Absorption of glucose entails transport from the intestinal lumen, across the epithelium and into blood. The transporter that carries glucose and galactose into the enterocyte is the sodium-dependent hexose transporter. As the name indicates, this molecule transports both glucose and sodium ion into the cell and in fact, will not transport either alone.

The absorptive cells, or enterocytes, lining your small intestine create a barrier between your gut and your bloodstream. To reach the cells throughout your body, amino acids must travel from your gut, following digestion to your blood, and your enterocytes accomplish this with the help of transporter molecules. These transporters are specific for individual amino acids depending on the chemistry of their R-groups. With the help of sodium, the transporter reaches through the cell membrane on the side of the enterocyte adjacent to your gut and grabs a single amino acid. It pulls it inside the enterocyte and release it, where a different transporter – this one not dependent on sodium – picks it up and carries it to the side of the cell next to your bloodstream. Here it deposits the amino acid into capillaries that enter into your general circulation.

アミノ酸の基本構造
一つの炭素に水素、アミノ基、カルボキシと側鎖Rが結合している。

Dietary lipids pass from the stomach to the small intestine in a mud-like mixture of food particles and stomach acid known as chyme. The presence of chyme triggers the release of bile from the gallbladder into the small intestine. Bile reacts with fat globules in chyme, breaking them into tiny bile-containing fat droplets. This process, known emulsification, prepares the ingested lipids for the next step in the digestive and absorptive process.

The presence of chyme in the small intestine stimulates the release of pancreatic digestive fluids and enzymes, including the fat-digesting enzyme lipase. Lipase reacts with the emulsified fat droplets breaking down the complex dietary fats into smaller lipid particles known as fatty acids and mono-glycerides, notes biologist David Sadava、 Ph.D., coauthor of “Life: The Science of Biology.” Thus, lipase converts dietary lipids into smaller, absorbable fat particles.

Fatty acids and mono-glycerides pass through the outer membrane into the intestinal lining cells. The smallest fatty acids pass through the intestinal cells into the bloodstream and travel with a carrier protein to the liver for further processing. Mono-glycerides, large fatty acids and cholesterol undergo processing within the intestinal lining cells. The cells reconstruct the absorbed mono-glycerides and large fatty acids into lipid molecules called triglycerides, explains biochemist Stephen Chaney, Ph. D., of the University of North Carolina School of Medicine. The cholesterol and triglycerides attach to protein carriers, forming chemicals known as chylomicrons. The protein carriers transform the water-insoluble lipids into a water-soluble form, enabling export from the intestinal cells.

The intestinal cells extrude the chylomicrons formed from absorbed dietary fat into a liquid transport network known as the lymphatic system. The lymphatic system transports the absorbed chylomicrons to the bloodstream. The liver and other body tissues process chylomicrons for storage or immediate utilization.