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Blood Carries Oxygen and Food to Every Cell · Systems That Work Together · 4-LS1-1 · circulatory system

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Blood Carries Oxygen and Food to Every Cell

with Medi

Medi stands inside a giant glowing red tunnel shaped like a blood vessel, holding a tray of tiny oxygen bubbles and nutrient packets, pointing excitedly as a cartoon red blood cell zooms past carrying its delivery toward a waiting muscle cell at the tunnel's far end.

Explain what job the circulatory system does inside the body.
Identify the three main parts of the circulatory system: heart, blood vessels, and blood.
Describe how blood picks up oxygen in the lungs and delivers it to body cells.
Explain how blood carries away waste products that cells do not need.
Compare blood vessels to tubes that form a delivery network throughout the body.

Key terms

circulatory system: the team that moves blood around you
heart: a strong muscle that pumps your blood
blood vessel: a tube that carries your blood
artery: a tube carrying blood away from the heart
red blood cell: a tiny cell that carries oxygen

The Delivery Team

Every cell in your body needs oxygen and food to stay alive. Your circulatory system delivers them. It has three parts. The heart is a muscle about the size of your fist that pumps blood all day. Blood vessels are the tubes that carry blood everywhere. Blood is the delivery truck, with red blood cells that carry oxygen to every part of you.

One Delivery Trip

First, blood goes to your lungs, where red blood cells pick up fresh oxygen. Then your heart pumps that blood through arteries to every cell, even in your toes. The blood drops off oxygen and food, then picks up carbon dioxide waste. Last, blood travels back to the heart through veins to start the whole trip again.

Worked examples

How does oxygen reach a cell in your toe?

Red blood cells pick up oxygen in the lungs.
The heart pumps the blood out through arteries.
Blood travels all the way down to your toe.
The blood drops off oxygen at the toe cell.

Answer: Blood carries oxygen from the lungs to the toe cell.

Hi, I'm Medi, and today we're going on an amazing delivery adventure — inside your own body! Your body is made of trillions of tiny cells, and every single one of them needs two things to stay alive: oxygen and food (nutrients). Oxygen comes from the air you breathe, and nutrients come from the food you eat. As your body digests food, nutrients are absorbed through the walls of your small intestine and enter the bloodstream there, ready to be delivered. But how do oxygen and nutrients reach every cell, even the ones in your pinky toe? That's the job of your circulatory system. The circulatory system has three main parts working as a team. First, the HEART — a powerful muscle about the size of your fist — pumps blood nonstop. It squeezes roughly 100,000 times every single day! Second, BLOOD VESSELS are the tubes that carry blood everywhere. Think of them like a road system stretching to every corner of your body. The big highways are arteries (carry blood AWAY from the heart), and the return roads are veins (bring blood BACK to the heart). Tiny side streets called capillaries reach into every neighborhood of your body. Third, BLOOD is the delivery vehicle. Inside blood are red blood cells, which are shaped like little life preservers and are experts at carrying oxygen. Here is how one trip works: Blood travels to your lungs, where red blood cells pick up fresh oxygen (just like loading packages onto a truck). The heart pumps this oxygen-loaded blood out through arteries to every part of your body. When blood reaches a cell, it drops off the oxygen and nutrients the cell needs. Then it picks up a waste gas called carbon dioxide that the cell has made. Finally, blood travels back through veins to the heart, then to the lungs to drop off the carbon dioxide (which you breathe out) and pick up fresh oxygen again. Round and round it goes — never stopping! Here is a hint: if you ever get confused about which direction blood flows, remember 'Arteries Away from the heart' — both start with the letter A.

Activity

Sort each item into the correct stop on the blood's delivery route: Lungs, Heart, Body Cell, or Blood Vessel.

Practice

What two things does blood deliver to your cells?

Where do red blood cells pick up fresh oxygen?

Common mistakes to avoid

Blood only carries oxygenBlood also carries food to cells and carries waste away.
The heart sends blood without tubesBlood vessels are tubes that carry blood everywhere it goes.

Check your understanding

What is the main job of the circulatory system?

A student says, 'Blood only carries oxygen — it does not carry food or waste.' What is wrong with that idea?

Where do red blood cells pick up fresh oxygen before delivering it to the rest of the body?

Recap

Your circulatory system has a heart, blood vessels, and blood. Blood picks up oxygen in the lungs, delivers oxygen and food to cells, and carries waste away around and around.

Reflect

Picture blood zooming through you to feed every cell!