Human Blood

Blood is a never-stationary fluid and it is always in motion from the heart to the arteries and back through the veins.

  • Colour: Bright red when taken from an artery and deep red when taken from a vein.
  • Volume: An average adult human has 5 to 6 litres blood.
  • Taste: Salty, slightly alkaline with a pH of 7.3 to 7.45.

Functions of Blood

  • It forms a clot which serves to prevent the loss of blood and the entry of disease-causing germs.
  • WBC protect the body from diseases by engulfing bacteria which may have entered the body.
  • Antibodies produced by the it neutralise poisonous substances or kill germs which enter the body.
  • It transports digested food from the alimentary canal to the tissues.
  • It transports excretory materials from the tissues to the liver, kidneys or skin for elimination.
  • It helps in keeping the temperature of the body uniform by distributing heat.
  • Haemoglobin of RBCs combines with oxygen to form oxyhaemoglobin which reaches tissues to deliver the oxygen.
  • Also Read Testes

Composition of Blood

It is made up of plasma and the blood corpuscles.

Plasma:

  • It is a light yellow-coloured alkaline liquid.
  • It mainly consists of :
    • Water- 90–92%
    • Proteins – 7–8%
    • Inorganic Salts – 1%
    • Other Substances – Trace amounts

Cellular Elements:

There are three kinds of cellular elements found in it:

  • RBC
  • WBC
  • Platelets

Red Blood Cells (RBCs/Erythrocytes)

  • RBCs are minute, disc-like structures.
  • RBCs are 7 µ in diameter.
  • In adults, RBCs are produced in the marrow of long bones such as ribs, breast bone and ileum of the hip girdle.
  • In children, RBCs are produced in the bone marrow of all the cells until 5 years of age.
  • Mature RBCs do not have nuclei.
  • The average life of RBCs is 120 days.

White Blood Cells (WBCs/Leucocytes)

  • WBCs are amoeboid.
  • WBCs are produced in the bone marrow, lymph nodes and sometimes even in the liver and spleen.
  • The average life of WBCs is about 2 weeks.
  • WBCs are classified into two categories based on their shape and characteristics.
    • Granular
    • Agranular
  • Leukaemia is a cancer in which the number of WBCs increases manifold at the cost of RBCs.
  • Leucopenia is the abnormal decrease in the number of WBCs.

Blood Platelets (Thrombocytes)

  • These are minute, oval or round, non-nucleated structures floating in the blood.
  • Platelets are derived from megakaryocytes in the red bone marrow.
  • Their life span is 3 to 5 days.
  • Platelets play an important role in blood clotting.

YOU MAY READ Connective Tissue


Follow us

Need more?

Discover more from Home of learning

Subscribe now to keep reading and get access to the full archive.

Continue reading

Scroll to Top