White blood cells. These include granular leukocytes (basophils, eosinophils, and neutrophils) as well as non-granular leukocytes (lymphocytes and monocytes).
White blood cells that protect the body from infectious diseases and provide immunity.
A diverse family of nucleated cells that has many immunological functions.
Any of the white cellular components of blood or lymph.
The white cells of the blood.
Blood cells that perform the function of destroying disease-causing bacteria.
Cells, commonly referred to as blood corpuscles, are integral components found within the bloodstream, persisting for varying durations throughout their lifespan. They encompass red blood cells, constituting approximately 45 percent of the normal blood volume, white blood cells, and platelets. The bone marrow serves as the site where all blood cells are generated through a series of divisions originating from a singular cell type known as a stem cell.
These cells are commonly referred to as RBCs (red blood cells), red blood corpuscles, or erythrocytes. Their primary function is to facilitate the transportation of oxygen from the lungs to the body’s tissues.
Red blood cells are derived from stem cells present in the bone marrow through a process known as erythropoiesis, which typically spans around five days. Adequate availability of essential nutrients, such as iron, amino acids, vitamin B12, and folic acid, is necessary for their proper formation. The rate at which red blood cells are produced is regulated by a hormone called erythropoietin, which is synthesized in the kidneys.
Recently released into the bloodstream from the bone marrow, immature red blood cells are referred to as reticulocytes. Over a span of approximately two to four days, these reticulocytes undergo further maturation and development, eventually transforming into fully mature red blood cells.
In every milliliter of blood, there are approximately 5 million red blood cells. Each of these cells exhibits a disc-shaped morphology, measuring about 0.0075 mm in diameter. Notably, the cells are thicker at their edges compared to their central region. This distinctive shape contributes to a relatively large surface area, enabling efficient absorption and release of oxygen molecules. Moreover, the flexibility of these cells allows them to deform as they traverse narrow blood vessels. Although the surface structure of red blood cells exhibits slight variations among individuals, it serves as the foundation for blood classification into different groups.
Red blood cells (RBCs) contain abundant amounts of haemoglobin, a pigmented protein rich in iron. Haemoglobin undergoes a chemical binding with oxygen, resulting in the formation of oxyhaemoglobin. This oxyhaemoglobin complex efficiently transports oxygen to the body’s tissues. Oxygenated blood, predominantly flowing through arteries, exhibits a bright red coloration attributed to oxyhaemoglobin. In contrast, venous blood appears darker as it contains the unbound (deoxygenated) form of haemoglobin.
In addition to haemoglobin, each red blood cell (RBC) contains enzymes that facilitate various biochemical reactions, minerals, and sugars. These components play essential roles in the cell’s metabolism, providing energy for its chemical processes and contributing to the maintenance of its shape, structure, and elasticity.
Red blood cells (RBCs) typically have a lifespan of approximately 120 days in the bloodstream. Over time, as they age, their internal chemical machinery deteriorates, resulting in reduced elasticity. Consequently, these aging cells can get trapped in narrow blood vessels, particularly in the spleen and other organs. Subsequently, they are eliminated by a type of white blood cell known as macrophages. The majority of the components of haemoglobin molecules are recycled for future use, while some are broken down to produce the waste product bilirubin.
Irregularities can arise in the production or destruction rate of red blood cells (RBCs), as well as in their quantity, shape, size, and haemoglobin content. These variations can lead to different forms of anemia, characterized by a deficiency in the number or function of RBCs, or polycythemia, marked by an excessive increase in RBCs.
White blood cells (WBCs), also known as white blood corpuscles or leukocytes, play a vital role in protecting the body against infections and combating them when they occur. Unlike red blood cells, white blood cells are larger in size (up to 0.015 mm in diameter) but considerably fewer in number (approximately 7,500 per milliliter of blood). They typically have a shorter lifespan within the bloodstream compared to red blood cells. The three primary types of white blood cells are granulocytes, also referred to as polymorphonuclear leukocytes, monocytes, and lymphocytes.
Granulocytes can be further categorized into neutrophils, eosinophils, and basophils, with each type fulfilling a specific role. Among these, neutrophils are of utmost importance as they play a crucial role in isolating and eliminating invading bacteria. Neutrophils have a relatively short lifespan in the bloodstream, typically lasting around six to nine hours before migrating through blood vessel walls into tissues. Eosinophils are involved in allergic reactions and tend to increase in number in response to certain parasitic infections. Basophils, on the other hand, are primarily associated with inflammatory and allergic reactions.
These cells also possess significant significance in the immune system, contributing to its overall functioning. They have a relatively short duration in the bloodstream, typically circulating for approximately one to three days.
Lymphocytes are typically produced in the lymph nodes, rather than in the bone marrow. They hold a significant responsibility in the immune system, actively moving throughout the body, navigating between the bloodstream, the lymph nodes, and the channels connecting them. The lifespan of lymphocyte cells can vary, ranging from three months to as long as ten years.
There are two primary types of lymphocytes: T-lymphocytes (or T-cells) and B-lymphocytes (or B-cells). T-lymphocytes play crucial roles in delayed hypersensitivity reactions and contribute to protection against cancer. These cells produce lymphokines, chemicals that influence the functioning of other cells. T-lymphocytes can be classified based on specific surface marker proteins. For instance, T-lymphocytes with CD4 surface marker proteins are particularly significant in monitoring HIV infection. Additionally, T-lymphocytes regulate the activity of B-lymphocytes, which are responsible for generating antibodies that can prevent subsequent attacks by certain infectious diseases.
Leukemias encompass a group of blood disorders characterized by the uncontrolled and excessive production of white blood cells in the bone marrow. On the other hand, various disorders can arise when there is an insufficient production of white blood cells.
Platelets, also known as thrombocytes, are the smallest type of blood cells, measuring approximately 0.002 mm to 0.003 mm in diameter. They exist in a quantity of approximately 250,000 per cubic millimeter of blood. Similar to other blood cells, platelets are produced in the bone marrow. They have a lifespan of around nine days while circulating in the bloodstream.
Platelets move through the bloodstream in a dormant state until triggered by specific conditions, at which point they adhere to the walls of blood vessels and to one another. These actions serve a crucial role in the process of coagulation, which aids in the healing of wounds. Nevertheless, the build-up of platelets can sometimes result in the development of clots within blood vessels.
The numerical count, morphology, and visual characteristics of different blood cell types hold significant diagnostic value in the identification of diseases.