🫀 Body Systems
6 major body systems · Click to explore · Facts & quiz · Grades 3–6
❤️ Circulatory System
HeartYour heart beats about 100,000 times every day, pumping blood to every cell
Blood vesselsIf you lined up all your blood vessels end-to-end, they'd stretch 60,000 miles
BloodRed blood cells carry oxygen; white blood cells fight germs; platelets stop bleeding
🫁 Respiratory System
LungsYou breathe about 20,000 times a day — your lungs hold about 6 liters of air
DiaphragmThis dome-shaped muscle under your lungs contracts to pull air in
Gas exchangeOxygen enters your blood in tiny air sacs called alveoli; CO₂ exits
🦴 Skeletal System
BonesAdults have 206 bones, but babies are born with about 270 (some fuse together!)
Biggest boneThe femur (thigh bone) is the longest, strongest bone in your body
Smallest boneThe stapes in your ear is the smallest bone — about the size of a grain of rice
💪 Muscular System
MusclesYour body has over 600 muscles — they make up about 40% of your body weight
StrongestThe masseter (jaw muscle) can close your teeth with up to 200 pounds of force
SmallestThe stapedius muscle in your ear is the smallest — it protects your hearing
🧠 Nervous System
BrainYour brain has about 86 billion neurons that send signals at up to 268 mph
Spinal cordThe spinal cord connects your brain to nerves throughout your body
ReflexesReflexes are automatic responses — your hand pulls away from heat before you 'think'
🍕 Digestive System
JourneyFood travels about 30 feet from your mouth through your digestive tract
StomachYour stomach uses strong acid (pH 1.5–3.5) to break down food
IntestinesMost nutrients are absorbed in the small intestine, which is about 20 feet long
🎯 Quiz Time!
⭐ 0Q 1/4
Learning About Body Systems
Understanding how the human body works is a cornerstone of elementary science education. By exploring the circulatory, respiratory, digestive, skeletal, muscular, and nervous systems, students build foundational knowledge that connects to health, nutrition, and physical education.
This interactive tool lets students click through each body system, discover fascinating facts, and test their knowledge with a built-in quiz. Aligned with Next Generation Science Standards (NGSS) for grades 3–6.
Last reviewed: April 2026
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