How is a visking tube not like real small intestine?

1. Porosity. Visking tubing is a semipermeable membrane, which means that it allows certain molecules to pass through while blocking others. Real small intestine, on the other hand, is not semipermeable and allows all molecules to pass through.

2. Composition. Visking tubing is made of regenerated cellulose, a type of plant fiber. Real small intestine, on the other hand, is made of epithelial cells, which are animal cells.

3. Thickness. Visking tubing is thin and has a consistent thickness. Real small intestine, on the other hand, varies in thickness. The proximal duodenum (just below the stomach) is thicker than the distal ileum (the lower part of the small intestine). The jejunum, where most of nutrient absorption occurs, has multiple layers of finger-like villi making it the thickest part of the small intestine.

4. Function. Visking tubing is used in laboratory experiments to model the diffusion of molecules across a membrane. Real small intestine, on the other hand, absorbs nutrients from food and expels waste. The epithelial cells secrete digestive juices to further chemical digestion and have microscopic villi to optimize nutrients absorption.

Despite these differences, visking tubing can be a useful tool for understanding the basic principles of diffusion and absorption in the small intestine.