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The formed elements are found freely suspended in the liquid plasma.
There are three types of formed elements:
- Red blood corpuscles (RBCs)
- White blood corpuscles (WBCs)
- Platelets
They are small biconcave circular cells also called erythrocytes.
They are thicker at the edges than in the centre.
The erythrocytes are flexible so that they can pass through the narrow capillaries easily.
They number 5 million per cubic mm in adult males and 4.5 million per cubic mm in adult females. Their number is higher in early infancy. The cells are composed of a network of fats and proteins between which are enmeshed numerous pigments called the haemoglobin which give the blood its colour.
Haemoglobin is composed of an iron containing pigment called haeme and a protein called globin. The haemoglobin pigments combine with oxygen to form oxyhaemoglobin in the lungs. Around the body cells, the oxyhaemoglobin dissociates due to low oxygen concentration. Here, some of them combine with the carbon dioxide.
Haemoglobin has a strong affinity for carbon monoxide (CO) with which it forms a stable compound. When carbon monoxide is present in the inhaled air, the pigments prefer it to oxygen thereby greatly reducing the oxygen supplied to the body. This is called carbon monoxide poisoning and can even result in death. This is one of the reasons why the vehicle exhaust gases that contain carbon monoxide are harmful.
The adult red blood cells do not have nucleus, mitochondria or endoplasmic reticulum. The lack of nucleus creates more space inside the cell for the haemoglobin. Lack of mitochondria means that all the oxygen carried by the cell is transported and none of it is used by the cells.
The red blood cells are synthesised in the bone marrows of ribs, sternum and vertebrae at the rate of 1.2 million cells per second. The life span of the cells is only about 120 days. They are destroyed in the liver. The iron part is retained and the pigment is excreted in the bile juice as bilirubin.
- They are carriers of oxygen and carbon dioxide
- They maintain the viscosity of blood
- They maintain acid-base balance
- They maintain ionic balance
- The disintegration of haemoglobin leads to formation of many other pigments like the bilirubin, biliverdin, etc. in the liver
They are also called leucocytes. They lack haemoglobin and are therefore colourless. They are nucleated and amoeboid.
The amoeboid nature of the leucocytes helps them to squeeze through the walls of the blood vessels in order to engulf bacteria. They do not contain haemoglobin. They number 6000 to 8000 per cubic mm. The ratio of WBC to RBC is 1:7.
Production of Antibodies
The WBCs are involved in the production of antibodies that either neutralise, kill or poison the germs. The WBCs can be induced to produce antibodies with the help of vaccinations thus preparing the body for an attack.
Inflammation at a spot is due to localised infection. The spot becomes red and swollen. There may be pus formation and oozing. The pus is nothing but dead WBCs that have died fighting the infection and dead tissue attacked by the bacteria.
Anti-allergic
Eosinophils are thought to protect the body against allergies. The count of eosinophils in the body goes up during some allergies.
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