Patient education
GI Anatomy & Intestinal Rehabilitation
A companion guide explaining how digestion works, what intestinal failure is, and how intestinal rehabilitation restores nutritional autonomy.
Before you begin. This guide builds on our companion resource, “Short Bowel Syndrome in Adults,” and explains how digestion normally works, what happens when the intestine can no longer sustain adequate nutrition, and how intestinal rehabilitation helps you work toward reducing or eliminating parenteral nutrition. It does not replace advice from your AIRI care team — always contact your team with questions specific to your condition or care plan.
How digestion works: step by step
Understanding how a healthy digestive tract functions helps explain why the location and length of any remaining bowel matters so much for your nutrition and care plan.
Step 1 — The mouth
Digestion begins at the mouth, where mechanical digestion starts. Saliva moistens and lubricates food before swallowing and begins partially digesting food particles.
Step 2 — The esophagus
Food moves from the mouth, down the esophagus, and into the stomach.
Step 3 — The stomach
Glands in the stomach secrete hydrochloric acid, which helps digest food and destroys bacteria that enter the body with food. Very little nutrient absorption happens here. The digested, semi-liquid food — called chyme — then moves from the stomach into the first section of the small intestine, the duodenum.
Step 4 — The small intestine
Most digestion and nutrient absorption happens here. Specialized enzymes break down carbohydrates, fats, and proteins into smaller components your intestinal cells can absorb and use throughout the body. The pancreas and liver also release substances into the small intestine to aid digestion.
Step 5 — The ileocecal valve and colon
Food passes from the ileum through the ileocecal valve and enters the colon, which serves two main roles: acting as a storage chamber for undigested material, and reabsorbing water.
Step 6 — Elimination
When triggered, contractions of the rectum and relaxation of the anal sphincter cause defecation, and stool is eliminated.
Why this matters for short bowel patients. Digestion and absorption depend on many components working together — proper muscle contractions, enzyme activity, and healthy cell function. If any of these are impaired or missing, as in intestinal failure, the process cannot proceed normally, which is why the location and health of your remaining bowel are so central to your care plan.
The small intestine: three key sections
Since different parts of the small intestine absorb different nutrients, the location of any bowel that has been removed determines which nutrient deficiencies you are at risk for.
| Section | Primary role |
|---|---|
| Duodenum | Main site for absorption of iron and folate. This is also where bile and pancreatic enzymes enter the intestine to aid digestion. |
| Jejunum | A major site of overall nutrient absorption. |
| Ileum | A major site of overall nutrient absorption, and the only section of intestine that can absorb vitamin B12. If your ileum is missing — common in short bowel syndrome — you will require lifelong vitamin B12 supplementation. |
From intestinal failure to rehabilitation
What is intestinal failure (IF)?
Short bowel syndrome may lead to intestinal failure. Intestinal failure develops when your small intestine can no longer provide the nutrition needed to sustain a normal life on its own. This results in the need for additional, long-term nutrition delivered through large veins in the body — a therapy called parenteral nutrition (PN).
What is intestinal rehabilitation?
Before pursuing a transplant, intestinal rehabilitation is usually attempted first in patients with intestinal failure. Intestinal rehabilitation is the process of restoring nutritional autonomy in patients with short bowel syndrome and intestinal failure — meaning weaning off PN and onto oral feedings, to the point where you can live life without PN and its associated complications.
There are multiple components to intestinal rehabilitation, and all therapies focus on one central goal: maximizing the absorptive capacity of the remaining bowel.
A basic overview of intestinal rehabilitation
Enteral nutrition — nutrition that passes through the intestine, either by mouth or tube feeding — is critical to maintaining normal intestinal structure and function. To transition from parenteral to enteral nutrition (EN), the intestinal lining (epithelium) must adapt to optimize nutrient absorption. Your team of surgeons, gastroenterologists, and dietitians will work with you to determine the optimal formula and diet to support this adaptation.
Diet considerations during rehabilitation
Carbohydrates are often poorly tolerated by intestinal failure patients. Gut bacteria break carbohydrates down into small, osmotically active organic acids that draw large amounts of water into the distal small intestine and colon, causing significant fluid losses. Moderate amounts of fat and protein are generally better tolerated in a short bowel syndrome diet.
Watch for dehydration. You can become dehydrated quickly due to large fluid losses from a high-output ostomy, persistent secretory diarrhea, or pseudo-obstruction causing large gastric and duodenal losses. In these situations, an oral rehydration solution containing glucose and sodium may be recommended, and you may be asked to monitor your urine and stool output to track your hydration status.
Tube feeding
If you have short bowel syndrome or persistent diarrhea and require tube feeding, a continuous feed through a nasogastric (NG) tube or gastrostomy tube may be recommended. This allows constant saturation of the carrier proteins that transport nutrients across the intestinal wall, making the most of your limited absorptive area.
A realistic timeline
It’s important to understand that the transition from intestinal failure to adequate intestinal function — and the ability to wean from parenteral to full enteral feeding — can take weeks, months, or even years. Progress is measured over a long timeline, and this is expected.
Predictors of successful adaptation and weaning from TPN
Several factors help predict how well your bowel will adapt and whether you may be able to wean from parenteral nutrition:
- The length of bowel remaining
- The anatomical section (location/portion) of bowel that remains
- Presence or absence of the ileocecal valve
- Presence or absence of the colon
- Health of the remaining bowel (for example, whether inflammation is present)
Because different parts of the bowel absorb different types of nutrients, the location of your intestinal resection determines which specific nutrient deficiencies your team will watch for and manage.
What is intestinal adaptation?
Intestinal adaptation is your bowel’s ability to adjust to the changes that have occurred within it. The intestine compensates for lost function in one area by adapting at another site. This is a slow process and can take up to two years to complete.
Intestinal rehabilitation relies on intestinal adaptation to successfully wean you from parenteral nutrition. During adaptation, the following changes occur:
- The diameter of the bowel increases
- The surface area available to absorb nutrients increases, through a rise in both the number and size of intestinal villi (the finger-like projections lining the intestine)
- The movement of contents through the bowel slows, increasing the time contents spend in contact with the intestinal wall for absorption
Components of intestinal rehabilitation
- Diet modification
- Oral rehydration therapy
- Vitamin and mineral supplements
- Medications
- Surgical procedures
Who is on your intestinal rehabilitation team?
At an intestinal rehabilitation center like AIRI, you’ll have a full team of clinicians supporting you through your journey. Typically, your intestinal rehabilitation care team includes:
- Medical Director — provides overall clinical oversight of your care plan, including acuity assessment, medical necessity determinations, and the parenteral/home nutrition plan. The Medical Director sets the clinical direction for your team and is the final point of escalation for complex or urgent decisions.
- Surgeon
- Gastroenterologist
- Nutritionist or dietitian
- Social worker
- Clinical nurse coordinator
- Advanced practice nurse (nurse practitioner)
- Mid-level providers
- Pharmacist
Each team member plays a specific role — from managing your medical and surgical care to coordinating home support, nutrition planning, and medication management — all working together toward the shared goal of helping you achieve the best possible intestinal function and quality of life.
This guide was prepared by the Advanced Intestinal Rehabilitation Institute (AIRI) for patient education purposes. It is not a substitute for medical advice from your care team. If you have questions about your specific condition, diet, medications, or symptoms, please contact your AIRI care team directly.