21.1: Structure and Functions of the Skin
By the end of this section, you will be able to:
- Review the anatomy of the integumentary system
- Identify the many functions of skin
- Recognize how assessment findings may vary in special populations
The integumentary system is the body’s first line of defense, serving as a physical barrier between the external and internal environments. The external environment includes microorganisms, radiation, temperature, or other threats of physical trauma or injury. The internal environment is the body that the integumentary system serves to protect and maintain homeostasis. The integumentary system includes the skin, hair, nails, as well as glands (e.g., sebaceous, sweat, mammary) (Kim & Dao, 2023).
Nurses play a vital role in maintaining skin integrity and promoting wound healing . To effectively protect and preserve a patient’s skin, the nurse must understand the anatomy and physiology of the integumentary system, factors affecting skin integrity, and how to appropriately manage wounds.
Anatomy of the Skin
The skin, which covers the body entirely, is the largest organ of the body. It serves as a protective barrier against heat, light, infection , and injury and performs additional essential functions. The skin varies in thickness, color, and texture across the body. For example, the palms of the hands and soles of the feet are thicker than skin on the abdomen. The skin is made up of three distinctive layers: the epidermis (the outermost layer of the skin); dermis (the layer below the epidermis); and hypodermis or subcutaneous tissue (the deepest layer) (Figure 21.2). Each layer varies in its anatomy and function (Yousef et al., 2022).
Epidermis
The epidermis is the thin outer layer of the skin and consists of epithelial cells. The main function of the epidermis is to protect deeper tissue layers from water, mechanical and chemical trauma, exposure to microorganisms, and damage from ultraviolet (UV) light. The epidermis has four or five layers depending on its location (Figure 21.3). There are five layers over the palms of the hands and soles of the feet, while the rest of the body has four layers. Starting from the bottom, the layers are the stratum basale , stratum spinosum , stratum granulosum , stratum lucidum , and stratum corneum.
The stratum basale (or stratum germinativum) is the deepest layer of the epidermis and contains a cell known as a melanocyte that produce melanin and a keratinocyte that produces keratin . Melanin forms a protective shield to protect the keratinocytes and nerve endings from damage caused by ultraviolet light. Melanin is also responsible for the color of the skin. Keratin is a fibrous, water-repellent protein that gives the epidermis its strong, protective quality. The keratinocytes move upward through the layers as they mature and become dead cells on the outermost layer of the skin (Osseiran et al., 2018). The Merkel cell is also found in the stratum basale and serves as a sensory receptor for light touch.
The next layer above the stratum basale is the stratum spinosum . This layer is several layers thick and contains cells that arise from the bone marrow and move up to the epidermis. The cells are “irregular, polyhedral cells with cytoplasmic processes and are often called ‘spines’ that extend outward and contact neighboring cells by desmosomes” (Yousef et al., 2022). The Langerhans cell is primarily located in the stratum spinosum. These cells are first-line defenders and are antigen-producing cells that determine the appropriate response to (e.g., inflammation) or tolerance of foreign substances.
The next layer, the stratum granulosum , is only two to three cell layers thick. This layer contains a glycolipid that slows water loss across the epidermis. The process of keratinization , a thickening of plasma membranes of a cell, begins in this layer. The next layer, the stratum lucidum , is only found in the thicker areas of the skin (e.g., palms and soles of feet). It is two to three cell layers thick and is made up of flattened, dead keratinocytes. The outermost layer of the epidermis, the stratum corneum , is the thickest layer and makes up about 75 percent of the total thickness. This layer contains dead keratinocytes that secrete defensin (a class of host-defense peptides found in neutrophils that have antimicrobial and/or cytotoxic properties) and is part of the body’s first immune defense.
Dermis
The second, deeper layer of the skin is the dermis , which is connected to the epidermis by dermal papillae. Its main function is regulating temperature and supporting, protecting, and nourishing the epidermis. This layer consists of the papillary layer and reticular layer . The upper papillary layer is the thinner of the two and is composed of loose connective tissue and contacts the epidermis. It also contains capillaries as well as touch and pain receptors. The deeper layer, the reticular layer, is the thicker of the two. This layer consists of dense connective tissue, collagen bundles, and houses most of the sweat glands, sebaceous glands, hair follicles, hair, muscles, blood vessels, and deep sensory neurons (Yousuf et al., 2022).
