TRANSPORT IN MAMMALS PART 4: WHITE BLOOD CELLS (LEUCOCYTES)

Characteristics of white blood cells:

• Colourless
• Irregular in shape
• Contains nucleus
• Contains no haemoglobin
• Larger in size than red blood cells
• Fewer in number than red blood cells
• The ratio of red to white blood cells is 700:1

There are two main kinds of white blood cells

• Lymphocytes
• Phagocytes

LYMPHOCYTES

• Produced by the lymph glands or the lymph nodes.
• Has large rounded nucleus with small amount of non-granular cytoplasm.
• Nearly round in shape.
• Show limited movement.
• Function: to produce antibodies which fight against micro-organisms other than bacteria (mainly viruses).

A Lymphocyte

PHAGOCYTES

• Produced by the bone marrow.
• Has lobed nucleus with granular cytoplasm.
• Irregular shape.
• Able to move.
• Function: to fight against foreign particles (mainly bacteria) by means of phagocytosis.
  

A Phagocyte

The following figure shows phagocytosis. In phagocytosis, first the phagocyte moves with the help of its pseudopodia towards the foreign particles (bacteria). Upon reaching the foreign particles, it will then engulf the foreign particles by surrounding them using the pseudopodia. A vacuole is formed as a result. Digestive enzyme is then secreted into the vacuole which digests the foreign particles. The products of digestion is then absorbed into the cytoplasm and when the phagocyte died, pus will be formed at the infected area.

TRANSPORT IN MAMMALS PART 3: RED BLOOD CELLS (ERYTHROCYTES)

The following are the characteristics of a mammalian red blood cell:

• Shape: biconcave (provides large surface area for more absorption of oxygen).
• No nucleus (this enables the red blood cell to accommodate more haemoglobin so that more oxygen molecules can be transported and to make the red blood cell more flexible so that it can squeeze itself through the blood capillaries).
• Produced by the bone marrow as shown below.

• Lifespan: 3 to 4 months (when they are worn out, they are destroyed in the liver).
• Contains haemoglobin (a speial kind of protein containing iron): this pigment enables red blood cell to transport oxygen from the lungs to all cells in the body (mind you carbon monoxide combines readily with haemoglobin than oxygen).
• When haemoglobin is broken down in the liver, the iron is released and stored in the liver (hence liver is very rich source of iron). Bile pigments are also produced during the breakdown of haemoglobin (bile pigments are excreted into the colon and gives faeces its colour - brownish and sometimes greenish depending on the amount of bile pigments being excreted).

BLOOD APPEARS RED IN COLOUR BECAUSE OF THE RED BLOOD CELLS