16 Integumentary System

The epidermis is composed of keratinized, stratified squamous epithelium. It is made of four or five layers of epithelial cells, depending on its location in the body. It is avascular.

• Thin skin has four layers of cells. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Most of the skin can be classified as thin skin.
• Thick skin is found only on the palms of the hands and the soles of the feet. It has a fifth layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum (see Figure 6.2).

The cells in all of the layers except the stratum basale are called keratinocytes.  Keratin is an intracellular fibrous protein that gives hair, nails, and skin their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced by cells from the deeper layers (see Figure 6.3).

Dermis

Hypodermis

The hypodermis serves to connect the skin to the underlying fascia of the bones and muscles. It is not strictly a part of the skin, although the border between the hypodermis and dermis can be difficult to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and adipose tissue, which functions as a mode of fat storage and provides insulation and cushioning for the integument.

The skin and accessory structures perform a variety of essential functions, such as protecting the body from invasion by microorganisms, chemicals, and other environmental factors; preventing dehydration; acting as a sensory organ; modulating body temperature and electrolyte balance; and synthesizing vitamin D. The underlying hypodermis has important roles in storing fats, forming a “cushion” over underlying structures, and providing insulation from cold temperatures.

Protection

The integumentary system helps regulate body temperature through its tight association with the sympathetic nervous system. The sympathetic nervous system is continuously monitoring body temperature and initiating appropriate motor responses.

1.  When the body becomes warm sweat glands, accessory structures to the skin, secrete water, salt, and other substances to cool the body.
   1. Even when the body does not appear to be noticeably sweating, approximately 500 mL of sweat are secreted a day.
2. If the body becomes excessively warm due to high temperatures, vigorous activity, or a combination of the two, sweat glands will be stimulated by the sympathetic nervous system to produce large amounts of sweat.
   1. When the sweat evaporates from the skin surface, the body is cooled as body heat is dissipated.
   2. In addition to sweating, arterioles in the dermis dilate so that excess heat carried by the blood can dissipate through the skin and into the surrounding environment (Figure 2b).
   3. This accounts for the skin redness that many people experience when exercising.
3. When body temperatures drop, the arterioles constrict to minimize heat loss, particularly in the ends of the digits and tip of the nose.
   1. This reduced circulation can result in the skin taking on a whitish hue.
   2. Although the temperature of the skin drops as a result, passive heat loss is prevented, and internal organs and structures remain warm.
   3. If the temperature of the skin drops too much (such as environmental temperatures below freezing), the conservation of body core heat can result frostbite .

Concept Check

Can you describe the thermoregulation process between the integumentary system and the sympathetic system?

• When body temperature is too warm.
• When body temperature is too cold.

• The absence of sun exposure can lead to a lack of vitamin D in the body, in children this can cause rickets.  Vitamin D deficiency in elderly individuals may lead to osteomalacia.

• In present day society, Vitamin D is added as a supplement to many foods, including milk and orange juice, compensating for the need for sun exposure. In addition to its essential role in bone health, Vitamin D is essential for general immunity against bacterial, viral, and fungal infections.

Watch this video:

Media 6.2. The Integumentary System, Part 2 – Skin Deeper: Crash Course A&P #7 [Online video]. Copyright 2015 by CrashCourse.

Accessory Structures

Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. These structures embryologically originate from the epidermis and can extend down through the dermis into the hypodermis.

Hair

Hair is a keratinous filament growing out of the epidermis. It is primarily made of dead, keratinized cells. Strands of hair originate in an epidermal penetration of the dermis called the hair follicle. The hair shaft is the part of the hair not anchored to the follicle, and much of this is exposed at the skin’s surface. The rest of the hair, which is anchored in the follicle, lies below the surface of the skin and is referred to as the hair root. The hair root ends deep in the dermis at the hair bulb, and includes a layer of mitotically active basal cells called the hair matrix. The hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis (see Figure 6.6).

Hair Function

A sebaceous gland is a type of oil gland that is found all over the body and helps to lubricate and waterproof the skin and hair. Most sebaceous glands are associated with hair follicles. They generate and excrete sebum, a mixture of lipids, onto the skin surface, thereby naturally lubricating the dry and dead layer of keratinized cells of the stratum corneum, keeping it pliable. The fatty acids of sebum also have antibacterial properties, and prevent water loss from the skin in low-humidity environments. The secretion of sebum is stimulated by hormones, many of which do not become active until puberty. Thus, sebaceous glands are relatively inactive during childhood.

