You see an anatomy chart on a classroom wall, a model in a doctor's office, or a diagram in a textbook: a long coiled tube packed into the middle of the body, framed by a wider tube around the edges. Both are called intestines, yet one is "small" and one is "large," and the names seem to argue with the picture. So how do the large and small intestine actually compare? Anatomists have precise answers, and the sizes may not be what the names suggest.

Plenty of people are asking. In Google Trends data for the US over the past 7 days, top related searches for the seed term "small intestine" included "large and small intestine" with a score of 100, "where is the small intestine" (50), "how long is small intestine" (25), "small intestine parts" (22), "parts of small intestine" (20), "layers of small intestine" (8), and "length of small intestine" (7). Two searches were rising: "is the small intestine bigger than the large intestine" showed growth of +200%, and "small intestine histology" showed growth of +60%. Top scores are relative interest, scaled so the top related search for a seed equals 100; they are not search counts. A rising percentage shows growth in search interest compared with the prior period. People want location first, then the parts, the layers, and the measurements.

Where is the small intestine? Large and small intestine in the abdomen

OpenStax Anatomy and Physiology 2e describes the small intestine as a coiled tube that starts at the pyloric sphincter, the muscular ring at the end of the stomach, and ends at the ileocecal valve, where it meets the large intestine. The Cleveland Clinic puts it in plainer terms: the small intestine sits under the stomach inside the abdominal cavity, and the large intestine surrounds it.

That "surrounds" matters for the picture in your head. OpenStax says the large intestine frames the small intestine on three sides.

How the small intestine is anchored

The coils do not float freely. OpenStax says the jejunum and ileum are tethered to the posterior abdominal wall by the mesentery, a vertical band of tissue in front of the lumbar vertebrae.

Small intestine parts: duodenum, jejunum, and ileum

The sources used here agree on the small intestine parts. There are three, in order from the stomach: the duodenum, the jejunum, and the ileum. If you are looking for the parts of the small intestine in one line, that is it. Here is how the sources describe each one.

• Duodenum: the first and shortest section. OpenStax gives 25.4 cm (10 in). StatPearls gives 20 to 25 cm on average and calls it the most proximal, widest, and shortest segment. The Cleveland Clinic describes it as a short, 10-inch-long section.
• Jejunum: the middle section. OpenStax gives about 0.9 m (3 ft). StatPearls gives about 2.5 m, beginning at the duodenojejunal junction.
• Ileum: the last section. OpenStax gives about 1.8 m (6 ft). StatPearls gives about 3 m, ending at the ileocecal valve. The Cleveland Clinic calls it the last and longest section.

The figures do not match across sources. The Cleveland Clinic, for example, lists the jejunum at 8 feet, while OpenStax lists about 3 feet. Measurements depend on how and when they are taken. The Cleveland Clinic adds that the jejunum is dark red because of its many blood vessels.

How long is the small intestine? Length of small intestine

This is the question behind the "length of small intestine" searches, and sources give different numbers, so here are the main ones side by side.

Why the gap between about 10 feet and about 22 feet? OpenStax explains part of it: the tube is shorter in a living person than in a cadaver, roughly half the length.

Is the small intestine bigger than the large intestine?

This is the fastest-rising search in the group, and the answer depends on what "bigger" means. By length, the small intestine is the longer tube. The Cleveland Clinic calls it the longest section of the gastrointestinal tract. By width, the large intestine wins. OpenStax gives the large intestine a diameter of about 7.62 cm (3 in), more than twice the small intestine's diameter of about 2.54 cm.

The Cleveland Clinic points out the naming logic: the small intestine is named for its width, not its length. So the labels "small" and "large" describe the diameter of the tube, and the numbers above show it.

The two also differ in how their walls are built. OpenStax says the large intestine lacks circular folds and villi, and its lining has many more intestinal glands than the small intestine's. It has the teniae coli, three bands of smooth muscle forming its longitudinal layer, and haustra, the pouches made by those bands. For a wider survey of the whole tract, our guide to the digestive system places each organ in order.

