Table 2.
Defense mechanisms of the gastrointestinal system
| Taste buds |
| Vomiting |
| Saliva |
| Flushing action, so potential pathogens are cleared from the oropharynx |
| Protective coating of the mucosa |
| Contains antimicrobial lysozyme, lactoferrin, lactoperoxidase, and immunoglobulins |
| Gastric pH Microbiota/microbiome—lower GI (damaged by toxicants; carcinogen activation) |
| 100 trillion (anaerobic) bacteria (10 × host); 3.3 million genes (150 × host) |
| Bacteriocins |
| Compete for nutrients |
| Compete for attachment sites |
| Promote immune system maturation |
| Biotransformation |
| Enterotype |
| Secreted immunoglobulins Extraintestinal secretions from the liver and pancreas |
| Lactoferrins |
| Peroxidase |
| Intestinal proteolytic enzymes |
| Intestinal biotransforming and metabolic enzymes |
| Phagocytes and other effector cells within the submucosa |
| High rate of epithelial turnover |
| Shedding of receptor laden ALP and catalase containing vesicles from microvilli |
| Large surface area |
| Dilution with ingesta |
| Increased peristalsis resulting in diarrhea |
| Mucus—contains phages that destroy bacteria > 1 × 104 |
| Paneth cells (antimicrobial peptides, lysozymes, phospholipase A2, defensins–cryptdins) |
| Innate lymphoid cells |
| Adaptive immune system |
| Kupffer cells (liver) |
| Genetic polymorphisms (HLA) and host gene expression |
Reproduced from Zachary, J. F. and McGavin, M. D. (2016). Pathologic basis of veterinary disease (6th edn.). Copyright © 2016 by Mosby, Inc, an affiliate of Elsevier Inc.