Changes Due to Aging

All systems in the body accumulate subtle and some not-so-subtle changes as a person ages. Among these changes are reductions in cell division, metabolic activity, blood circulation, hormonal levels, and muscle strength (see Figure 6.9). In the skin, these changes are reflected in decreased mitosis in the stratum basale, leading to a thinner epidermis. The dermis, which is responsible for the elasticity and resilience of the skin, exhibits a reduced ability to regenerate, which leads to slower wound healing. The hypodermis, with its fat stores, loses structure due to the reduction and redistribution of fat, which in turn contributes to the thinning and sagging of skin.

The accessory structures also have lowered activity, generating thinner hair and nails, and reduced amounts of sebum and sweat. A reduced sweating ability can cause some elderly to be intolerant to extreme heat. Other cells in the skin, such as melanocytes and dendritic cells, also become less active, leading to a paler skin tone and lowered immunity. Wrinkling of the skin occurs due to breakdown of its structure, which results from decreased collagen and elastin production in the dermis, weakening of muscles lying under the skin, and the inability of the skin to retain adequate moisture.

Disease and Disorders

The integumentary system is susceptible to a variety of diseases, disorders, and injuries. These range from annoying but relatively benign bacterial or fungal infections that are categorized as disorders, to skin cancer and severe burns, which can be fatal. In this section, you will learn several of the most common skin conditions.

One of the most talked about diseases is skin cancer. Most cancers are identified by the organ or tissue in which the cancer originates. One common form of cancer is skin cancer.

In general, cancers result from an accumulation of DNA mutations. These mutations can result in cell populations that do not die when they should and uncontrolled cell proliferation that leads to tumors. Although many tumors are benign, some metastasize. Cancers are characterized by their ability to metastasize.

It requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially. Dark-skinned individuals can also get sunburns, but are more protected than are pale-skinned individuals. Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular structure of the skin, and in severe cases, can cause sufficient DNA damage to result in skin cancer. When there is an irregular accumulation of melanocytes in the skin, freckles appear. Moles are larger masses of melanocytes, and although most are benign, they should be monitored for changes that might indicate the presence of cancer (see Figure 6.10).

Basal Cell Carcinoma (BCC)

Basal cell carcinoma is a form of cancer that affects the mitotically active stem cells in the stratum basale of the epidermis. It is the most common of all cancers that occur in the United States and is frequently found on the head, neck, arms, and back, which are are as that are most susceptible to long-term sun exposure. Although UV rays are the main culprit, exposure to other agents, such as radiation and arsenic, can also lead to this type of cancer. Wounds on the skin due to open sores, tattoos, burns, etc. may be predisposing factors. Basal cell carcinomas start in the stratum basale and usually spread along this boundary. At some point, they begin to grow toward the surface and become an uneven patch, bump, growth, or scar on the skin surface (see Figure 6.11). Like most cancers, basal cell carcinomas respond best to treatment when caught early. Treatment options include surgery, freezing (cryosurgery), and topical ointments.

Squamous Cell Carcinoma (SCC)

Squamous cell carcinoma is a cancer that affects the keratinocytes of the stratum spinosum and presents as lesions commonly found on the scalp, ears, and hands (see Figure 6.12). It is the second most common skin cancer. The American Cancer Society reports that two of 10 skin cancers are squamous cell carcinomas, and it is more aggressive than basal cell carcinoma. If not removed, these carcinomas can metastasize. Surgery and radiation are used to cure squamous cell carcinoma.

Melanoma

A melanoma is a cancer characterized by the uncontrolled growth of melanocytes, the pigment-producing cells in the epidermis. Typically, a melanoma develops from a mole. It is the most fatal of all skin cancers, as it is highly metastatic and can be difficult to detect before it has spread to other organs. Melanomas usually appear as asymmetrical brown and black patches with uneven borders and a raised surface (see Figure 6.13). Treatment typically involves surgical excision and immunotherapy.

ABCDE for Early Diagnosis

Doctors often give their patients the following ABCDE mnemonic to help with the diagnosis of early-stage melanoma. If you observe a mole on your body displaying these signs, consult a doctor.