The sebaceous gland is attached to the hair follicles and is present over the body minus the palms of hands and soles of feet. The sebaceous glands secrete sebum, an oily substance that makes the hair and skin waterproof. There are two types of sweat glands: eccrine glands and apocrine glands. The eccrine gland is located over the skin entirely, secretes sweat, and aids in thermoregulation . The apocrine gland correlates with the hair follicles present in the perineum, axillae, and areolae of the breasts. These glands are nonfunctioning and small until puberty has been reached. After the onset of puberty, the glands secrete a milky sweat.
Hypodermis
The hypodermis ( subcutaneous tissue ) is the subcutaneous fatty layer beneath the dermis that separates the skin from the underlying tissue. The hypodermis also anchors the dermis to the underlying tissues of the body and insulates, protects, and stores fat for the body. This layer is made up of loose connective tissue and stores about half of the body’s fat cells. This layer provides a cushion for the body against trauma, stores fat for energy, and insulates the body from heat loss. Some skin appendages (e.g., hair follicles, blood vessels, sensory neurons) are found in the hypodermis. This layer also contains blood and lymph vessels and nerves. The blood vessels supply nutrients to the tissues, and the lymph vessels provide a pathway for the movement of waste products to and from the skin.
Functions of the Skin
The skin performs essential functions including protection, thermoregulation, sensation , absorption , elimination , and vitamin D production . The skin contributes to the psychosocial aspect of an individual because of its contribution to the external appearance of the person and plays a role in self-esteem. The skin also aids in communication with the brain via the sensory neurons located in the skin.
Protection
The skin provides protection because it covers the body entirely and serves as the physical barrier between the internal and external environments. Breaks in the skin trigger an immune response to promote healing and fight off foreign debris that may lead to infection . The many layers of the skin provide protection from injury to underlying tissues and organs. The skin also acts as a shield from microorganisms, damaging ultraviolet rays, and other substances including water. The layers of keratin and glycolipids in the skin serve to protect the body against moisture loss from both the surface and underlying structures.
Thermoregulation
Temperature regulation is another function of the skin. The skin is highly vascularized, which allows the body to regulate body temperature through vasoconstriction and vasodilation of blood vessels. When body temperature decreases, blood vessels vasoconstrict to decrease blood flow to the periphery in an effort to conserve core body heat. The arrector pili muscle triggers hair follicles on the body to flex causing the hair to rise up (goosebumps), which further prevents heat loss (Figure 21.4). When body temperature increases, blood vessels vasodilate to increase blood flow. Sweat is secreted, which evaporates from the skin contributing to heat loss and bringing the body temperature down (Kim & Dao, 2023).
During the first hours of life, newborns experience difficulties regulating their body temperature. The balance of heat production and heat loss is linked to the metabolism and oxygen consumption of the newborn. Newborns can attempt to conserve heat and increase their heat production by increasing peripheral vasoconstriction, metabolic rate, and muscular activity through moving. Newborns may also assume a fetal position to hold in heat and decrease body surface area exposure. Nursing interventions to aid in maintaining body temperature of newborns include the following (Albahrani & Hunt, 2019):
- Dry newborns completely after birth or baths to prevent heat loss through evaporation. (Baths should be performed after newborn is stable, and a radiant heat source should be used.)
- Prewarm blankets and caps to reduce heat loss through conduction.
- Place a cap on a newborn after drying thoroughly.
- Use a warm cover on the scale when weighing a newborn.
- Warm stethoscopes and hands before touching a newborn.
- Avoid placing a newborn near air vents or areas with drafts, and avoid placing cribs near cold outer walls.
- Keep infant transporter fully charged and heated.
- Avoid placing skin temperature probes over brown fat areas (found on the back, neck, and shoulders in babies to help regulate body temperature).
