Functions of the Skin

  • Enclosing Barrier— The most important function. This function makes it possible for all other body tissues to live and function.
  • Environmental Protection – The skin provides protection against the entrance of chemical, physical and microbiological agents into the body.
  • Motion and Shape— The elasticity of the skin allows the body to move and provide much of the shape of the body.
  • Adnexa Production— The skin produces hair, nails, and certain glands such as sweat glands and mammary tissue.
  • Temperature Regulation— The hair coat and cutaneous (skin) blood circulation are important in temperature regulation. Sweat glands function to cool the body also. Heat regulation in the dog is mostly via the respiratory system by panting. The cat will produce a large amount of saliva that it will spread over the skin to aid in cooling.
  • Storage— The skin is a reservoir of electrolytes, water, vitamins, fat, carbohydrates, proteins and other materials.
  • Indicator— The skin is important in reflecting the general health of the pet. Internal disease, external disease, and the effects of topical substances can be seen on the skin.
  • Immunoregulation— The skin produces defenses against microbes and tumors of the skin.
  • Pigmentation— The skin produces the pigment melanin that causes the skin to turn darker in response to damage or sunlight. This pigment helps prevent damage from the sun.
  • Antimicrobial Action— The surface of the skin has anti-bacterial and anti-fungal actions.
  • Sensory Perception— Skin is a primary sense organ for touch, heat, pain, itch, cold, and pressure.
  • Secretion— The skin functions to secrete the substances produced in the glands of the skin e.g., oils, waxes, milk.
  • Excretion— The elimination of waste is a limited function of the skin.
  • Blood Pressure Control— In a limited way, the skin pressure effects blood flow.
  • Vitamin D Production— The skin allows radiation from the sun to convert the inactive form of vitamin D to the active form. It then transfers active vitamin D to the rest of the body through the capillary system of the skin.

Human Skin Verses Canine Skin

Many people believe that human products are good for dogs. This is false! Many differences in human and canine skin make human preparations harmful to a pet’s skin. That a human’s skin is thicker than a dog’s skin is very important as the human skin is more resistant to topical products than canine skin.

Canine Skin Human Skin
* Epidermis 3 – 5 cells thick * Epidermis 10 – 15 cells thick
* Coat consists of hair bundles * Generally solitary hair
* Apocrine sweat glands * Apocrine and eccrine sweat glands
* pH 7.5 average * pH 5.5 average
* Cyclic hair growth * Continual hair growth
* Epidermal turnover rate about 20 days * Epidermal turnover rate about 28 days

Dermatology Terms

Primary Lesions

Macule— An area on the skin that is flat and is a different color than the surrounding skin – freckle.
Patch— A patch is a large macule caused by pigmentation changes – birthmark.
Bleeding into the tissue of the skin causes characteristic lesions.
Petechia— A pinpoint hemorrhage usually found first in gum tissues and may be an early sign of poor platelet function or low platelet numbers.
Ecchymosis— A larger form of hemorrhage that has “paintbrush” type discoloration – hickey.
Extravasation— Frank hemorrhages under the skin as in a severe injury or severe clotting factor deficiency – rat poisoning.
Papule— A solid, elevated area of the skin, up to one cm. in diameter.
Plaque— A larger papule, but has a flat top.
Pustule— A small elevation of the epidermis, filled with pus.
Nodule— A small, solid elevation of the skin, greater than 1 cm that extends deep into the dermis and usually has a rounded top.
Tumor/Neoplasm— “Neo” means NEW — “plasm” means GROWTH. A neoplasm is a “new growth”. A tumor is any enlargement of the skin that is caused by a neoplasm.
Vesicle— A sharp elevation of the epidermis, filled with clear fluid. A vesicle is less than 1 cm.
Bulla— A vesicle that is greater than 1 cm. Vesicles and bullas are both rare in dogs.
Wheal— A sharply circumscribed, raised lesion consisting of fluid infiltration in the skin (edema) that appears and disappears within minutes to hours. The wheal is usually white-to-pink, and usually is caused by allergic reaction – hive.

Secondary Lesions

Secondary lesions are the result of the skins response to disease or damage and are not specific to any one disease process.
Scale— An accumulation of loose fragments of the horny layer of the skin (cornified cells, keratinized cells). The consistency varies among branny, flaky, powdery, platelike, greasy, dry, loose or adhering.
Epidermal Collarette – a special type of scale that is in a circular rim of loose keratin flakes. This structure represents a pustule that is healing.
Crust— Debris formed when dried exudate of serum and scales adhere to the skin. A crust that contains blood is a scab.
Scar— Area of fibrous tissue that has replaced damaged skin.
Ulcer— A loss of skin all the way down to the dermis resulting in bleeding and scab formation.
Erosion— A defect in the epidermis that does not extend to the dermis and will not bleed. Erosions cause crusts – scuff.
Comedo— A dilated hair follicle filled with waxy material like a pimple. A comedo is secondary to seborrhea – blackhead.
Fissure— A crack in the skin that usually occurs in very thick, dry skin such as the nose or footpads but may occur anywhere. A fissure resembles the muddy bottom of a lake that has dried.
Excoriation— The same as erosion. A good example is a mild hot spot or carpet burn.
Hyperpigmentation— An area of skin that is darker than normal. This color change is a response of the skin to damage.
Hypopigmentation— Hypopigmentation is the result of less pigment in the skin and can be caused by damage to the pigment producing cells. For example, a dog bowl that is plastic and causes the brown nose of the dog to turn pink from the action of the plastic on the pigment producing cells.
Hyperkeratosis— Excessive thickening of the horny layers of the skin. This process is a normal response of the damaged skin and characteristic of many diseases. The epidermal layers increase in thickness as the number of cells increases due to increased production of cells by the basal cell layer.

Lesion Distribution

Generalize— Covering most of the body in an equal manner.
Localized— Concentrated on one area of the body, may be localized to the head, to the paws of the feet, or to the body.
Symmetric— Equal distribution with relation to the right side of the body to the left side.
Asymmetric— Unequal as to right verses left.
Pruritus— The presence or absence of pruritus (itchiness) is one of the most important clinical facts in the differential diagnosis of dermatosis. Itchy skin is typical of either allergies or parasitic type infections.
Alopecia— The loss of hair. Alopecia is an important sign in determining the cause of skin disease in pets. The distribution is important, as is the ability to tell if the hair fell out or was pulled out or chewed off. Being able to determine if the hair loss is associated with pruritus or some other disease mechanism is essential to treating the problem correctly.