Team Biology at Examples.com
Created by: Team Biology at Examples.com, Last Updated: May 15, 2024


Red Blood Cells (RBCs) and White Blood Cells (WBCs) serve crucial, distinct roles within the human body, functioning as essential components of our circulatory and immune systems, respectively. RBCs, also known as erythrocytes, primarily transport oxygen from the lungs to various tissues and aid in the removal of carbon dioxide. In contrast, WBCs, or leukocytes, play a vital role in defending the body against infections and foreign invaders. Understanding the differences in structure, function, and significance of RBCs and WBCs helps in appreciating how they contribute to overall health and disease management. This comparison sheds light on their unique features and the critical balance they maintain in sustaining life and health.

What are Red Blood Cells (RBCs)?

Red blood cells (RBCs), also known as erythrocytes, are the most common type of blood cell and the principal means of delivering oxygen from the lungs to body tissues via the blood through the circulatory system. These cells are produced through a process called erythropoiesis in the bone marrow and are designed to carry oxygen with the help of a protein called hemoglobin.

Structure and Function of Red Blood Cells


  • Shape: RBCs have a distinctive biconcave, disk-like shape that increases the cell’s surface area and enables flexibility. This unique shape aids in traveling through the tiny capillaries and facilitates the exchange of oxygen and carbon dioxide.
  • Size: They are approximately 6-8 micrometers in diameter.
  • Composition: They lack a nucleus and organelles in mature state, which allows more room for hemoglobin, the protein that binds oxygen.


  • Oxygen Transport: Hemoglobin within the RBCs binds to oxygen in the lungs and carries it to cells throughout the body. It then picks up carbon dioxide from the body’s cells, a waste product of metabolism, transporting it back to the lungs to be expelled.
  • CO2 Transport: About 20% of carbon dioxide is carried back to the lungs dissolved in the red blood cells, which is then exhaled.

What are White Blood Cells (WBCs)?

White blood cells (WBCs), also known as leukocytes, are a vital part of the immune system, responsible for protecting the body against both infectious disease and foreign invaders. Unlike red blood cells, WBCs are diverse in their structure and function. They circulate through the bloodstream and the lymphatic system, responding to signs of infection or inflammation.

Types and Functions of White Blood Cells

WBCs are categorized into two major types, each with different roles in the immune response:

  • Granulocytes: These cells contain granules with enzymes that are released during infections, allergic reactions, and asthma. They are subdivided into neutrophils, eosinophils, and basophils:
    • Neutrophils: The most abundant type of WBC, essential for fighting bacteria and fungi.
    • Eosinophils: Mainly deal with parasitic infections and are also involved in allergic responses.
    • Basophils: Least common and are involved in allergic and antigen response by releasing histamine causing inflammation.
  • Agranulocytes: These do not contain granules and include lymphocytes and monocytes:
    • Lymphocytes: Key players in the immune system, divided into B-cells, T-cells, and natural killer cells. B-cells produce antibodies, T-cells destroy the body’s own cells that have been taken over by viruses, and natural killer cells attack cells infected by viruses and tumors.
    • Monocytes: They become macrophages and dendritic cells which are crucial for phagocytosis of pathogens and presenting antigens to T-cells.

Differences between Red Blood Cells (RBCs) and White Blood Cells (WBCs)

Primary FunctionTransport oxygen and remove carbon dioxide.Defend the body against infectious disease and foreign materials.
Also Known AsErythrocytesLeukocytes
Life SpanApproximately 120 daysRanges from a few hours to several years, depending on the type.
ShapeBiconcave disk, which increases surface area.Varied, often spherical or amorphous.
SizeAbout 6-8 micrometers in diameterGenerally larger, 12-17 micrometers in diameter.
NucleusAbsent in mature cellsPresent, can be lobed or segmented depending on type.
Count per µL of Blood4.5 to 5.9 million4,000 to 11,000
TypesUniform in typeMultiple types, including neutrophils, lymphocytes, etc.
Staining PropertiesEosinophilic due to hemoglobin, stains pinkVaries; basophilic or eosinophilic, stains range from blue to pink.
Role in ImmunityNoneCritical in both innate and adaptive immune responses.
Content of HemoglobinHigh, contains hemoglobin to bind oxygen.None
Production SiteBone marrowBone marrow (primarily)
Response to InfectionNo direct roleIncrease in number, especially neutrophils during infection.
MobilityCirculates in blood vessels but does not move independently.Highly mobile, can move through vessel walls into tissue.
StorageNo storage capabilityStored in lymph nodes and spleen.
Regulation of ProductionErythropoietin stimulates production during hypoxia.Growth factors like G-CSF and GM-CSF regulate production.
Presence in Other FluidsPrimarily in bloodFound in blood, lymph, and other body fluids.

