ANATOMY

Detailed explanation-1: -Anatomical and physiological barriers provide the crucial first line of defense against pathogens. These barriers include intact skin, vigorous mucociliary clearance mechanisms, low stomach pH and bacteriolytic lysozyme in tears, saliva and other secretions.

Detailed explanation-2: -The innate immune system uses a diversity of receptors to recognize and respond to pathogens. Those that recognize pathogen surfaces directly often bind to repeating patterns, for example, of carbohydrate or lipid moieties, that are characteristic of microbial surfaces but are not found on host cells.

Detailed explanation-3: -The correct answer is option b. Innate immune responses represent the first line of defense against invading pathogens because the innate immune response provides general protection against a wide variety of pathogens through antimicrobial peptides, mucous and skin barriers, complement antibodies, etc.

Detailed explanation-4: -The primary barrier to the entrance of microorganisms into the body is the skin. Not only is the skin covered with a layer of dead, keratinized epithelium that is too dry for bacteria in which to grow, but as these cells are continuously sloughed off from the skin, they carry bacteria and other pathogens with them.