Jejunal Mucosa – Structure, Function and Diseases

What is the Jejunal Mucosa?

The jejunal mucosa (Latin: Tunica mucosa jejuni) is the innermost layer of the wall of the jejunum -- the middle section of the small intestine, located between the duodenum and the ileum. This highly specialized mucosal lining is essential for the digestion and absorption of nutrients into the bloodstream.

Structure and Anatomy

The jejunal mucosa features a highly complex surface architecture designed to maximize nutrient absorption efficiency:

• Circular folds (Plicae circulares / Kerckring folds): Large, permanent folds of the mucosa that dramatically increase the absorptive surface area.
• Villi (intestinal villi): Finger-like projections of the mucosa that protrude into the intestinal lumen, further expanding the surface area available for absorption.
• Microvilli (brush border): Tiny hair-like extensions on the surface of intestinal cells (enterocytes) that together form the so-called brush border, multiplying the absorptive surface area many times over.

The mucosa contains several specialized cell types, including enterocytes (responsible for nutrient absorption), goblet cells (which produce protective mucus), and enteroendocrine cells (which secrete digestive hormones).

Functions of the Jejunal Mucosa

The jejunal mucosa performs several critical functions in the digestive process:

• Nutrient absorption: Carbohydrates, proteins, fats, fat-soluble vitamins (A, D, E, K), and water-soluble vitamins (e.g., B vitamins) are primarily absorbed here.
• Protective barrier: A layer of mucus protects the delicate mucosal surface from digestive acids, enzymes, and pathogens.
• Immune defense: The gut-associated lymphoid tissue (GALT) present in the jejunum actively defends against infections and foreign antigens.
• Hormone secretion: Enteroendocrine cells produce hormones such as secretin and cholecystokinin (CCK) that regulate digestion and gastric activity.

Common Diseases of the Jejunal Mucosa

Several conditions can damage the jejunal mucosa and impair nutrient absorption:

• Celiac disease: An autoimmune disorder in which gluten triggers inflammation of the small intestinal mucosa, leading to villous atrophy (flattening of the villi) and significantly reduced nutrient absorption.
• Crohn disease: A chronic inflammatory bowel disease that can affect any part of the gastrointestinal tract, but frequently involves the jejunum and ileum.
• Tropical sprue: A malabsorption disorder with villous atrophy occurring primarily in tropical regions, likely triggered by infectious agents.
• Short bowel syndrome: Following surgical removal of large segments of the jejunum, severe malabsorption and nutritional deficiencies can occur.
• Small intestinal infections: Bacterial or viral infections can inflame the mucosa, causing diarrhea and malabsorption.

Diagnosis of Jejunal Mucosal Disorders

Several diagnostic methods are used to evaluate the condition of the jejunal mucosa:

• Small intestinal biopsy: Tissue sampling (typically performed via upper endoscopy) for histological analysis is the gold standard for diagnosing conditions such as celiac disease.
• Capsule endoscopy: A small swallowable camera capsule allows visual inspection of the entire small intestinal mucosa without invasive procedures.
• Double-balloon enteroscopy: A specialized endoscopic technique that allows direct examination and biopsy of the jejunum.
• Laboratory tests: Blood tests for specific antibodies (e.g., anti-tissue transglutaminase antibodies in celiac disease) and absorption tests can indicate mucosal damage.

Treatment and Protection of the Jejunal Mucosa

Treatment depends on the underlying cause of mucosal damage:

• In celiac disease, a strict lifelong gluten-free diet is the only effective therapy and allows the mucosa to heal over time.
• In Crohn disease, anti-inflammatory drugs, immunosuppressants, and biologic therapies are used to control inflammation and protect the mucosa.
• A balanced diet rich in fiber, vitamins, and minerals supports the general health and integrity of the intestinal mucosa.
• Probiotics may support the intestinal microbiome and help strengthen the mucosal barrier function.

References

1. Kasper, D. L. et al. (eds.) - Harrison's Principles of Internal Medicine, 20th edition, McGraw-Hill Education, 2018.
2. Waheed, A. & Bhimji, S. S. - Histology, Small Intestinal Mucosa. StatPearls Publishing, Treasure Island (FL), 2023. Available at: https://www.ncbi.nlm.nih.gov/books/NBK537304/
3. Marsh, M. N. - Gluten, major histocompatibility complex, and the small intestine. A molecular and immunobiologic approach to the spectrum of gluten sensitivity. Gastroenterology, 102(1):330-354, 1992.