Skin

Lore & Background

Skin is composed of two primary layers in mammals: the epidermis, which provides waterproofing and serves as a barrier to infection, and the dermis, which serves as a location for the appendages of skin. The epidermis is a stratified squamous epithelium composed mostly of keratinocytes, and contains no blood vessels. The dermis consists of connective tissue, harbors mechanoreceptors, hair follicles, sweat glands, and blood vessels. The subcutaneous tissue (hypodermis) lies below the dermis and attaches skin to underlying bone and muscle.

Reader's Guide

Skin plays a crucial role in protecting the body against pathogens and excessive water loss, and its other functions include insulation, temperature regulation, sensation, and production of vitamin D folates. Severely damaged skin may heal by forming scar tissue, sometimes discoloured and depigmented. The speed and quality of wound healing is promoted by estrogen. Fur, dense hair, augments insulation and can serve as secondary sexual characteristics or camouflage. Reptiles and most fish have hard protective scales, birds have hard feathers made of tough beta-keratins. Amphibian skin is not a strong barrier and is often subject to osmosis.

Did You Know?

• The word skin originally referred only to dressed and tanned animal hide; the usual word for human skin was hide.
• All mammals have some hair on their skin, even marine mammals like whales, dolphins, and porpoises that appear hairless.
• The skin on the palms and soles of the feet is the thickest on the human body at 4 mm thick.
• Amphibian skin is not a strong barrier; a frog sitting in an anesthetic solution would be sedated quickly as the chemical diffuses through its skin.