Final answer:
New surface epithelial cells and intestinal epithelial cells in adults come from stem cells. These stem cells divide to maintain the epithelial layer, supported by the avascular nature of epithelial tissues and the diffusion of nutrients from underlying tissues.
Step-by-step explanation:
In adults, new surface epithelial cells and the epithelial cells lining the intestine are derived from stem cells. These stem cells undergo mitotic division to replenish the epithelium. The intestine, in particular, has a high turnover rate, with stem cells located at the base of the crypts of Lieberkühn providing a continuous source of new cells. This rapid cell turnover allows for the replacement of epithelial cells that are damaged or have a short lifespan.
Epithelial tissues are known for their ability to rapidly replace damaged and dead cells. Since epithelial tissues are avascular, with no direct blood supply, the cells derive their nutrients via diffusion or absorption from underlying tissues or from the surface.
It’s important to note that epithelial cells exhibit polarity and form specialized intercellular connections, such as cell junctions. They are attached to and supported by a basal lamina, which separates them from the underlying connective tissues.