Final answer:
Celiac disease causes villous atrophy and malabsorption of nutrients in the GIT, resulting from an immune response to gluten that damages the microvilli of the small intestine.
Step-by-step explanation:
The effects on the gastrointestinal tract (GIT) due to Celiac disease are villous atrophy and malabsorption of nutrients. When individuals with celiac disease ingest gluten, it triggers an immune response that results in damage to the microvilli lining the small intestine. This damage leads to the flattening of the intestinal villi, reducing the surface area and hampering the organ's ability to absorb nutrients. The consequent malabsorption can manifest as symptoms like diarrhea, nutritional deficiencies, and weight loss.
Damage to the villi can disrupt normal peristalsis, the wave-like muscular contractions that move food through the digestive tract, though excessive mucus production and impaired peristalsis are not characteristic effects of celiac disease. Therefore, the correct answer to the effects on the GIT due to celiac disease is A) Villous atrophy and malabsorption of nutrients.