Digestion Series: Part 7 - Small intestine lining, enzymes, & absorption

While #digestion of most nutrients in the small intestine mostly occurs by #enzymes secreted by the #pancreas, other enzymes located in the lining (called the brush border membrane) are responsible for completing the process of releasing molecules that can be transported from the small intestine to your bloodstream. These enzymes include alpha-glucosidases, a beta-galactosidase, and several peptidases. As you can see, it takes a village!

#Absorption

For nutrients to be absorbed, they have to move across the lining of the small intestine's #epithelial cells, or the cells that cover the surface. This uptake is driven by at least one of four mechanisms: mediated #transport, passive #diffusion, pinocytosis, and paracellular pathway.

Here is a simplified description of each:

Mediated transport - carrier #proteins help move specific individual nutrients across the small intestine lining

Passive diffusion - water, some gases and many fat-soluble molecules (such as short chain fatty acids) move somewhat freely by themselves through the lining

Pinocytosis - a process where a cell membrane folds, creating small pockets which capture #cellular fluid and dissolved substances (like nutrients)

Paracellular pathway - nutrients pass between #cells through tight junctions

For a visual of the lining of the small intestine and how nutrients need to pass through the lining to the bloodstream, I have included a figure from Nursing Times that shows a simplified structure.

Next we'll discuss #metabolism of nutrients once they pass through the lining of the small intestine.