Structure of the monocyte bone cell

Image by, courtesy of Adreson Vita Sá

Bone is a living, changing tissue that protects our organs and works with our musculature system to allow us to move. Bone also stores minerals and is responsible for making all of our red and white blood cells. Monocytes are huge white blood cells involved in immune functioning.

The most distinctive characteristics of monocyte cell structure are the large, folded nucleus and the presence of many granules throughout the cell cytoplasm.

White Blood Cells

All blood cells, both white and red, are made in our bone marrow. Monocytes are one of six different types of white blood cell. White blood cells are part of our immune system and help the body ward off attacks from invading pathogens, such as bacteria or viruses. Monocytes perform phagocytosis, which means to "eat" foreign substances in the body (such as bacteria) or degrading tissue like old bone matter so that new bone can grow.

Cell Structure

A basic understanding of some terms in cellular biology will help make the structure of the cell easier to understand. The nucleus is the "control centre" of the cell. It is here that the cell's genetic information (usually in the form of DNA) is stored. The DNA holds the "blueprints" or instructions for everything the cell needs to do. The cytoplasm is the cellular fluid that surrounds the other cell organelles ("little organs") and allows for movement of substances around the cell. The cell membrane encloses the cell and, because it is semi-permeable, acts as the cell's "gatekeeper," allowing only certain substances to come in or out of the cell.

Monocyte Structure

Monocytes are the largest of the white blood cells, with an average diameter of 18 micrometers. Monocytes have abundant cytoplasm and a large, distinctive U-shaped nucleus. Many fine granules in the cytoplasm of monocyte cells, especially near the cell membrane, produce digestive enzymes, which help the monocyte "eat" foreign material in the body as it assists in immune functioning.


Monocytes differentiate into two basic types in the body: fixed macrophages and wandering macrophages. ("Macro" means large and "phage" means to digest.) Wandering macrophages roam the body, searching for bacteria, viruses and other foreign material to ingest. Fixed macrophages deposit themselves in various body tissues, like the liver, spleen, lungs or skin and release chemicals that signal other immune system cells to respond to infections.


When your doctor orders a CBC, or blood cell count, from the lab, one of the readings will usually be the monocyte count in your blood. Typically, monocytes make up about 4 per cent of our total white blood cell count. An elevated monocyte count in the blood can indicate the presence of an infection or other issues.