The primary defences are those that attempt to prevent pathogens from entering the body.
The main primary defence is the skin. The outer layer of the skin is called the epidermis. At the base of the epidermis, cells called keratinocytes are produced by mitosis. As they migrate outwards, their cytoplasm is replaced by the protein keratin so they are dead by they reach the surface of the skin. They act as an effective barrier to pathogens.
Mucous membranes are also a primary defence. Goblet cells secrete mucus which traps dirt and particles which may be pathogens. The cilia then move in a co-ordinated fashion to waft the mucus along to the top of the trachea, where it can enter the oesophagus and enter the stomach where their enzymes are denatured.
Other primary defences are antibodies in the tear ducts to protect the eyes, wax in ear canals and acidic conditions in the vagina.
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