15.1.2. Formed Elements

Erythrocytes, leucocytes and platelets are collectively called formed elements and they constitute nearly 45 per cent of the blood.

Formed elements are the cellular components of blood, making up around 45% of its volume. These components include erythrocytes (red blood cells), leucocytes (white blood cells), and platelets. Understanding the role of each of these components is essential for comprehending how blood functions in the body.

Think of formed elements as the ingredients in a recipe. Just as each ingredient contributes to the overall flavor and texture of a dish, each formed element plays a unique role in maintaining health. For example, erythrocytes are like the flour in a cake – essential and abundant.

Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood. A healthy adult man has, on an average, 5 million to 5.5 million of RBCs mm–3 of blood. RBCs are formed in the red bone marrow in the adults. RBCs are devoid of nucleus in most of the mammals and are biconcave in shape. They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells.

Erythrocytes, or red blood cells, are vital for oxygen transport. They are produced in the red bone marrow and do not have a nucleus, which allows more space for hemoglobin, the protein that carries oxygen. The biconcave shape increases surface area for gas exchange, making them efficient at transporting oxygen throughout the body. A healthy adult typically has around 5 million to 5.5 million RBCs per cubic millimeter of blood.

Imagine erythrocytes as delivery trucks that carry oxygen to various parts of your city (the body). Their design (biconcave shape) is optimized for navigating through narrow streets (capillaries) and efficiently delivering their precious cargo (oxygen) to every neighborhood (tissue).

Leucocytes are also known as white blood cells (WBC) as they are colourless due to the lack of haemoglobin. They are nucleated and are relatively lesser in number which averages 6000-8000 mm–3 of blood. Leucocytes are generally short lived.

Leucocytes, or white blood cells, play a crucial role in the immune response and defense against infections. Unlike erythrocytes, they have nuclei and are fewer in number, averaging between 6000 and 8000 per cubic millimeter of blood. They are short-lived but essential for protecting the body from pathogens. They are divided into two main types: granulocytes and agranulocytes, each serving specific functions in immunity.

Think of leucocytes as the police force of the body. Just as police officers are dispatched to respond quickly to crime scenes (infections), white blood cells are deployed to sites of infection to fight off invaders and help keep the body safe.

We have two main categories of WBCs – granulocytes and agranulocytes. Neutrophils, eosinophils and basophils are different types of granulocytes, while lymphocytes and monocytes are the agranulocytes.

Granulocytes are characterized by the presence of granules in their cytoplasm and include neutrophils (which engulf and destroy pathogens), eosinophils (which fight parasitic infections), and basophils (which are involved in inflammatory responses). Agranulocytes, such as lymphocytes and monocytes, are responsible for specific immune responses, with lymphocytes playing a vital role in recognizing and combating pathogens.

Imagine a specialized SWAT team (granulocytes) that is called in for immediate action against specific threats (e.g., bacterial infections), while the intelligence officers (agranulocytes) work on long-term strategies to recognize and prevent future threats (e.g., identifying viruses).

Platelets also called thrombocytes, are cell fragments produced from megakaryocytes (special cells in the bone marrow). Blood normally contains 150,000-350,000 platelets mm–3. Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood.

Platelets are essential for blood clotting and wound healing. They are not whole cells but fragments derived from megakaryocytes in the bone marrow. A normal healthy blood sample contains between 150,000 and 350,000 platelets per cubic millimeter. When a blood vessel is injured, platelets activate, forming a plug that helps stop bleeding and releases substances that facilitate further clotting.

Think of platelets as the first responders at the scene of an accident (wound). They quickly arrive at the site, stop the bleeding, and call for additional help (a sequence of clotting factors) to ensure there is no further blood loss, just like emergency teams do in a crisis.

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