Nearly every cell in your body that isn’t a sperm or egg cell divides through mitosis. These are called somatic cells, and they include skin cells, blood cell precursors, muscle cells, organ cells, and virtually every other cell type that makes up your tissues. Mitosis produces two genetically identical daughter cells, each with the same two sets of chromosomes as the original. It’s the process behind growth, tissue repair, and cell replacement throughout your life.
Somatic Cells: The Main Category
Somatic cells are defined as every cell in the body other than the reproductive cells (sperm and eggs). In humans, somatic cells are diploid, carrying 46 chromosomes arranged in 23 pairs, one set from each parent. When these cells divide by mitosis, the result is two identical copies with the same 46 chromosomes.
This covers an enormous range of cell types: epithelial cells lining your gut, white blood cells fighting infections, bone cells, liver cells, lung cells, connective tissue cells, and many more. The sheer scale of mitosis in your body is staggering. Your bone marrow alone produces roughly 100 million new red blood cells every minute to replace old ones that wear out after about four months. Skin cells are constantly shed and renewed. The lining of your intestines replaces itself every few days.
Where Mitosis Happens in Plants
Plants rely on mitosis too, but the dividing cells are concentrated in specific zones called meristems. Apical meristems sit at the tips of roots and shoots, where cell division drives the plant’s growth in length. Axillary buds, the small bumps at branch junctions, also contain meristematic tissue ready to produce new growth.
Plants that grow wider, like trees developing thicker trunks, use lateral meristems. Two types are especially important: vascular cambium, which produces new water-conducting and nutrient-conducting tissue, and cork cambium, which generates the protective outer bark. Lateral roots also form through meristematic activity deeper inside the root. In every case, the dividing cells are undergoing mitosis to produce genetically identical daughter cells.
Early Embryonic Cells
Mitosis begins almost immediately after fertilization. Once a sperm and egg fuse to form a single-celled zygote, that cell launches into a rapid series of mitotic divisions called cleavage. The resulting cells are called blastomeres, and they divide so quickly that the normal growth phases between divisions are essentially skipped. The cells go straight from DNA replication to mitosis and back again, splitting the zygote’s large volume of cytoplasm into progressively smaller cells without the overall embryo growing in size.
During cleavage, a contractile ring of protein filaments pinches each cell in two, creating a visible groove called a cleavage furrow. This eventually bisects the cell along the plane of division, producing two genetically equivalent blastomeres. These early divisions build the initial cell mass that will eventually specialize into every tissue type in the body.
Germ Cell Precursors Also Use Mitosis
Reproductive cells are often contrasted with somatic cells because sperm and eggs are produced through meiosis, a different type of division that halves the chromosome number. But the precursor cells that eventually become sperm or eggs first multiply through mitosis before ever entering meiosis.
In males, cells called spermatogonia go through several rounds of mitotic division. Intermediate spermatogonia divide mitotically to produce type B spermatogonia, which are the last cells in the line to use mitosis. Type B spermatogonia then divide one final time to generate primary spermatocytes, the cells that enter meiosis and ultimately produce sperm. A similar process occurs in females with egg precursor cells. So even the reproductive cell lineage depends on mitosis for its early stages.
Stem Cells and Tissue Repair
Adult stem cells use mitosis to maintain and repair tissues throughout your life. These cells can divide to produce one copy of themselves (keeping the stem cell pool intact) and one cell that goes on to specialize. This is how your body heals wounds, replenishes blood cells, and maintains organ function over decades.
Mesenchymal stem cells, found in bone marrow and other tissues, are a well-studied example. When injected into damaged heart tissue in research settings, they appear to boost repair primarily by stimulating the body’s own regeneration mechanisms rather than by directly replacing damaged cells. Researchers have observed that endogenous precursor cells and heart muscle cell mitosis increase with stem cell treatment, suggesting these cells can wake up repair pathways that would otherwise stay dormant.
Cells That Rarely or Never Divide
Not all cells keep dividing throughout life. Some exit the cell cycle and enter a resting state called G0. Mature neurons in the brain are the classic example. Once they’ve fully differentiated, they generally stop dividing. Heart muscle cells also largely stop dividing after birth. A key cell cycle regulator called cyclin A2 is silenced in heart muscle cells after the postnatal period. There is evidence of low-level heart cell turnover in healthy adults, but it is very limited and declines further with age.
Other cells sit in G0 but can be pulled back into active division when needed. T lymphocytes, a type of immune cell, are a good example. Most circulate in a truly quiescent state until they encounter a threat. When activated through specific receptor signals, they commit to re-entering the cell cycle within about 3 to 5 hours and begin dividing rapidly through mitosis to mount an immune response.
When Mitosis Goes Wrong: Cancer
Cancer is fundamentally a disease of uncontrolled mitosis. Normal cells pass through a series of internal checkpoints before they’re allowed to divide. Protein signals assess whether the DNA has been copied correctly, whether the cell is large enough, and whether conditions are right for division. If something is off, the cell cycle stalls until the problem is fixed or the cell self-destructs.
Cancer cells bypass these checkpoints. They divide when they shouldn’t, accumulating mutations that further accelerate their growth. Pathologists measure this by counting mitotic figures, cells caught in the act of dividing, in tumor tissue samples. For melanoma, the number of dividing cells per square millimeter of tumor is an independent predictor of survival. A threshold of at least 1 dividing cell per square millimeter marks a significant jump in risk. For certain gut and pancreatic tumors, the World Health Organization grades severity partly by mitotic count: fewer than 2 dividing cells per 10 high-power microscope fields is grade 1 (low), 2 to 20 is grade 2, and more than 20 is grade 3, the most aggressive category.
The difference between healthy mitosis and cancerous mitosis isn’t the mechanism itself. The same machinery of chromosome duplication and cell splitting is at work. The difference is that normal cells divide only when told to, and cancer cells have lost the ability to listen.