Asymmetry – the two sides are not symmetrical
Borders – the edges are irregular in shape
Color – the color is varied shades of brown or black
Diameter – it is larger than 6 mm (0.24 in)
Evolving – its shape has changed

Some specialists cite the following additional signs for the most serious form, nodular melanoma:

Elevated – it is raised on the skin surface
Firm – it feels hard to the touch
Growing – it is getting larger

 Albinism

Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, hair, and eyes. This is primarily due to the inability of melanocytes to produce melanin. Individuals with albinism tend to appear white or very pale due to the lack of melanin in their skin and hair. Recall that melanin helps protect the skin from the harmful effects of UV radiation. Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and skin cancer. They also tend to be more sensitive to light and have vision problems due to the lack of pigmentation on the retinal wall (Betts, et al., 2013)

Treatment of this disorder usually involves addressing the symptoms, such as limiting UV light exposure to the skin and eyes. In vitiligo, the melanocytes in certain areas lose their ability to produce melanin, possibly due to an autoimmune reaction. This leads to a loss of color in patches (see Figure 6.14). Neither albinism nor vitiligo directly affects the lifespan of an individual (Betts, et al., 2013)

Changes in Skin Colouration

Other changes in the appearance of skin colouration can be indicative of diseases associated with other body systems.

• Liver disease or liver cancer can cause the accumulation of bile and the yellow pigment bilirubin, leading to the skin appearing yellow or jaundiced.
• Tumors of the pituitary gland can result in the secretion of large amounts of melanocyte-stimulating hormone (MSH), which results in a darkening of the skin.
• Addison’s disease can stimulate the release of excess amounts of adrenocorticotropic hormone (ACTH), which can give the skin a deep bronze color
• A sudden drop in oxygenation can affect skin color, causing the skin to initially turn ashen (white).
• A prolonged reduction in oxygen levels, dark red deoxyhemoglobin becomes dominant in the blood, making the skin appear blue, a condition referred to as cyanosis. This happens when the oxygen supply is restricted, as when someone is experiencing difficulty in breathing because of asthma or a heart attack. However, in these cases the effect on skin color has nothing do with the skin’s pigmentation (Betts, et al., 2013)

Skin Disorders

Two common skin disorders are eczema and acne. Eczema is an inflammatory condition and occurs in individuals of all ages. Acne involves the clogging of pores, which can lead to infection and inflammation, and is often seen in adolescents. Other disorders, include seborrheic dermatitis (on the scalp), psoriasis, fungal infections, cold sores, impetigo, scabies, hives, and warts (Betts, et al., 2013).

Eczema

Eczema is an allergic reaction that manifests as dry, itchy patches of skin that resemble rashes (see Figure 6.15). It may be accompanied by swelling of the skin, flaking, and in severe cases, bleeding. Symptoms are usually managed with moisturizers, corticosteroid creams, and immunosuppressants (Betts, et al., 2013).

Acne

Acne is a skin disturbance that typically occurs on areas of the skin that are rich in sebaceous glands (face and back). It is most common along with the onset of puberty due to associated hormonal changes, but can also occur in infants and continue into adulthood. Hormones, such as androgens, stimulate the release of sebum. An overproduction and accumulation of sebum along with keratin can block hair follicles. This plug is initially white. The sebum, when oxidized by exposure to air, turns black. Acne results from infection by acne-causing bacteria (Propionibacterium and Staphylococcus), which can lead to redness and potential scarring due to the natural wound healing process (see Figure 6.16) (Betts, et al., 2013).

Ringworm

Tinea or dermatophytosis is often referred to as ringworm. Ringworm presents as a circular rash that is itchy and red and can be found on various parts of the body. It is referred to by the location that it is found:

• • Tinea Pedis – feet or commonly referred to as athlete’s feet
  • Tinea Capitis – scalp
  • Tinea barbae – beard
  • Tinea manuum – hands
  • Tinea unguium – Toenails and fingernails also called onychomycosis
  • Tinea corporis – Body parts such as arms and legs (Center for Disease Control and Prevention, 2018a)

To learn more about ringworm, visit the Center for Disease Control and Prevention’s web page on fungal infections. 

Psoriasis

Psoriasis is a chronic autoimmune disorder that results in patches of thick red skin with the appearance of silvery scales. These patches can be found on elbows, knees, scalp, low back, face, feet, fingernails, toenails and even the mouth. Psoriasis can be confused with other skin disease so a dermatologist is the best physician to diagnosis psoriasis. Treatments may include creams, ointments, ultraviolet light therapy and medication (Center for Disease Control and Prevention, 2018).  To learn more, visit the Center for Disease Control and Prevention’s web page on psoriasis.

