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Protein Digestion and Absorption Disorders

*Morbus celiacus*

For medical students2 min readUpdated 2026-10-10

Gastrointestinal protein metabolism disorders occur due to enzyme deficiencies, reduced gastric acidity, and mucosal pathologies. This leads to impaired hydrolysis, allergic reactions, and malabsorption syndrome.

Main TargetPlant gluten and gliadin in celiac disease

Critical DeficiencyLack of pancreatic proteases and enteropeptidases

Stool FindingCreatatorrhea with remnants of muscle fibers

Pathogenesis OutcomeBody sensitization and villous atrophy

Impaired Protein Breakdown in the Stomach

The initial stage of proteolysis suffers in pepsin deficiency and hypochlorhydria caused by mucosal atrophy, gastritis, or peptic ulcer disease. Pyloric stenosis and functional dyspepsia in children are also risk factors.

Consequences:

Hydrolysis and swelling of protein molecules are delayed, blocking enzyme access.
Breakdown of collagen and muscle fibers is impaired.
Motility and chyme evacuation into the duodenum are disrupted.

Intestinal Phase and Enzymatic Deficiency

At the intestinal level, problems arise against the background of acute and chronic enteritis, malabsorption syndrome, or congenital pancreatic hypoplasia. The key pathogenetic link is the insufficiency of pancreatic proteases and enteropeptidase due to genetic mutations.

Mechanism of pathology development:

Proteins are not broken down into ultimate amino acids and dipeptides.
Large oligo- and polypeptides accumulate in the intestinal lumen.
These incomplete molecules are absorbed into the systemic circulation.
Pronounced immune sensitization of the body develops.

Celiac Disease: Gluten-Sensitive Enteropathy

The disease is associated with impaired digestion of plant protein — gluten and gliadin, ingested with cereal grains. Normally, these peptides are cleaved by the brush border enzymes of the small intestine.

However, the resulting $\alpha$-gliadin peptide is resistant to hydrolysis by gastric, pancreatic, and intestinal enzymes. The immune system recognizes it as a foreign antigen, triggering a cascade of reactions that damage the epithelium and cause villous atrophy.

Clinical manifestations:

Abdominal pain, nausea, vomiting, flatulence, and constipation.
In adults, a latent course, chronic diarrhea, anemia, and chronic fatigue syndrome often predominate.

Creatatorrhea: Meat Utilization Disorders

The terms kreatos (meat) and rhoia (flow) refer to a condition where excess undigested muscle and connective tissue fibers, as well as non-hydrolyzed nitrogenous substances, are found in the feces.

Main causes and symptoms:

Decreased secretory function of the pancreas and deficiency of trypsin and chymotrypsin.
Impaired protein hydrolysis and nutrient absorption.
Clinical features include diarrhea, flatulence, weight loss, recurrent vomiting, and the development of malabsorption in severe cases.

Mnemonic

Celiac disease features a 'solid' (celiac) gliadin that the intestine cannot break down, prompting the immune system to attack its own villi.

Frequently asked questions

What histological changes in the small intestinal mucosa, besides villous atrophy, are characteristic of celiac disease?

In addition to villous atrophy, celiac disease is characterized by the following small intestinal mucosal histological changes:

Crypt hyperplasia: shortening of the villi is accompanied by elongation and widening of the crypts.
Cellular infiltration: massive infiltration of the lamina propria by lymphocytes and plasma cells with an admixture of eosinophils.
Increased number of intraepithelial lymphocytes.
Enterocyte alterations: microvilli lose regularity, appearing deformed and shortened.
Widening of intercellular junctions, associated with epithelial barrier disruption.

Which HLA genetic markers predispose individuals to gluten-sensitive enteropathy?

Susceptibility to gluten-sensitive enteropathy is conferred by specific haplotypes (alleles) of the major histocompatibility complex. An obligate genetic component of the disease is the presence of markers:

HLA-DQ2
HLA-DQ8

In pathogenesis, these molecules bind gliadin peptides and present the antigen to gluten-specific CD4+ T lymphocytes. This triggers cytokine aggression and an immunoinflammatory cascade, ultimately leading to intestinal epithelial cell damage.

Which specific autoantibodies are tested in blood for the serological diagnosis of celiac disease?

For the serological diagnosis of celiac disease, specific autoantibodies, predominantly of the IgA class, are tested against three targets:

tissue transglutaminase (anti-tTG / TG2 antibodies);
endomysium (anti-EMA antibodies);
deamidated gliadin peptides (anti-DGP antibodies).

Gliadin antibodies are also noted in literature. Pre-evaluation of total serum IgA is mandatory. In selective IgA deficiency, IgG-class antibodies to tissue transglutaminase and/or IgG-class antibodies to endomysium are assessed.

Why does the $\alpha$-gliadin peptide trigger an immune response in celiac disease?

This peptide is resistant to hydrolysis by gastric, pancreatic, and small intestinal enzymes. Consequently, it persists unchanged, penetrates the tissues, and is recognized by the immune system as a foreign antigen.

What changes are found in the stool in creatatorrhea?

Stool analysis reveals a large amount of non-hydrolyzed nitrogenous substances, as well as altered and unaltered muscle and connective tissue fibers.

How does celiac disease manifest in adults?

In adults, the disease often has a hidden or latent course. It may manifest as chronic diarrhea, flatulence, anemia, and chronic fatigue syndrome.

Go deeper

Functional dyspepsia as a cause of maldigestion
The role of enteropeptidase and trypsin in intestinal digestion
Immunopathogenesis of epithelial damage in gluten-sensitive enteropathy
Differential diagnosis of creatatorrhea and steatorrhea
Systemic manifestations of protein malabsorption syndrome