Support and Movement The Integumentary device The Integumentary mechanism advent

Figure 5.1 Your skin is a vital part of your life and also appearance (a–d). Some people select to embellish it v tattoos (a), assembly (b), and also even piercings (c). (credit a: Steve Teo; credit b: “spaceodissey”/flickr; credit c: Mark/flickr; credit d: Lisa Schaffer)


After studying the chapter, you will be may be to: 

Describe the integumentary system and also the duty it theatre in homeostasisDescribe the great of the skin and the functions of every layerDescribe the accessory frameworks of the skin and the features of eachDescribe the changes that occur in the integumentary system throughout the aging processDiscuss several typical diseases, disorders, and also injuries that impact the integumentary systemExplain treatments for some typical diseases, disorders, and also injuries of the integumentary system

What perform you think as soon as you look at at her skin in the mirror? carry out you think around covering it v makeup, including a tattoo, or possibly a body piercing? Or execute you think about the truth that the skin belonging to among the body’s most essential and also dynamic systems: the integumentary system? The integumentary system refers come the skin and its accessory structures, and also it is responsible because that much an ext than merely lending to your outside appearance. In the adult human body, the skin makes up about 16 percent of human body weight and also covers one area of 1.5 to 2 m2. In fact, the skin and accessory structures space the largest organ device in the human body. Together such, the skin protects your inner organs and it is in need of everyday care and protection to preserve its health. This thing will introduce the structure and functions of the integumentary system, and also some the the diseases, disorders, and also injuries that can influence this system.

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by the end of this section, you will be able to:Identify the materials of the integumentary systemDescribe the layers of the skin and also the functions of every layerIdentify and also describe the hypodermis and deep fasciaDescribe the function of keratinocytes and their life cycleDescribe the duty of melanocytes in skin pigmentation

Although you may not frequently think the the skin as an organ, that is in reality made of tissues that work-related together together a solitary structure come perform distinct and critical functions. The skin and its accessory structures comprise the integumentary system, which gives the body with as whole protection. The skin is do of multiple class of cells and tissues, which are held to underlying structures by connective tissue (Figure 5.2). The deeper layer of skin is fine vascularized (has many blood vessels). It also has countless sensory, and autonomic and sympathetic nerve yarn ensuring communication to and from the brain.


Figure 5.2 Layers that Skin The skin is written of two key layers: the epidermis, do of very closely packed epithelial cells, and the dermis, made of dense, irregular connective organization that homes blood vessels, hair follicles, sweat glands, and also other structures. In ~ the dermis lies the hypodermis, which is composed greatly of loosened connective and fatty tissues.


The skin consists of two key layers and a closely connected layer. View this animation to learn more about class of the skin. What room the straightforward functions of each of these layers?

The Epidermis

The epidermis is written of keratinized, stratified squamous epithelium. That is made of four or five layers the epithelial cells, relying on its place in the body. The does not have any type of blood vessels within it (i.e., that is avascular). Skin that has four layers of cells is referred to as “thin skin.” native deep to superficial, this layers space the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Many of the skin have the right to be classified together thin skin. “Thick skin” is discovered only top top the palms of the hands and also the soles the the feet. It has a 5th layer, referred to as the stratum lucidum, located between the stratum corneum and also the stratum granulosum (Figure 5.3).


The cells in every one of the layers except the stratum basale are called keratinocytes. A keratinocyte is a cell the manufactures and stores the protein keratin. Keratin is an intracellular fibrous protein that offers hair, nails, and skin their hardness and water-resistant properties. The keratinocytes in the stratum corneum space dead and regularly slough away, being replaced by cell from the deeper class (Figure 5.4).



View the University of Michigan WebScope to check out the tissue sample in higher detail. If you zoom ~ above the cell at the outermost class of this section of skin, what do you an alert about the cells?

Stratum Basale

The stratum basale (also referred to as the stratum germinativum) is the deepest epidermal layer and also attaches the epidermis to the basal lamina, listed below which lied the layers of the dermis. The cell in the stratum basale bond come the dermis via intertwining collagen fibers, referred to as the basement membrane. A finger-like projection, or fold, known as the dermal papilla (plural = dermal papillae) is found in the superficial portion of the dermis. Dermal papillae boost the stamin of the connection in between the epidermis and also dermis; the greater the folding, the stronger the connections made (Figure 5.5).


Figure 5.5 Layers that the Epidermis The epidermis of thick skin has 5 layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and also stratum corneum.

