various constituents of blood

Q: What is blood. Describe various constituents of blood?

 

ANS:  BLOOD

           Blood is the circulatory fluid present within the blood vessels. It is a highly complex substance composed of suspended materials.

Volume relationship of plasma and blood cells in human blood

CONSTITUENTS OF BLOOD

              If blood is put in a test tube along with some anticoagulant, it quickly separates into two layers: the upper yellowish and semi-transparent layer is the plasma and the lower layer contains mainly the blood cells.

PLASMA

                It is the liquid portion of the blood which is about 55% of the volume of the blood. It is mainly water which is about 90% by weight of the plasma. A large number of organic and inorganic substances are dissolved in water.

BLOOD PROTEINS

              7 to 8 percent of the plasma is made up of different kinds of proteins which play many functions.

1-       Transport of Iron:- Inorganic iron is attached with a special type of protein which transports the iron in the body to various places.

2-   Maintenance of Osmotic Pressure:- Proteins help to maintain the osmotic pressure of blood.

3-  Blood clotting:- A blood protein called fibrinogen helps in blood clotting.

4-  Antibodies:- These are also blood proteins which provide immunity against certain diseases.

5-  Hormones:- Some blood proteins are hormones.

                  Plasma also contains salts and sugar constituents.

Salts:-  They constitute about 0.9%. Sodium chloride and calcium ions are abundant while potassium and magnesium ions are in lesser amounts.

Simple Sugars:- They constitute about 0.1%. Glucose is more important.

Products of Digestion of Metabolic Wastes:- 2 to 3% of the plasma is made up  of products of digestion like amino acids, fatty acids etc. and metabolic wastes such as urea, uric acid, carbon dioxide etc.

BLOOD CELLS

               They constitute about 45% of the blood. There are three types of blood cells: red blood cells, and platelets.

Red Blood Cells

a)      The red blood cells or erythrocytes are most abundant. One cubic millimeter of blood has about 5 million red blood cells.

 

Composition of human blood

b)     The human or mammalian red blood cell, are biconcave in shape and lack nucleus.

c)      They contain oxygen carrying protein, called hemoglobin which is an iron- containing, pigmented compound that gives red colour to the blood.

d)     The average life of a red blood cell is about 120 days.

e)      They are formed in the liver and spleen in embryonic stages, but after birth they are formed in red marrow of certain bones such as the ribs and breast bones. The old cells worn out and are destroyed chiefly in the spleen and liver. A portion of the hemoglobin is finally changed in to bile pigment and most of the iron is returned to the bone marrow.

White Blood Cells or Leucocytes

a)      They are colour less and have a nucleus.

b)     They are larger than red blood cells but much less in number. One cubic millimeter of blood contains 7000 to 8000 W.B.C.

c)      There are many types of white blood cells however they can be classified, broadly, into two groups on the basis of structural difference.

 

Phagocytosis of a bacterium by a neutrophil

 

i)                   Those with a single nucleus and a clear cytoplasm. Lymphocytes and monocytes that arise from the lymphatic tissue.

ii)                Those having an incompletely partitioned nucleus and a cytoplasm containing fine granules. Basophils and neutrophils that arise from the red bone marrow.

 

d)       White blood cells have short life time i,e., 3 to 4 days.

e)        The major function of the W.B.C is to protect the body from invading microorganism. Some white blood cells like neutrophils and monocytes engulf foreign particles, such as bacteria, by forming pseudopodia around them. These and other leucocytes also gather at the site of infection and help to combat the disease by destroying bacteria. The pus that forms in an infected wound is largely a collection of leucocytes that have died in fighting bacteria.

Platelets

         Blood platelets are quite smaller than both the red and white blood cells. They are small, oval pieces of specialized bone marrow cells and are without nucleus. They play a central role in the clotting of blood i.e., they tend to stop blood from flowing out of damaged blood vessels.