Histology of the Small Intestine

Small intestine villi are fingerlike projections covered by simple columnar epithelium containing absorptive cells and goblet cells. The lamina propria core houses blood capillaries and a lacteal, a large lymphatic vessel that transports absorbed lipids. At the villus base lie intestinal glands that secrete digestive juices to aid nutrient breakdown and absorption.

Enterocytes, also called absorptive cells, possess microvilli that dramatically increase surface area for nutrient uptake from chyme. These specialized epithelial cells actively transport absorbed nutrients into blood capillaries within the lamina propria. Their extensive microvilli and enzymatic activity make them essential for efficient mechanical and chemical digestion in the small intestine.

Paneth cells, located in intestinal glands, secrete lysozyme and perform phagocytosis to regulate microbial populations. Enteroendocrine cells including S, CCK, and K cells secrete hormones like secretin and cholecystokinin that regulate digestion and nutrient absorption throughout the gastrointestinal tract. These specialized cells maintain intestinal health and digestive function.

The jejunum features prominent circular folds and large villi, facilitating maximum nutrient absorption. The distal ileum has fewer folds and smaller villi but contains Peyer's patches, aggregated lymphoid nodules in the lamina propria that provide immune protection against gastrointestinal pathogens.

Goblet cells, housed within intestinal villi epithelium, secrete mucus that protects the intestinal lining and facilitates smooth movement of chyme through the small intestine. This mucus layer enables efficient nutrient absorption while shielding epithelial cells from mechanical damage and digestive enzymes.

The duodenum prioritizes neutralizing acidic chyme from the stomach and mixing it with bile and pancreatic enzymes for fat, protein, and carbohydrate breakdown. Its smaller surface area reflects this preparatory role, while the jejunum's prominent folds and villi maximize absorption of partially digested nutrients.

Three structural levels increase absorptive surface area: circular folds in the intestinal wall, fingerlike villi projecting from the mucosa, and microvilli on enterocyte cell membranes. This hierarchical arrangement creates an enormous surface area for absorption of nutrients from chyme throughout the small intestine.