Circular foldsFolds of the mucosa and submucosa; only the small intestine has them.
MucosaThe layer that touches the food. It makes enzymes and mucus and absorbs.
SubmucosaCarries blood and lymph vessels and fills the core of each fold.
MuscularisAn inner circular and an outer lengthwise layer that squeeze food along.
SerosaThe outermost layer, continuous with the mesentery.
Villi and glands 4
VilliThey raise the surface for absorbing food many times over.
Intestinal glandsAlso called crypts; their cells make intestinal juice and new lining cells.
Muscularis mucosaePart of the mucosa, not the main muscle layer.
Duodenal glandsFound only in the duodenum; they make an alkaline mucus.
Inside a villus 5
Absorptive cellsThey take in the digested food; also called enterocytes.
Goblet cellsThey make mucus.
MicrovilliTiny projections that form the brush border.
LactealA lymph capillary that takes up fats.
CapillariesSugars and amino acids pass into the blood here.
How this list was compiled: Every name and detail checked on 2026-09-29 against OpenStax Anatomy and Physiology 2e, section 23.5 The Small and Large Intestines (circular folds, villi, microvilli and the brush border, intestinal glands, lacteal and capillaries, absorptive cells, goblet cells, duodenal or Brunner's glands), https://openstax.org/books/anatomy-and-physiology-2e/pages/23-5-the-small-and-large-intestines, and section 23.1 Overview of the Digestive System (mucosa, submucosa, muscularis, serosa, muscularis mucosae), https://openstax.org/books/anatomy-and-physiology-2e/pages/23-1-overview-of-the-digestive-system, and against Wikipedia, Small intestine, text only. Licence: own work
The drawing: Drawn for this site on 2026-09-29 from plain geometry; nothing traced. Licence: own work
How it works
The small intestine packs a huge surface into a short tube in three steps: big circular folds, finger-like villi on the folds, and microvilli on every cell. The three drawings zoom in on each step.
Read the full guide
Zoom in three times
Numbers 1 to 5 are the wall: the circular folds and the four layers, from the lining out to the covering. Numbers 6 to 9 are part of one fold: the villi, the glands between them, the thin muscle under the lining and the duodenal glands. Numbers 10 to 14 are inside one villus: its cells and their brush border, the lacteal and the capillaries.
Two muscles are easy to mix up: the muscularis mucosae is a thin band inside the lining; the muscularis is the thick muscle wall below.
Questions and answers
What are circular folds?
Permanent ridges of the mucosa and submucosa that run around the inside of the small intestine. They slow the food down and add surface for absorbing it. They are also called plicae circulares.
What is the difference between villi and microvilli?
Villi are finger-like projections of the lining, each made of many cells. Microvilli are tiny projections on the surface of each single cell, forming the brush border.
What is a lacteal?
A lymph capillary in the middle of each villus. It takes up the products of fat digestion, while sugars and amino acids enter the blood capillaries around it.