Injuries

Because the skin is the part of our bodies that meets the world most directly, it is especially vulnerable to injury. Injuries include burns, wounds, as well as scars and calluses. They can be caused by sharp objects, heat, or excessive pressure or friction to the skin (Betts, et al., 2013).

Skin injuries set off a healing process that occurs in several overlapping stages.

• The first step to repairing damaged skin is the formation of a blood clot that helps stop the flow of blood and scabs over with time. Many different types of cells are involved in wound repair, especially if the surface area that needs repair is extensive.
• Before the basal stem cells of the stratum basale can recreate the epidermis, fibroblasts mobilize and divide rapidly to repair the damaged tissue by collagen deposition, forming granulation tissue.
• Blood capillaries follow the fibroblasts and help increase blood circulation and oxygen supply to the area.
• Immune cells, such as macrophages, roam the area and engulf any foreign matter to reduce the chance of infection (Betts, et al., 2013).

Burns

A burn results when the skin is damaged by intense heat, radiation, electricity, or chemicals. The damage results in the death of skin cells, which can lead to a massive loss of fluid. Dehydration, electrolyte imbalance, and renal and circulatory failure follow, which can be fatal. Burn patients are treated with intravenous fluids to offset dehydration, as well as intravenous nutrients that enable the body to repair tissues and replace lost proteins. Another serious threat to the lives of burn patients is infection. Burned skin is extremely susceptible to bacteria and other pathogens, due to the loss of protection by intact layers of skin (Betts, et al., 2013).

Burn Classification

Burns are sometimes measured in terms of the size of the total surface area affected. This is referred to as the rule of nines, which associates specific anatomical areas with a percentage that is a factor of nine (see Figure 6.17) (Betts, et al., 2013).

Burns are also classified by the degree of their severity.

• A first-degree burn is a superficial burn that affects only the epidermis. Although the skin may be painful and swollen, these burns typically heal on their own within a few days. Mild sunburn fits into the category of a first-degree burn.
• A second-degree burn goes deeper and affects both the epidermis and a portion of the dermis. These burns result in swelling and a painful blistering of the skin. It is important to keep the burn site clean and sterile to prevent infection. If this is done, the burn will heal within several weeks.
• A third-degree burn fully extends into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function. These are serious burns that may appear white, red, or black; they require medical attention and will heal slowly without it.
• A fourth-degree burn is even more severe, affecting the underlying muscle and bone.

Oddly, third and fourth-degree burns are usually not as painful because the nerve endings themselves are damaged. Full-thickness burns cannot be repaired by the body, because the local tissues used for repair are damaged and require debridement, or amputation in severe cases, followed by grafting of the skin from an unaffected part of the body, or from skin grown in tissue culture for grafting purposes. Skin grafts are required when the damage from trauma or infection cannot be closed with sutures or staples (Betts et al., 2013).

Scars and Keloids

Most cuts or wounds, with the exception of ones that only scratch the epidermis, lead to scar formation. Scarring occurs in cases in which there is repair of skin damage, but the skin fails to regenerate the original skin structure. Fibroblasts generate scar tissue in the form of collagen, and the bulk of repair is due to the basket-weave pattern generated by collagen fibers and does not result in regeneration of the typical cellular structure of skin. Instead, the tissue is fibrous in nature and does not allow for the regeneration of accessory structures, such as hair follicles, sweat glands, or sebaceous glands (Betts, et al., 2013).

Sometimes, there is an overproduction of scar tissue, because the process of collagen formation does not stop when the wound is healed; this results in a keloid. In contrast, scars that result from acne and chickenpox have a sunken appearance and are called atrophic scars (Betts, et al., 2013)

Scarring of skin after wound healing is a natural process and does not need to be treated further. Application of mineral oil and lotions may reduce the formation of scar tissue. However, modern cosmetic procedures, such as dermabrasion, laser treatments, and filler injections have been invented as remedies for severe scarring. All of these procedures try to reorganize the structure of the epidermis and underlying collagen tissue to make it look more natural (Betts, et al., 2013).

