IMMUNOLOGY

Detailed explanation-1: -The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, ‘friendly’ bacteria and white blood cells called neutrophils.

Detailed explanation-2: -The innate immune system consists first of physical and chemical barriers to infection including the skin and mucous membranes and their secretions, ciliated surfaces, and body hairs.

Detailed explanation-3: -The epidermis is the tough outer layer that acts as the first line of defense against the external environment. It is composed of stratified squamous epithelial cells that further break down into four to five layers.