Introduction

Dermatologic conditions are frequently seen in veterinary practice. From ectoparasitic problems to allergies, veterinarians are continually combating companion animal skin problems. As a veterinary technician, this is one area in which your expertise will be used because clients will ask many questions about shampoos, dips, conditioners, soaks, lotions, creams, ointments, sprays, powders, and topical products designed to have activity against fleas, ticks, and mosquitoes. Each of these products may be used to treat a full spectrum of dermatologic problems from parasites to pyoderma. Patients are often presented for examination of a skin disease when in reality they have an underlying systemic illness. Veterinarians use various diagnostic procedures (e.g., skin scrapings, allergy testing, and dermatophyte tests) to determine the cause of skin disease. Technicians play a vital role by obtaining a complete history, knowing how to perform the diagnostic procedures used in a dermatologic workup, and providing client education. Client education is essential when skin disease is treated because clients must understand the purpose of medications and how they should be properly used.

Anatomy and Physiology

The three primary layers of the skin are the epidermis, the dermis or corium, and the hypodermis or subcutis (also called the panniculus). The dermis provides most of the thickness of the skin. The epidermis comprises five distinct layers. These layers are the basal (deepest), spinous, granular, clear, and horny/cornified (superficial) layers. Epidermal cells are replenished in the basal layer and are pushed outward by newly forming layers. As these cells reach the surface, they are flattened and hardened to form a protective barrier. It normally takes 21 to 22 days for cells to reach the outer layer; this process is called the epidermal turnover rate. The epidermal turnover rate may be sped up in some disease processes. Continual shedding of these cells is called desquamation. When the process becomes excessive, scale or dandruff is seen. The epidermis includes a population of normal microorganisms that help to prevent overgrowth of pathogenic microorganisms.

The dermis or corium is located directly beneath the epidermis and is separated from and attached to it by the basement membrane. The dermis is a thick layer that comprises collagen fibers, blood vessels, nerves, lymphatics, and other structures such as hair follicles, sebaceous glands, and sweat glands. Sebaceous glands are found throughout haired skin, and their ducts empty into hair shafts. One type of sweat gland (eccrine) is found only in footpads and may play a role in body temperature regulation. The dermis gives stability and flexibility to the skin and acts to maintain and repair the skin.

The hypodermis is the deepest layer of the skin. It is made up of fat and connective tissue. Its functions are to provide padding and insulation and to serve as an energy store.

The skin produces hair and other keratinized structures like nail, horn, nasal pads, and footpads. Hair grows from follicles found in the dermis. In contrast to humans, who have one hair per follicle, dogs and cats have multiple hairs per follicle. Individual hair follicles have associated glandular structures (see earlier) and arrector pili muscles that are responsible for piloerection (hair standing on end). The hair follicle is frequently involved in bacterial, fungal, and demodectic infections. If a hair follicle loses the hair and becomes plugged with sebaceous secretions and keratin, a comedo (blackhead) results. There are three stages or phases of hair growth called anagen (growth), telogen (rest), and catagen (intermediate). Hair grows until it reaches a predetermined length, enters a resting phase, and then is shed. The hair cycle is controlled by day–night length (photoperiod), environmental temperature, hormones, and nutritional status. General illness, skin disorders, poor nutrition, overbathing, and stress are conditions that may result in excessive shedding.

Wound Healing