Question

In a healthy adult man, the commonest and smallest type of leucocytes are (a) basophits (b) monocytes (c) eosinophils (d) lymphocytes.

Short answer

The commonest and smallest type of leucocytes in a healthy adult man are (d) lymphocytes.

Step-by-step solution

Understanding the question

The question is asking to identify the commonest and smallest type of leucocytes (white blood cells) found in a healthy adult man.

Recall the types of leucocytes

Leucocytes can be classified into granulocytes (basophils, eosinophils, and neutrophils) and agranulocytes (lymphocytes and monocytes). Each type has a different abundance and size.

Identifying the commonest and smallest type

Among the given options, lymphocytes are generally the most common type of leucocytes found in the bloodstream and they are also smaller in comparison to monocytes. Basophils are rare and not the smallest, while eosinophils are also not the most common.

Choose the correct answer

Based on the knowledge of the relative size and abundance of the different types of leucocytes, lymphocytes are both the commonest and smallest type of leucocytes in a healthy adult man.

Key concepts

Lymphocytes

Lymphocytes play an essential role in the immune system, acting as the body's defenders against viral infections, abnormal cells, and various other intruders. As one of the main types of white blood cells, they come in several forms, primarily T cells, B cells, and natural killer (NK) cells. T cells are involved in directly killing infected host cells, activating other immune cells, and regulating immune responses. B cells are responsible for producing antibodies, which are proteins that target and neutralize pathogens. NK cells provide a rapid response to virally infected cells and are instrumental in the defense against tumors.

Lymphocytes are produced in the bone marrow and can be found throughout the body, including in the lymph nodes, spleen, and thymus gland. In comparison to other types of white blood cells, lymphocytes are smaller in size and are the most numerous, making them the 'commonest,' as mentioned in the exercise. Their prevalence in the body reflects their importance in maintaining a robust immune system.

White Blood Cells

White blood cells, also known as leucocytes, are a critical component of the blood and immune system. They function as the primary cellular defenders of the body and vary widely in both appearance and role. Their primary job is to fight off infections caused by bacteria, viruses, and other pathogens.

There are five main types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each type has a unique function, with neutrophils being the most abundant and first responders to infections, ingesting and destroying invaders. The distinction between granulocytes and agranulocytes—based on the presence of granules in their cytoplasm—allows a further classification that is fundamental to understanding their functions in the immune response.

Granulocytes and Agranulocytes

Granulocytes and agranulocytes are two broader categories of white blood cells, distinguished by the presence or absence of granules in their cytoplasm. Granulocytes include basophils, eosinophils, and neutrophils. These cells are characterized by the granules that contain enzymes and other substances that are released during infections, allergic reactions, or asthma. For example, basophils play a role in allergic reactions and are least common among white blood cells.

Agranulocytes, on the other hand, encompass lymphocytes and monocytes, which do not contain visible granules when stained and observed under a microscope. Monocytes become macrophages upon leaving the bloodstream and entering body tissues, where they engulf and digest pathogens and debris. Each type of white blood cell has a distinct role in the immune system, and their balance is crucial for a healthy immune response against pathogens.