17 The integumentary system
The integumentary system consists of the hair, nails, and skin and performs many functions that influence the perianesthesia nursing interventions in the postanesthesia care unit (PACU). Although the skin has many functions, the most important is to act as a barrier between the internal and external environments. In addition, skin plays an important role in body temperature and fluid regulation, excretion, secretion, vitamin D production, sensation, appearance, and many other functions. The integumentary system is the body’s largest organ and first line of defense against many communicable diseases and mechanisms of injury that could cause permanent harm.
In the hospital setting, patients are at risk for many unwanted infections caused by pathogens and normal flora that are present in the environment. The intent of this chapter is to provide the reader with the anatomy and physiology of the integumentary system. It will provide background information to assist the perianesthesia nurse in understanding infection control and aseptic technique. There will be an overview of the patient with acquired thermal injury. Greater understanding of the integumentary system will facilitate the perianesthesia nurse in providing the needed vital care to the patient with a compromised first line of defense.
The skin, or integument, provides a boundary between the internal and external environments of the body. With aging, the skin becomes thinnerwith less elasticity and diminished collagen. There is less inflammatory response and integumentary immunity protection with aging. Skin generally accounts for about 15% of the total body weight. The skin is divided into two major layers: the epidermis and the dermis, which includes the hypodermis (Fig. 17-1). Depending on location, skin varies in number of layers and thickness. The soles of the feet and palms of the hands have the thickest skin (approximately 1.5 mm) and have five layers. Eyelids have the thinnest skin (approximately 0.10 mm) and have four layers.
FIG. 17-1 Layers of epidermis.
(From Monahan FD, et al: Medical-surgical nursing health and illness perspectives, ed 8, St. Louis, 2007, Mosby.)
The outermost layer of the skin is called the stratum corneum. It is composed of dead keratinocytes that are continually sloughing as new ones replace them. In addition to dead cells, the corneum also contains keratin, surface lipids, and dirt. The epidermis does not have any blood vessels.
Dead cells are shed at a fairly constant rate with a process called desquamation. The epidermis also has keratinizing and glandular appendages. Keratinizing appendages develop into hair and nails; glandular appendages include the sweat, scent, and sebaceous glands. The pigment that determines skin color (i.e., melanin) is also found in the epidermis in structures called melanosomes. Manufactured by melanocytes, melanosomes are transported to the keratinocytes and surround them. When skin is exposed to the sun or ultraviolet radiation, the quantity of melanosomes increases, causing a change in skin color.
The innermost layer of epidermis is the stratum basale/germinativum, which contains squamous cells, and is the site of origin for squamous cell carcinoma. Squamous cell cancer is more aggressive than basal cell carcinoma, and often invades surrounding tissues and lymph glands. It is often found on surfaces of the skin which have the most exposure to the sun.
The cells of the lowest, or basal, layer of the epidermis are constantly dividing and producing epidermal cells. Basal cell cancer develops from this layer. It tends to be slow growing, is the most common skin cancer (8 out of 10 cases are basal cell cancer), and has a high rate of recurrence. It is usually found in areas of the body with the most sun exposure.
The granular layer, or stratum granulosum, contains three or four layers of cells. It is composed of cells called keratinocytes, which undergo a maturation process called keratinization. This process produces lipid granules that form waterproof structures and helps in preventing fluid loss and evaporation through the skin into the environment.
The hypodermis functions as a shock absorber and heat insulator. Located under the dermis, it comprises fat, smooth muscle, and adipocytes. These cells store and accumulate necessary fats. The hypodermis acts as a site of energy production, and insulation. This area of the body stores fat in characteristic locations: hips on women, abdomen in men.2
The skin has many important functions, the most important of which is to act as a barrier between the internal and external environments. In addition, the skin has an important role in body temperature and fluid regulation, excretion, secretion, vitamin D production, sensation, appearance, and many other functions that have yet to be determined.
Skin, subcutaneous tissue, and fat in the subcutaneous tissue provide heat insulation for the body. Heat is lost from the body to the surroundings by radiation, conduction, convection, and evaporation (Fig. 17-2). Radiation of heat from the body accounts for approximately 60% of the total heat loss. In this mechanism, heat is lost in the form of infrared heat waves. Conduction of heat to objects represents approximately 3% of the total heat loss, whereas conduction of heat to the air represents approximately 15% of the total heat loss. When water is carried away from the skin by air currents, convection of heat occurs. Evaporation constitutes approximately 22% of the heat loss. Even without sweating, water still evaporates from the skin and the lungs; this is called insensible loss and totals approximately 600 mL/day.
FIG. 17-2 Major mechanisms of heat loss from body.
(From Hall JE: Guyton and Hall textbook of medical physiology, ed 12, St. Louis, 2011, Saunders.)