Small Intestine

What is the small intestine?

Your small intestine (small bowel) is an important part of your digestive system. It connects your stomach to your large intestine. You rely on your small intestine to extract nutrients from the food your eat. Your small intestine:

• Breaks food down.
• Absorbs nutrients and water.
• Moves food along your gastrointestinal tract.

You may not have a reason to think about your small intestine as it churns through the continuous job of digesting what you eat and drink. But there are several common conditions and diseases that can affect small intestine function. Symptoms from them can make you feel miserable and disrupt your daily life. Understanding how your small intestine works can help you keep it in good shape and running smoothly.

What does the small intestine do?

Your small intestine turns semi-solid food into liquid so your body can absorb the nutrients you need. To do that, your small intestine:

• Delivers digestive juices and enzymes that combine with bile to allow the digestive process.
• Breaks down and liquefies semi-solid food so your body can absorb and use the nutrients.
• Absorbs nutrients and water through the villi in mucosa, which is the inner lining of your small intestine.
• Turns what’s left behind into digestive waste that moves to your large intestine and eventually leaves your body in the form of poop (stool).

Where is my small intestine located?

Your small intestine is inside your abdominal cavity. It’s a long coil of tissues and muscle that looks like a very long, thin, pink or red tube with many folds. Your large intestine surrounds your small intestine.

How long is it?

Despite its name, your small intestine is the longest section of the gastrointestinal tract, measuring about 22 feet long.

Its inner lining is also impressively large, thanks to microvilli. These are the tiny, finger-like projections lining the wall of your small intestine. They increase the surface area that absorbs nutrients. (Think of shaking out a very large tarp with many folds and scrunched-up sections — in this case, the open tarp would cover a tennis court.)

The one small part of your small intestine is its width: it measures about 2 centimeters in diameter, or about as big around as your index (pointer) finger.

What are the parts of the small intestine?

Your small intestine has three parts. Each part is responsible for specific tasks that are essential to digesting food. Those parts are:

The duodenum

This is the first part of your small intestine. It’s a short (10-inch-long) chute that receives food from your stomach. Your duodenum is the place where your small intestine makes the digestive juices and enzymes to break down food. Your gallbladder delivers bile, and your pancreas delivers digestive enzymes to your duodenum to help it break down food.

The jejunum

This section of your small intestine is 8 feet long. It lays in many coils inside the lower abdominal cavity. The jejunum is dark red because it has many blood vessels. It has muscles that churn food back and forth and mix it with digestive juices. Peristalsis, which is an involuntary muscle movement in your digestive system, keeps food moving toward your ileum.

The ileum

This is the last and longest section of your small intestine. It absorbs nutrients from digested food for your body to use, like vitamins, minerals, carbohydrates, fats and protein. Your ileum moves food waste toward your large intestine. The ileum is where food spends the most time in the small intestine before moving to the large intestine.

What common conditions and diseases may affect the small intestine?

There are many illnesses that can affect your small intestine. Some of the more common ones include:

• Celiac disease.
• Crohn’s disease.
• Enteritis.
• Gastrointestinal neuroendocrine tumor (carcinoid tumor).
• Irritable bowel syndrome (IBS).
• Malabsorption.
• Meckel’s diverticulum.
• Peptic ulcer disease.
• Scleroderma.
• Small bowel obstruction.
• SIBO.

What are common symptoms of small intestine conditions and diseases?

Your small intestine absorbs nutrients and water from your food. Diseases and conditions that keep your small intestine from absorbing nutrients and water may cause the following symptoms:

• Belly pain.
• Bloated stomach.
• Constipation.
• Diarrhea.
• Nausea and vomiting.
• Unexplained weight loss.

How do you know if something is wrong with your small intestine?

A healthcare provider may order different tests depending on your symptoms. For example, if you’re losing weight without trying, a provider may order blood tests and other lab tests. If you have symptoms like belly pain, constipation or diarrhea, a healthcare provider may order tests that will let them see what’s going on inside your small intestine.

Blood and lab tests

These tests may include:

• Complete blood count (CBC).
• Comprehensive metabolic panel (CMP).
• Urinalysis.
• Tests for specific diseases like celiac disease and Crohn’s disease.
• Stool tests.

Imaging tests

These tests may include:

• Capsule endoscopy.
• CT scan (computed tomography scan).
• Enteroscopy.
• Small bowel X-ray series.
• Upper endoscopy.

What are common treatments for small intestine issues?

There are many conditions and diseases that can affect your small intestine and cause symptoms that disrupt your daily life. Treatments may range from making changes in what you eat to medication to surgery.

For example, if you have celiac disease, your treatment may be following a gluten-free diet. If you have peptic ulcer disease, a provider may prescribe medications that protect your small intestine while it heals. But if you have a small intestine obstruction, you may need surgery to remove the obstruction.

What helps my small intestine function?

Taking care of your overall gut health is the best way to keep your small intestine healthy. Here are some suggestions:

• Eat well: Plan meals that highlight fruits, vegetables and whole grains. Ask a dietitian about adding prebiotics and probiotics to your food plan.
• Drink up: A steady flow of fluids — water and non-carbonated or caffeine-free drinks — helps your digestive system, including your small intestine, break down food.
• Get your rest: Resting, specifically sleeping well, helps repair cells and support your immune system.
• Manage stress: Stress can trigger conditions that affect your small intestine, like Crohn’s disease and irritable bowel syndrome.
• Stay active: Regular activity improves blood flow to your intestines and vital organs and strengthens your muscles. It also boosts gut motility — the muscle contractions that move food through your GI tract.