(6) Small Intestine

Small intestine

Principal organ of the digestive system and the primary site of nutrient absorption.

Three sections of small intestine

Duodenum, jejunum, and ileum.

Duodenum

First section of the small intestine; receives chyme, pancreatic enzymes, and bile.

Duodenum function

Neutralizes acidic chyme and begins/continues chemical digestion.

Duodenal pH

Approximately 8.

Jejunum

Major site where products of digestion are absorbed and metabolized.

Jejunum absorbs

Sugars, amino acids, and fatty acids.

Ileum

Final section of the small intestine; absorbs bile acids, remaining nutrients, and vitamin B12.

Villi

Finger-like projections that increase the surface area of the small intestine.

Microvilli

Microscopic projections on villi that further increase absorptive surface area.

Why does the small intestine have villi and microvilli?

To greatly increase surface area and improve nutrient absorption.

Where does most chemical digestion occur?

The small intestine.

Small intestine enzymes

Include sucrase, maltase, and lactase, which digest simple carbohydrates.

Pancreatic enzymes in small intestine

Digest proteins, fats, and carbohydrates.

Hindgut fermenter small intestine

Most enzymatic breakdown and absorption occur here.

Hindgut fermenter small intestine length

Longer than that of carnivores and omnivores.

Effect of diet quality on intestinal length

As natural diet quality decreases, intestinal length increases to allow more time to break down and absorb nutrients.