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What's in blood?

posted Jan 27, 2015, 10:47 PM by Ranmini Perera   [ updated May 15, 2015, 1:02 PM by Upali Salpadoru ]
 Nelly, sharpening a pencil cut her finger. She washed it under a tap. The bleeding continued. Her mother covered the wound with a piece of gauze.


The bleeding stopped. How did the bleeding stop?
Fig. 1.   Nelly cut her finger.   


The blood is the  mysterious fluid in your body. If you consider the body to a State, and the brain to be the President, two major ministries. What are they?
  • The Ministry of Transport.
  • The Ministry of Defense are handled by blood.

There is a network of arteries, veins and capillaries in our body. If even a tiny puncture occurs in any of these vessels you can bleed unto death. But this does not happen. When ever an injury occurs in one of the vessels a vigilant fleet of servicemen rush there. They bind together and cover up the lesion in a jiffy. Then they weave a fabric to strengthen it further. This amazing repair job is performed by the Thrombocytes (Platelets), smallest cells in your blood  

The defense is handled by  two battalions, Phagocytes and Lymphocytes. Although there are several units among the Phagocytes they all  swallow up and digest the harmful  bacteria .

The Lyphocytes  have their own unique way of attack. They observe the enemy pathogens , bacteria and viruses and manufacture a chemical which will cling on to them making them inactive. This kind of defensive chemicals are called ‘anti bodies’.

Transport Activity.

The materials to be transported fall into three categories.
(i)  Gases,     (ii)   nutrients and    (iii)   waste products.

Transport of gases is mainly performed by an iron rich organic compound called Haemoglobin. This substance is packed into Erythrocytes. (Red blood corpuscles) They have even discarded the nuclei for this purpose. So they cannot do most of the functions done by other cells. They only provide berth to Haemoglobin. As their life time is short, they have to be continually assembled by the cells inside certain bones. (bone marrow)  

Haemoglobin has the special ability to take Oxygen when there is excess of it and release oxygen when there is a scarcity. The two reactions are shown below as a reversible reaction:

The reaction moves to the right in the lungs, taking Oxygen  from the air sacs . The reaction proceeds to left breaking down Oxy-haemoglobin,  when inside the tissues. (A tissue is a group of similar cells performing a certain function)   

The blood cells float or swim in a solution of water, called Blood plasma. There are many salts, glucose, amino acds, vitamins  and chemical messengers dissolved in this. This has a pale yellowish colour and can easily mix with the fluid surrounding the cells in the tissues. Plasma carries the nutrients to tissues and brings back the harmful products formed.
Red circle  = Red blood cells.    Blue circle = O2   CO2 = Carbon dioxide.

 Fig. 2.0   How the Red Blood Cells tackle the gases.

[ The pumping system by the heart and the waste disposal by kidneys etc, are not shown here]

                                     Functions of Blood



3. Protective

4. Other

i. Taking Oxygen from the lungs to various parts of the body.

i. Distribute the heat, produced in muscles to maintain the body temperature at 37o C.

i.Blood is in a closed system. If a puncture occurs it can seal it off by clotting.

i.Maintains certain physical factors such as pressure, viscosity, volume,

male, 5-6L,

Female 4-5L .

(8% of body weight)


ii.Carbon dioxide formed in the cells is taken to lungs for removal.

ii. Maintain the concentration  of electrolytes,

Na+ (0.9%),                   K+,  Ca2+, HCO3-, Mg2+), C1-, HPO42-, and HCO3-


i.Most of the harmful invaders are tackled by white blood cells (leucocytes) and anti bodies.

ii.Certain glands secrete hormonesinto the bblood. These are delivered to stimulate various reactions.

iii.Nutrients such as glucose, amino acids, vitamins are carried to cells .

ii.   Controls the intake and removal of water.



iv.Lactic acid in the muscles and Urea  produced in the liver  could be toxic. This is taken by blood  to be filtered out by the kidneys.

iii. pH level (acidity)of the blood is kept between 7.3 and 7.4.



                                  Function of Blood cells