Raven lays a long strip of paper across the Windowsill and draws a nose at one end.
"Follow one breath," she says. "What do you notice first? The air goes in through the nose."
Rocket grabs a pencil and draws a tube. "Then a pipe down to the lungs. Then it splits."
"Splits and splits and splits," Nova says, hovering over the strip, "until the tubes are thinner than a hair."
"And at the very end?" Rocket asks.
Raven draws a cluster of tiny bubbles. "Air sacs. That is where oxygen leaves the air and joins the body."
Rocket draws a heart next to the bubbles. "And this sends it everywhere. Two systems, one strip of paper."
During inhalation the diaphragm descends. The lungs begin to inflate and draw in air from outside the body.
Air enters through the nasal cavity, just inside the nose. There it is warmed to body temperature and made moist.
Floating particles are removed in the nasal passages by hairs, mucus and cilia. The air is also chemically sampled by the sense of smell.
From the nasal cavity, air passes through the pharynx, the throat, and the larynx, the voice box, to the trachea.
The trachea is a cylinder about 25 to 30 centimeters long. Its job is to funnel air to the lungs and back out.
The end of the trachea divides into two bronchi, one for each lung. The bronchi divide into smaller and smaller tubes.
When the passages are under 1 millimeter across, they are called bronchioles. At their ends are the alveoli.
Each alveolar sac holds 20 to 30 alveoli. Gas exchange occurs only in the alveoli.
The alveoli are thin-walled and look like tiny bubbles. They sit in direct contact with capillaries, the narrowest vessels.
Oxygen moves from the alveoli into the vessels. Carbon dioxide moves from the vessels into the alveoli to be exhaled.
Estimates for the surface area of all the alveoli in the lungs are around 100 square meters. That is about half a tennis court.
From the lungs, the heart pumps oxygen-rich fluid to the organs and muscles. There, oxygen is exchanged for carbon dioxide, a cellular waste.
Carbon dioxide travels back to the lungs and is breathed out. Around and around, with every breath and every beat.
| Statement | True or false? |
|---|---|
| Air is warmed and moistened in the nasal cavity. | ? |
| Gas exchange happens all along the trachea. | ? |
| Bronchioles are tubes under 1 millimeter across. | ? |
| Carbon dioxide travels back to the lungs to be breathed out. | ? |
Clear tracing. Tomorrow is Windowsill Lab: counting breaths and pulse before and after a short run.