Skin is a wonderful invention -- it guards against dehydration by preventing fluid loss; protects man's best friend from exposure to the weather by presenting a tough surface to the outside world and providing follicles for hair growth; and makes pets huggable.
Skin is the body's largest organ -- without it, hair would have no place to grow, internal body parts would become external body parts, and people would not want to hug and stroke their pets.
Skin is both tough and elastic. It is moist on the inside, relatively dry on the outside. It helps regulate Sparky's body temperature through the blood vessels and reduces exposure to extreme cold by muscular action that fluffs the hair and traps heated air next to the body.
In short, skin is a wonderful invention.
Skin comes in three layers: epidermis, dermis, and panniculus. The epidermis is the body's environmental shield made up of tough keratinized cells glued together in stacks by fats. This layer is constantly replaced; the glue dries out, the outer layer of cells sloughs off and new cells rise from the basal cell layer of the epidermis, elongate, and harden to keep the horny outer layer intact.
The epidermis is a barrier against injury, disease, and damage from ultraviolet light. Obviously, the horny layer protects the internal organs from exposure and massive fluid loss. The ability to quickly replace a damaged epidermis is critical in mending trauma, particularly in cases where burns, abrasions, or cuts leave the body vulnerable to infection and dehydration.
The chief guardians against infection that penetrates the skin's horny outer layer are the amoeba-like Langerhans cells that capture foreign proteins (antigens) and send them on the road to destruction. If the Langerhans cells are overzealous in their work, the dog can develop an allergy -- a intensified immune response to a common substance.
Skin protects dogs from ultraviolet rays of the sun by providing a foundation for the haircoat and by producing melanin to color hair and skin. Melanin is a natural sunscreen. Humans can increase the production of melanin by repeated exposure to the sun, but dogs do not tan.
The epidermis is joined to the dermis at the basement membrane, a layer of collagen and other products of the basal cells. Collagen is a tough, durable, fibrous protein that makes up 90 percent of the dermis and provides strength to the skin. How tough? Tanned collagen from cattle skin is otherwise known as leather.
Collagen occurs in bundles. Between the bundles are the skin's “rubber bands,” the elastin cells that help provide skin flexibility. The third component of the dermis are glycosaminoglycans molecules composed of sugar and protein. These cells keep the skin layer moist.
The cells of the dermis provide a framework for blood vessels to bring oxygen and nutrients to the skin and nerves to help the dog react to and interact with his world.
Blood vessels in the dermis help control Fido's body temperature. When he runs and romps and builds up body heat, the blood flow to Fido's skin increases to release the heat to the environment. In cold weather, blood flow to the skin dwindles to keep the heat where it does the most good.
Under the dermis is the subcutaneous fatty layer that has two widely disparate jobs as protective shock absorber and food storage locker for certain vitamins and energy bits called lipids.
Hair follicles rise from the dermis layer. For more about hair development and coat color, see What's fur?
Yes and no. The dog's dermal skin layer has two types of glands that produce fluids. The apocrine glands, which produce sweat in humans, have two other functions in dogs — they help seal the outer layer of the epidermis and they secret pheromones that give dogs a distinctive body odor. The eccrine glands in the pads of the paws do produce a watery secretion similar human perspiration. This secretion leaves damp pawprints behind nervous or stressed canines and may also improve traction for a quick getaway.
The skin is subject to attack from without and from within. Injury from foreign objects, licking tongue, nibbling teeth, or scratching feet, ambush from external parasites, and assault from internal infections or autoimmune deficiencies.
Inhalant and contact allergies are common causes of skin irritation that can develop into more serious problems if Sassy digs and bites at her skin. Hot spots, hair loss, skin inflammation and crusty lesions can result from constant bothering of the skin.
Allergies are the result of an overactive immune system that releases histamines in its effort to cleanse the body of foreign proteins from pollen, dust mites, or other materials. The histamines cause the itching.