The stratum basale is a single layer that cells mostly made the basal cells. A basal cell is a cuboidal-shaped stem cell the is a precursor the the keratinocytes that the epidermis. All of the keratinocytes are created from this single layer that cells, which room constantly going with mitosis to produce new cells. As new cells are formed, the existing cell are pushed superficially far from the stratum basale. Two other cell species are uncovered dispersed among the basal cell in the stratum basale. The an initial is a Merkel cell, which features as a receptor and also is responsible because that stimulating sensory nerves the the mind perceives as touch. This cells are specifically abundant ~ above the surface of the hands and feet. The 2nd is a melanocyte, a cell that produces the pigment melanin. Melanin gives hair and skin its color, and additionally helps defend the living cell of the epidermis from ultraviolet (UV) radiation damage.

In a growing fetus, fingerprints form where the cells of the stratum basale accomplish the papillae that the basic dermal class (papillary layer), causing the development of the ridges on your fingers that you identify as fingerprints. Fingerprints are distinctive to every individual and are provided for forensic analyses due to the fact that the patterns perform not readjust with the growth and also aging processes.

Stratum Spinosum

As the name suggests, the stratum spinosum is spiny in appearance because of the protruding cell processes that sign up with the cell via a structure dubbed a desmosome. The desmosomes interlock v each other and strengthen the bond in between the cells. The is exciting to note that the “spiny” nature of this great is one artifact of the staining process. Unstained epidermis samples perform not exhibit this characteristic appearance. The stratum spinosum is written of eight come 10 layers of keratinocytes, formed as a an outcome of cell department in the stratum basale (Figure 5.6). Interspersed among the keratinocytes of this class is a form of dendritic cell referred to as the Langerhans cell, which functions as a macrophage through engulfing bacteria, international particles, and damaged cell that take place in this layer.



View the University the Michigan WebScope to discover the organization sample in better detail. If you zoom on the cells at the outermost class of this section of skin, what perform you an alert about the cells?

The keratinocytes in the stratum spinosum start the synthesis of keratin and also release a water-repelling glycolipid that helps avoid water loss from the body, making the skin fairly waterproof. As new keratinocytes are developed atop the stratum basale, the keratinocytes of the stratum spinosum room pushed into the stratum granulosum.

Stratum Granulosum

The stratum granulosum has a grainy appearance due to further alters to the keratinocytes together they are driven from the stratum spinosum. The cells (three to 5 layers deep) come to be flatter, your cell membranes thicken, and also they generate huge amounts of the protein keratin, i m sorry is fibrous, and keratohyalin, i m sorry accumulates as lamellar granules within the cell (see Figure 5.5). These 2 proteins consist of the mass of the keratinocyte massive in the stratum granulosum and also give the class its grainy appearance. The nuclei and other cabinet organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin, and cell membranes the will type the stratum lucidum, the stratum corneum, and also the accessory structures of hair and nails.

Stratum Lucidum

The stratum lucidum is a smooth, seemingly translucent layer of the epidermis situated just above the stratum granulosum and also below the stratum corneum. This slim layer of cells is uncovered only in the special skin that the palms, soles, and also digits. The keratinocytes that write the stratum lucidum are dead and also flattened (see Figure 5.5). This cells room densely pack with eleiden, a clear protein rich in lipids, obtained from keratohyalin, which provides these cells their transparent (i.e., lucid) appearance and also provides a obstacle to water.

Stratum Corneum

The stratum corneum is the many superficial class of the epidermis and is the layer exposed to the outside setting (see Figure 5.5). The enhanced keratinization (also dubbed cornification) that the cells in this layer gives it the name. There space usually 15 to 30 layers of cell in the stratum corneum. This dry, dead great helps avoid the penetration that microbes and also the dehydration of underlying tissues, and provides a mechanically protection versus abrasion because that the an ext delicate, underlying layers. Cell in this great are melted periodically and are changed by cells pushed up indigenous the stratum granulosum (or stratum lucidum in the situation of the palms and soles the feet). The entire layer is replaced during a period of around 4 weeks. Cosmetic procedures, such together microdermabrasion, assist remove several of the dry, upper layer and also aim to save the skin spring “fresh” and healthy.


The dermis might be thought about the “core” that the integumentary mechanism (derma- = “skin”), as distinct from the epidermis (epi- = “upon” or “over”) and hypodermis (hypo- = “below”). It contains blood and lymph vessels, nerves, and also other structures, such together hair follicles and sweat glands. The dermis is do of 2 layers the connective tissue that create an interconnected mesh that elastin and also collagenous fibers, created by fibroblasts (Figure 5.7).