Bedsores and Stretch Marks

Skin and its underlying tissue can be affected by excessive pressure. One example of this is called a bedsore. Bedsores, also called decubitus ulcers, are caused by constant, long-term, unrelieved pressure on certain body parts that are bony, reducing blood flow to the area and leading to necrosis . Bedsores are most common in elderly patients who have debilitating conditions that cause them to be immobile. Most hospitals and long-term care facilities have the practice of turning the patients every few hours to prevent the incidence of bedsores. If left untreated bedsores can be fatal if they become infected (Betts, et al., 2013)

The skin can also be affected by pressure associated with rapid growth. A stretch mark results when the dermis is stretched beyond its limits of elasticity, as the skin stretches to accommodate the excess pressure. Stretch marks usually accompany rapid weight gain during puberty and pregnancy. They initially have a reddish hue, but lighten over time. Other than for cosmetic reasons, treatment of stretch marks is not required. They occur most commonly over the hips and abdomen (Betts, et al., 2013).

Calluses

When you wear shoes that do not fit well and are a constant source of abrasion on your toes, you tend to form a callus at the point of contact. This occurs because the basal stem cells in the stratum basale are triggered to divide more often to increase the thickness of the skin at the point of abrasion to protect the rest of the body from further damage. This is an example of a minor or local injury, and the skin manages to react and treat the problem independent of the rest of the body. Calluses can also form on your fingers if they are subject to constant mechanical stress, such as long periods of writing, playing string instruments, or video games. A corn is a specialized form of callus. Corns form from abrasions on the skin that result from an elliptical-type motion (Betts, et al., 2013).

Medical Terms in Context

Medical Specialties and Procedures Related to the Integumentary System

A dermatologist is a medical doctor with specialized training in treating diseases, disorders and injuries related to the integumentary system and its accessory structures. There are many dermatologic subspecialties such as cosmetic dermatology, dermatopathology and pediatric dermatology. To learn more visit the Dermatology and Subspecialties section of the Canadian Dermatology Association website.

Dermatologists can be specially trained to perform a procedure called Mohs surgery. Mohs surgery excises skin cancers in thin layers until all cancer is removed from the tissue (Mayo Clinic Staff, 2017).

Integumentary System Vocabulary

Adipocytes

Fat cells.

Adipose tissue

Fat tissue.

Autonomic nerve fibers

Unconsciously regulates communication to and from the brain.

Avascular

Without blood vessels.

Benign

Noncancerous, harmless.

Cancer

A process where abnormal cells in the body divide uncontrollably.

Cyanosis

Abnormal condition of blue (bluish colour, lips and nail beds). Typically caused by low oxygenation.

Debridement

Excision of damaged tissue or foreign object.

Dehydration

Loss of fluids/water is greater than what is taken in.

Dermatologic

Pertaining to dermatology.

Dermatopathology

Study of diseases of the skin.

Dermis

The layer of skin that is made of dense, irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures.

Epidermis

Outer layer of skin, made of closely packed epithelial cells.

Excises

Remove by cutting out.

Exocytosis

Active transport of molecules out of the cell.

Fascia

Fibrous tissue.

Frostbite

Conservation of core body heat results in the skin actually freezing.

Hypodermis

Literally means below the dermis. The layer of skin below the dermis that is composed mainly of loose connective and fatty tissues.

Infection

Invasion by disease-causing organisms.

Intravenous

Pertaining to within the vein.

Jaundiced

Yellow-coloured.

Keloid

Formation of a raised or hypertrophic scar.

Keratinocytes

Cells that manufacture and store the protein keratin.

Meissner corpuscle

Tactile corpuscle that responds to light and touch, touch receptor.

Meissner corpuscles

Tactile corpuscle that responds to light and touch, touch receptors.

Melanocytes

Specialized cells that produce melanin which is a dark pigment responsible for colouration of skin and hair.

Metastasize

Production of cells that can mobilize and establish tumors in other organs of the body.

Necrosis

Tissue death.

Osteomalacia

Softening of the bones.

Pacinian corpuscle

Lamellated corpuscle that responds to vibration.

Pathogens

Disease-causing agents.

Phagocytes

Cells that engulf and absorb bacteria and cell particles.

Reticulated

Net like.

Rickets

A painful condition in children where bones are misshapen due to a lack of calcium, causing bow leggedness.

Scar

Collagen-rich skin formed after the process of wound healing that differs from normal skin.

Stratum Basale

Deepest layer of the epidermal.

Sympathetic nerve fibers

Flight or fight response determines communication to and from the brain.

Sympathetic Nervous System

Responsible for fight or flight responses.

Vascularized

Has numerous blood vessels.

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