Answer:
<u>The complete explanation of the immune response to a pathogen through the oral (oral-anus) and respiratory route is given below in explanation part .</u>
Explanation:
In order to provide host protection against pathogens wherever they can enter or spread, the immune system can be seen as an organ distributed throughout the body. A collection of anatomically distinct compartments can be distinguished within the immune system, each of which is specifically adapted to produce a response to pathogens present in a specific set of body tissues. The basic concepts underlying the initiation in the compartment of the peripheral lymph nodes and spleen of an adaptive immune response. This is the compartment that responds to antigens that have dispersed through the blood or penetrated the tissues. The mucosal immune system (commonly represented by the MALT) is a second compartment of the adaptive immune system of equal size to this, and situated near the surfaces where most pathogens enter. Body cavities (peritoneum and pleura) and skin are two other distinct compartments. These compartments are characterized by two main characteristics. The first is that immune responses induced within one compartment are generally restricted to that specific compartment in terms of speech. The second is that by expressing homing receptors that are bound by ligands, known as addressins, which are specifically expressed within the tissues of the compartment, lymphocytes are limited to particular compartments. The body's mucosal surfaces are particularly susceptible to infection. Because of their physiological roles in gas exchange (the lungs), food absorption (the gut), sensory roles (eyes , nose , mouth, and throat), and reproduction (uterus and vagina), they are thin and permeable barriers to the interior of the body. Obvious susceptibility to infection is provided by the need for permeability of the surface lining of these sites and it is not surprising that the vast majority of infectious agents via these routes enter the human body.
When contemplating the immunobiology of mucosal surfaces, a second essential aspect to bear in mind is that the gut serves as a conduit of entry in the form of food to a large array of foreign antigens. The immune system has developed mechanisms to prevent, on the one hand, a robust immune response to food antigens and, on the other, to detect and destroy the entry of pathogenic organisms via the gut. The majority of the gut is heavily colonized by commensal microorganisms, which live in symbiosis with their host, to further complicate matters. In certain ways, these bacteria are beneficial to their hosts. They provide protection by occupying the ecological niches for bacteria in the gut against pathogenic bacteria. By synthesizing vitamin K and some of the components of the vitamin B complex, they also serve a nutritional role in their host.
Peyer's patches of the small intestine, the appendix, and solitary lymphoid follicles of the large intestine and rectum are the other major sites inside the gut mucosal immune system for the activation of immune responses. The patches of Peyer are an extremely important location in the small intestine for the activation of immune responses and have a distinctive shape, forming domelike structures that reach into the intestinal lumen. Specialized epithelial cells reside in the overlying layer of follicle-associated epithelium of the Peyer's patches. Instead of the microvilli present on the absorptive epithelial cells of the intestine, they have microfolds on their luminal surface and are known as microfold cells or M cells. By endocytosis or phagocytosis, M cells pick up molecules and particles from the gut lumen. This material is then transported to the basal cell membrane, where it is released into the extracellular space, via the interior of the cell in vesicles. This mechanism is referred to as transcytosis. The cell membrane of M cells is extensively folded at their basal surface around underlying lymphocytes and antigen-presenting cells that take up the transported material released from the M cells and process it for the presentation of antigen.
