3. what component of the subcutaneous layer provides protection to the underlying organs?

The Integumentary System

Layers of the Peel

Learning Objectives

Past the stop of this section, you lot will be able to:

• Identify the components of the integumentary arrangement
• Describe the layers of the skin and the functions of each layer
• Identify and depict the hypodermis and deep fascia
• Describe the office of keratinocytes and their life bike
• Draw the role of melanocytes in skin pigmentation

Although you may non typically think of the skin as an organ, information technology is in fact made of tissues that work together equally a single structure to perform unique and critical functions. The pare and its accessory structures make upwards the integumentary system, which provides the body with overall protection. The skin is made of multiple layers of cells and tissues, which are held to underlying structures by connective tissue ((Figure)). The deeper layer of skin is well vascularized (has numerous blood vessels). It also has numerous sensory, and autonomic and sympathetic nerve fibers ensuring communication to and from the encephalon.

Layers of Skin

The skin is composed of two main layers: the epidermis, made of closely packed epithelial cells, and the dermis, made of dense, irregular connective tissue that houses blood vessels, pilus follicles, sweat glands, and other structures. Beneath the dermis lies the hypodermis, which is equanimous mainly of loose connective and fatty tissues.

The peel consists of two main layers and a closely associated layer. View this animation to larn more about layers of the skin. What are the basic functions of each of these layers?

The Epidermis

The epidermis is composed of keratinized, stratified squamous epithelium. It is fabricated of four or five layers of epithelial cells, depending on its location in the body. It does not accept any blood vessels within it (i.east., it is avascular). Peel that has four layers of cells is referred to as "thin skin." From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Nearly of the skin can exist classified as sparse peel. "Thick skin" is institute but on the palms of the hands and the soles of the feet. It has a fifth layer, called the stratum lucidum, located betwixt the stratum corneum and the stratum granulosum ((Figure)).

Sparse Skin versus Thick Skin

These slides show cross-sections of the epidermis and dermis of (a) thin and (b) thick skin. Note the pregnant deviation in the thickness of the epithelial layer of the thick pare. From elevation, LM × 40, LM × xl. (Micrographs provided past the Regents of University of Michigan Medical Schoolhouse © 2012)

The cells in all of the layers except the stratum basale are called keratinocytes. A keratinocyte is a prison cell that manufactures and stores the protein keratin. Keratin is an intracellular fibrous protein that gives hair, nails, and peel their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough abroad, being replaced by cells from the deeper layers ((Figure)).

Epidermis

The epidermis is epithelium composed of multiple layers of cells. The basal layer consists of cuboidal cells, whereas the outer layers are squamous, keratinized cells, then the whole epithelium is oft described as beingness keratinized stratified squamous epithelium. LM × 40. (Micrograph provided by the Regents of Academy of Michigan Medical Schoolhouse © 2012)

View the University of Michigan WebScope to explore the tissue sample in greater detail. If you zoom on the cells at the outermost layer of this section of skin, what do y'all notice about the cells?

Stratum Basale

The stratum basale (also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis. The cells in the stratum basale bail to the dermis via intertwining collagen fibers, referred to as the basement membrane. A finger-like projection, or fold, known equally the dermal papilla (plural = dermal papillae) is found in the superficial portion of the dermis. Dermal papillae increase the force of the connexion between the epidermis and dermis; the greater the folding, the stronger the connections made ((Figure)).

Layers of the Epidermis

The epidermis of thick skin has five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

The stratum basale is a single layer of cells primarily made of basal cells. A basal jail cell is a cuboidal-shaped stalk cell that is a forerunner of the keratinocytes of the epidermis. All of the keratinocytes are produced from this unmarried layer of cells, which are constantly going through mitosis to produce new cells. Equally new cells are formed, the existing cells are pushed superficially away from the stratum basale. Two other jail cell types are plant dispersed among the basal cells in the stratum basale. The showtime is a Merkel cell, which functions as a receptor and is responsible for stimulating sensory nerves that the encephalon perceives as touch. These cells are particularly abundant on the surfaces of the hands and feet. The second is a melanocyte, a cell that produces the pigment melanin. Melanin gives hair and skin its color, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiation impairment.

