Blood is a connective tissue. It consists of a fluid matrix, plasma and formed elements.

1.) Blood plasma:- Constitutes 55% of blood, it is pale yellow in color, slightly alkaline and viscous fluid. It consists of about 90% water, 1% inorganic salts in solution and 7-8% proteins in colloidal state. Remaining are gases, cholesterol and waste materials.

2.) Formed elements:- Blood corpuscles are known as formed elements. They are produced in the red bone marrow. These include a) Red blood cells:- They are round, unnucleate, membrane bound cells that carry pigment haemoglobin. Healthy man containa 25 trillion RBCs . Cell organelles are present in mature RBCs. The pigment "Haemoglobin" binds to oxygen and oxygen is then transported throughout the body. Average life spa of RBCs is120 days.

b) White Blood cells:- They are colorless because they lack haemoglobin. They are nucleated, with cell organelles, have ameboid activity. They are also called as "leucocytes". WBCs further comprise of

"Granulocytes and Agranulocytes". WBC's are the main defense system of our body. Further WBCs include Neutrophils, Basophils, Eosinophils, Monocytes, and Lymphocytes.

3) Blood Platelets:- Also called as " Thrombocytes". They are uninucleate, colorless and lack hemoglobin. Their number varies between 150000-350000. The life span of platelets is 3-7 days and they are responsible for clotting.