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White Blood Cells vs. Red Blood Cells

Chandramita Bora
White blood cells (WBCs) and red blood cells (RBCs) differ in various aspects, right from their structure and composition to their functions.

Did You Know?

All blood cells - RBCs, WBCs, and platelets - originate from the hematopoietic stem cells present in our blood and bone marrow, and the umbilical cords of newborn babies.
On an average, a human adult contains about 5 liters of blood, which is mainly composed of plasma and blood cells. The plasma accounts for about 55% to 60% of human blood, while the blood cells form about 40% to 45% of total blood volume.
There are basically three types of blood cells, white blood cells or WBCs, red blood cells or RBCs, and platelets. All these cells play an important role in various functions of the body. However, they differ greatly in their structure and composition.

Difference Between WBCs and RBCs

Difference in Structure and Composition

RBCs are cells that impart the characteristic red color to our blood, due to the presence of an iron-containing protein called hemoglobin. This protein is not found in WBCs.
RBCs are also known as erythrocytes, and they appear as flat biconcave discs. The biconcave shape helps increase the surface area of these cells, so that oxygen and carbon dioxide can move promptly through their membranes.
On the other hand, WBCs or leukocytes can have irregular shapes. Another point of difference between RBCs and WBCs is the presence or absence of a nucleus.
Mature RBCs do not possess nuclei, while nuclei are present in WBCs. White blood cells also possess a white outer buffer coat, which is absent in red blood cells.

Difference in Types

RBCs do not have different types. Unlike RBCs, WBCs can be classified into two main types, granulocytes and agranulocytes. Granulocytes possess granules in their cytoplasm, while agranulocytes do not contain granules.
Granulocytes are further classified into three types, neutrophils, basophils, and eosinophils. On the other hand, lymphocytes, monocytes, and macrophages are the main types of agranulocytes.

Site of Production
Erythrocytes are produced in the bone marrow, from the hematopoietic stem cell. The production of erythrocytes is regulated by a hormone, known as erythropoietin, that is synthesized by the kidneys. Leukocytes are also produced from the hematopoietic stem cells present in the bone marrow, but some of them mature in the lymph nodes, thymus gland, and spleen.

Life Span and Count of RBCs and WBCs

An erythrocyte lives for about 120 days, while a WBC or leukocyte can live for 3 to 4 days on an average. However, the life span of leukocytes can reduce to a great extent in case of a severe infection.
In a healthy adult, the count of white blood cells can be somewhere between 4,000 to 11,000 cells per cubic millimeter of blood. On an average, the count of WBCs is 7,000 cells per cubic millimeter blood. Leukocytes, along with platelets, account for only 1% of total blood volume.
RBCs are the most abundant cells in the blood. There are about 5 million red blood cells in every cubic millimeter of blood, which account for about 40% to 45% of total blood volume.

Movement

RBCs primarily travel within the cardiovascular system. They circulate through  blood vessels and capillaries to supply oxygen and nutrients to cells. WBCs circulate between the cardiovascular and lymphatic system. As mentioned already, many leukocytes mature in lymph nodes. Leukocytes escape from the blood vessels and move to the site of infection/injury.

Difference in Functions

Functions of RBCs

RBCs are mainly concerned with the transportation of oxygen and nutrients to the body cells, and removal of waste. Hemoglobin can bind with both oxygen and carbon dioxide. In the lungs, oxygen molecules attach to hemoglobin.
Hemoglobin then carries oxygen to the body tissues and cells through the blood vessels. It also collects carbon dioxide from the tissues and cells and transports it to the lungs, where it is expelled from the body.

Functions of WBCs

WBCs are an integral part of the immune system and play a key role in immune functions. They basically protect the body from foreign materials and infectious agents. They defend the body against various types of infections by producing antibodies.
Neutrophils typically fight against bacterial and fungal infections, while eosinophils are largely responsible for fighting parasitic infections. Eosinophils are also associated with allergic response, along with basophils.
Lymphocytes, on the other hand, produce antigen, coordinate the immune response of the body, and destroy virus-infected cells. They destroy tumor and cancerous cells as well. Monocytes are responsible for removing the dead cells and microorganisms with the help of a process called phagocytosis.

Irregularity in the Count of RBCs and WBCs
The number of RBCs and WBCs in the blood can serve as an indicator of certain diseases. For example, an increase in the number of WBCs, which is known as leukocytosis, is often associated with infections. However, a consistently high level of immature and abnormal leukocytes can be an indicator of leukemia, a type of cancer.
A low WBC count, or leukopenia, can compromise the immune functions. Leukopenia can be caused by conditions that can disrupt the functions of the bone marrow, such as viral infections, a severe infection, cancer, and use of certain medications.
A low count of RBCs is usually known as anemia. There are several types of anemia, out of which iron deficiency anemia, and anemia caused by the deficiency of vitamin B12, are more common. Anemia can impair the oxygen-carrying capacity of the blood, which can manifest in increased tiredness, shortness of breath, and pallor.
So, both RBCs and WBCs differ greatly in their appearance, composition, and functions. Both the types of blood cells have some unique and crucial functions in the body. A reduction in their numbers can therefore, result in various health problems.