Skin Disorder by Chemicals
Skin diseases that result from
chemical and physical agent as well as infectious organism include contact dermatitis, sunburn, heat rush, and bunions, corns, and calluses. Contact
dermatitis characterized by itching and burning sensations reddening, and blistering, ‘weeping’, and crusting of areas of the skin. it is an acute or chronic skin inflammation caused by skin contact with irritants such as chemical or poison ivy or with substances to which an individual is allergic, although the causes of the form of dermatitis known as
eczema are often unclear.
Ultraviolet light causes erythema solare, or sunburn, signs of which can vary from simple reddening to blistering. The symptoms can range from simple pain in the skin to gastrointestinal disorder, malaise, and prostration. Miliaria (heat rush or prickly heat) is frequently seen in infantand obese adult. It is characterized by burning and itching and the aggregationof small blisters on covered areas during hot humid weather.
Bunions, corns, and calluses on the feet or toes result from pressure and friction due to body deformities or from poorly fitting shoes. When the skin is exposed to heat, electricity, radiation, severity of the burn, that is the depth of the skin layers destroyed and the area affected, a skin graft may be required.
Lesions on Skin
The skin is subject to many disorders. They occur through the direct action of external agents or as symptoms of disease in other parts of the body. Susceptibility to skin disorders is modified and sometimes determined by genetic factors.
The appearance of abnormal changes, or lesions, in the skin is an important element in diagnosis and treatment. Various lesions can occur, not all of them disease related. A flat lesion of a color differing from surrounding skin is called a freckle. A papule is a solid, elevated but superficial mass, such as a rise mole or a wart. A wheal is a transitory lesion resulting from an allergic response, such as to an
insect bite. A nodule is a solid mass that extent deeper, such as in certain tumors and cysts. A vesicle is a tiny blister filled with clear fluid, such as in early
chicken pox. A bulla is a large blister, most often seen as the result of a burn. A pustule is an elevated skin area containing pus, as in the later chicken pox lesion. Purpura is a skin discoloration caused by deposits of
blood or blood pigments within the skin.
The appearance of such lesions may be modified by secondary changes. These include scales or flakes of dead skin, as seen in psoriasis and dandruff; crusts, typically dried masses of material that have oozed out, as in impetigo, fissures, or sharp breaks, as seen in athlete's foot, ulcers, or destruction of one or more
skin layers, exposing underlying tissue; scars, resulting from newly formed connective tissue replacing lost tissue; and lichinification, a thickened scaly area in which normal skin creases and lines are exaggerated. Lesions may be seen in several different diseases, any one of which may have several different lesions.
Sweat Glands
Human skin contains very many sweat glands, with secrete a watery fluid. These glands are especially numerous in hairless regions such as the palms and soles. Their ducts also form dimples, lined with epidermal cells, that descend into the dermis and connect with gland cells. They are well supplied with nerves and respond to excessive heat by the secretion of sweat, whose evaporation cools the skin. This in turn cools the capillary blood in the
dermis. Stimulation by the para sympathetic nervous system also causes secretion the “cold sweat” of emotion.
The so called apocrine sweat glands found in the arm pits and the public region are attached to hair follicles and secrete an odorless milky fluid. Bacterial action on this fluid produces the distinctive body odor of an
animal. The mammary glands, or breasts, are large, modified apocrine glands.
Skin functions.
The skin protects against mechanical injury and attack by bacteria, fungi, viruses, and parasites; its melamine blocks ultraviolet radiation. The skin controls body temperature in several ways, as well. Variable amounts of heat are lost through the skin by transfer from the dermis capillaries to the cooler epidermal cells, the amounts dependent on constriction or dilation of the dermal blood cells. Sweating cools the
epidermis by evaporation.
The five distinct sensations arising from stimulation of skin nerves include touch, pain, heat, cold, and pressure. Other skin sensation, such as vibration, are composites of these basic sensations.
The skin responds to challenges to the immune system, as various allergy reactions show. Certain dermal cells release
chemicals that cause changes in capillary diameter (redness and warmth) and permeably (swelling), and stimulation of nerve endings (pain)- all sign of inflammation.
Dermis Layer
The strength of the
skin is due to the fibrous dermis. An outer layer beneath the basement membrane consists of tiny “hillocks” called papillae. They contain fine collagen fibers and are well supplied with
blood vessels, nerves, and lymphatic structures. Beneath this layer is a far thicker one containing larger budles of collagen fibers running in several directions. The fibers, synthesized by fibroblasts, are made of cross-linked collagen and are strong and resistant to enzymatic attack. This layer also contains elastic fibers, blood vessels, nerves and lymphatic structures as well as specialized nerve endings and the various skin appendages, including hair, sweat and oil glands, and nails.
Except for the palms, soles, lips,
eyelids, nipples, and parts of external genitalia, the mammalian body is usually covered with hair. In humans the hair is often thin and short and not readily seen on much of the body. Hair follicles are lined by
epidermal cells. They form by a dimpling of the epidermis into the dermis. As the cells fill with keratin, they adhere to one another and form hair, which elongates as new cells form at the hair base. Melanosomes find their way into the hair cells, giving them color. From the wall of the follicle an oil gland provides a protective hair coating. Plugged oil glands form black heads, and if these become infected they produce acne. Cold or fear can stimulate the tiny muscle attached to each hair follicle to erect the hair.
