Final answer:
The process by which secretory dimeric IgA crosses epithelial cells in the gut is known as transcytosis, involving the polymeric Ig receptor. Peyer's patches and M cells are integral to the immune surveillance and response within the gut, leading to the secretion of IgA.
Step-by-step explanation:
The secretory dimeric IgA reaches the lumen of the gut from the lamina propria by crossing epithelial cells in a process called transcytosis, which involves the polymeric Ig receptor. This process is vital in the immune defense of mucosal surfaces such as those in the gastrointestinal tract. The dimeric IgA, once transported across the epithelial layer, functions to neutralize pathogens and prevent infection by immobilizing and marking pathogens for destruction without inducing an inflammatory response.
The Peyer's patches and M cells are also crucial for the immune surveillance of the gut. These structures allow the immune system to detect and respond to potential pathogens, triggering a cascade of immune responses that lead to the secretion of dimeric IgA into the intestinal lumen, which plays a key role in mucosal immunity.