The integumentary system includes skin, hair, scales, feathers, hooves, claws, and nails.

It has a variety of additional functions: it may serve to maintain water balance, protect the deeper tissues, excrete wastes, and regulate body temperature, and is the attachment site for sensory receptors which detect pain, sensation, pressure, and temperature.

[1] The skin (integument) is a composite organ, made up of at least two major layers of tissue: the epidermis and the dermis.

[3] Between the integument and the deep body musculature there is a transitional subcutaneous zone made up of very loose connective and adipose tissue, the hypodermis.

Substantial collagen bundles anchor the dermis to the hypodermis in a way that permits most areas of the skin to move freely over the deeper tissue layers.

The predominant cell keratinocyte, which produces keratin, a fibrous protein that aids in skin protection, is responsible for the formation of the epidermal water barrier by making and secreting lipids.

[6] The majority of the skin on the human body is keratinized, with the exception of the lining of mucous membranes, such as the inside of the mouth.

The lunula is the crescent-shape area at the base of the nail, lighter in color as it mixes with matrix cells.

These layers serve to give elasticity to the integument, allowing stretching and conferring flexibility, while also resisting distortions, wrinkling, and sagging.

The fats contained in the adipocytes can be put back into circulation, via the venous route, during intense effort or when there is a lack of energy-providing substances, and are then transformed into energy.

[8][9] Its main functions include: Small-bodied invertebrates of aquatic or continually moist habitats respire using the outer layer (integument).