Some dogs react well to one of the over-the-counter anti-histamines such as Benadryl, Tavist, Seldane, or Chlortrimeton. Atarax, another anti-histamine, is available by prescription.
Some dogs need stronger medication to break the itch cycle. Veterinarians may prescribe a steroid drug such as prednisone to depress the immune system so that histamines are not produced. Steroids have several potentially serious side effects, so should be used sparingly and only under veterinary supervision.
Some dogs develop lesions as a result of constant scratching. These lesions can become infected and require antibiotic treatment.
Mange mites, fleas, and ticks can cause disease in dogs. Demodectic and sarcoptic mange mites live under the skin and cause irritation and hair loss. There is some suspicion that susceptibility to demodectic mange mite infestation is inherited because the disease manifests in puppies and dogs that may have compromised immune systems. Most affected puppies do recover and have no immune deficiency; those puppies that continue to be affected by the mites may have impaired immune systems.
Sarcoptic mange (aka scabies) drives dogs crazy with intense itchiness. This mite burrows under the skin to lay its eggs. Some dogs can harbor the mites without reaction, but others develop a severe allergy to the presence of these spider cousins. This mange can seriously debilitate an affected animal. and even cause death.
Mange can be treated with ivermectin (except in Collies, which seem to have a severe reaction to this pesticide) or with various types of insecticide dips.
Some dogs become allergic to flea bites, making flea control an important part of the family's dog care plan. One flea can cause a reaction in a sensitive dog. Fleas are also vectors for tapeworms. However, the wide variety of flea treatments available — both organic and manufactured insecticides and genetically engineered natural controls — provides an appropriate choice for all pet owners.
Ticks don't hang around long enough or bite frequently enough to cause major skin problems, but they are vectors for Rocky Mountain Spotted Fever and Lyme Disease that they can transfer to dogs through their bites. Ticks are more difficult to kill than fleas and there are no organic or biological controls for these spider and mite kin. The best preventive is to examine the dog after he has been in fields or woods, remove any ticks, and place them in a vial of alcohol.
Canine autoimmune diseases can cause skin problems ranging from loss of hair or pigment to blindness. The immune system malfunction that allows these diseases to develop may be inherited, although related dogs may have different diseases.
Autoimmune skin diseases are still rare but seem to be increasing in occurrence. Some of them seem to be breed specific. For example, Collies, German Shepherds, Shetland Sheepdogs, and Siberian Huskies are particularly susceptible to discoid lupus erythematosus, the most common autoimmune disease of the skin. Akitas, Chows, Dobermans, Newfoundlands, Bearded Collies, and Dachshunds seem to be most vulnerable to Pemphigus foliaceus, a disease in which skin breakdown causes thin blisters to appear mostly on the face, nose, lips, and ears. Akitas, Samoyeds, and Siberian Huskies are the most frequent victims of VKH, a rare autoimmune disease that causes loss of pigment in lips, nose, and eyelid margins and whitening of facial hairs. The eyes can be affected, and the dog can become blind.
Treatment for autoimmune diseases involves the use of steroids or other immune system suppressers, carefully balanced to control the disease without opening the door to infections. Dogs can be made more comfortable with medicinal baths with shampoos recommended by the veterinarian.
Healthy skin is a reflection of the general health of the dog. A bright, shiny coat, smooth skin, and normal body odor trumpet a dog's condition to all who watch him romp and play or recline by the fire on a winter evening. Owners who put their hands on their pets quickly notice changes in the skin and can take steps to remedy any problems.
Dry skin from winter heat? Add some Vitamin E and omega oils to the diet. Dull coat? Watch for signs of depression or illness. Afraid he's going bald? Check with the veterinarian to discover the reason for hair loss. Think she'll chew right through her paws or rub her nose raw on the carpet? As the veterinarian about inhalant allergies.
The skin, the first line of defense, does its job well, but it sometimes needs a boost, so the wise dog owners monitors his pet's skin condition.
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