∞ generated and posted on 2016.02.03 ∞

Outer covering of vertebrate animals which serves as a barrier to both parasite invaders and the leaking of water, nutrients, and colloidal substances out of bodies

Skin is the outer covering of us, mammals generally, birds, reptiles, amphibians, and fish (that is, vertebrates), but not the outer covering of other types of animals (i.e., invertebrates).

Skin serves as a barrier to both the leaking of materials out of your body and a number of things from "leaking" in including organisms found in an animal's environment (particularly microorganisms but also various invertebrate animals) along with various potentially compounds that also can be found especially outside of the body.

The skin is often described as the largest organ of the body and this is true in terms of overall size and mass. The skin also is a key constituent of the . It can be distinguished into an outer layer of epithelial tissue called the and an underlying layer of known as the . Yet further downward there is the .

While still serving as an outer covering, skin is not necessarily also a tough, outer covering in all animals, i.e., as we may view our own skin versus, for example, that of a , or indeed a fish.

Our skin has these latter properties because it represents a special kind of skin that is described as keratinized (as in keratonized skin), which in turn is a characteristic of the amniotes (that is, the reptiles, mammals, and birds).

The following videos also provide further discussion of what especially our skin is all about:

The following videos provide some discussion of :