs and have waste products removed by the kidneys.

In this way, the placenta serves as a vital interface for the exchange of oxygen, nutrients, and waste products between the maternal and fetal circulatory systems without direct mixing of blood, ensuring the proper development and nourishment of the growing fetus.