Types of Blood Cells With Their Structure, and Functions

Blood cells are broadly classified into three types: 1) red blood cells (RBCs), 2) white blood cells (WBCs), and 3) platelets, together they make up 45% of the total blood volume. 

Structure: A typical mammalian red blood cell is biconcave disk-shaped that is flattened and depressed at the center with a diameter of approximately 6.2-8.2 µm. A cross-sectional view of RBC looks like dumbbell-shaped.

Abundance:  They are the most abundant of all circulating blood cells, accounting for 40 to 45 percent of the total blood volume.

Composition: They are rich in hemoglobin, an iron-containing protein that binds oxygen and provides its red color.  Nucleus and most other organelles are absent in RBCs.

Lifespan: 100 to 120 days

Functions: Plays an important role in gas exchange, which include:

• Carrying oxygen from the lungs and delivering them to all parts of the body.
• Picking up carbon dioxide from all end-tissues and delivering them to the lungs for excretion.

Structure: Based on structure, WBCs are classified into two types –

a) Granulocytes: Contain granules in the cytoplasm

b) Agranulocytes: Absence of distinct granules in the cytoplasm

Abundance: Found throughout the body including connective tissues, bloodstream, and lymphatic system. It makes up only 1% of the total blood volume.

Composition: All white blood cells contain a nucleus, that makes it unique among all other blood cells.

Lifespan: 1 to 3 days, and are constantly replaced by the bone marrow

Types

Broadly, WBCs are classified into five types: Neutrophils (Granulocytes), Eosinophils (Granulocytes), Basophils (Granulocytes), Lymphocytes (Agranulocytes), and Monocytes (Agranulocytes). 

Functions:

• Producing antibodies that provide us protection and immunity against foreign infectious agents
• Generating cellular response against any attack by microorganisms such as bacteria, viruses, protozoa, and fungi. 
• Engulfing foreign particles and destroying them inside the cell

Apart from these common functions, there are some specific functions performed by each of the five types of WBCs.

Structure: Tiny, irregular shaped cells with a diameter of 2–3 µm.

Abundance: Present in less than 1% of the total blood cell count. Platelets are about 1/10th to 1/20th as abundant as white blood cells.

Composition: Lacks nucleus and contains dense granules in the cytoplasm.

Lifespan: 5 to 9 days

Functions:

• Helping in blood clotting, the process of preventing hemorrhage in a damaged blood vessel.
• Releasing multiple growth factors, such as platelet-derived growth factor (PDGF), chemotactic agent, and TGF beta, all of which have been found to have a role in the repair and regeneration of connective tissues.