Blood and blood cells

Blood is a tissue fluid that runs in the body’s circulation to provide nutrients to every part of the body. It is responsible for carrying oxygen from the lungs to every part of the body, as well as removing carbon dioxide from every part of the body to the lungs for exhalation.

Due to the obvious red nature of blood, some people do not know that there are different components in blood other than red blood cells. Blood formation begins in intrauterine life and progresses until a person dies.

An adult has about 5 litres of blood available to the body being reduced in females due to the monthly menstrual cycle, while a new-born baby has about 450 millilitres.

Components of blood

Blood is made up of three types of cells and plasma which is the liquid portion of blood. Plasma further consists of organic substances such as proteins, carbohydrates, enzymes, amino acids, antibodies, etc. and inorganic substances such as sodium, chloride, iodide, phosphate, etc. Plasma also contains water which makes up the majority of it (over 90%).

Cells in the blood

The three cells present in blood include

• Red blood cells or erythrocytes
• White blood cells or leucocytes
• Blood platelets or thrombocytes.

Each of these cellular components has a specific function and role in the body.

Red Blood cells

Red blood cells form the majority of cellular components of the blood. They are biconcave or disc like in shape to adapt to their function of transportation and circulation of nutrients round the body.
Red cells have a diameter of 7.2µ, with a surface area of 120 sq µ which is large enough to permit exchange of substances and gases.

White Blood cells

So many people would say; if white blood cells are a component of blood, why does the blood appear totally red? White blood cells are so-called in comparison to red blood cells, therefore they are not ‘white’ as their name implies, but have a colour lighter than that of red cells.

They are further classified into Granulocytes which have granules in their cytoplasm, and agranulocytes with an absence of granules in their cytoplasm.

Granulocytes include Neutrophils, Basophils, and Eosinophils; named in relation to the dye colour they are able to absorb o take up. Eosinophils will take up acidic dyes, basophils will take up basic dyes and neutrophils will take up both acidic and basic dyes.

Agranulocytes are of two types; Monocytes and lymphocytes, both having their specific functions.

Unlike red blood cells, each white blood cell differs in size, and in shape as a means of adaptation to their various functions.

Blood Platelets

Platelets are very few in the blood, irregular in shape but important for stopping bleeding.

Functions of blood

There are a variety of functions the blood performs; as a matter of fact, anything that affects any cell in the blood directly affects a person’s life. Some of the functions of blood are

• Nutrition
  When we eat food and our bodies break down this food, it is absorbed into the blood from our gastrointestinal tract and then transported to various parts of the body.
• Excretion
  The kidney is one of the major organs of excretion as it acts to filter blood and produce urine. Waste products from different parts of the body are transported to the kidney, liver, or even the skin for excretion.
• Defence
  The white blood cells play a major role in defending the body against microorganisms and other foreign bodies. Monocytes and neutrophils can undergo a process called phagocytosis to engulf bacteria that may invade the body. Lymphocytes are responsible for the development of immunity in an individual.
• Respiration
  When the veins return blood to the heart through the superior and inferior vena cava, this blood is taken to the lungs to be oxygenated (the process of adding oxygen) and remove carbon dioxide and circulation is continued.
• Regulation of body pH
  The pH of blood is defined as the level of acidity or alkalinity of the blood. It is maintained at a constant value of 7.4 which is neutral. The pH of blood is maintained by several buffer mechanisms and is responsible for maintaining a constant environment for various reactions to occur.
• Transport of substances
  Some substances like hormones which are secreted from ductless glands are transported in the blood to their site of action.