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The Hair and Skin

The terms in red will pop up definitions when you mouse over them.
The definitions of the epidermal appendages will bring you to a hair follicle diagram.

    What is skin?

    Nature's miracle wrap, skin shields the dog from its environment. It functions to provide form and contour to the body while elasticity allows movement. The epidermis also possess several appendages which further assist in its function to control inward or outward diffusion of fluids, regulate body temperature, lubricate the skin's surface, and generally provide additional protection from its environment. The skin's sensory capabilities allow the perception of pain, heat, touch and together with it's hair, provides insulation and protection from external elements. But most importantly, it is the barrier that typically prevents the loss of essential water and body fluids.
    The skin is comprised of the epidermis, dermis and hypodermis. The topical management and conditioning takes place on the epidermal layer. Couple with its specialized appendages/coat, the epidermis/skin forms the first line of defense against the environment as the body's protective wrap.

    The epidermal appendages consist of the:

    1) Hair Follicle which unlike human follicles that support only one hair per follicle, canine hair follicles are compound supporting one primary coarse hair sometimes referred to as guard hair and many (from seven to twenty) secondary fine soft hairs(undercoat). Whiskers also called vibrissae are abundant with nerve endings and as such provide specialized sensory capabilities; however, they are present in only a few prime sensory areas (nose, eyelashes, etc.). The hair follicle unit also known as the pilosebaceous unit consist of the hair follicle, its arrector pili muscle together with apocrine and sebaceous glands.

    While primary and secondary hairs share the same common opening, below the skin's surface, the secondary hairs form their own philosebaceous units.

    2) The Sebaceous Gland is connected to the upper part of the hair follicles by a duct. They have a central mass of foamy lipid cells that are surrounded by a layer of basal cells. When foamy cells become too plentiful and/or are disrupted, their oily material is pushed upward through their connective duct and deposited within the hair follicle. The oils spread themselves along the hair shafts and are pushed upward to spread over the surface of the skin. Sebaceous oils help waterproof the skin, thereby maintaining proper hydration. The oily secretion also keeps the skin soft and pliable, and is spread onto each hair shaft imparting a glossy sheen.

    Inadequate functioning of the sebaceous glands may cause the hair to become dull and dry due to the lack of oily secretions. Conversely, overproduction and constant disruption of the sebaceous glands may result in abnormal sebum production causing the skin and hair to appear excessively greasy while altering the normal, healthy flora of the follicle and skin surface.

    3) The Apocrine Gland is located deep within the dermis. One gland is associated with each hair follicle unit, and the proteinaceous, white odorless milky fluid secreted by the apocrine glands is responsible for body odors when it combines with bacteria on the skin's surface.

    Pheromones, a sexually attracting chemical, is produced and emitted by the apocrine glands.

    4) Eccrine Sweat Glands are numerous in man and aid the body's mechanisms to dissipate heat. However, in dogs these glands are only present in the footpads and nose. The distinct absence of eccrine sweat glands greatly hinders the dogs' ability to dissipate heat thereby increasing the risk of being overcome by excessive temperatures.

    5) The Erector Pili Muscle while not specifically an epidermal component, its influence is visualized as a function of the epidermis. It is an involuntary, smooth muscle closely associated with each hair follicle. Constriction of the muscle causes the hair to stand erect thus improving the insulating properties of the skin. Over activity of this muscle whether by stress, irritation, etc. can cause excessive pressure on the pilosebaceous unit resulting in excessive glandular material (oils, cholesterol esters, and squalene waxes) being dispensed into the follicle causing an oily skin and coat. On the other hand, inactivity of the erector pili muscle could be responsible for reduced oils being dispersed on the skin and coat causing brittle hair and dry skin.

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