Jejunal Mucosal Barrier – Function and Disorders

What Is the Jejunal Mucosal Barrier?

The jejunal mucosal barrier refers to the functional and structural protective layer of the mucosa in the jejunum – the middle segment of the small intestine. It separates the intestinal lumen from the surrounding tissue and bloodstream. Its primary roles are the selective absorption of nutrients, water, and electrolytes, as well as the defense against pathogens, toxins, and other harmful substances.

Structure of the Jejunal Mucosal Barrier

The barrier is composed of several layers and components:

• Epithelial cell layer: A single layer of specialized cells (enterocytes, goblet cells, Paneth cells, and enteroendocrine cells) lining the intestinal lumen.
• Tight junctions: Protein complexes between adjacent epithelial cells that strictly regulate paracellular transport (transport between cells) and prevent unwanted substances from passing through.
• Mucus layer: A layer of mucus produced by goblet cells that acts as a first physical barrier against microorganisms and harmful substances.
• Secretory IgA (sIgA): An immunoglobulin secreted into the intestinal mucus that neutralizes pathogens.
• Gut-associated lymphoid tissue (GALT): Supports immunological defense and tolerance within the intestinal wall.
• Microbiome: The microbial community in the jejunum contributes to barrier function by outcompeting pathogens and promoting epithelial integrity.

Physiological Function

The jejunum is the primary site of nutrient absorption in the human body. The mucosal barrier enables the targeted uptake of amino acids, carbohydrates, fatty acids, vitamins, and minerals, while simultaneously preventing bacteria, viruses, undigested food particles, or toxins from entering the body uncontrolled. This process is referred to as selective permeability.

Disorders of the Jejunal Mucosal Barrier

Impairment of the barrier function is described as increased intestinal permeability, colloquially known as leaky gut. The following factors and conditions can damage the barrier:

• Coeliac disease: An autoimmune reaction to gluten destroys intestinal villi and significantly damages the epithelial layer.
• Crohn disease: A chronic inflammatory bowel disease that can also affect the jejunum.
• Infections: Bacterial or viral gastroenteritis can temporarily damage tight junctions.
• Medications: Non-steroidal anti-inflammatory drugs (NSAIDs) and certain antibiotics can compromise mucosal integrity.
• Malnutrition: Deficiencies in nutrients such as zinc, vitamin A, or glutamine can weaken barrier function.
• Chronic stress: Psychophysiological stress can increase intestinal permeability via neuroendocrine signaling pathways.

Diagnosis of Barrier Defects

Several diagnostic methods are available to assess the jejunal barrier function:

• Lactulose-mannitol test (sugar permeability test): Measures the uptake of sugar molecules of different sizes to assess intestinal wall permeability.
• Histological examination (small intestinal biopsy): Tissue samples from the jejunum are analyzed microscopically, for example when coeliac disease is suspected.
• Serological markers: Elevated levels of zonulin, fatty acid-binding protein (FABP), or sIgA may indicate a compromised barrier.
• Endoscopy: Direct assessment of the mucosal surface via capsule endoscopy or enteroscopy.

Treatment and Support of Barrier Function

Treatment is always guided by the underlying cause. General measures to support the jejunal mucosal barrier include:

• Glutamine supplementation: The amino acid glutamine is the primary energy source for enterocytes and supports cell regeneration.
• Zinc intake: Zinc plays a key role in maintaining tight junction integrity and immune function.
• Probiotics and prebiotics: Promote a healthy microbiome that strengthens barrier function.
• Dietary modification: A strict gluten-free diet is essential in coeliac disease; an anti-inflammatory diet may be beneficial in general.
• Pharmacological therapy: In inflammatory bowel diseases, corticosteroids, immunosuppressants, or biologics may be used.
• Stress reduction: Relaxation techniques can indirectly improve gut health.

References

1. Camilleri M. - Leaky gut: mechanisms, measurement and clinical implications in humans. Gut, 2019. BMJ Publishing Group.
2. World Gastroenterology Organisation (WGO) - Celiac Disease: Global Guidelines, 2017. Available at: https://www.worldgastroenterology.org
3. Turner J.R. - Intestinal mucosal barrier function in health and disease. Nature Reviews Immunology, 2009; 9(11): 799-809.