Wednesday, 15 September 2021 09:16

Human Body - Class 7 Science Revision Notes

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The Blood Circulatory System

Parts of the Circulatory System

  • The heart-The pumping organ
  • The blood-The transport fluid.
  • The blood vessel-They are pipes through which the blood flows

Blood Components and their Functions

  • Plasma-The liquid part of the blood which transport digested food materials, salts and other dissolved substances.
  • Red blood cells-They contain red colouring matter called haemoglobin, which gives blood the red colour, red blood cells
    helps in transporting oxygen.
  • White blood cells-They have a nucleurs, they help in fighting and killing disease-causing germs.
  • Platelets-They help in blood clotting ie further loss of blood through wound.

Types of Blood Vessels and their Functions.


  • They carry blood away from the heart
  • They have thick walls
  • They have a narrow lumen.
  • They have no valves since they carry blood at a high pressure  from the heart.
  • They carry oxgyeneted blood except pulmonary artery which carry deoxgeneted blood from the heart to the lungs.
  • Main artery is Aorta.


  • They carry blood from other body parts to the heart.
  • They have thin walls.
  • They have a wide lumen.
  • They carry blood at a low pressure.
  • They carry deoxygenated blood except pulmonary vein which carry oxygenated blood from lungs to the heart.
  • Main vein is Venacava.


  • They are small blood vessels that help to take blood to all parts of the body.
  • They are found all over the body.
  • They cover a wide surface of the body.

The Heart

  • It has four chambers, two chambers are on the upper parts(Auricles) and two chambers on the lower parts(Ventricles)
  • The heart is also divide into left and right side which is vertically lateral to how it faced(Your left hand side becomes the right when in paper and vice versa).
  • The parts include: Right auricle, Left auricle, Right ventricle and Left ventricle.
  • The heart also have valves ie semi lunar valve, tricuspid valve and bicuspid valve.

The Circulation of Blood.

  • Blood from all parts of the body flows into the right auricle of the heart through venacava, then its pumped through pulmonary artery to the lungs for oxidation.
  • In the lungs, oxygen is added to the blood and carbon dioxide is removed.
  • Oxygenated blood then flows to the left auricle of the heart through the pulmonary vein.
  • The muscular left ventricle then pumps the blood to all parts of the body through the aorta. This process repeats back and forth making another cycle.
    NB: When one inhales carbon monoxide the chamber of the heart that receives it first will be left auricle, but when one is bitten by a snake the poison will first reach the right auricle through venacava.

The Importance of Blood Circulation.

  • It transports food from the small intestine to all parts of the body.
  • Transports oxygen from the lungs to all cells of the body.
  • Transports carbondioxide from the body tissues to the lungs.
  • Wastes materials like urea to the kidney.
  • Transports heat to all parts of the body.

Activity: Draw a well labelled diagram of the heart.

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Read 1563 times Last modified on Wednesday, 15 September 2021 09:33