• Blood is a liquid connective tissue that contains cellular elements (blood cells) and fluid matrix (plasma).
• Blood helps in the transportation of different substances throughout the body.
• Study of blood and its disease is known as Hematology

Composition of Blood:

1. Cellular substances (Blood cells) : 45% (44% RBC & 1% buffy coat containing platelets & WBC)
2. Plasma: 55% (Of total: 91% liquid & Solid 9%).

Blood cells:

• Erythrocytes or Red blood cells (RBC), Leucocytes or White blood cells (WBC) and Platelets or Thrombocytes

1. Erythrocytes or Red blood cells (RBC)

• Biconcave, anucleate disc shaped of 7µm in size.
• The normal count= 4.5-5.5 lakhs/mm³. It is measured by haemocytometer
•  The life span of RBC is 120 days.
• RBC contain blood pigment called Haemoglobin.
• Total haemoglobin in our body is about 900 gm. It occupies about 1/3 of RBC.
• RBC is produced in bone marrow by the process called Erythropoiesis
• The immature nucleated RBC is called Reticulocyte.

 2. Leucocytes or White blood cells (WBC)

• Large size, oval in shape, cell contain nuclei & some of them have granules.
• Normal count-4000-11,000 per mm³.
• 2 types-Granulocytes and Agranulocytes. These differ in size, shape, life span & functions.
• Granulocytes includes- Neutrophils, Basophils & Eosinophils
• Agranulocytes include –lymphocytes and monocytes

i. Neutrophils

• It is most abundant WBC (40-70%) of total WBCs.
• It is phagocytic in nature.
• It is the first line of defense against bacteria.
• Phagocytosis by Neutrophil is facilitates by Opsonization by antibody
• The life span is 6 hrs.

 ii. Eosinophils

• 1-4% of total WBCs
• It destroys parasites & neutralize histamine released during allergic reaction. So, it is increased in parasitic infestation & in allergic reactions.
• It is stained by acidic dye. Eg, eosin dye.

 iii. Basophils                                             

• About 1% of total WBCs.
• It contain basophilic granules.
• It resembles mast cells in connective tissue.
• It contains histamine, heparin & serotonin.
• It is stained by basic dye

 iv. Lymphocytes                                      

• 20-40% of total WBCs. It is the smallest WBC.
• There are 2 types of lymphocytes.
•  B-lymphocytes is concerned with humoral immunity.
• T lymphocytes is concerned with cell mediated immunity.

v. Monocytes

• 2-8 % of total WBCs, Have horse-shoe kidney shaped nucleus. It is the largest WBC.
• It differentiates into Macrophages as it enters the tissues which express MHC (Major histocompatibility complex).
• Macrophages in different parts of the body are given different names as follows
• Kupffers cells= liver
• Osteoclast cells= bone
• Microglial cells= brain and spinal cord
• Histiocytes =Connective tissue
• Dust cells (alveolar macrophage)= Lungs
• Hassal’s corpuscles= Thymus

3. Platelets or Thrombocytes

• They are small non granulocytes disc
• They are derived from pinching off the cytoplasm of the Giant cell megakaryotes in the red bone marrow.
• Normal count is 1.5-4.5 lakh/mm³.
• Life span 7-10 days.
• Platelet is to help in coagulation. Thromboplastin is secreted by platelets during blood clotting.

Plasma

• Plasma = (Blood- Blood cells)
• It is the liquid part of blood and is composed of 90-92 % water, 7-8 % plasma protein and 1-2% other substances (glucose, amino acids, electrolytes, ammonia, enzymes, hormones, vitamins, etc).
• Translucent, yellowish, little viscous when centrifuged.
• Normal range: 60-80 gm/dl of blood.
• Plasma proteins: Helps in maintaining osmotic pressure, coagulation of blood, viscosity, blood pressure, defensive action, transport of gases.
• The solvent property of water helps in transport of nutrients as well as metabolic wastes from one part of body to another part
• Liver produces about 30gm of plasma protein each day.
• They are of three types:
• Albumin: (58-60%) most abundant, main function is to maintain is to maintain plasma osmotic pressure (Oncotic pressure).
• Globulin: (36-38%) – It is important for immunoglobulin. The most important globulin is gamma globulin.
• Fibrinogen: (3-4%) – It helps in blood clotting.
• Electrolytes- Na, K, Cl, Ca, HCO₃
• Nutrients- Glucose, amino acids, fatty acids, Vitamins & minerals.
• Gases: Oxygen, Carbon dioxide, Nitrogen.
• Waste products: Urea, Uric acid, Creatinine.

Properties of Blood:

• Amount: : 7-9% of total body weight; 79ml/kg
• Blood volume: 5-6 liters
• Viscosity: (3.5-5.5) times more than water.
• Specific Gravity:045-1.065
• PH:3-7.4 (slightly alkaline)
• Venous blood has low pH than the arterial blood as venous blood has more CO
• Temperature- 38⁰C (100.4F)
• Osmotic pressure– 25 mm Hg.
• Color: red, due to haemoglobin

Functions of Blood

i. Transportation:

• transport of O2 from lungs to body tissue and CO2 from tissue to lungs
• transport of wastes of cellular metabolism from body tissue to kidney, liver or sweat gland and eventually removal out of body
• Transport of hormones, enzymes, other chemicals throughout the body.
• Nutrients absorbed in the digestive tract, such as glucose, amino acids, vitamins, minerals etc and are circulated to all body tissues.
• Waste products of the tissues, such as urea and creatinine, circulate through the kidneys and are excreted in urine.

ii. Regulation (Homeostasis):

• regulate body temperature
• distribution of heat throughout the body

iii. Balance

• Maintaining electrolyte balance
• Maintain acid base balance

iv. Protection:

• protect body from harmful microorganisms, by WBCs, protein and antibody
• develop immune response (plasma protein).

Blood: composition, properties and functions

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