Alveoli and breathing in

The idea

Air passages in the lungs end in balloon-like alveoli, richly supplied with blood vessels, where blood releases carbon dioxide and takes up oxygen; breathing in (ribs lifted, diaphragm flattened) fills them, and residual air always remains, allowing time for exchange.

A balloon with tiny balloons

Inside the lungs the air tubes divide again and again, and they end in tiny balloon-like bags.

What do you think happens in these tiny bags?

• Gases are exchanged with the blood
• Food is digested
• Urine is made

Inside the lungs

Press Next step to walk through the lungs.

How the lungs fill

The air passages end in alveoli, small balloons whose walls are wrapped in blood vessels. Blood brings carbon dioxide to the alveoli and takes up oxygen from them. When we breathe in, the ribs lift and the diaphragm flattens, so the chest cavity grows larger and air is sucked in. Some air always stays behind in the lungs, which gives time for the exchange.

Air passages in the lungs end in balloon-like alveoli, richly supplied with blood vessels, where blood releases carbon dioxide and takes up oxygen; breathing in (ribs lifted, diaphragm flattened) fills them, and residual air always remains, allowing time for exchange.

Notes

Air passages end in alveoli with blood vessels, where blood releases CO₂ and takes up oxygen; breathing in: ribs lifted, diaphragm flattened; residual air remains for time to exchange.

Check yourself

What happens to the ribs and the diaphragm when we breathe in?

Why is air sucked into the lungs when we breathe in?

Where does blood release carbon dioxide and take up oxygen in the lungs?

Why do the lungs always contain a residual volume of air?

• The ribs are lowered and the diaphragm is domed. This is the opposite of what happens when we breathe in.
• The ribs are lifted and the diaphragm is flattened — correct. Yes!
• The ribs are lifted and the diaphragm is domed. When we breathe in, the diaphragm is flattened.
• The chest cavity becomes smaller. A smaller chest cavity would push air out, not suck it in.
• The alveoli are empty of blood vessels. The walls of the alveoli have an extensive network of blood vessels.
• The chest cavity becomes larger — correct. Yes!
• In the alveoli — correct. Yes!
• In the nostrils. In the nostrils, fine hairs and mucus filter the air.
• In the rings of cartilage. Rings of cartilage in the throat keep the air-passage from collapsing.
• So that the ribs stay lifted. The residual air gives time for exchange; it does not hold the ribs up.
• So that there is enough time for oxygen to be absorbed and carbon dioxide to be released — correct. Yes!
• So that no blood reaches the alveoli. The alveoli are richly supplied with blood vessels.