In a growing fetus, fingerprints form where the cells of the stratum basale meet the papillae of the underlying dermal layer (papillary layer), resulting in the formation of the ridges on your fingers that y'all recognize equally fingerprints. Fingerprints are unique to each individual and are used for forensic analyses because the patterns exercise not modify with the growth and crumbling processes.

Stratum Spinosum

As the name suggests, the stratum spinosum is spiny in appearance due to the protruding jail cell processes that join the cells via a structure chosen a desmosome. The desmosomes interlock with each other and strengthen the bond betwixt the cells. Information technology is interesting to note that the "spiny" nature of this layer is an antiquity of the staining procedure. Unstained epidermis samples practise non exhibit this characteristic advent. The stratum spinosum is composed of eight to x layers of keratinocytes, formed as a event of jail cell partitioning in the stratum basale ((Effigy)). Interspersed amidst the keratinocytes of this layer is a type of dendritic cell chosen the Langerhans cell, which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer.

Cells of the Epidermis

The cells in the unlike layers of the epidermis originate from basal cells located in the stratum basale, nonetheless the cells of each layer are distinctively dissimilar. EM × 2700. (Micrograph provided by the Regents of University of Michigan Medical Schoolhouse © 2012)

View the University of Michigan WebScope to explore the tissue sample in greater detail. If y'all zoom on the cells at the outermost layer of this section of pare, what exercise y'all find about the cells?

The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a h2o-repelling glycolipid that helps preclude water loss from the trunk, making the skin relatively waterproof. As new keratinocytes are produced atop the stratum basale, the keratinocytes of the stratum spinosum are pushed into the stratum granulosum.

Stratum Granulosum

The stratum granulosum has a grainy appearance due to further changes to the keratinocytes equally they are pushed from the stratum spinosum. The cells (three to 5 layers deep) get flatter, their jail cell membranes thicken, and they generate big amounts of the proteins keratin, which is fibrous, and keratohyalin, which accumulates as lamellar granules within the cells (run into (Figure)). These two proteins make upward the bulk of the keratinocyte mass in the stratum granulosum and requite the layer its grainy advent. The nuclei and other cell organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin, and jail cell membranes that will course the stratum lucidum, the stratum corneum, and the accessory structures of hair and nails.

Stratum Lucidum

The stratum lucidum is a smoothen, seemingly translucent layer of the epidermis located just higher up the stratum granulosum and below the stratum corneum. This thin layer of cells is found merely in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened (see (Effigy)). These cells are densely packed with eleiden, a articulate protein rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.eastward., lucid) appearance and provides a barrier to h2o.

Stratum Corneum

The stratum corneum is the most superficial layer of the epidermis and is the layer exposed to the outside environment (see (Figure)). The increased keratinization (also called cornification) of the cells in this layer gives it its name. There are ordinarily 15 to 30 layers of cells in the stratum corneum. This dry, expressionless layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion for the more fragile, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed up from the stratum granulosum (or stratum lucidum in the case of the palms and soles of feet). The unabridged layer is replaced during a period of about 4 weeks. Cosmetic procedures, such equally microdermabrasion, help remove some of the dry out, upper layer and aim to proceed the pare looking "fresh" and good for you.

Dermis

The dermis might be considered the "core" of the integumentary system (derma- = "peel"), equally distinct from the epidermis (epi- = "upon" or "over") and hypodermis (hypo- = "beneath"). It contains blood and lymph vessels, nerves, and other structures, such as pilus follicles and sweat glands. The dermis is fabricated of two layers of connective tissue that etch an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts ((Figure)).

Layers of the Dermis

This stained slide shows the two components of the dermis—the papillary layer and the reticular layer. Both are made of connective tissue with fibers of collagen extending from ane to the other, making the border between the two somewhat indistinct. The dermal papillae extending into the epidermis belong to the papillary layer, whereas the dense collagen fiber bundles below belong to the reticular layer. LM × 10. (credit: modification of piece of work by "kilbad"/Wikimedia Commons)

Papillary Layer

The papillary layer is fabricated of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer course a loose mesh. This superficial layer of the dermis projects into the stratum basale of the epidermis to grade finger-similar dermal papillae (see (Figure)). Inside the papillary layer are fibroblasts, a small number of fatty cells (adipocytes), and an abundance of modest blood vessels. In addition, the papillary layer contains phagocytes, defensive cells that help fight leaner or other infections that have breached the pare. This layer also contains lymphatic capillaries, nerve fibers, and touch receptors called the Meissner corpuscles.

