Lumen (anatomy) facts for kids

A lumen (say: LOO-men) is the open space inside a tube-like part of your body. Think of it like the hollow center of a straw. Many parts of your body are shaped like tubes, and the lumen is the space through which things can pass. For example, your blood vessels (like arteries and veins) have a lumen where blood flows. Your digestive system, which is a long tube from your mouth to your end, also has a lumen where food travels.

Cross section of the gut. The lumen is the space in the middle also known as the volume.

What is a Lumen?

In biology, a lumen (plural: lumina) is the open space inside a tube-shaped structure. This term is used for many different parts of the body. It helps describe the inside of organs that are like pipes or tunnels.

Where Can You Find Lumina?

You can find lumina in many places throughout your body. They are essential for how your body works. Here are some common examples:

Blood Vessels

• Arteries: These are tubes that carry blood away from your heart. Their lumen is the space where blood flows to all parts of your body.
• Veins: These tubes bring blood back to your heart. The lumen of a vein is where the blood travels on its return journey.
• Capillaries: These are tiny blood vessels that connect arteries and veins. They have very small lumina, just wide enough for blood cells to pass through in a single file.

Digestive System

• Gastrointestinal Tract: This is a long tube that starts at your mouth and ends when waste leaves your body. It includes your esophagus, stomach, and intestines. The lumen of your gastrointestinal tract is the space where food moves and is digested.

Other Body Parts

• Kidney Tubules: In your kidneys, there are tiny tubes called tubules. Their lumina are where your body filters waste from your blood to make urine.
• Airways: Your windpipe (trachea) and the smaller tubes in your lungs (bronchi and bronchioles) also have lumina. This is the space where air travels when you breathe in and out.
• Glands and Ducts: Many glands in your body make substances like sweat or hormones. These substances often travel through small tubes called ducts, which also have lumina.

Why is the Lumen Important?

The lumen is very important because it allows things to move through your body. Without these open spaces, blood couldn't flow, food couldn't be digested, and air couldn't reach your lungs. The size of a lumen can change. For example, blood vessels can get wider or narrower, changing the size of their lumen to control blood flow.