🩸 THE CIRCULATORY SYSTEM
PAGE 1 OF 5 · THE MIGHTY PUMP
LUB-DUB
YOUR HEART NEVER CLOCKS OUT
The heart is a muscular organ about the size of your fist. It squeeze-releases about 100,000 times a day, pushing blood into thick-walled arteries. The double beat you hear is valves snapping shut after each push. This pump started before you took your first breath and plans to outlast your homework — if you treat it well.
⚡ DID YOU KNOW?
If you laid every blood vessel end to end, adults could stretch roughly 100,000 km — enough to wrap around Earth more than twice.
BEAT!
FOUR CHAMBERS
💓 Two atria receive blood.
💪 Two ventricles shoot it onward.
💪 Two ventricles shoot it onward.
MILES OF TUBING
🌍 Arteries split into tiny branches.
🔄 Veins merge as blood heads home.
🔄 Veins merge as blood heads home.
PAGE 2 OF 5 · WHAT BLOOD CARRIES
PLASMA & CELLS
NOT JUST RED GOO
Plasma is the watery, salty fluid that keeps cells swimming and carries hormones, nutrients, and heat. Red blood cells haul oxygen on hemoglobin. White blood cells police infections. Platelets patch leaks when you scrape a knee. Every microliter is a crowded teamwork scene.
CARRY!
PLASMA
🟡 ~55% of blood; mostly water + proteins.
RBC
🔴 No nucleus — room for O₂ pick-up in lungs.
WBC + PLT
🛡️ Immune clean-up + 🩹 quick clotting plugs.
PAGE 3 OF 5 · THE HIGHWAY SIZES
ARTERIES
⬆️ Carry blood away from the heart under high pressure.
🫀 The aorta is the super-highway exit.
🫀 The aorta is the super-highway exit.
VEINS
⬅️ Return blood toward the heart; many have valves so gravity cannot undo flow.
🦵 Skeletal muscle squeeze helps move venous blood.
🦵 Skeletal muscle squeeze helps move venous blood.
CAPILLARIES
EXCHANGE ALLEY
The walls of capillaries are only one cell thick. Oxygen, glucose, and waste slip between blood and tissues in slow, controlled diffusion. This is the delivery dock where general circulation actually meets the cells of muscles, brain, and every organ. Slow flow + huge surface = efficient swaps.
SWAP!
PAGE 4 OF 5 · LUNGS & LOOPS
CIRCUIT
PULMONARY + SYSTEMIC
In the pulmonary circuit, the right side of the heart sends deoxygenated blood to the lungs; red blood cells load oxygen and dump carbon dioxide. The left side then launches the systemic circuit, feeding the whole body. Two loops, one heart — timing coordinated so you never run out of fresh supplies during a sprint or a test.
LOOP!
GAS SWAP
🫁 Alveoli: thin air-blood border for O₂/CO₂.
DUAL PATH
🔴 Oxygen-rich = systemic path.
🔵 Lungs return pink blood to the left.
🔵 Lungs return pink blood to the left.
FED ORGANS
🧠 Brain & 💪 muscle always first-class passengers.
PAGE 5 OF 5 · CARE FOR THE PUMP
HABITS
EARN EASY BEATS
Aerobic exercise trains heart muscle to pump more blood per beat — fewer wasted beats. Colourful plant foods, lower excess salt, and not smoking keep vessels springy. Sleep and stress care keep blood pressure from riding high. Your circulatory system never stops; small habits decide how comfortable that marathon feels decades from now.
STRONG!
CHECKLIST
🏃 Cardio most days
🥬 Veg & fruit colours
💧 Water steady
🚭 Skip smoke & vape
🥬 Veg & fruit colours
💧 Water steady
🚭 Skip smoke & vape
RECAP
🩸 KEY FACTS
Heart pumps → arteries → capillaries exchange → veins return → lungs re-oxygenate. Blood = plasma + RBC + WBC + platelets. One continuous delivery loop, ~100k beats daily.
✅ Arteries away, veins to heart.
✅ Capillaries do the hand-offs.
✅ You can help vessels stay stretchy.
✅ Capillaries do the hand-offs.
✅ You can help vessels stay stretchy.
🧠 QUIZ TIME!
THE CIRCULATORY SYSTEM · 5 QUESTIONS
QUESTION 01
Which organ pumps blood through the entire circulatory system?
QUESTION 02
Which blood cells carry most of the oxygen in your body?
QUESTION 03
Arteries carry blood ___ the heart to the rest of the body (systemic circulation).
QUESTION 04
Where do gases, nutrients, and wastes mainly move between blood and body cells?
QUESTION 05
The mostly watery liquid part of blood is called:
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