- Encourage parent skin-to-skin contact with stable newborns.
- Use heated and humidified oxygen.
Sensation
The skin provides sensation for the body and allows a patient to feel temperature, pressure, pain, and touch through the various sensory nerve endings. Each type of sensory receptor sends signals to the brain and spinal cord that allow a patient to respond and adjust to the environment as needed. For example, when a patient touches something that is extremely hot, they typically move their hand away quickly, which is the body’s reflex in response to the external stimuli in an effort to protect itself from harm.
Scenario: A nurse is assessing an older adult with diabetic neuropathy who is being seen in the clinic for a sore on his right foot.
Nurse: Hi. My name is Linda, and I will be your nurse today. Will you tell me your name and date of birth?
Patient: Yes. Hi, my name is Joseph Gellar. My date of birth is April 25, 1941.
Nurse: Thank you. What brings you in today?
Patient: Well, I have this sore on my foot, and I am not sure how I got it.
Nurse: Okay, let me take a look.
Nurse: [after assessing the wound] Let’s verify your health history.
Patient: Well, I have diabetes, high blood pressure, and high cholesterol.
Nurse: What medications do you currently take?
Patient: I take my insulin, metoprolol, and atorvastatin. But I forgot to check my blood sugar today and take my insulin.
Nurse: Okay, have you noticed any changes in sensation? Like being able to feel things that are painful, hot, or cold?
Patient: Yeah, I noticed that a few years ago, but I just thought it was normal.
Nurse: Diabetic neuropathy is common with uncontrolled blood sugar and high levels of fat that can cause nerve damage. Because of this, it is important to be aware of your surroundings to avoid injury. Check your feet every day for any injuries like cuts, scrapes, or bruises. It is also important to try to manage your blood sugar as much as possible with your diet, exercise, and medications.
Patient: Oh, that makes sense. I think my wife and I have a friend who had something similar happen.
Nurse: Yes sir. Do you have any questions for me before I give an update to your doctor, so he can come in and see you?
Patient: No, that will be it for now.
Nurse: Okay, great. I will be in after the doctor sees you to go over any orders or treatments he prescribes for you.
Absorption
The skin is porous and therefore absorbs substances that may be on it. Substances that can be absorbed through the skin will enter the bloodstream. Certain medications may be absorbed by transdermal administration (placed on the skin and absorbed either locally or systemically), including scopolamine , estrogen , testosterone , some opioids, nicotine , and some contraceptives. It is important to note that anything on the skin may be absorbed and thus has the potential to cause harm. Certain chemicals and medications require appropriate handling to avoid the risk of harm or injury. For example, when administering fentanyl , it is important to wear gloves to avoid accidental absorption into the bloodstream. This is also why sunscreen or other lotions are not used on babies under 6 months old due to thin skin and increased absorption.
Elimination
The elimination function of the skin helps the body get rid of excess water and salts through sweat produced by the sweat glands. This perspiration or sweat may contain electrolytes, water, and nitrogenous wastes like urea, uric acid, and ammonia. In the event other organs become unable to eliminate toxins, the skin will try to push out toxins to aid in removal. In addition to removing wastes, the excretion function of the skin aids in regulating body temperature as previously described.
Vitamin D Production
The skin initiates the biochemical processes necessary for vitamin D production . Ultraviolet sun exposure leads to the conversion of 7-dehydrocholesterol to cholecalciferol (vitamin D 3 ) in the skin. Cholecalciferol is hydroxylated in the liver and then in the kidneys, which converts it into the active, metabolite form, calcitriol. The chemical process in which a hydroxl group (–OH) is introduced into an organic compound is termed hydroxylation . This metabolite leads to enhanced calcium production in the gut and is vital for bone health (Kim & Dao, 2023).
Assessment Findings for Special Populations
There are distinct considerations for special populations that the nurse must consider when assessing a patient’s skin. The assessment’s findings may vary among different cultures and ethnicities, developmental levels, and age groups. It is essential that the nurse be aware of the variations when performing a skin assessment to avoid stereotypes and to ensure accuracy when developing a plan of care to promote optimal outcomes. For example, a darker-skinned patient may not show pallor in the same way a lighter-skinned patient would. The nurse must assess the mucous membranes, such as the gums or palpebral conjunctiva, of a darker-skinned patient to adequately assess for pallor.
