4.1 Crypts of Lieberkuhn and Enterocyte Maturation

Crypts of Lieberkuhn & Enterocyte Maturation

There are some additional anatomical and physiological features of the small intestine that are important to understand before defining uptake and absorption processes. Crypts of Lieberkuhn are pits located between the villi as pointed out by the green arrow in the figure below.

Figure 4.11 A crypt of Lieberkuhn is the pit between the villi in the small intestine as pointed out by the green arrow1

The crypts of Lieberkuhn (often referred to simply as crypts) are similar to the gastric pits in the stomach. The crypts contain stem cells at their bases that can produce a number of different cell types, including enterocytes2. From these stem cells, immature enterocyte cells are formed. As they mature, the enterocytes rise, or migrate up, the villi. Thus, the tips of villi are where the mature, fully functioning enterocytes are located, as represented by the purple cells in the figure below3.

Figure 4.12 Crypts are represented by green arrows, while fully mature enterocytes are represented by the purple cells at the top of the villi

This maturation and migration is a continuous process. The life cycle of an enterocyte is 72 hours once it enters the villus from the crypt2. At the top, enterocytes are sloughed off and, unless they are digested (they contain proteins and lipids) and components are taken up by enterocytes still on villi, they will be excreted in feces as depicted in the figure below.

Figure 4.13 Enterocytes sloughed off the villus. Unless these cells are digested and their components are taken up by other enterocytes on the villus, they will be excreted in feces.

Thus, we define absorption as reaching the bloodstream, because some compounds taken up into enterocytes will not always make it into the bloodstream. So remember, uptake is moving from the GI tract into the enterocyte, and absorption is moving from the enterocyte into the bloodstream.

References & Links

• http://digestive.niddk.nih.gov/ddiseases/pubs/celiac/
• Stipanuk MH. (2006) Biochemical, Physiological, & Molecular Aspects of Human Nutrition. St. Louis, MO: Saunders Elsevier.
• Gropper SS, Smith JL, Groff JL. (2008) Advanced Nutrition and Human Metabolism. Belmont, CA: Wadsworth Publishing.