Key Similarities Between Red Blood Cells (RBCs) and White Blood Cells (WBCs)

Red Blood Cells (RBCs) and White Blood Cells (WBCs) are crucial components of the blood, but despite their different primary functions, they share several key similarities:


  • Bone Marrow Production: Both RBCs and WBCs are produced in the bone marrow. They originate from hematopoietic stem cells, which have the potential to develop into various types of blood cells. This shared origin is central to their development and function within the body’s circulatory and immune systems.

Lifespan Management

  • Regulated Lifespan: Both types of cells have a defined lifespan, after which they are recycled or removed from the bloodstream. RBCs generally last about 120 days, whereas WBCs can vary greatly in lifespan, ranging from hours to years depending on the type.
  • Recycling: Old or damaged RBCs and WBCs are broken down in the body, with their components recycled. For RBCs, the spleen plays a significant role in filtering out old cells. WBCs are typically handled by the lymphatic system and other immune components.

Essential for Health

  • Health Impact: Both RBCs and WBCs are essential for maintaining health. RBCs are vital for transporting oxygen to tissues, and any imbalance in their numbers can lead to conditions like anemia or polycythemia. WBCs are crucial for the immune response, protecting against infection, and imbalances can lead to increased susceptibility to infections (leukopenia) or inflammatory diseases (leukocytosis).

Response to Signals

  • Regulatory Response: Both cell types are produced in response to physiological demands and signals. For instance, erythropoietin stimulates the production of RBCs during hypoxia (low oxygen levels). Similarly, various cytokines and growth factors can increase the production of WBCs during an immune response or infection.

Circulatory System Involvement

  • Transportation Through Bloodstream: Both RBCs and WBCs travel throughout the body via the bloodstream, although WBCs can also navigate the lymphatic system. Their movement is crucial for their functions, delivering oxygen and defending against pathogens respectively.

Cellular Structure

  • Cell Types: While vastly different in appearance and internal structure, both RBCs and WBCs are classified as cells, despite RBCs lacking nuclei and other organelles in their mature form, which is a unique adaptation among human body cells.

Which Should Be Higher, RBC or WBC?

RBCs should typically be higher in number than WBCs to effectively transport oxygen throughout the body.

What Level of RBC Is Concerning?

A concerning RBC level falls below 4 million cells per microliter, signaling potential anemia.

What Is an Alarming RBC Count?

An alarming RBC count exceeds 6 million cells per microliter, suggesting polycythemia or other disorders.

Is 3.7 RBC Count Too Low?

Yes, an RBC count of 3.7 million cells per microliter is generally considered too low and may indicate anemia.

What Is the Most Common Cause of High RBC?

The most common cause of high RBC is dehydration; other causes include lung disease and polycythemia vera.

What Is a Normal Abnormal RBC Count?

A normal abnormal RBC count can vary widely, but typically, any deviation from 4.5 to 5.9 million cells per microliter is notable.

How High Is Too High for RBC Count?

An RBC count higher than 6 million cells per microliter is considered too high and could be harmful.

What Foods Should You Avoid If You Have High Red Blood Cells?

Avoid high-iron foods like red meat and spinach if you have high RBCs, as iron can increase red cell production.

What Raises Red Blood Cell Count?

Factors raising RBC count include high altitude, smoking, and conditions like chronic hypoxia or heart disease.

What Is an Alarming RBC?

An RBC count over 6 million cells per microliter is considered alarming and warrants medical evaluation.

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