Name:
Bailey, BSN
Clinical setting:
Pediatric clinic
Years in practice:
3
Facility location:
Rural area of Kansas
Our pediatric clinic is the only one in a 50-mile radius so we are always swamped. One day, I was working in the well-baby side of our clinic. I was assessing a baby who was here for her six-month wellness visit. Her mother, Ali, brought her in and introduced her baby girl as Alexis. After taking her medical history, I began the physical assessment. I noticed what appeared to be bruises along Alexis’s back similar to those seen in abuse cases (Figure 21.5). I was concerned and thought that the baby may be experiencing abuse at home. The spots were bluish in color and along the baby’s backside, so the areas were not visible to others.
As I began to plan my next steps, Alexis’s mother stated, “I am ready for the spots to start disappearing!” Then, I recalled learning about these spots in nursing school. I put my fingers on the skin to blanch the area and was relieved when I observed that the spots were nonblanchable, confirming dermal melanocytosis, formerly known as Mongolian spots. The spots are actually pigmented skin lesions that may be present at birth or develop within the first few weeks of life.
I asked Ali about the first noticeable spot and said they showed up when Alexis was about 2 weeks old. We then discussed how the spots may disappear by childhood. Ali said she understood but would be happy when they were gone. It was the first time I had actually seen Mongolian spots, and I was really relieved that they were not bruises from abuse.
Cultural Considerations
While people share a similar number and distribution of eccrine gland s over the body, the glands vary in activity depending on patient-specific characteristics and environmental adaptations. For example, those born in tropical areas have more functioning eccrine glands than those who move there later in life. People who acclimate to hot environments do not excrete as much chloride in their sweat as others. People of Asian and American Indian descent have fewer functioning apocrine gland s than Whites and Blacks. The amount of sweat and body odor an individual has is genetically determined and is in relation to the functionality of the apocrine glands. Therefore, Asians and American Indians have little to no underarm sweat or body odor. People born farther from the equator usually have fairer skin and are at a greater risk of developing skin cancer s due to lower levels of the protective pigment, melanin . Additional factors for fair-skinned individuals include the presence of freckles and an increased susceptibility to sunburn. However, all people with excessive levels of sun exposure are at risk for sun damage to skin and skin cancer and should, therefore, avoid excessive exposure to UV light. Darker-skinned patients, including those of ethnicities such as Black, Latinx, Hispanic, Asian, and American Indian, typically produce more melanin in general. The higher level of melanin is a protective factor and reduces the risk of developing skin cancers. However, darker-skinned individuals are more susceptible to certain skin abnormalities (Figure 21.6), including the following:
- postinflammatory hyperpigmentation , a temporary pigmentation that occurs after an injury or inflammatory skin condition, most commonly seen in patients with darker skin types
- dermatosis papulose nigra , small dark or skin-colored bumps on the face, neck, and upper torso, common in patients with darker skin colors
- keloid , a thick fibrous scar caused by excessive collagen formation in response to trauma or a surgical incision
- pityriasis , any of various skin conditions characterized by dry scaling patches of skin
- vitiligo , a chronic autoimmune disorder that causes partial or total loss of skin color in patches
- hair loss
- dry skin
Developmental Considerations of Infants and Children
A person’s skin undergoes changes throughout the life span. Sebaceous glands do not function maturely at birth. Sebum production increases in the prepubescent and adolescent years, which makes individuals within these age ranges more prone to acne. The sweat glands of an infant function to some degree and produce sweat in response to heat or emotional stimuli. By the time the child reaches middle child years, the sweat glands are fully functional. Until the glands function fully, temperature regulation is not as efficient as it is with the fully functioning glands of older children and adults.