Reticular Layer

Underlying the papillary layer is the much thicker reticular layer, composed of dense, irregular connective tissue. This layer is well vascularized and has a rich sensory and sympathetic nerve supply. The reticular layer appears reticulated (net-similar) due to a tight meshwork of fibers. Elastin fibers provide some elasticity to the skin, enabling motion. Collagen fibers provide construction and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis. In addition, collagen binds water to keep the skin hydrated. Collagen injections and Retin-A creams assistance restore skin turgor by either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively.

Hypodermis

The hypodermis (too called the subcutaneous layer or superficial fascia) is a layer direct below the dermis and serves to connect the skin to the underlying fascia (fibrous tissue) of the bones and muscles. It is not strictly a office of the peel, although the border between the hypodermis and dermis tin 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.

Everyday Connection

Lipid Storage The hypodermis is abode to most of the fatty that concerns people when they are trying to go along their weight nether control. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes. This stored fat can serve as an energy reserve, insulate the trunk to forbid heat loss, and act as a cushion to protect underlying structures from trauma.

Where the fat is deposited and accumulates within the hypodermis depends on hormones (testosterone, estrogen, insulin, glucagon, leptin, and others), as well as genetic factors. Fat distribution changes as our bodies mature and age. Men tend to accumulate fatty in different areas (neck, artillery, lower dorsum, and belly) than do women (breasts, hips, thighs, and buttocks). The torso mass index (BMI) is often used every bit a measure of fat, although this measure is, in fact, derived from a mathematical formula that compares body weight (mass) to acme. Therefore, its accurateness as a wellness indicator tin be chosen into question in individuals who are extremely physically fit.

In many animals, there is a blueprint of storing backlog calories as fatty to be used in times when food is not readily available. In much of the adult world, bereft exercise coupled with the ready availability and consumption of high-calorie foods have resulted in unwanted accumulations of adipose tissue in many people. Although periodic accumulation of excess fatty may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, information technology is now becoming chronic and considered a major health threat. Recent studies indicate that a lamentable percentage of our population is overweight and/or clinically obese. Not only is this a problem for the individuals afflicted, but it as well has a severe touch on on our healthcare system. Changes in lifestyle, specifically in nutrition and exercise, are the best ways to control body fatty accumulation, particularly when it reaches levels that increase the hazard of heart disease and diabetes.

Pigmentation

The color of skin is influenced past a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced past cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred into the keratinocytes via a cellular vesicle called a melanosome ((Effigy)).

Skin Pigmentation

The relative coloration of the pare depends of the corporeality of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes.

Melanin occurs in ii primary forms. Eumelanin exists as blackness and chocolate-brown, whereas pheomelanin provides a carmine color. Dark-skinned individuals produce more than melanin than those with pale peel. Exposure to the UV rays of the sun or a tanning salon causes melanin to exist manufactured and congenital up in keratinocytes, equally sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The accumulation of melanin in keratinocytes results in the darkening of the pare, or a tan. This increased melanin accumulation protects the DNA of epidermal cells from UV ray impairment and the breakdown of folic acid, a nutrient necessary for our health and well-existence. In contrast, also much melanin tin can interfere with the production of vitamin D, an important nutrient involved in calcium absorption. Thus, the amount of melanin present in our skin is dependent on a balance between bachelor sunlight and folic acid destruction, and protection from UV radiation and vitamin D production.

It requires about ten days later on initial sunday exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to endure sunburns of the epidermis initially. Night-skinned individuals tin also go sunburns, but are more protected than are stake-skinned individuals. Melanosomes are temporary structures that are somewhen destroyed by fusion with lysosomes; this fact, along with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.

Too much dominicus exposure tin can eventually pb to wrinkling due to the devastation of the cellular structure of the skin, and in severe cases, tin cause sufficient DNA harm to result in skin cancer. When there is an irregular aggregating of melanocytes in the skin, freckles appear. Moles are larger masses of melanocytes, and although well-nigh are benign, they should be monitored for changes that might indicate the presence of cancer ((Figure)).

