The small intestine itself doesn't secrete a huge variety of digestive substances like the stomach or pancreas do. Instead, it relies on secretions from other organs and its own specialized cells to complete digestion. Here's a breakdown:

Secretions from the small intestine itself:

* Brush border enzymes: These enzymes are embedded in the microvilli of the intestinal lining. They play a key role in the final stages of digestion, breaking down carbohydrates, proteins, and fats into their smallest units (monosaccharides, amino acids, fatty acids, etc.). Examples include lactase, sucrase, maltase, peptidases, and lipases.

* Mucus: Goblet cells in the intestinal lining secrete mucus, which lubricates the intestinal passage and protects the lining from damage.

Secretions from other organs:

* Bile: Produced by the liver and stored in the gallbladder, bile is secreted into the small intestine via the bile duct. It emulsifies fats, breaking them down into smaller droplets to increase surface area for digestion by lipase enzymes.

* Pancreatic juice: Secreted by the pancreas, pancreatic juice contains a variety of digestive enzymes (amylase, lipase, proteases) and bicarbonate ions. The bicarbonate helps neutralize the acidic chyme coming from the stomach, creating a suitable pH for the intestinal enzymes to function.

Overall, the small intestine relies on a combination of its own secretions and those from other organs to complete the digestion process. This teamwork ensures that the nutrients in food are broken down into absorbable components, ready to be absorbed into the bloodstream.