Body Fluids and Blood

Chapter 5

Body Fluids and Blood

Introduction

Blood is described as a connective tissue. It carries:

• Oxygen from the lungs to the tissues and carbon dioxide from the tissues to lungs for elimination.
• Nutrients from the alimentary tract to the tissues and waste materials from the tissues to the kidney for excretion.
• Hormones secreted by endocrine glands to their target organs.

• Heat produced in active tissues to other less active tissues.
• Protective substances, e.g. antibodies to the sites of infection.

• Clotting factors which help in preventing loss of blood.

Blood constitutes about 8 per cent of the body weight. For a 70 kg man, the volume of blood is expected to be 5.6 lit. Blood in the vessels is always in motion. The flow is such that the cells have a fairly constant environment.

Composition of Blood

• It is composed of a yellowish fluid, plasma, in which different types of cells are suspended. Plasma constitutes about 55 per cent and cells constitute about 45 per cent of the blood volume.

Plasma

• It consists of about 90-92 per cent water in which the following substances are dissolved:

• Plasma proteins: Albumin, globulin, fibrinogen, clotting factors.
• Inorganic salts: Sodium chloride, sodium bicarbonate, potassium, magnesium, phosphorus, iron, calcium, iodine, and cobalt.

• Nutrients obtained from digested food: Monosaccharides from carbohydrates, amino acids from proteins, fatty acids and glycerol from fats and vitamins from food.

• Organic waste materials: Urea, uric acid, creatinine.

• Hormones

• Enzymes

• Antibodies Gases: Oxygen, carbon dioxide, nitrogen.

Blood Groups

• Different blood groups are associated with genetically determined differences in antigens on the surface of membrane of RBCs and antibodies in blood serum. There are two main systems used to classify blood donated for administration by transfusion. If the donor’s blood does not match with that of the recipient, the incompatibility results in agglutination and lysis of donated red cells after transfusion. The agglutinated cells block capillaries and the products of lysis, when in excessive amounts, damage the kidney tubules. The resultant condition is serious and can cause death.

ABO System

• In some people there are genetically determined antigens on the surface of membrane of RBCs and natural antibodies in serum. The antibodies are inherited and are not associated with acquired immunity. Summary of ABO system is presented as follows.

Disorders of Blood Exercise

Major disorders of blood are:

(i) Anemias,                                     (ii) Polycythemia,
(iii) Bleeding disease,                       (iv) Leukemias

(v) Agranulocytosis,                        (vi) Thalassemia.

• In Thalassemia, the hemoglobin defect results in a decreased life span of the circulating red cells. The shape of red cells is altered, but a large number of nucleated cells are also observed. Many hemolytic anemias are caused by certain drugs, bacterial toxins, malarial parasite etc. Rh incompatibility can cause hemolytic disease of the newborn. Aplasia or atrophy of the bone marrow can cause aplastic anemia which results in the reduction in the number of red cells, leukocytes and blood platelets.