Blood transports materials around the body — Biology, 7–10 years
Blood moves through vessels, carrying useful materials to cells and taking some waste away. The heart keeps this transport moving around the body.
A moving delivery system
Blood is a liquid tissue that travels through tubes called blood vessels. It carries oxygen, water, digested nutrients, and chemical messages to different places. It also collects carbon dioxide and some waste, so the body can deal with them.
Why the body needs transport
Cells are spread throughout the body, but oxygen and nutrients enter in particular places, such as the lungs and intestines. A delivery system is needed to connect all those places. The heart provides the push that keeps blood moving through the vessels.
Following one oxygen molecule
1. You breathe oxygen into your lungs. 2. Oxygen crosses into nearby blood. 3. The heart pumps that blood through vessels. 4. A muscle cell receives the oxygen and uses it to release energy from food. 5. The blood then carries some carbon dioxide back towards the lungs, where you breathe it out.
Blood is not only red liquid
People often picture blood as one red fluid, because that is what we see in a cut. In fact, it contains liquid plasma and different kinds of cells, each with jobs such as carrying oxygen or helping stop bleeding. Veins may look blue through skin, but the blood inside them is still red.
Pulse shows transport in action
Each heartbeat pushes a wave through nearby arteries. You can often feel this pulse at your wrist or neck, though a grown-up should help if you are unsure where to look. Doctors measure pulse because exercise, illness, fear, and rest can change how fast the heart beats.
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