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Types of Blood Cells With Their Structure, and Functions

Blood cells, also known as a hematopoietic cell, hemocyte, or hematocyte, are specialized cells that are found in the blood. Blood cells are produced from bone marrow by a process known as hematopoiesis.

What are the different types of blood cells in the human body

Blood cells in the human body are broadly classified into three types: the i) red blood cells (RBCs), ii) white blood cells (WBCs), and iii) platelets.

1. Red Blood Cells (RBCs) or Erythrocytes

Structure: A typical mammalian red blood cell is biconcave disk-shaped with a diameter of approximately 6.2-8.2 µm. Structurally RBCs are flattened and depressed in the center, which helps in better diffusion of gases. A cross-sectional view of RBC looks dumbbell-shaped.

Abundance: Also known as erythrocytes, these are the most abundant cell types in the peripheral blood, accounting for 40 to 45 percent of the total blood volume.

Composition: The cytoplasm of RBC is rich in hemoglobin, an iron-containing protein that binds oxygen and is responsible for its red color. A typical human red blood cell lacks a nucleus and most other organelles.

Lifespan of a Mature Cell: 100 to 120 days

Functions: Plays one of the most important roles in gas exchange, with their functions including –

  • Carrying oxygen from the lungs to all cells of the body.
  • Picking up carbon dioxide from all end-tissues and deliver them to the lungs for excretion.
  • Mediate binding to components of the extracellular matrix (cell-adhesion).

2. White Blood Cells (WBCs) or Leukocytes

Structure: Based on structure Leukocytes are classified into two types –

a) Granulocytes – Having granules in the cytoplasm

b) Agranulocytes – Having no distinct granules in the cytoplasm

Abundance: Found throughout the body (i.e., connective tissue, bloodstream, and lymphatic system) but accounting only 1% of the total blood volume.

Composition: All white blood cells, except lymphocytes and monocytes, have a nucleus, thus distinguishing them from RBCs and platelets.

Lifespan of a Mature Cell: 1 to 3 days, and constantly replaced by the bone marrow

Functions:

  • Protecting our body from foreign pathogens and other disease-causing germs.
  • Key mediators of allergy or any kind of inflammation.
  • Found to have relevance in the formation of cancer.

Apart from the above functions, specific types of WBCs are found to have other distinct functions in the body.

Types

Broadly Leukocytes can be divided into five types: Neutrophils or Polymorphonuclear (PMN) leukocytes (Granulocytes), Eosinophils (Granulocytes), Basophil (Granulocytes), Lymphocytes (Agranulocytes) and Monocytes (Agranulocytes).

3. Platelets or Thrombocytes

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

Abundance: Present in less than 1% of the total blood count, which accounts for 1/10th to 1/20thof WBCs.

Composition: Derived from disintegrated cytoplasm of megakaryocytes, the precursor large bone marrow cells.

Lifespan of a Mature Cell: 5 to 9 days

Functions:

  • Helping in blood clotting and thus function in hemostasis, 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.

FAQs

Q.1. What is the basic composition of blood?

RBCs, WBCs, and Platelets make up almost 45% of the total blood volume, and the remaining 55% is composed of plasma, the liquid portion of the blood.

Q.2. Which blood cell is most abundant?

Red Blood Cell (RBC) is the most abundant blood cell, accounting for almost 40 to 45 percent of the total blood volume.

Q.3. Which blood cell is the least abundant?

Basophil is the least abundant of all blood cells, accounting for only 0.5% of the total leukocyte count.

Article was last reviewed on Tuesday, December 3, 2019

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