🔬 ScienceGrade 3Lesson 26
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Circulatory and Respiratory Systems

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Learning Objectives

  • 1Identify the organs of the circulatory and respiratory systems
  • 2Match each body part to the system it belongs to
  • 3Explain how the circulatory and respiratory systems work together
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Mini Lesson

Two of the most important body systems are the circulatory system and the respiratory system. They work closely together: the respiratory system brings oxygen into the body, and the circulatory system distributes that oxygen to every cell.

The Circulatory System

  • Heart — a powerful muscle that beats about 70 times per minute, pumping blood through the body.
  • Arteries — thick-walled blood vessels that carry oxygen-rich blood AWAY from the heart to the body.
  • Veins — thinner blood vessels that carry oxygen-poor blood BACK to the heart.
  • Capillaries — tiny, hair-thin blood vessels that connect arteries and veins in every tissue.
  • Blood — the fluid that carries oxygen, nutrients, hormones, and waste products.

The Respiratory System

  • Lungs — two spongy organs that take in oxygen and release carbon dioxide.
  • Trachea (windpipe) — the tube that carries air from the nose/mouth to the lungs.
  • Bronchi — two tubes that branch from the trachea into each lung.
  • Diaphragm — a large muscle below the lungs that pulls air in (contracts) and pushes air out (relaxes).

How They Work Together

  1. You breathe in air through your nose or mouth.
  2. Air travels down the trachea, through the bronchi, and into the lungs.
  3. Oxygen passes from the lungs into the bloodstream (capillaries around the lungs).
  4. The heart pumps this oxygen-rich blood through arteries to the entire body.
  5. Cells use the oxygen and produce carbon dioxide as waste.
  6. Veins carry carbon dioxide back to the lungs, where it is breathed out.
Body parts and their systemsSix rows matching body parts to their systems: Heart to Circulatory, Lungs to Respiratory, etc.Body Part and Its SystemHeartCirculatory SystemLungsRespiratory SystemFemur (bone)Skeletal SystemBicep muscleMuscular SystemBrainNervous SystemStomachDigestive System
Circulatory and Respiratory working togetherA simple diagram showing how oxygen moves from the lungs to the heart and then to the body cells.Oxygen Journey1Breathe in air (nose/mouth)2Air reaches the lungs3Oxygen enters the blood4Heart pumps blood to body5CO2 breathed back out
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Remember: arteries go AWAY from the heart (A for Away), veins RETURN to the heart (V for back).

Vocabulary
Heart
The muscular pump that pushes blood through the bodye.g. Your heart beats faster when you exercise.
Lungs
The two organs that take in oxygen and release carbon dioxidee.g. Your lungs expand when you breathe in.
Artery
A blood vessel that carries blood away from the hearte.g. The main artery from the heart is called the aorta.
Vein
A blood vessel that carries blood back to the hearte.g. The veins appear blue under the skin.
Trachea
The windpipe — the tube carrying air from the mouth to the lungse.g. Air passes through the trachea before reaching the lungs.
Diaphragm
The muscle below the lungs that controls breathinge.g. The diaphragm contracts when you take a deep breath.
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← Lesson 25: Body Systems OverviewLesson 27: Balanced Diet and Nutrients →