Blood

The blood is a fluid connective tissue. It consists of liquid plasma and
cells. The plasma makes up 55% of the total volume and 45% of cells or
formed elements. The total blood volume in human female is about 4-5 litres
and 5-6 litres in males.

Plasma

The blood plasma is a slightly alkaline fluid. It is straw coloured.

Composition of plasma

Components Functions

1. Water – as a slovent and suspending medium
for blood components.

2. Plasma proteins- Albumin – Osmotic pressure.
Globulins – Antibody formation
Fibrinogen – Blood clotting.

3. Ions – Na, K, Ca, Mg, Cl
2
, – Osmosis, acid-base balance.
Fe, PO

4
, H and HCO
3
– buffer etc.,

4. Nutrients – Glucose, amino – source of energy, building blocks
acids, triglycerides, cholesterol, – enzyme activity.
vitamins.

5. Waste products – Urea, uric – excreted by the kidneys.
acid creatinine, ammonia
Bilirubin – breakdown product of erythrocytes
Lactic acid – product of anaerobic respiration.

6. Gases
Oxygen – for aerobic respiration
CO
2
– waste product of respiration
Nitrogen – inert gas.

7. Regulating substances
Hormones and Enzymes – body functions
Blood cells or formed elements
There are three types of blood cells or corpuscles. They are

1. Red Blood Corpuscles (RBC) or Erythrocytes

These are circular, biconcave and non-nucleated cells. Males have
about 5.2 million erythrocytes per cubic millimeter of blood (range : 4.2-5.8
million). Females have about 4.5 million/mm3 (range 3.6-5.2 million). Each disc shaped RBC is about 7.5 mm in diameter. Their main
component is a pigmented protein, haemoglobin. It gives red colour to the
blood. The haemoglobin transports O2. The oxygenated form of
haemoglobin is called oxyhaemoglobin.
Erythrocytes stay in circulation for about 120 days in males and 110
days in females. They are manufactured in the marrow of bones such as ribs
and vertebrae. They disintegrate in the spleen and liver.

2. White Blood Corpuscles (WBC) or Leucocytes

These are clear cells lacking haemoglobin. They are nucleated cells
exhibiting amoeboid movement. They protect the body against invading
micro-organisms and remove dead cells from the body. There are five types
of leucocytes.
a). Neutrophils – These are the most common type of leucocytes (60-70%)
in the blood. Their nuclei can occur in more than one form. Hence they are
called polymorphonuclear neutrophils (PMN).
b). Eosinophils (0.5-3.0%) – They are motile cells that leave the circulation
to enter the tissues during an inflammatory reaction. During allergy reaction
their number increases.
c). Basophils (0.1%) – They play a role in allergic and inflammatory
reaction. They contain heparin which inhibits blood clotting.
d). Lymphocytes (20-30%) – These are smallest leucocytes. They are more
common in lymphatic tissues namely the lymph nodes, spleen, tonsils and
thymus. Lymphocytes, called B-cells can produce proteins called
antibodies that can get attached to the bacteria and destroy them. T-cells protect us against viruses by attacking and destroying cells in which viruses
are reproducing.
e). Monocytes (1-4%) – These are largest leucocytes. They destroy
bacteria, dead cells and cell fragments. During chronic infection their number
increases.

3. Blood Platelets or Thrombocytes

These are minute fragments of cells that play a very important role in
coagulation of blood. Their life expectancy is 5-9 days.