Mitosis is a fundamental biological process where one parent cell divides to produce two genetically identical daughter cells. This process ensures each new cell receives a complete and identical set of chromosomes from the original. It is part of the larger cell cycle, during which a cell grows, replicates its DNA, and then divides.
The Purpose of Mitosis
Mitosis serves several roles in living organisms. Its functions include growth, development, and the repair or replacement of cells. Through repeated divisions, a single-celled zygote develops into a complex, multicellular organism, increasing its cell number.
Mitosis also maintains tissues by replacing old or damaged cells. For instance, cells in the skin and digestive tract are constantly shed and replaced through mitosis.
Key Locations in the Human Body
In the human body, mitosis occurs extensively in various tissues that require continuous renewal or growth.
Skin cells, for example, undergo constant mitosis to replace those shed from the surface. The entire outer layer of skin is replaced approximately every 28 to 40 days, which helps maintain its protective barrier and aids in wound healing.
Hair follicles also exhibit high rates of mitosis, contributing to hair growth.
Cells lining the digestive tract, particularly the epithelial cells of the stomach and intestines, divide frequently to replace cells damaged by the digestive process and constant exposure to food and waste.
Bone marrow is another highly active site of mitosis, continuously producing various blood cells, including red blood cells, which have a relatively short lifespan.
During wound healing, cells around the injury site undergo mitosis to generate new cells and repair the damaged tissue.
Mitosis in Other Organisms
Mitosis is a universal process found across a wide range of living organisms. In plants, growth occurs at specific regions called meristematic tissues, located at the tips of roots and shoots, and in the cambium. Cells in these areas actively divide through mitosis, enabling the plant to grow in length and girth.
For many single-celled eukaryotic organisms, such as yeast and amoebas, mitosis is their primary method of asexual reproduction, creating genetically identical offspring rapidly. While bacteria, which are prokaryotes, do not undergo mitosis due to the absence of a nucleus and multiple chromosomes, they employ a similar division process called binary fission to reproduce.
Cells with Limited Division
While many cells in the body regularly undergo mitosis, some specialized cell types exhibit very limited or no division after reaching maturity. Mature neurons, the primary cells of the brain and nervous system, generally do not undergo mitosis. This lack of division is attributed to their high specialization and the complex, interconnected networks they form, where adding new cells could disrupt established pathways.
Mature muscle cells, including skeletal muscle fibers and cardiac muscle cells, also have very limited capacity for mitosis. These cells are considered “permanent” cells that typically do not reproduce. Red blood cells, which lack a nucleus, are also incapable of division. The inability of these cells to divide means that damage or loss in these tissues can be challenging to repair through cell replacement.