Transport System In Man

        Today we will be discussing about the transport system in mammals especially man.

     Generally, there are four major transport media which are;
1) Cytoplasm
2) Cell Sap or Latex
3) Blood
4) Lymph.

     This transportation system provides an efficient way of distribution of materials within the body and this is made possible by the blood and lymph. They represent the media of transportation in man but I will be discussing only about the Blood as a transportation medium in this article.

 COMPOSITION AND STRUCTURE OF BLOOD

STRUCTURE: The blood is a tissue in a fluid form. An adult man has about 5-6 litres of blood. The blood is made up of two major components, which are; (1) The blood cells and corpuscles [they are solid] and (2) The plasma [Liquid].

Blood Cells or Corpuscles: 

There are three types of blood cells or corpuscles. They are;1) Red blood cells (Erythrocytes)
2) White blood cells (Leucocytes)
3) Blood platelets (Thrombocytes)

     RED BLOOD CELLS (ERYTHROCYTES)

Description: Red blood cells also called erythrocytes are small, round and biconcave or disk-like in shape. They have no nucleus. One cubic litres of blood contains about 51/2 million red blood cells. Their normal life span is about 120 days (i.e 4 months) before they are destroyed by the liver. They are produced in the bone marrow. The red colour of the cells is due to the presence of ion compound called Haemoglobin.       The pigment haemoglobin in the red blood cell helps to transport oxygen from the lungs to the body cells. It combines readily with oxygen to form oxyhaemoglobin in the lungs.

WHITE BLOOD CELLS (LEUCOCYTES)

Description: The white blood cells which are also called leucocytes are irregular and amoeboid in shape. They are large, colourless and unlike the red blood cell I earlier discussed, they have a nucleus but lack haemoglobin.
     They are larger in diameter than the red blood cells but fewer in number than the red blood cells, only about 5000-10,000 of them are contained in a cubic millilitre of blood. They are made in the red bone marow, spleen or lymph nodes. They can live for many months.
         There are two types of white blood cells:

1) Phagocytes: The phagocytes are found in the lymphatic system where they ingest bacteria, virus and dead cells and help in preventing diseases. This process of ingesting these bacteria is known as Phagocytosis, and hence such white corpuscles are called phagocytes.

2) Lymphocytes: Unlike the phagocytes, the lymphocytes produce antibodies and are made in the lymph glands. They produce chemicals called antibodies which stick to the surface of germs and kill them.

Function: The white blood cells help to defend the body against diseases by ingesting the bacteria and virus that cause diseases.

      Now we know we have two types of white blood cells and have also learnt about their functions, so let's assume you find this kind of question in your exams;

"Which blood cells are involved in the immune response of vertebrates?"
A. Lymphocytes
B. Erythrocyes
C. Monocytes
D. Phagocytes

What will your answer be now? Think about it and comment your answer.

BLOOD PLATELETS (THROMBOCYTES)

Description: The blood platelets also called thrombocytes are tiny, irregular cell fragments without nucleus. They are produced in the red bone marrow. They are much fewer than the red blood cells, i.e., 250,000 - 40,000 per mm3 of human blood.

Function: Platelets aid the clothing of blood

                            PLASMA

Plasma is the liquid component of the blood. It is a pale yellow liquid which is made up mainly of water (about 90% water). There are so many substances dissolved in the blood plasma which include Plasma proteins, Antibodies, Salts, Gases, Hormones, Enzymes, Digested foods and other waste products.

Function: It helps to transport the substances that are dissolved in it as well as the cells that float in it

The next and concluding part of this post will be published soon. Stay tuned!

Drop your comments or questions.