3.6 Integumentary System

Epidermis: The outermost skin layer; composed of keratinized, stratified squamous epithelium

Dermis: The middle skin layer; contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands

Hypodermis: Lies below the dermis; also known as the subcutaneous layer. Composed primarily of adipose tissue, it connects the skin to the fibrous tissues of the bones and muscles.

Digits: An animal’s toes. The number of digits in mammals varies greatly.

Hair: A protein filament that grows from follicles in the epidermis. Each hair root is connected to a smooth muscle called the arrector pili that contracts in response to nerve signals from the sympathetic nervous system, making the hair “stand up.” The primary purpose for this is to trap a layer of air to add insulation, which is visible in humans as goosebumps (Betts et al., 2012).

Clinical Insight

When an animal is stressed or cold, their hair stands erect because of contraction of the arrector pili muscles (called piloerection). When an animal “raises their hackles,” the arrector pili on the dorsal side of their neck contracts to make the hair stand up, as seen in Figure 3.23 (Jennings & Premanandan, 2017).

 

Sebaceous gland:  A type of oil gland that helps to lubricate and waterproof the skin and hair. Most sebaceous glands are associated with hair follicles. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the skin (Betts et al., 2012).

Sweat glands: Glands that produce sweat to cool the body when it becomes warm

Abscess: A localized collection of pus (Anspaugh et al., 2013).

Acne: An inflammatory and pustular eruption of the skin (Anspaugh et al., 2013).

Acute moist dermatitis: Localized infection and inflammation of the skin, is usually associated with excessive licking and scratching of the area; also known as a “hot spot“.

Alopecia: A condition characterized by hair loss or lack of hair.

Carcinoma: A malignant tumour that originates in the epithelium.

Cyst: A thin-walled, fluid-filled structure.

Dermatitis: Inflammation of the skin.

Ectoparasites

Ectoparasites are organisms that infest the skin and hair of an animal. Clinical signs include seeing the parasite itself, its eggs, or the irritation caused by them. The animal usually presents with alopecia and pruritus. Ectoparasites include ticks, fleas, lice, and mites. The term used for skin infections by mites is mange. The severity of mange will depend on the number of mites infecting the animal and the body’s reaction to the infestation.

 

 

Clinical Insight

Some ectoparasites can also transmit disease. For example, the deer tick (black-legged tick) can transmit Lyme disease.

Flea allergy dermatitis: Inflammation of the skin caused by flea saliva. Fleas are blood-sucking, wingless insects that live and breed in the hair coat of an animal and often cause pruritus.

Example

Figure 3.25 shows a dog that has been diagnosed with fleas. The redness of the skin, erythema, seen on the back and tail, is from the irritation of the fleas’ saliva.

 

Frostbite: Damage to the tissues caused by extreme cold

Laceration: A cut into the skin, usually accidental.

Lipoma: A benign tumour composed of adipose tissue (Anspaugh et al., 2013).

Pyoderma: An inflammatory skin disease with pus.

Ringworm: A fungal infection of the skin that usually presents with a circular, ring-shaped rash. This disease is zoonotic.

Biopsy: Sampling tissue for histology.

Cauterization: A medical practice or technique that involves burning a part of the body to remove or close off a part of it.

Culture: A diagnostic test to identify microbes. The sample is placed in a sealed medium with specialized nutrients, allowing the fungal or bacterial culture to reproduce. 

Debridement: The removal of dead tissue from a wound.

Clinical Insight

Declaw: To surgically remove the most distal of the digital bones in cats; also called onychectomy. Many Canadian provinces have banned the declawing procedure in cats unless deemed necessary by a veterinarian.

Fine needle aspiration: Sampling cells via aspiration through a needle and syringe for cytology.

Intradermal skin testing: A procedure that introduces allergens to the skin to determine the body’s response, allowing the veterinarian to determine the specific allergy a patient may have. 

Example

Figure 3.29 shows allergy testing on a dog. The black spots are markers identifying which allergen was placed in that location. The swelling and redness seen beside the markers is the reaction to the allergen.

 

Skin scrape: The microscopic examination of skin for the presence of mites; skin is sampled by scraping a scalpel blade across an area that is squeezed or raised to obtain a deep skin sample.