Cell Kinetics of the Enterocyte

The life span and kinetics of small intestinal enter-ocytes are particularly important in understanding the process of absorption. Enterocytes have a pi* Microvilli ^^ I

Villi Crypt

Mucosa Muscularis mucosae Submucosa

Circular muscle

Longitudinal muscle Serosa-[

Villi Crypt

Mucosa Muscularis mucosae Submucosa

Circular muscle

Longitudinal muscle Serosa-[

Absorptive cells

Submucosal artery and vein Submucosal plexus

Peyer's patch

Myenteric plexus

Endocrine cells

Goblet cells

Muscularis mucosae

Figure 1 Wall of the small intestine. The intestinal surface area is enhanced by finger-like villi.

Submucosal artery and vein Submucosal plexus

Peyer's patch

Myenteric plexus

Endocrine cells

Absorptive cells

Goblet cells

Muscularis mucosae

Figure 1 Wall of the small intestine. The intestinal surface area is enhanced by finger-like villi.

particularly short life and the epithelium of the small intestine is replaced every 3-6 days, making it one of the fastest growing tissues in the body. The high mitotic rates in small intestinal crypts make the tissue particularly vulnerable to irradiation and cancer chemotherapy. New cells are born in a proliferative zone within the crypts of Lieberkuhn below the villus.

After birth, new cells move in the direction of the lumen and mitosis continues for two or three more divisions while each cell remains within the crypt. As the enterocyte emerges out of the crypt, proliferation ceases and the process of differentiation proceeds so that the cell, now passing up the outer surface of the villus, reaches functional maturity with a full capacity of membrane-bound brush border enzymes toward the villus tip. On reaching the tip, enterocytes are sloughed off into the intestinal lumen and digested.

The short life span of the enterocyte bestows massive adaptive potential within the tissue since the rate of differentiation may be influenced by changes in any nutrient or other luminal factor to induce a rapid functional response.

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