Lesson Notes By Weeks and Term - Junior Secondary School 3






  • Basis Science Made Easy for JSS Three by F.I Kehinde et al
  • Basis Science Made Easy for JSS Two by F.I Kehinde et al
  • STAN Integrated Science for JSS Three
  • Precious Seeds Basic Science for JSSThree by J.O Otugboyega et al.




  • Blood Components and Functions.
  • The Heart and Blood Vessels.
  • The Human Circulatory System
  • Blood Defects and Diseases

Blood Components and Functions

Blood is a liquid connective tissue, which is maintained in constant circulation round the body. In certain organisms, blood flows within a closed system of inter connecting vessels while the reverse holds in other organisms.

The human blood is of PH 7.4 and comprises four components:

  1. Plasma [liquid part of blood]
  2. Red Blood cells [Erythrocytes]
  3. White Blood Cells [Leucocytes]
  4. Blood platelets [Thrombocytes]


This is the liquid part of blood, which makes up about 55% volume of blood. The plasma itself is made of about 90% water, proteins and mineral salts. It takes digested food from the small intestine to places where needed and also takes waste product to the excretory organs for removal.

RED BLOOD CELLS: These are the most numerous cells in the blood. They account for the redness of blood. Each red cell contains HEAMOLOGIN, a respiratory pigment which enables Red Blood Cells to transport oxygen in the blood. Red blood cells are also called ERYTHROCYTES. They are formed in the BONE MARROW and destroyed in the LIVER and SPLEEN when too old to perform their functions completely after about 120days of existence.


They are the least numerous cells in the blood. They fight microorganisms and infections in the blood. WBC also helps the body to destroy bacteria and viruses through the agency of ANTIBODIES in the blood plasma.


The second most numerous blood cells which help blood to clot in wounds. They are also called THROMBOCYTES. They are tiny cells, which are much smaller than either the RBCs or WBCs. Most often they are found as fragments.


  1. What is Blood?
  2. State the components of blood.
  3. Explain briefly each blood component.

The Heart and Blood vessels

The heart is the muscular pumping organ, which maintains a continual flow of blood round the body. The human heart comprises four chambers namely:

  1. The 2 upper and smaller chambers [ARTRIA or AURICLES]
  2. The 2 Lower and bigger chambers called VENTRICLES

The heart is connected to blood vessels within which blood is transported round the body.


Three types of blood vessels known are:

Veins : Return blood to the heart

Arteries: Carry blood away from the heart.

Capillaries: Link arteries with venules

Differences between

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Carry blood away from the heart Returns blood to the heart
Carry oxygenated blood at highCarry deoxygenated blood under low pressure
Are deeply located under the skin.Are superficially located beneath the skin


  1. Mention the chambers associated with blood vessels and valves of the human heart.
  2. State two differences between arteries and veins.


It is described as a closed circulatory system in that blood is circulated round the body through a system of interconnecting blood vessels. The human circulatory system is also described as double circulation in that blood has to flow twice through the heart before one complete circulation can be made through each time it does. It flows through separate pathways.

The two pathways are known as the:

  1. Lung or Pulmonary pathway.
  2. Body or systemic pathway.

The lung pathway ensures re-oxygenation of the blood while the body pathway ensures delivery of oxygen to the tissues and cells of the body.


  1. What does it mean to describe the human circulatory system as:a. Closed circulationb.Double circulation?
  2. What kind of blood is conveyed by the a. Pulmonary artery b. Pulmonary vein c.Aorta d. Vena cava?

Blood Defects and Diseases

Some people may suffer through not having enough RBCs and hence are unable to get sufficient supply of oxygen.These people can be said to be Anaemic.Thus, anemia is a serious blood defect. Other blood diseases abound and are named below viz:

  1. Leukaemia
  2. Haemophilia
  3. Sickle cell
  4. Septicemia
  5. Hypertension
  6. Hypotension

Leukaemia: Imbalance of red and white blood cells as there is a preponderance of defective and cancerous WBCs. This is caused by exposure to radioactive fall-out from atomic bombs or by over exposure to x-rays.

Sickle Cell: This is a disease which arises from the formation of sickle shaped red blood cells in the blood and which are unable to deliver the oxygen requirement of the body promptly and effectively. It is hereditary.

Haemophilia: Inability ofthe blood to check blood loss automatically when minor injuries are sustained. It is also hereditary.

Septicemia: Blood poisoning due to certain bacterial infections and which results in lacking of the blood

Hypertension: Describes the clinical condition of high blood pressure.

Hypotension: Low blood pressure. Occasionally, bleeding may occur when blood vessels are damaged or ruptured in accidents, wounds and certain illnesses.


  1. Mention two heritable blood diseases.
  2. Distinguish between hypertension and hypotension.
  3. What is Blood?
  4. State the components of blood.
  5. Explain briefly each blood component.


Integrated Science Made Easy, bk two pgs 21-25


  • Which one of these is NOT a Blood compound cell?A. Plasma B. Erythrocytes C. Leucocytes D.Thrombocytes
  • A disease caused by a preponderance of cancerous and defective white blood cells in the blood describes A. Septicemia B. Leukemia C. Hemophilia D. Hypertension
  • The blood vessels, which look arterioles up with vennules, are known as A. Arterioles B. Vena cava C. Capillaries D. Vennules
  • The chamber of the heart with the thickest wall is the A. Left ventricle B. right auricle C. left auricle D. right ventricle
  • The largest artery in the body is the A. Pulmonary artery B. aorta C. hepatic artery D. renal artery


  1. Draw and label the human heart.
  2. Write briefly on the human circulatory system.

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