Figure 5.7 Layers of the Dermis This stained slide reflects the two materials of the dermis—the papillary layer and also the reticular layer. Both room made that connective tissue through fibers that collagen prolonging from one come the other, making the border between the two somewhat indistinct. The dermal papillae expanding into the epidermis belong to the papillary layer, vice versa, the thick collagen fiber bundles listed below belong to the reticular layer. LM × 10. (credit: modification of occupational by “kilbad”/Wikimedia Commons)

Papillary Layer

The papillary layer is do of loose, areolar connective tissue, which way the collagen and elastin yarn of this layer form a loose mesh. This superficial class of the dermis projects right into the stratum basale the the epidermis to type finger-like dermal papillae (see Figure 5.7). Within the papillary layer are fibroblasts, a small number of fat cells (adipocytes), and an abundance of small blood vessels. In addition, the papillary layer consists of phagocytes, protective cells that aid fight bacteria or various other infections that have breached the skin. This layer likewise contains lymphatic capillaries, nerve fibers, and touch receptors referred to as the Meissner corpuscles.

Reticular Layer

Underlying the papillary class is the much thicker reticular layer, written of dense, rarely often, rarely connective tissue. This layer is fine vascularized and also has a well-off sensory and also sympathetic nerve supply. The reticular layer shows up reticulated (net-like) because of a tight meshwork that fibers. Elastin fibers provide some elasticity come the skin, allowing movement. Collagen fibers carry out structure and also tensile strength, v strands that collagen prolonging into both the papillary layer and the hypodermis. In addition, collagen binds water to save the skin hydrated. Collagen injections and Retin-A creams aid restore skin turgor by either introducing collagen externally or stimulating blood flow and repair the the dermis, respectively.


The hypodermis (also referred to as the subcutaneous layer or superficial fascia) is a class directly listed below the dermis and serves to affix the skin come the underlying fascia (fibrous tissue) the the bones and also muscles. That is no strictly a component of the skin, although the border in between the hypodermis and also dermis deserve to be an overwhelming to distinguish. The hypodermis consists of well-vascularized, loose, areolar connective tissue and adipose tissue, which attributes as a setting of fat storage and also provides insulation and cushioning because that the integument.


Lipid Storage

The hypodermis is house to many of the fat the concerns people when they are trying to keep their load under control. Adipose tissue present in the hypodermis is composed of fat-storing cells referred to as adipocytes. This save fat have the right to serve together an energy reserve, insulate the body to prevent warmth loss, and act together a cushion to safeguard underlying structures from trauma.

Where the fat is deposited and also accumulates in ~ the hypodermis depends on hormones (testosterone, estrogen, insulin, glucagon, leptin, and also others), and genetic factors. Fat distribution transforms as our body mature and age. Guys tend to accumulate fat in different locations (neck, arms, reduced back, and abdomen) than do women (breasts, hips, thighs, and also buttocks). The human body mass index (BMI) is regularly used as a measure up of fat, although this measure up is, in fact, acquired from a mathematics formula that compares body weight (mass) to height. Therefore, that is accuracy as a wellness indicator deserve to be dubbed into inquiry in people who are extremely physically fit.

In plenty of animals, there is a pattern of storing overabundance calories as fat come be offered in times once food is not conveniently available. In much of the emerged world, poor exercise coupled through the ready accessibility and intake of high-calorie foodstuffs have caused unwanted accumulations of adipose organization in numerous people. Back periodic accumulation of overfill fat may have provided an evolutionary benefit to our ancestors, who knowledgeable unpredictable bouts the famine, it is now ending up being chronic and also considered a major health threat. Current studies suggest that a distressing percentage of our populace is overweight and/or clinically obese. Not only is this a trouble for the individuals affected, but it additionally has a severe affect on our healthcare system. Transforms in lifestyle, particularly in diet and also exercise, room the best ways to regulate body fat accumulation, particularly when it reaches level that rise the threat of heart an illness and diabetes.


The shade of skin is affected by a variety of pigments, consisting of melanin, carotene, and hemoglobin. Recall the melanin is developed by cells referred to as melanocytes, i m sorry are found scattered throughout the stratum basale of the epidermis. The melanin is transferred right into the keratinocytes via a moving vesicle dubbed a melanosome (Figure 5.8).


Figure 5.8 Skin Pigmentation The loved one coloration the the skin depends of the lot of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes.

