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The Intestinal Mucosal Barrier

Location of Mucosal Barriers in the Body


Our bodies contain numerous mucosal barriers, which are mucous membranes made of a layer of epithelial cells that protect the internal environment from the external environment. These membranes line the digestive, respiratory, and reproductive tracts, as well as the eyes.


Our primary focus is on the digestive tract, essentially a continuous tube that runs from the mouth to the anus. It includes a section called the small intestine, where the majority of nutrient breakdown and absorption occurs. This segment also houses a large percentage of the immune system and protects the body from antigens (toxins and foreign substances) and unfriendly microorganisms. A healthy functioning small intestine is essential for overall health.


Mucosal Barriers in the Body
Mucosal Barriers in the Body

The Intestinal Mucosal Barrier serves two main functions:


1) The foundation of our gut immune system


  • It is a physical barrier, like a second skin. It protects the bloodstream from bad bacteria, toxins and parasites that are naturally coming in from the things we eat, drink, and breathe.

  • It is a chemical barrier. Secretory IgA, or SIgA, is our primary immunoglobulin secreted from the mucosal surface. It is tasked with identifying friend versus foe.


Mucosal Barrier Immune Function Anatomy


  • The first layer is the internal cavity of the intestine, called the lumen. This is where food particles, normal bacteria, and unfriendly flora pass from the stomach to the large intestine.

  • Under the lumen is a thin layer of epithelial cells. They are closely bound together by so-called “tight junctions”. The epithelial cells make up a single-cell layer protecting the immune system underneath.

  • The lamina propria houses the gut immune system. SIgA is produced here and is excreted through the epithelial cells to the lumen. The lamina propria is where the gut connects to the bloodstream, making immune function here critical to survival.


Intestin Mucosal Barrier Permiability
Anatomy of Intestinal Mucosal Barrier

2) The intestinal mucosal barrier absorbs nutrients


The intestine is a long tube with embedded folds to increase surface area for nutrient absorption. Refer to diagrams below. These folds are finger-like projections called villi. The top of the epithelial cells contains hair-like projections called microvilli, which make up the brush border. The villi stand tall and wave flexibly in the gut lumen, pulling nutrients in, passing them through the lamina propria and into the bloodstream to be utilized by the body.


Nutrition Absorption Digestion Mucosa Lumen
Mucosal Barrier Nutrient Absorption Anatomy
Villi Microvilli Intestinal Crysp
Villi & Microvilli (Brush Border)

How does Mucosal Barrier Damage happen?


  • Infections: Pathogenic microorganisms, such as bacteria, viruses, and fungi.

  • Inflammation: Chronic inflammation, whether due to infections, autoimmune disorders, or food alergies and sensitivities.

  • Chemical Irritants: Exposure to certain chemicals, irritants, toxins, pollutants, or ingesting substances.

  • Trauma: Physical trauma or injury through accidents, surgical procedures, or other forms of physical trauma.

  • Immunological Reactions: In some cases, the immune system may mistakenly target and attack the body's own mucosal tissues, leading to damage.

  • Ischemia: Inadequate blood supply to mucosal tissues, known as ischemia, can result in damage.

  • Malnutrition: Inadequate nutrition, particularly deficiencies in essential nutrients, can weaken mucosal tissues and impair their ability to maintain a healthy barrier. For example, deficiencies in vitamins and minerals, such as vitamin A and zinc.

  • Chronic Diseases: Certain chronic diseases, such as inflammatory bowel disease (IBD) and celiac disease.

Leaky Gut & Villous Atrophy / Blunted Brush Border
Leaky Gut & Villous Atrophy / Blunted Brush Border

What is the result of mucosal barrier damage?


Leaky Gut affects the whole body. A whole host of symptoms and health issues develop as a result of a damaged intestinal mucosal barrier. Here are some of the potential consequences and related health issues associated with mucosal barrier damage:


  • Digestive Issues: Impaired mucosal barrier function can lead to digestive problems such as bloating, gas, diarrhea, and abdominal discomfort.

  • Nutrient Malabsorption: A compromised barrier may result in poor absorption of nutrients, leading to nutritional deficiencies.

  • Systemic Inflammation: Increased permeability allows the passage of substances (e.g., bacteria, toxins) from the gut into the bloodstream, triggering an immune response and systemic inflammation.

  • Immune System Dysfunction: The gut is a significant part of the immune system. Mucosal barrier damage can disrupt the balance of the immune system, potentially contributing to autoimmune conditions and increased susceptibility to infections.

  • Brain Function: Some theories propose a connection between a compromised mucosal barrier and neurological symptoms. This is often referred to as the "gut-brain axis," where changes in the gut can influence brain function and may contribute to conditions like brain fog, mood disorders, and cognitive issues.

  • Skin Issues: Skin conditions such as eczema, psoriasis, and acne have been linked to intestinal permeability. The immune system's response to substances leaking from the gut may contribute to skin inflammation.

  • Thyroid Dysfunction: There is some evidence suggesting a link between mucosal barrier damage and thyroid disorders, possibly due to the impact on immune function and inflammation.

  • Colon Health: Mucosal barrier damage can contribute to the development or exacerbation of conditions such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and colorectal issues.

  • Adrenal Function: Chronic stress and inflammation resulting from mucosal barrier damage may affect adrenal function and contribute to adrenal fatigue or dysfunction.

  • Joint Pain: Increased systemic inflammation and immune system dysregulation may contribute to joint pain and inflammation.

  • Sinus and Mouth Issues: The immune response triggered by substances leaking from the gut can contribute to sinusitis, allergies, and oral health problems.



Mucosal Barrier Assessment 


As an FDN-P I suggest a Dried Blood Spot (DBS) test for assessing mucosal barrier function and intestinal permeability.

It is a convenient and less invasive method compared to traditional blood draws. This test evaluates intestinal permeability (leaky gut) as well as any systemic inflammation that has developed in response to that. 

It tests for Zonulin, the protein that leads to leaky gut and assesses for any histamine intolerance which can develop as a result of gut imbalances.

To go even further, it looks at Diamine Oxidase (DAO) in the body, the enzyme that breaks down the histamines in the food you eat. 


Feel free to Book Consultation with me to gain access to the Functional Labs.


Sending Optimal Health & Ultimate Wellness,

Julia Smila, FDN Practitioner


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