The epidermis is responsible for protecting the body against invasion of bacteria and other foreign agents primarily because it is composed of keratinized, stratified squamous epithelium. Here's why:

* Keratin: This protein makes the outermost layer of the epidermis (the stratum corneum) tough and waterproof. It acts as a physical barrier, preventing microbes from penetrating the skin.

* Stratified: The epidermis is made up of multiple layers of cells, with newer cells constantly being produced in the lower layers and pushing older cells towards the surface. This continuous renewal process helps to maintain a protective barrier.

* Squamous: The cells in the outermost layer are flat and scale-like, contributing to the skin's barrier function.

Additionally:

* Tight Junctions: Cells in the epidermis are tightly connected by junctions that prevent microbes from squeezing between them.

* Natural Skin Flora: The skin surface is also home to a diverse population of beneficial bacteria that can compete with harmful microbes for resources.

These features work together to create a formidable barrier against invaders, making the epidermis a vital part of the body's immune system.