Small intestine histology: layers of the small intestine

Histology is the study of tissue under the microscope, and the "layers of small intestine" are where it starts. OpenStax says the wall has the same four layers found throughout the alimentary canal. Working from the inside out, they are:

• Mucosa: the inner lining. OpenStax describes it as a simple columnar epithelium in the stomach and intestines, pulled into folds by a thin muscle layer called the muscularis mucosae.
• Submucosa: in OpenStax's words, a broad layer of loose connective tissue that connects the mucosa to the muscle layer.
• Muscularis externa: OpenStax says the muscularis in the small intestine is a double layer of smooth muscle, with an inner circular layer and an outer longitudinal layer.
• Serosa: OpenStax says the serosa is a layer of visceral peritoneum over loose connective tissue, present only where the canal lies within the abdominal cavity. StatPearls says it is found in the jejunum, ileum, and intraperitoneal part of the duodenum.

Different textbooks group these layers slightly differently. StatPearls, for example, also lists the lamina propria, a layer of loose connective tissue, as part of the mucosal lining.

Villi, microvilli, and circular folds

Look at the inner surface and the small intestine looks furry. OpenStax explains why. Circular folds are deep ridges of the mucosa and submucosa. Villi are hairlike, blood-vessel-rich projections of the mucosa, 0.5 to 1 mm long, with about 20 to 40 per square millimeter. Microvilli are cylindrical extensions of the cell membrane about 1 micrometer long, with about 200 million per square millimeter, and together they form what histologists call the brush border. OpenStax states that these features combined increase the surface area of the lining more than 600-fold, to roughly 200 square meters.

StatPearls says the circular folds, which it calls plicae circulares or valves of Kerckring, are present in the jejunum and ileum. OpenStax says they run from near the start of the duodenum to about the middle of the ileum, so the two sources frame the range a little differently.

Our take on reading the intestines

We think the names "small" and "large" cause more confusion than any other part of this topic. They sound like a size contest, and the real answer is a tie in a sense: one is longer, the other is wider. Once you hold both facts, the diagrams make sense.

We also think the numbers deserve a grain of salt. When one source says 10 feet and another says 22, ask how each was measured. Look for the conditions, not just the number.

And we think histology is the most rewarding way to read the small intestine. Four layers, one furry inner surface, and a few precise measurements tell you more about the organ's design than any single length figure does. If you enjoy the bigger picture of what lives alongside the tract, our explainer on the microbiome is a separate subject from organ structure, and a good companion read.

Why we carry the Women's Daily Essentials Bundle at PRSPR

We wrote this anatomy guide as part of our Learn library, which sits alongside our Women's Daily Essentials Bundle. This article is about the structure of the small and large intestine, nothing more, and it is not about the bundle or its contents. Here is what the listing states about the product:

• Name: Women's Daily Essentials Bundle.
• What it is: a five-product bundle made up of Flore' Probiotic, Black Seed Oil 1000 mg, Vitamin D3 + K2, Magnesium Glycinate, and Chelated Zinc + Elderberry.
• Price: $184.99.

Each product in it is made in a GMP-certified facility and third-party batch tested. You can see it with the rest of our bundles in the Bundles collection.

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FAQ

Where is the small intestine?

The Cleveland Clinic says the small intestine sits under the stomach inside the abdominal cavity, surrounded by the large intestine. OpenStax Anatomy and Physiology 2e describes it as a coiled tube from the pyloric sphincter to the ileocecal valve.

What are the parts of the small intestine?

The duodenum, the jejunum, and the ileum, in that order from the stomach. OpenStax gives about 25.4 cm for the duodenum, about 0.9 m for the jejunum, and about 1.8 m for the ileum.

How long is the small intestine?

OpenStax gives about 3.05 m (10 ft) in a living person and roughly twice that in a cadaver. NCBI StatPearls gives 3 to 5 m on average, and the Cleveland Clinic says about 22 feet.

Is the small intestine bigger than the large intestine?

The Cleveland Clinic calls the small intestine the longest section of the gastrointestinal tract, but OpenStax gives the large intestine the wider diameter, about 7.62 cm versus about 2.54 cm.

What are the layers of the small intestine?

OpenStax describes four layers: mucosa, submucosa, muscularis externa, and serosa.