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Human Body (Circulatory System) - Class 7 Science

Human Body (Circulatory System)

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Human Body: The Circulatory System

Last Updated: 31st May 2020

The Circulatory System

- Blood circulation is the flow of blood from the heart to all parts of the body and then back to the heart.
- The circulatory system is made up of the heart, blood as well as the blood vessels.

The Human Circulatory System

- Blood is circulated in two main ways:
  1. From the heart to the lungs for oxygenation and then back to the heart
  2. From the heart to the rest of the body

The Heart

- The heart is a muscular organ located in the chest cavity. Its purpose is to pump blood to all parts of the body.
- It is divided into two main parts; the left side and the right side
- The heart is made up of 4 chambers; the upper two chambers are identified as auricles while the bottom two chambers are identified as ventricles.
- Four main blood vessels connect to the heart:
  • Pulmonary artery
  • Pulmonary vein
  • Vena Cava
  • Aorta

The Heart
Cross-sectional picture of the heart

- Deoxygenated blood from all parts of the body (except the lungs) enters the heart through the vena cava, which is largest vein in the human body.
- Oxygenated blood leaves the heart through the aorta, which is the largest artery in the human body.
- The right auricles receives blood from all parts of the body and directs it to the right ventricle which pumps this blood to the lungs for oxygenation. This blood is carried to the lungs through the pulmonary artery.
- Oxygenated blood flows from the lungs to the left auricle through the pulmonary vein. It then flows to the muscular left ventricle and is pumped to the rest of the body through the aorta.


- Blood is made up of 4 main components:
  • Plasma
  • Red blood cells
  • White blood cells
  • Platelets
- Plasma is identified as the liquid part of the blood and is responsible for transporting substances through the body.
- White blood cells fight germs in the body and gives the human body the much required immunity against diseases.

The White Blood Cell

- Red blood cells carry oxygen from the lungs to all parts of the body.

The Red Blood Cell

- Platelets helps prevent excessive bleeding by clotting.

A Platelet

Blood Vessels

- These are tubes through which blood flows.
- There are three types of blood vessels
  1. Arteries
  2. Veins
  3. Capillaries


- Are thick walled with a narrow lumen.
- All arteries, except the pulmonary artery, carry oxygenated blood from the heart.

An Artery


- They have a wide lumen.
- They have valves are intervals.
- All veins, except the pulmonary vein carry deoxygenated blood towards the heart.

A Vein


- They are thin-walled.
- They are the point of exchange between the arteries and the veins.

A Capillary

Importance of blood

  • Blood helps distribute digested products to all parts of the body
  • Blood carries waste materials from body cells to the excretory organs for removal
  • Blood distributes heat to body parts as it flows
  • Red blood cells carry oxygenated blood to all parts of the body. This oxygen is used for respiration in the cells
  • The white blood cells helps fight germs found in the body
  • Blood carries hormones from their area of production to the area of their action

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