BODY FLUIDS AND CIRCULATION 193
CHAPTER 15
BODY FLUIDS AND CIRCULATION
15.1 Blood You have learnt that all living cells have to be provided with nutrients, O2
and other essential substances. Also, the waste or harmful substances
15.2 Lymph (Tissue
produced, have to be removed continuously for healthy functioning of
Fluid)
tissues. It is therefore, essential to have efficient mechanisms for the
15.3 Circulatory movement of these substances to the cells and from the cells. Different
Pathways groups of animals have evolved different methods for this transport. Simple
15.4 Double organisms like sponges and coelenterates circulate water from their
Circulation surroundings through their body cavities to facilitate the cells to exchange
these substances. More complex organisms use special fluids within their
15.5 Regulation of bodies to transport such materials. Blood is the most commonly used body
Cardiac fluid by most of the higher organisms, including humans, for this
Activity purpose. Another body fluid, lymph, also helps in the transport of
15.6 Disorders of certain substances. In this chapter, you will learn about the composition
Circulatory and properties of blood and lymph (tissue fluid) and the mechanism of
System circulation of blood is also explained herein.
15.1 BLOOD
Blood is a special connective tissue consisting of a fluid matrix, plasma,
and formed elements.
15.1.1 Plasma
Plasma is a straw coloured, viscous fluid constituting nearly 55 per cent of
the blood. 90-92 per cent of plasma is water and proteins contribute 6-8
per cent of it. Fibrinogen, globulins and albumins are the major proteins.
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Fibrinogens are needed for clotting or coagulation of blood. Globulins
primarly are involved in defense mechanisms of the body and the albumins
help in osmotic balance. Plasma also contains small amounts of minerals
like Na+, Ca++, Mg++, HCO3–, Cl–, etc. Glucose, amino acids, lipids, etc., are
also present in the plasma as they are always in transit in the body. Factors
for coagulation or clotting of blood are also present in the plasma in an
inactive form. Plasma without the clotting factors is called serum.
15.1.2 Formed Elements
Erythrocytes, leucocytes and platelets are collectively called formed
elements (Figure 15.1) and they constitute nearly 45 per cent of the blood.
Erythrocytes or red blood cells (RBC) are the most abundant of all
the cells in blood. A healthy adult man has, on an average, 5 millions to
5.5 millions of RBCs mm–3 of blood. RBCs are formed in the red bone
marrow in the adults. RBCs are devoid of nucleus in most of the mammals
and are biconcave in shape. They have a red coloured, iron containing
complex protein called haemoglobin, hence the colour and name of these
cells. A healthy individual has 12-16 gms of haemoglobin in every
100 ml of blood. These molecules play a significant role in transport of
respiratory gases. RBCs have an average life span of 120 days after which
they are destroyed in the spleen (graveyard of RBCs).
Leucocytes are also known as white blood cells (WBC) as they are
colourless due to the lack of haemoglobin. They are nucleated and are
relatively lesser in number which averages 6000-8000 mm–3 of blood.
Leucocytes are generally short lived. We have two main categories of WBCs
– granulocytes and agranulocytes. Neutrophils, eosinophils and basophils
are different types of granulocytes, while lymphocytes and monocytes
are the agranulocytes. Neutrophils are the most abundant cells (60-65
per cent) of the total WBCs and basophils are the least (0.5-1 per cent)
among them. Neutrophils and monocytes (6-8 per cent) are phagocytic
cells which destroy foreign organisms entering the body. Basophils secrete
histamine, serotonin, heparin, etc., and are involved in inflammatory
reactions. Eosinophils (2-3 per cent) resist infections and are also
Eosinophil Neutrophil T lymphocyte
RBC
Platelets Basophil Monocyte B lymphocyte
Figure 15.1 Diagrammatic representation of formed elements in blood
Reprint 2026-27
CHAPTER 15
BODY FLUIDS AND CIRCULATION
15.1 Blood You have learnt that all living cells have to be provided with nutrients, O2
and other essential substances. Also, the waste or harmful substances
15.2 Lymph (Tissue
produced, have to be removed continuously for healthy functioning of
Fluid)
tissues. It is therefore, essential to have efficient mechanisms for the
15.3 Circulatory movement of these substances to the cells and from the cells. Different
Pathways groups of animals have evolved different methods for this transport. Simple
15.4 Double organisms like sponges and coelenterates circulate water from their
Circulation surroundings through their body cavities to facilitate the cells to exchange
these substances. More complex organisms use special fluids within their
15.5 Regulation of bodies to transport such materials. Blood is the most commonly used body
Cardiac fluid by most of the higher organisms, including humans, for this
Activity purpose. Another body fluid, lymph, also helps in the transport of
15.6 Disorders of certain substances. In this chapter, you will learn about the composition
Circulatory and properties of blood and lymph (tissue fluid) and the mechanism of
System circulation of blood is also explained herein.
15.1 BLOOD
Blood is a special connective tissue consisting of a fluid matrix, plasma,
and formed elements.
15.1.1 Plasma
Plasma is a straw coloured, viscous fluid constituting nearly 55 per cent of
the blood. 90-92 per cent of plasma is water and proteins contribute 6-8
per cent of it. Fibrinogen, globulins and albumins are the major proteins.
Reprint 2026-27
, 194 BIOLOGY
Fibrinogens are needed for clotting or coagulation of blood. Globulins
primarly are involved in defense mechanisms of the body and the albumins
help in osmotic balance. Plasma also contains small amounts of minerals
like Na+, Ca++, Mg++, HCO3–, Cl–, etc. Glucose, amino acids, lipids, etc., are
also present in the plasma as they are always in transit in the body. Factors
for coagulation or clotting of blood are also present in the plasma in an
inactive form. Plasma without the clotting factors is called serum.
15.1.2 Formed Elements
Erythrocytes, leucocytes and platelets are collectively called formed
elements (Figure 15.1) and they constitute nearly 45 per cent of the blood.
Erythrocytes or red blood cells (RBC) are the most abundant of all
the cells in blood. A healthy adult man has, on an average, 5 millions to
5.5 millions of RBCs mm–3 of blood. RBCs are formed in the red bone
marrow in the adults. RBCs are devoid of nucleus in most of the mammals
and are biconcave in shape. They have a red coloured, iron containing
complex protein called haemoglobin, hence the colour and name of these
cells. A healthy individual has 12-16 gms of haemoglobin in every
100 ml of blood. These molecules play a significant role in transport of
respiratory gases. RBCs have an average life span of 120 days after which
they are destroyed in the spleen (graveyard of RBCs).
Leucocytes are also known as white blood cells (WBC) as they are
colourless due to the lack of haemoglobin. They are nucleated and are
relatively lesser in number which averages 6000-8000 mm–3 of blood.
Leucocytes are generally short lived. We have two main categories of WBCs
– granulocytes and agranulocytes. Neutrophils, eosinophils and basophils
are different types of granulocytes, while lymphocytes and monocytes
are the agranulocytes. Neutrophils are the most abundant cells (60-65
per cent) of the total WBCs and basophils are the least (0.5-1 per cent)
among them. Neutrophils and monocytes (6-8 per cent) are phagocytic
cells which destroy foreign organisms entering the body. Basophils secrete
histamine, serotonin, heparin, etc., and are involved in inflammatory
reactions. Eosinophils (2-3 per cent) resist infections and are also
Eosinophil Neutrophil T lymphocyte
RBC
Platelets Basophil Monocyte B lymphocyte
Figure 15.1 Diagrammatic representation of formed elements in blood
Reprint 2026-27
