2.3 Cell Types Found in Blood

Introduction

Blood is not just a liquid — it contains different types of cells, each with a specific job. These cells are produced in the bone marrow and circulate throughout the body. The three main types of blood cells are red blood cells, white blood cells, and platelets. This topic explains the structure, types, and functions of each blood cell.

Definition

Blood cells are the cellular components of blood. They form about 45% by volume of the blood. These include:

• Red blood cells (erythrocytes)
• White blood cells (leukocytes)
• Platelets (thrombocytes)

Main Idea

Blood cells form about 45% by volume of the blood. Each type of blood cell has a specific structure and function:

• Red blood cells carry oxygen and a small amount of carbon dioxide.
• White blood cells defend the body against diseases.
• Platelets help in blood clotting.

Core Concept

Types of Blood Cells

Detailed Explanation

1. Red Blood Cells (Erythrocytes)

What they are: These are called erythrocytes.

Structure:

• A single RBC is a circular, flattened, biconcave disc.
• It has no nucleus.
• RBCs have iron-containing pigment haemoglobin in their cytoplasm, which gives red colour to the blood.

Where they are formed: RBCs are formed in bone marrow after birth.

Life span: Their life span is 120 days.

What happens when they are worn out: When they are worn out, they are destroyed in the spleen and liver.

Function:

- RBCs carry oxygen and also transport a small amount of carbon dioxide.

Simple explanation: Red blood cells are like tiny delivery trucks that carry oxygen from the lungs to all body cells. They are red because of haemoglobin, which contains iron.

Why they have no nucleus:

• Without a nucleus, there is more space for haemoglobin.
• This allows RBCs to carry more oxygen.

Why they are biconcave:

• The biconcave shape increases the surface area for oxygen exchange.
• It also allows the cell to be flexible and squeeze through narrow capillaries.

2. White Blood Cells (Leukocytes)

What they are: White blood cells are called leukocytes.

Life span: Their life span is 3–4 days.

Structure:

• Each white blood cell is irregular in shape.
• It contains a nucleus.

Types: WBCs can be divided into two main types:

• Granular leukocytes
• Agranular leukocytes

Granular Leukocytes

What they are: Their nucleus is variable in shape. Cytoplasm contains fine granules.

Where they originate: These cells originate in bone marrow.

Types: Granular leukocytes are of three types:

Simple explanation: Granular leukocytes have granules in their cytoplasm. They include neutrophils (eat germs), eosinophils (control allergies), and basophils (release histamine during allergic reactions).

Agranular Leukocytes

What they are: The cytoplasm of agranular leukocytes is clear.

Types: These are of two types:

Simple explanation: Agranular leukocytes do not have granules. They include monocytes (eat bacteria and dead cells) and lymphocytes (fight germs and produce antibodies).

3. Platelets (Thrombocytes)

What they are: Platelets are cell fragments (not complete cells).

Structure:

• They are small, irregularly shaped fragments.
• They do not have a nucleus.

Where they are formed: They are formed in bone marrow.

Function:

• Platelets patch damaged blood vessels.
• They release substances essential for blood clotting.

Simple explanation: Platelets are like tiny bandages that plug holes in damaged blood vessels and help blood clot.

Why this is important:

• Without platelets, even a small cut would cause continuous bleeding.
• Platelets are essential for wound healing.

Summary of Blood Cell Types

Intermediate Level

Blood cells are of three main types:

• Biconcave, no nucleus.
• Contain haemoglobin.
• Life span: 120 days.
• Function: Oxygen transport.
• Destroyed in spleen and liver.

• Irregular shape, contain nucleus.
• Life span: 3–4 days.
• Function: Defence against disease.
• Types:
• Granular: Neutrophils, eosinophils, basophils.
• Agranular: Monocytes, lymphocytes.

• Small fragments, no nucleus.
• Life span: 7–10 days.
• Function: Blood clotting.

Important Points

• - Blood cells form about 45% by volume of the blood.
• - Red blood cells are called erythrocytes.
• - A single RBC is a circular, flattened, biconcave disc and has no nucleus.
• - RBCs have iron-containing pigment haemoglobin.
• - RBCs are formed in bone marrow after birth.
• - Life span of RBCs is 120 days.
• - Worn-out RBCs are destroyed in spleen and liver.
• - RBCs carry oxygen and a small amount of carbon dioxide.
• - White blood cells are called leukocytes.
• - Life span of WBCs is 3–4 days.
• - Each white blood cell is irregular in shape and contains a nucleus.
• - WBCs are divided into granular and agranular leukocytes.
• - Granular leukocytes: neutrophils, eosinophils, basophils.
• - Agranular leukocytes: monocytes, lymphocytes.
• - Neutrophils engulf pathogens during phagocytosis.
• - Eosinophils are involved in the control of allergic reactions.
• - Basophils release histamine in injured tissue and in allergic response.
• - Monocytes are phagocytic and ingest bacteria and dead cells.
• - B lymphocytes protect us by producing antibodies.
• - T lymphocytes directly destroy harmful cells.
• - Platelets patch damaged blood vessels.
• - Platelets release substances essential for blood clotting.

Remember

• - RBCs = erythrocytes, biconcave, no nucleus, haemoglobin, oxygen transport, 120 days
• - WBCs = leukocytes, nucleus, defence, 3–4 days
• - Granular WBCs = neutrophils, eosinophils, basophils
• - Agranular WBCs = monocytes, lymphocytes
• - Neutrophils = phagocytosis
• - Eosinophils = allergic reactions
• - Basophils = histamine
• - Monocytes = phagocytic
• - B lymphocytes = antibodies
• - T lymphocytes = destroy harmful cells
• - Platelets = thrombocytes, clotting

Common Mistakes

• 1. Thinking RBCs have a nucleus.
• - Mature mammalian RBCs have no nucleus. This allows more space for haemoglobin.
• 2. Confusing granular and agranular leukocytes.
• - Granular = neutrophils, eosinophils, basophils.
• - Agranular = monocytes, lymphocytes.
• 3. Mixing up the functions of WBCs.
• - Neutrophils = phagocytosis.
• - Eosinophils = allergic reactions.
• - Basophils = histamine release.
• - Monocytes = phagocytic.
• - B lymphocytes = antibodies.
• - T lymphocytes = destroy harmful cells.
• 4. Thinking platelets are complete cells.
• - Platelets are cell fragments, not complete cells.
• 5. Forgetting the life span of blood cells.
• - RBCs = 120 days.
• - WBCs = 3–4 days.
• - Platelets = 7–10 days.
• 6. Believing RBCs carry only oxygen.
• - RBCs carry oxygen and a small amount of carbon dioxide.
• 7. Thinking all WBCs have the same function.
• - Different types of WBCs have different functions.

Quick Revision

60-Second Revision

• RBCs = erythrocytes; biconcave; no nucleus; haemoglobin; oxygen transport; 120 days; destroyed in spleen and liver
• WBCs = leukocytes; nucleus; defence; 3–4 days
• Granular: neutrophils (phagocytosis), eosinophils (allergy), basophils (histamine)
• Agranular: monocytes (phagocytic), lymphocytes (B cells = antibodies, T cells = destroy harmful cells)
• Platelets = thrombocytes; clotting; cell fragments
• Warning: Do not confuse granular (neutrophils, eosinophils, basophils) with agranular (monocytes, lymphocytes) leukocytes.