5

Introduction

Physiological Consideration
The main functions of the skin are:
Physical protection from trauma, temperature variations, invasion of microorganisms and over exposure to sunlight.
The skin acts as biological barrier, which prevents the passage of harmful agents into the body. Mechanical protection of the keratinized structures against the environment.
Skin maintains the internal conditions of the individual so it acts as a barrier for water and electrolytes and prevents their loss.
Synthesizing vitamin D by the action of ultraviolet rays and transforming steroids to vitamin D.
Aids in maintaining the normal Blood proteins by the action of peripheral vascular dynamics.

Skinlesions and their terminology

Nodules
A nodule is a circumscribed, solid elevation greater than lcm indiameter that does not deform when palpated.
Nodule extends into the deeper layers of the skin, and it results from cellularinfiltrates into the dermis and subcutis.

Ulcers

An ulcer is a cutaneous defect resulting from a complete loss of the epidermisand usually part of the underlying tissues.
Erosion
Erosion is a cutaneous defect resulting from partial loss of theepidermis thatdoes not penetrate beneath the basal laminar zone.
Papules
A papule is a solid, circumscribed, elevated lesion up to l cm in diameter. Papules are essentially small nodules that do not extend beneath the dermis.
Pustules
A pustule is a pus-fined, fluctuant, circumscribed, and elevated accumulation of pus up to l cm in diameter.


Vesicles
A Vesicle is a fluid-filled, a cellular, circumscribed, elevated lesion
up to l cm indiameter. While, a bulla is a vesicle that is greater than l cm in diameter.
Scaling
Scale is a visible accumulation of fragments of the horny layer of the skin(Stratum corneum). It represents the final product of epidermal keratinization.
Crusts
The crusts are dried exudate that adheres to the skin surface and hair.
Crusts oftencover erosions or ulcer; crusts are composed of serum, cells,
fibrin, and infectiousagents. Dirt and medications.

Diseases of the skin and its associated structures

Classification of skin diseases
(1) According to its origin
1- Primary skin diseases:
In this type of diseases initially at least the lesions are restricted to skin and its associated structures, spread to other tissues may occur later as secondary complications. It is evidenced by the clinical examination, which reveals that thelesions are restricted to the skin without systemic reactions.
2- Secondary skin diseases:
In this type the lesions occur as the result of extension of the disease processfrom another organ or tissues other than the skin, system reactions are presentwith cutaneous lesions.
(2) According to the causative agent:
(A) Non-infectious skin diseases include:
Diseases affect Epidermis
Pityriasis.
Parakeratosis.
Hyperkeratosis.
Pachydermia.
Impetigo.
Urticaria.
Dermatitis.
Eczema.
Photosensitization.
Diseases affect skin appendages
Alopecia.
Achromotrichia.
Seborrhea.
Acne.
Disease of subcutis:
Subcutaneous edema.
Angio neurotic edema.
Subcutaneous emphysema.
Lymphangitis.
Skin-Hemorrhages.
Gangrene.
Skin. Abscess.
(B) Infectious skin diseases include:
(a) Viral diseases:
Cowpox - pseudo cow pox.
Contagious pustular dermatitis.
Sheep, goat pox.
Bovine ulcerative mammilitis.
Warts = viral papillomatosis.
Viral popular dermatitis.
(b) Bacterial diseases:
Dermatophillosis = mud fever.
Impetigo.
Contagious acne.
Streptothrichosis.
Ulcerative Lymphangitis.
Glanders (Farcy).
Subcutaneous abscesses.
(C) Mycotic diseases:
Ring worm.
Epizootic Lymphangitis.
Sporothricosis.
(D) Parasitic diseases:
Lice infestation.
Ticks infestation.
Mange.
Psoropitc mange (Body mange, ear mange).
Sarcoptic mange (Red mange, Barn itch).
Demodectic mange (Follicular mange).
Chorioptic mange (Leg mange, tail mange).
Other diseases.
Parafilaria multipillosa.