The Human Body
The Circulatory System
Your heart beats roughly 100,000 times a day without you ever consciously thinking about it — a lifetime total in the billions.
The Nervous System
A communication network so fast that a signal can travel from your toe to your brain and back in a fraction of a second — all without you ever consciously noticing it happen.
The Microbiome
Your gut is home to trillions of microorganisms — and increasingly, scientists suspect at least some of them may have a say in your mood.
The Immune System
A defense network so effective it can remember an enemy it fought off years ago, and respond to it faster the second time around.
The Digestive System
Despite its name, the small intestine is actually the longest section of your entire digestive tract — it's just narrower than the large intestine.