Final answer:
The immune system protects the gastrointestinal tract through the secretion of antibodies such as IgA, the function of mucosal-associated lymphoid tissue (MALT), and the gut-associated lymphoid tissue (GALT), which includes Peyer's patches.
Step-by-step explanation:
Three ways that the immune system samples and protects the gastrointestinal tract (GIT) are as follows:
- Antibody secretion: The mucosal immune system produces antibodies such as IgA and occasionally IgM. These antibodies are secreted into mucus and other secretions, where they can neutralize pathogens by preventing them from binding to receptors on the mucosa. This forms a crucial part of the local humoral response at epithelial surfaces.
- Mucosal-associated lymphoid tissue (MALT): This is a collection of lymphatic tissue that functions alongside the epithelium lining the mucosa. It serves as both a barrier and an active immune response facilitator, where antigens are passed from the lumen of the GIT to the lymphocytes, stimulating an immune reaction.
- Gut-associated lymphoid tissue (GALT), including Peyer's patches: Located primarily in the small intestine, these tissues are important in detecting pathogens and inducing an immune response. Microfold (M) cells transfer antigens to the lymphocytes within Peyer's patches, leading to the secretion of IgA and other antibodies to maintain a safe level of intestinal microbes.
Among the options presented, the answer 'd. Antibody secretion, mucosal-associated lymphoid tissue, gut-associated lymphoid tissue' most accurately reflects the immune system's sampling and protective mechanisms in the GIT.