Infants also have a thinner epidermis than adults. Infants have less subcutaneous tissue , so the blood vessels lie closer to the skin’s surface. Therefore, an infant loses more heat through the skin’s surface than an older child or adult. In addition, substances absorb more readily through the skin of an infant than an adult because of the thinness of the skin. Infant skin contains more water than adult skin. The epidermis is loosely bound to the dermis , and this means that friction may easily separate the layers which can result in blisters or skin breakdown.
Regardless of ethnicity, infant skin is less pigmented, and this places them at higher risk of skin damage from sun exposure . As the infant ages, the skin becomes tougher and less hydrated, making them less susceptible to invasions from microorganisms. When the child reaches teenage years, the skin characteristics and thickness are at the adult level. Infant skin and mucous membranes are more easily injured and susceptible to infection ; therefore, the nurse must carefully handle infants to protect them from harm or infection.
Overheating an infant can easily happen if a caregiver fears that the infant is cold. Newborns and infants do not have a mature thermoregulatory system. This means that they are more vulnerable to overheating. Signs and symptoms of overheating include the infant
- feeling warm to the touch;
- having flushed or red skin;
- developing heat rash;
- sweating or having damp hair;
- developing tachycardia;
- developing tachypnea;
- acting fussy;
- appearing sluggish, confused, or dizzy; or
- becoming unresponsive.
Nurses should be aware of these signs and the interventions needed: administer fluids (e.g., breast milk, water, or formula depending on their age), apply cold compresses, take off any excessive clothing or bedding, and go to a well-ventilated area. If the nurse is educating a caregiver, they should also include the need to call 911 if the child is unresponsive. Interventions to prevent overheating include avoiding the use of excessive clothing and bedding, keeping the room temperature between 68°F and 72°F (20°C and 22°C), ensuring adequate room ventilation, using curtains if needed to block out excessive light and heat, and avoiding the use of heating pads.
Other developmental considerations the nurse must consider include patients with cognitive disabilities. Individuals with cognitive dysfunction may not know how to check their own skin for abnormalities or impairments, or they may not recognize any changes in their skin. These patients may also neglect skin care. This can lead to itching, scratching, and picking because of buildup of dead skin and other debris, which can lead to injury or infection. The nurse may need to establish rapport with those who have disabilities to gain their trust. This enables the nurse to perform an assessment and provide coaching to teach them how to perform a skin assessment at home. If a patient with a disability has a caregiver, the caregiver should be included in education of skin assessment as well as findings to report.
The nurse must also consider the patient’s developmental level when communicating and when describing the steps of assessment. For example, an infant may be examined in the caregiver’s lap versus the school-aged child who can sit on the examination table. The nurse should speak with terms that are appropriate for the age or developmental level. The nurse should also speak to the patient regardless of the developmental level, especially school-age children and adolescents, to help them feel included in the plan of care.
Age-Related Considerations
Much like the infant’s skin changes from birth to adulthood, the skin continues to change as a person ages (Figure 21.7). The thickness of the epidermis in older people decreases, making the skin more delicate and at risk of tears or injury. The subcutaneous tissue s also become thinner, making thermoregulation more difficult and increasing the risk of pressure ulcers. The mitotic activity , or the degree in which a population of cells proliferates, decreases, leading to delayed wound healing . As the subcutaneous and dermal tissues thin with age, the skin becomes more prone to wrinkles, and pressure and pain sensation is reduced.
As the activity levels of the sebaceous and sweat glands decrease, the skin becomes dryer, and older people may experience pruritus , itching. Melanin declines with age leading to unevenly pigmented skin and gray or white hair. Hyperplasia of the melanocytes may lead to small areas of hyperpigmentation , darkened patches of skin called liver spots. Decreased melanin in an area can cause hypopigmentation , lighter patches of skin (age spots). The elastic fibers degenerate causing the skin to lose its elasticity. There is often a redistribution of adipose tissue leading to cellulite (lumpy skin), increased abdominal fat, sagging of breasts, and reduced tenting (the skin does not snap back when pinched; instead, it maintains a tentlike shape, which may indicate dehydration ). Decreased vitamin D production , which is normal with aging, increases the risk of osteomalacia (bone demineralization) and osteoporosis (decrease in bone mass and density).