Cell division does not occur in the villus itself. It happens in the crypts of Lieberkühn, the small pocket-shaped glands that sit at the base of each villus. The villus is made up of mature, non-dividing cells that were produced in the crypt and pushed upward. Understanding this distinction is central to how the small intestine maintains itself.
The Crypt Is the Proliferative Zone
Each villus in the small intestine is surrounded by several crypts, tube-like indentations that extend downward into the intestinal wall. All cell division takes place within these crypts. The crypt is organized linearly: stem cells sit at the very bottom, dividing cells occupy the middle and upper portions, and fully mature cells exit at the top to begin their journey up the villus.
At the base of each crypt, a small population of stem cells (known as Lgr5+ cells) divides roughly once every 24 hours. These stem cells are interspersed between specialized Paneth cells, which provide chemical signals and physical support to keep the stem cells functioning. Together, these cells form what’s called the “stem cell zone.”
Transit-Amplifying Cells Do the Heavy Lifting
The stem cells themselves don’t directly produce the bulk of the intestinal lining. Instead, they give rise to a rapidly dividing population called transit-amplifying cells, which occupy the middle and upper region of the crypt. These cells go through several rounds of division in quick succession, generating the sheer number of new cells the intestine needs. Transit-amplifying cells are the primary site of proliferation and differentiation in the intestinal lining, producing the majority of the mature absorptive cells that will eventually coat the villus surface.
Because these cells divide so rapidly, they are especially vulnerable to damage from chemotherapy drugs and radiation, which target fast-dividing cells. This is why nausea and intestinal problems are such common side effects of cancer treatment.
How New Cells Reach the Villus
Once transit-amplifying cells finish dividing near the top of the crypt, they stop proliferating and begin to mature. They then migrate upward onto the villus, pushed along by the pressure of newer cells being produced below them. Research has confirmed that cell proliferation within the crypt is the primary mechanical force driving this upward migration. When proliferation is experimentally halted, cell movement on the villus stops in sync.
The journey from crypt base to villus tip takes roughly 92 hours in the duodenum of mice. Of that, about 60 hours is spent traveling along the villus itself. In the ileum, where villi are shorter, the villus portion of the trip takes closer to 49 hours. By the time a cell reaches the villus, it is fully differentiated and specialized for absorbing nutrients. It will never divide again.
What Happens at the Villus Tip
The entire epithelial lining of the intestine replaces itself every four to five days. To keep this turnover balanced, old cells must be removed at the same rate new ones are produced. This removal happens primarily at the villus tip through a process called cell extrusion, where aging cells are shed into the gut lumen. About 92% of these extrusions involve living cells that are actively pushed out, not cells that have already died.
Extrusion isn’t purely random. Cells at the villus tip are under mechanical tension, and the system preferentially ejects the least contractile, or “weakest,” cells. This means the intestine doesn’t just maintain a constant cell number. It also maintains mechanical quality, replacing its weakest links continuously.
Signaling Keeps Division Confined to the Crypt
A key molecular signal called Wnt is what keeps crypt cells in a dividing state. Wnt signaling is strongest at the crypt base and fades as cells move upward along the crypt-villus axis. When cells move far enough from the Wnt-rich environment at the bottom, they stop dividing and begin to mature. In experiments where the Wnt pathway was disabled in mice, crypts failed to form entirely, and the intestine consisted only of differentiated villus cells with no capacity for self-renewal.
This gradient is what enforces the strict boundary between the proliferative crypt and the non-dividing villus. The villus is, by design, a zone of function rather than production.
Why This Matters in Disease
In a healthy intestine, the ratio of villus height to crypt depth is about 3:1. In conditions like celiac disease, this architecture breaks down. The villi shorten or disappear entirely (villous atrophy), while the crypts deepen and show abnormally increased cell division (crypt hyperplasia), with more than one dividing cell visible per crypt instead of the normal single mitosis. This combination of flat villi and overactive crypts is a hallmark diagnostic finding. The intestine is trying to compensate for damage by ramping up cell production, but the newly produced cells can’t form proper villi, leading to poor nutrient absorption.
This pattern reinforces the core principle: cell division belongs to the crypt. The villus depends entirely on the crypt to supply it with new cells, and when that supply chain is disrupted or the villus structure is damaged, the consequences show up as malabsorption and disease.