Where do the digestive enzymes come from in small intestine?

The digestive enzymes in the small intestine come from two main sources: the pancreas and the small intestinal epithelial cells themselves.

Pancreas: The pancreas is a glandular organ located behind the stomach. It produces and secretes several digestive enzymes, including:

- Amylase: Breaks down carbohydrates into simple sugars like maltose, dextrins, and glucose.

- Lipase: Breaks down fats into fatty acids and glycerol.

- Proteases: Break down proteins into smaller peptides and amino acids. The main proteases produced by the pancreas are trypsin, chymotrypsin, and elastase.

These pancreatic enzymes are secreted into the pancreatic duct and then released into the small intestine through the opening called the ampulla of Vater.

Small Intestinal Epithelial Cells: The epithelial cells lining the small intestine also produce several digestive enzymes, including:

- Enteropeptidase: Activates trypsin from its inactive form (trypsinogen).

- Peptidases: Further break down peptides into amino acids.

- Disaccharidases: Break down disaccharides (double sugars like sucrose, maltose, and lactose) into monosaccharides (single sugars like glucose, fructose, and galactose). Examples of disaccharidases include lactase, sucrase, and maltase.

- Nucleases: Break down nucleic acids into nucleotides and nucleosides.

These enzymes are produced and released directly by the small intestinal epithelial cells into the intestinal lumen, where they contribute to the digestion of food.

In addition to these main sources, some digestive enzymes are also present in the saliva (e.g., salivary amylase) and the brush border of the small intestine (e.g., alkaline phosphatase).