The Small Intestine - Where Nutrients Are Absorbed

The Small Intestine — Where Nutrients Are Absorbed

After leaving the stomach, food moves into the small intestine — the longest part of your dog’s digestive system and the key player in nutrient absorption. It’s where all the hard work from the mouth, esophagus, and stomach pays off.

What Is the Small Intestine?

The small intestine is a long, twisting tube divided into three parts:

• Duodenum: Where stomach contents mix with enzymes from the pancreas and bile from the liver.
• Jejunum: The main site of nutrient absorption.
• Ileum: Absorbs vitamin B12, bile salts, and whatever else wasn’t absorbed earlier.

How Digestion Happens Here

Enzymes from the pancreas break down proteins, fats, and carbohydrates into tiny molecules your dog’s body can absorb. Bile from the liver helps emulsify fats, making them easier to digest.

The small intestine is lined with millions of tiny finger-like projections called villi and microvilli. These structures increase surface area dramatically — giving your dog’s gut a huge area to absorb nutrients efficiently.

What Nutrients Are Absorbed?

• Amino acids from proteins
• Fatty acids and glycerol from fats
• Simple sugars from carbohydrates
• Vitamins and minerals
• Some water

Common Issues Affecting the Small Intestine

• Inflammatory bowel disease (IBD): Chronic inflammation that disrupts absorption.
• Exocrine pancreatic insufficiency (EPI): When the pancreas doesn’t produce enough enzymes (learn more here).
• Parasitic infections: Such as giardia and hookworms.
• Food intolerances: Leading to inflammation and malabsorption.

Supporting Your Dog’s Small Intestine

• Feed a balanced diet with high-quality ingredients (how to choose the best dog food).
• Consider adding prebiotics and probiotics (benefits of probiotics for dogs).
• Ensure regular parasite prevention and vet checkups.
• Avoid unnecessary antibiotics that can disrupt gut bacteria.

What Happens Next?

Once the small intestine finishes absorbing nutrients, leftover waste moves into the large intestine for water absorption and final processing. We’ll explore that in the next post: The Large Intestine & Colon — The Final Steps.

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Infographic: The Small Intestine at Work

(Image idea: “The Small Intestine at Work” infographic)

• Diagram showing the three sections: duodenum, jejunum, ileum.
• Magnified view of villi and microvilli structure.
• Arrows showing absorption of proteins, fats, carbs, vitamins.
• Quick facts:
  • Length: 10–13 feet in medium dogs.
  • Main site of nutrient absorption.
  • Surface area increased by villi and microvilli.

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References

1. Hall, E. J., German, A. J., & Day, M. J. (2014). Small intestinal diseases in dogs. In Textbook of Veterinary Internal Medicine (8th ed.).
2. Simpson, K. W., & Jergens, A. E. (2011). Pitfalls and progress in the diagnosis and management of canine inflammatory bowel disease. Veterinary Clinics of North America: Small Animal Practice, 41(2), 381–398.
3. Suchodolski, J. S. (2011). Intestinal microbiota of dogs and cats: a bigger world than we thought. Veterinary Clinics: Small Animal Practice, 41(2), 261–272.

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Digestive System Series
1. The Mouth — Where Digestion Begins
2. The Esophagus — Your Dog’s Food Highway
3. The Stomach — The Powerhouse of Digestion
4. The Small Intestine — Where Nutrients Are Absorbed (You are here)
5. Large Intestine & Colon — The Final Steps (coming soon)