Capillaries - Definition, Examples, Quiz, FAQ, Trivia
Discover how the smallest blood vessels in your body deliver oxygen and nutrients to every cell!
What are Capillaries?
Capillaries are the smallest blood vessels in your body, so tiny that ten capillaries side-by-side would be as thin as a human hair! They form a network called capillary beds that reach every part of your body.
These microscopic tubes connect arteries (which carry oxygen-rich blood from your heart) to veins (which return oxygen-poor blood to your heart). Capillaries are so numerous that if you lined up all the capillaries in your body, they would stretch about 60,000 miles - that's long enough to circle Earth twice!
Science Fact!
Your body has over 10 billion capillaries - that's more capillaries than there are people on Earth!
Size
About 5-10 micrometers wide - just wide enough for a single blood cell to pass through
Structure
Made of a single layer of cells with thin walls for easy exchange
Location
Found throughout your body, especially in tissues that need lots of oxygen like muscles and brain
How Capillaries Work
Capillaries work through a process called microcirculation - the movement of blood through the tiniest vessels. Their thin walls allow important exchanges to happen:
Oxygen Delivery
Oxygen moves from blood in capillaries into body tissues
Nutrient Transport
Nutrients like glucose pass from blood to cells
Waste Removal
Carbon dioxide and other wastes move from tissues into blood
This exchange happens through a process called diffusion - molecules naturally move from areas of high concentration to low concentration. Capillaries have such thin walls that oxygen and nutrients can easily pass through to reach your cells.
Blood flow in capillaries is slow to allow enough time for this exchange to happen. Special mechanisms control tissue perfusion - the delivery of blood to capillary beds based on which tissues need the most oxygen.
Why Capillaries Are Important
Capillaries are essential to life for several important reasons:
Oxygen Supply
Deliver oxygen to every cell in your body
Nutrient Delivery
Bring nutrients from food to your cells
Waste Removal
Carry away carbon dioxide and other waste products
Without capillaries, oxygen and nutrients couldn't reach your cells, and waste products couldn't be removed. This would mean:
• Your muscles couldn't get energy to move
• Your brain wouldn't get oxygen to think
• Your organs couldn't function properly
• Your body couldn't heal injuries
Capillaries also help regulate body temperature by increasing or decreasing blood flow near the skin's surface. When you exercise, capillaries in your skin expand to release heat, making your face look flushed!
Capillaries Quiz
Test your knowledge about capillaries with this fun quiz! Answer all 5 questions to see how much you've learned.
Frequently Asked Questions
Here are answers to common questions about capillaries:
Fun Capillaries Trivia
Discover some amazing facts about capillaries:
Size Matters
Capillaries are so small that red blood cells have to bend and fold to squeeze through them! Some capillaries are narrower than the blood cells themselves.
Cold-Blooded Capillaries
Some fish have special capillaries in their gills that work in reverse - they absorb oxygen from water and release carbon dioxide back into the water.
Space Adaptation
Astronauts' capillaries change in space! Without gravity, blood flows differently, causing "puffy face syndrome" as fluid shifts toward the head.
Amazing Length
If you lined up all the capillaries in your body end-to-end, they would stretch about 60,000 miles - long enough to circle the Earth twice at the equator!
