The skin, or integument, functions to protect the body from outside foreign invaders and from water loss. It provides a focus for the sense of touch and assists in the regulation of the temperature within the body.
In addition, special modifications of the skin, such as claws and pads, provide a means of traction and defense, as well as shock absorbency.
Anatomy and Physiology
The skin is composed of three layers: the epidermis, the dermis, and the hypodermis. The epidermis is the outermost layer of the skin. Beneath the epidermis lie the dermis and hypodermis, which are composed of, among other things, an array of connective and fatty tissue.
Sebaceous glands, embedded within these layers, secrete natural oils out onto the skin surface that lubricate and moisturize the skin. The haircoats of dogs and cats consist of guard hairs, which make up the rougher outer coat, and the wool hairs, which constitute the fine dense undercoat of most breeds.
In addition, special hairs called tactile hairs (more commonly known as “whiskers”) can be found on the head region. These fulfill a sensory function.
A hair cycle exists in cats that involves the seasonal shedding of old hair and replacement by new hair. This cycle is dependent on light, not on temperature, and increasing or decreasing amounts of daylight trigger it.
As a result, peak shedding periods for the dog and cat occur in the springtime, when the days begin to get longer, and in the fall when the days get shorter. Of course, as more pets spend more time indoors with artificial lighting, the hair cycle can be altered, with shedding occurring year-round.
Hair color is dependent on the amount of pigment present within the hair shaft. Large amounts of pigment result in black hair; hairs that lack pigment are white. Different levels of pigmentation that fall between these two extremes result in all other coat colors.
Changes in the natural color of the hair can occur with inflammation, trauma, or constant licking of a particular region or regions of the coat. Of course, as a pet enters its senior years, the appearance of gray hairs is not an uncommon sight as well.