The blood is red viscous connective tissue. It means opaque, sticky, viscous, bright red also slightly chemical (ph 7.4) in nature. 

1. Plasma (55%)
2. Blood corpuscles(45%)

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• It is a faint yellow-coloured part of blood and forms about 55-60% of blood volume. It is formed of water (90-92%),  proteins like albumins, globulins, fibrinogen, materials, hormones, anticoagulants, antibodies, etc(1-2%).

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1. Transportation of materials like food components. e.g. glucose, amino acids, respiratory gases, waste material, hormones, minerals etc.
2. Transportation of heat so helps in homeothermy.
3. Prothrombin and fibrinogen proteins help in blood clotting at the injury.
4. Globulin provides immunity (resistance against diseases).
5. Bicarbonates and certain plasma proteins help in the ph constancy of blood.

• In human blood, RBCs are biconcave and enucleated. each is about 7-8um in size. These are most numerous and the RBC count of a normal adult human male is 5-5.5 million per cubic mm of blood and is slightly more than a normal adult woman.

• Each RBC is bounded by an elastic and semipermeable plasma membrane while cytoplasm lacks a nucleus, mitochondria, endoplasmic reticulum, Golgi body etc, but contains about 280 million molecules of an iron-containing pigment haemoglobin average life span of RBC’s are haemolysed in the cells of liver, spleen and bone marrow.

• During haemolysis, haemoglobin is changed in bile pigments like bilirubin and biliverdin. but even the RBC count remains normal because new RBCs are formed at the same rate by the haematocytoblasts of the red bone marrow of long bones and the process is called haemopoiesis.

• The function of RBC is to transport about 97-99% of oxygen from the lungs to the body tissues and about 23% of carbon dioxide from the body tissues to the lungs.

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• In human blood, these are rounded or amoeboid, nucleated, non-pigmented cells and about 8-15um in size. These are less in number and the total leucocyte count (TLC) of human blood is about 6000-8000 per cubic mm of blood. they produce antibodies and antitoxins. Based on cytoplasmic granules,

1. Granulocytes and
2. Agranulocytes. 

• These have granular cytoplasm and lobed nucleus and are formed in the red bone marrow. these are again of three subtypes i.e. neutrophils, basophils ( cyanophils) and acidophils ( eosinophils).

Agranulocytes