Melanin wake up in two main forms. Eumelanin exists together black and also brown, conversely, pheomelanin offers a red color. Dark-skinned people produce more melanin than those v pale skin. Exposure to the UV light ray of the sun or a tanning salon causes melanin to be made and collected in keratinocytes, as sun exposure stimulates keratinocytes come secrete chemicals that stimulate melanocytes. The build-up of melanin in keratinocytes results in the darkening of the skin, or a tan. This raised melanin buildup protects the DNA that epidermal cells from UV beam damage and the break down of folic acid, a nutrient vital for our health and well-being. In contrast, too lot melanin have the right to interfere with the manufacturing of vitamin D, an essential nutrient involved in calcium absorption. Thus, the quantity of melanin existing in our skin is dependent on a balance between available sunlight and also folic acid destruction, and protection from UV radiation and also vitamin D production.

It requires about 10 work after initial sunlight exposure because that melanin synthetic to peak, i beg your pardon is why pale-skinned people tend to endure sunburns that the epidermis initially. Dark-skinned individuals can additionally get sunburns, however are an ext protected than are pale-skinned individuals. Melanosomes room temporary frameworks that room eventually ruined by fusion with lysosomes; this fact, in addition to melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.

Too much sun exposure can ultimately lead to wrinkling because of the destruction of the cellular framework of the skin, and also in major cases, can reason sufficient DNA damage to an outcome in skin cancer. Once there is one irregular accumulation of melanocytes in the skin, summer sprouts appear. Moles are bigger masses the melanocytes, and although many are benign, they need to be monitored for alters that can indicate the visibility of cancer (Figure 5.9).


Figure 5.9 Moles Moles variety from light accumulations the melanocytes come melanomas. These structures populate the see of ours skin. (credit: the national Cancer Institute)


Integumentary System

The very first thing a clinician sees is the skin, and so the examination of the skin must be component of any type of thorough physics examination. Many skin obstacle are fairly benign, but a few, consisting of melanomas, have the right to be deadly if untreated. A pair of the an ext noticeable disorders, albinism and vitiligo, influence the figure of the skin and also its accessory organs. Although no is fatal, it would be tough to case that they are benign, at the very least to the individuals so afflicted.

Albinism is a genetic disorder the affects (completely or partially) the coloring of skin, hair, and also eyes. The defect is primarily because of the inability of melanocytes to produce melanin. People with albinism often tend to show up white or really pale as result of the lack of melanin in their skin and also hair. Recall the melanin helps protect the skin from the harmful effects of UV radiation. Individuals with albinism tend to need more protection native UV radiation, as they are much more prone to sunburns and skin cancer. They additionally tend come be an ext sensitive come light and also have vision difficulties due to the absence of pigmentation on the retinal wall. Treatment of this disorder usually requires addressing the symptoms, such as limiting UV light exposure come the skin and also eyes. In vitiligo, the melanocytes in details areas shed their ability to develop melanin, possibly as result of an autoimmune reaction. This leads to a ns of color in job (Figure 5.10). Neither albinism no one vitiligo directly affects the lifespan of one individual.

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Figure 5.10 Vitiligo Individuals with vitiligo experience depigmentation that results in lighter colored patches that skin. The problem is especially noticeable top top darker skin. (credit: Klaus D. Peter)

Other transforms in the figure of skin coloration deserve to be indicative that diseases linked with other body systems. Liver condition or liver cancer can cause the accumulation of bile and also the yellow colors bilirubin, resulting in the skin showing up yellow or jaundiced (jaune is the French word because that “yellow”). Tumors the the pituitary gland can result in the cheap of big amounts that melanocyte-stimulating hormone (MSH), which outcomes in a darkening that the skin. Similarly, Addison’s an illness can stimulate the relax of excess quantities of adrenocorticotropic hormone (ACTH), i m sorry can provide the skin a deep copper color. A sudden drop in oxygenation can affect skin color, resulting in the skin to at first turn ashen (white). Through a an extensive reduction in oxygen levels, dark red deoxyhemoglobin becomes dominant in the blood, do the skin appear blue, a problem referred to together cyanosis (kyanos is the Greek word for “blue”). This happens when the oxygen it is provided is restricted, as as soon as someone is experiencing challenge in breathing due to the fact that of asthma or a love attack. However, in these instances the result on skin shade has nothing carry out with the skin’s pigmentation.


This ABC video follows the story that a pair of fraternal African-American twins, among whom is albino. Clock this videoto learn about the difficulties these children and their family members face. Which ethnic backgrounds do girlfriend think room exempt indigenous the opportunity of albinism?