Moles

Moles range from benign accumulations of melanocytes to melanomas. These structures populate the landscape of our skin. (credit: the National Cancer Institute)

Disorders of the…

Integumentary System The showtime matter a clinician sees is the peel, and so the examination of the skin should be office of whatsoever thorough physical examination. Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, touch the appearance of the pare and its accessory organs. Although neither is fatal, information technology would be hard to claim that they are beneficial, at least to the individuals so affected.

Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, pilus, and optics. The defect 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 peel and hair. Recollect that melanin helps protect the skin from the harmful effects of UV radiations. Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and peel cancer. They too tend to be more sensitive to calorie-free and have vision problems due to the lack of pigmentation on the retinal wall. Treatment of this disorder usually involves addressing the symptoms, such every bit limiting UV light exposure to the skin and eyes. In vitiligo, the melanocytes in certain areas lose their ability to produce melanin, mayhap due to an autoimmune reaction. This leads to a loss of color in patches ((Figure)). Neither albinism nor vitiligo straight affects the lifespan of an individual.

Vitiligo

Individuals with vitiligo experience depigmentation that results in lighter colored patches of skin. The condition is especially noticeable on darker skin. (credit: Klaus D. Peter)

Other changes in the advent of skin coloration tin be indicative of diseases associated with other body systems. Liver disease or liver cancer can crusade the accumulation of bile and the xanthous pigment bilirubin, leading to the skin appearing yellowish or jaundiced (jaune is the French word for "yellow"). Tumors of the pituitary gland tin can result in the secretion of large amounts of melanocyte-stimulating hormone (MSH), which results in a darkening of the pare. Similarly, Addison'south disease tin can stimulate the release of backlog amounts of adrenocorticotropic hormone (ACTH), which can give the skin a deep bronze colour. A sudden drop in oxygenation tin can bear upon skin color, causing the skin to initially turn cadaverous (white). With a prolonged reduction in oxygen levels, dark red deoxyhemoglobin becomes dominant in the claret, making the skin announced blue, a status referred to as cyanosis (kyanos is the Greek discussion for "blue"). This happens when the oxygen supply is restricted, equally when someone is experiencing difficulty in breathing because of asthma or a heart attack. Withal, in these cases the result on skin color has nix do with the skin's pigmentation.

This ABC video follows the story of a pair of congenial African-American twins, i of whom is albino. Watch this video to learn virtually the challenges these children and their family face. Which ethnicities exercise you think are exempt from the possibility of albinism?

Affiliate Review

The skin is composed of two major layers: a superficial epidermis and a deeper dermis. The epidermis consists of several layers showtime with the innermost (deepest) stratum basale (germinatum), followed past the stratum spinosum, stratum granulosum, stratum lucidum (when present), and ending with the outermost layer, the stratum corneum. The topmost layer, the stratum corneum, consists of dead cells that shed periodically and is progressively replaced past cells formed from the basal layer. The stratum basale likewise contains melanocytes, cells that produce melanin, the pigment primarily responsible for giving skin its color. Melanin is transferred to keratinocytes in the stratum spinosum to protect cells from UV rays.

The dermis connects the epidermis to the hypodermis, and provides strength and elasticity due to the presence of collagen and elastin fibers. Information technology has but 2 layers: the papillary layer with papillae that extend into the epidermis and the lower, reticular layer equanimous of loose connective tissue. The hypodermis, deep to the dermis of skin, is the connective tissue that connects the dermis to underlying structures; it also harbors adipose tissue for fat storage and protection.

Interactive Link Questions

The peel consists of two layers and a closely associated layer. View this blitheness to learn more about layers of the pare. What are the basic functions of each of these layers?

The epidermis provides protection, the dermis provides support and flexibility, and the hypodermis (fat layer) provides insulation and padding.

(Figure) If you zoom on the cells at the outermost layer of this section of skin, what do you discover nearly the cells?

(Figure) These cells do non have nuclei, so you can deduce that they are dead. They appear to be sloughing off.

(Figure) If you zoom on the cells of the stratum spinosum, what is distinctive almost them?

(Effigy) These cells have desmosomes, which give the cells their spiny advent.

This ABC video follows the story of a pair of fraternal African-American twins, one of whom is albino. Scout this video to learn about the challenges these children and their family face. Which ethnicities do you think are exempt from the possibility of albinism?

