24 Intestinal Function and Integrity in Health and Disease: Current Knowledge in Swine

Abstract

Abstract Optimal lean tissue accretion is contingent on the ability of the pig to efficiently establish and maintain host defenses, and to digest and absorb nutrients and water. Epithelial cells in the mucosa of the gastrointestinal tract interconnect with each other by tight junctions, adherens junctions, and desmosomes, forming a complete intestinal barrier. Of the secretory cells in this epithelial barrier, mucus secreting goblet cells and hormone producing enteroendocrine cells can be found interspersed, while Paneth cells lie in the base of the crypts and secrete antimicrobial proteins/peptides into the mucus layer. In the small intestine, enterocytes lining the villi allow for efficient nutrient transport. Maintenance of the epithelial barrier and its function is dependent on intestinal stem cells residing at the crypt base. Two major signaling pathways controlling intestinal stem cell proliferation and differentiation are the β-catenin/Wnt and Notch signaling pathways. Thus, achieving and maintaining optimal nutrient absorptive capacity requires an intricate balance amongst β-catenin/Wnt and Notch signaling pathways, wherein dysregulation of either can result in inefficiency of nutrient absorption. Weaning transition, off-feed events, hypophagia, and enteric and respiratory diseases can all compromise the structural and secretory barrier of the gastrointestinal tract mucosa via changes in tight and adherens junction proteins and mucin production. As a result, these stressors can increase the incidence of gastric ulcers, villous atrophy, and colitis in pigs. Depending on the severity and duration of the mucosal damage, repair and restitution occurs due to increased stem cell proliferation, migration, and repolarization. Thus, efficiency of digestive and absorptive function depends on several factors, including the types of epithelial cells present and their functionality, the rate of cell renewal, and epithelial surface area. This paper will discuss what we know about the regulation and repair of the mucosal epithelium in growing pigs during health, stress, and disease.