IMMUNOLOGY

Detailed explanation-1: -Protection offered by the skin and mucous membranes All outer and inner surfaces of the human body a key part of the innate immune system. The closed surface of the skin and of all mucous membranes already forms a physical barrier against germs, which protects them from entering.

Detailed explanation-2: -The mucus layer provides an essential first host barrier to inhaled pathogens that can prevent pathogen invasion and subsequent infection.

Detailed explanation-3: -The first line of defence is your innate immune system. Level one of this system consists of physical barriers like your skin and the mucosal lining in your respiratory tract. The tears, sweat, saliva and mucous produced by the skin and mucosal lining are part of that physical barrier, too.

Detailed explanation-4: -The gut barrier operates via a system that includes physical and biological barriers [3]. The physical barrier is composed of gut microbiota, mucus which contains antimicrobial compounds and antibodies, epithelial and immune cells. The mucus layer consists of gel produced by epithelial cells.