Review Questions

The papillary layer of the dermis is nigh closely associated with which layer of the epidermis?

1. stratum spinosum
2. stratum corneum
3. stratum granulosum
4. stratum basale

Langerhans cells are ordinarily institute in the ________.

1. stratum spinosum
2. stratum corneum
3. stratum granulosum
4. stratum basale

The papillary and reticular layers of the dermis are composed mainly of ________.

1. melanocytes
2. keratinocytes
3. connective tissue
4. adipose tissue

Collagen lends ________ to the skin.

1. elasticity
2. construction
3. color
4. UV protection

Which of the following is not a function of the hypodermis?

1. protects underlying organs
2. helps maintain body temperature
3. source of blood vessels in the epidermis
4. a site to long-term energy storage

Critical Thinking Questions

What determines the color of skin, and what is the process that darkens skin when it is exposed to UV light?

The paint melanin, produced past melanocytes, is primarily responsible for skin color. Melanin comes in unlike shades of brown and blackness. Individuals with darker pare have darker, more abundant melanin, whereas fair-skinned individuals have a lighter shade of skin and less melanin. Exposure to UV irradiation stimulates the melanocytes to produce and secrete more melanin.

Cells of the epidermis derive from stem cells of the stratum basale. Describe how the cells change equally they become integrated into the unlike layers of the epidermis.

As the cells motility into the stratum spinosum, they begin the synthesis of keratin and extend cell processes, desmosomes, which link the cells. As the stratum basale continues to produce new cells, the keratinocytes of the stratum spinosum are pushed into the stratum granulosum. The cells become flatter, their prison cell membranes thicken, and they generate large amounts of the proteins keratin and keratohyalin. The nuclei and other cell organelles disintegrate every bit the cells dice, leaving behind the keratin, keratohyalin, and prison cell membranes that form the stratum lucidum and the stratum corneum. The keratinocytes in these layers are mostly dead and flattened. Cells in the stratum corneum are periodically shed.

Glossary

albinism

genetic disorder that affects the pare, in which at that place is no melanin production

basal prison cell

blazon of stalk cell found in the stratum basale and in the hair matrix that continually undergoes prison cell division, producing the keratinocytes of the epidermis

dermal papilla

(plural = dermal papillae) extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis

dermis

layer of skin between the epidermis and hypodermis, equanimous mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures

desmosome

structure that forms an impermeable junction between cells

elastin fibers

fibers made of the poly peptide elastin that increment the elasticity of the dermis

eleiden

clear protein-bound lipid institute in the stratum lucidum that is derived from keratohyalin and helps to forbid h2o loss

epidermis

outermost tissue layer of the skin

hypodermis

connective tissue connecting the integument to the underlying os and muscle

integumentary system

skin and its accessory structures

keratin

type of structural protein that gives skin, hair, and nails its hard, h2o-resistant properties

keratinocyte

prison cell that produces keratin and is the most predominant type of cell found in the epidermis

keratohyalin

granulated protein constitute in the stratum granulosum

Langerhans prison cell

specialized dendritic jail cell institute in the stratum spinosum that functions as a macrophage

melanin

pigment that determines the color of pilus and skin

melanocyte

cell found in the stratum basale of the epidermis that produces the pigment melanin

melanosome

intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis

Merkel jail cell

receptor cell in the stratum basale of the epidermis that responds to the sense of touch on

papillary layer

superficial layer of the dermis, made of loose, areolar connective tissue

reticular layer

deeper layer of the dermis; it has a reticulated appearance due to the presence of abundant collagen and elastin fibers

stratum basale

deepest layer of the epidermis, made of epidermal stalk cells

stratum corneum

most superficial layer of the epidermis

stratum granulosum

layer of the epidermis superficial to the stratum spinosum

stratum lucidum

layer of the epidermis between the stratum granulosum and stratum corneum, constitute just in thick pare covering the palms, soles of the feet, and digits

stratum spinosum

layer of the epidermis superficial to the stratum basale, characterized by the presence of desmosomes

vitiligo

skin condition in which melanocytes in certain areas lose the ability to produce melanin, possibly due an autoimmune reaction that leads to loss of colour in patches

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Source: https://opentextbc.ca/anatomyandphysiologyopenstax/chapter/layers-of-the-skin/

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