What Skin Layer Produces Melanin

The Integumentary System

Layers of the Skin

OpenStaxCollege

Learning Objectives

By the terminate of this department, yous will be able to:

• Place the components of the integumentary system
• Depict the layers of the peel and the functions of each layer
• Identify and describe the hypodermis and deep fascia
• Describe the role of keratinocytes and their life cycle
• Describe the function of melanocytes in skin pigmentation

Although you may not typically think of the skin as an organ, information technology is in fact fabricated of tissues that work together as a unmarried structure to perform unique and critical functions. The skin and its accessory structures make up the integumentary system, which provides the body with overall protection. The pare is made of multiple layers of cells and tissues, which are held to underlying structures past connective tissue ([link]). 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 brain.

Layers of Skin

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

The skin consists of two chief layers and a closely associated layer. View this animation to learn 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 have any claret vessels within it (i.e., it is avascular). Peel that has four layers of cells is referred to equally "thin pare." From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Most of the skin tin be classified equally thin skin. "Thick skin" is found simply 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 ([link]).

Thin Skin versus Thick Skin

These slides bear witness cross-sections of the epidermis and dermis of (a) sparse and (b) thick skin. Notation the significant difference in the thickness of the epithelial layer of the thick skin. From tiptop, LM × 40, LM × 40. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)

The cells in all of the layers except the stratum basale are called keratinocytes. A keratinocyte is a jail cell that manufactures and stores the protein keratin. Keratin is an intracellular fibrous poly peptide that gives pilus, nails, and skin their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough abroad, beingness replaced by cells from the deeper layers ([link]).

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, so the whole epithelium is frequently described as existence keratinized stratified squamous epithelium. LM × xl. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

View the University of Michigan WebScope to explore the tissue sample in greater detail. If you lot zoom on the cells at the outermost layer of this section of skin, what do you 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, beneath which lie the layers of the dermis. The cells in the stratum basale bond to 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 increase the strength of the connection between the epidermis and dermis; the greater the folding, the stronger the connections made ([link]).

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 unmarried layer of cells primarily made of basal cells. A basal cell is a cuboidal-shaped stem prison cell that is a precursor of the keratinocytes of the epidermis. All of the keratinocytes are produced from this single layer of cells, which are constantly going through mitosis to produce new cells. Every bit new cells are formed, the existing cells are pushed superficially away from the stratum basale. Ii other jail cell types are institute dispersed among the basal cells in the stratum basale. The starting time is a Merkel cell, which functions every bit a receptor and is responsible for stimulating sensory nerves that the encephalon perceives equally impact. These cells are especially abundant on the surfaces of the hands and feet. The second is a melanocyte, a prison cell that produces the pigment melanin. Melanin gives pilus and skin its color, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiations damage.

In a growing fetus, fingerprints course where the cells of the stratum basale encounter the papillae of the underlying dermal layer (papillary layer), resulting in the germination of the ridges on your fingers that you recognize as fingerprints. Fingerprints are unique to each private and are used for forensic analyses because the patterns exercise not alter with the growth and crumbling processes.

Stratum Spinosum

Every bit the name suggests, the stratum spinosum is spiny in appearance due to the protruding jail cell processes that bring together the cells via a construction called a desmosome. The desmosomes interlock with each other and strengthen the bond between the cells. It is interesting to notation that the "spiny" nature of this layer is an antiquity of the staining process. Unstained epidermis samples practice not exhibit this characteristic advent. The stratum spinosum is composed of eight to 10 layers of keratinocytes, formed as a result of cell sectionalization in the stratum basale ([link]). Interspersed amidst the keratinocytes of this layer is a blazon of dendritic cell called the Langerhans cell, which functions equally a macrophage by engulfing leaner, foreign particles, and damaged cells that occur in this layer.

Cells of the Epidermis

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

View the Academy 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 you notice about the cells?

The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid that helps prevent h2o loss from the body, making the peel 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 advent due to farther changes to the keratinocytes every bit they are pushed from the stratum spinosum. The cells (three to v layers deep) get flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is gristly, and keratohyalin, which accumulates every bit lamellar granules within the cells (see [link]). These two proteins make up 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 dice, leaving behind the keratin, keratohyalin, and cell membranes that volition form the stratum lucidum, the stratum corneum, and the accompaniment structures of hair and nails.

Stratum Lucidum

The stratum lucidum is a polish, seemingly translucent layer of the epidermis located only above the stratum granulosum and below the stratum corneum. This sparse layer of cells is institute but in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened (see [link]). These cells are densely packed with eleiden, a clear protein rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.e., lucid) advent 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 [link]). The increased keratinization (too called cornification) of the cells in this layer gives it its name. There are usually 15 to 30 layers of cells in the stratum corneum. This dry, dead layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection confronting abrasion for the more delicate, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed upward from the stratum granulosum (or stratum lucidum in the case of the palms and soles of feet). The unabridged layer is replaced during a menstruum of about 4 weeks. Cosmetic procedures, such every bit microdermabrasion, assistance remove some of the dry, upper layer and aim to keep the skin looking "fresh" and healthy.

Dermis

The dermis might be considered the "core" of the integumentary system (derma- = "skin"), equally singled-out from the epidermis (epi- = "upon" or "over") and hypodermis (hypo- = "below"). It contains blood and lymph vessels, nerves, and other structures, such every bit hair follicles and sweat glands. The dermis is made of 2 layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts ([link]).

Layers of the Dermis

This stained slide shows the 2 components of the dermis—the papillary layer and the reticular layer. Both are made of connective tissue with fibers of collagen extending from one 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 beneath belong to the reticular layer. LM × ten. (credit: modification of work by "kilbad"/Wikimedia Commons)

Papillary Layer

The papillary layer is made of loose, areolar connective tissue, which means the collagen and elastin fibers of this layer form a loose mesh. This superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae (encounter [link]). Inside the papillary layer are fibroblasts, a pocket-size number of fat cells (adipocytes), and an abundance of small blood vessels. In addition, the papillary layer contains phagocytes, defensive cells that help fight bacteria or other infections that take breached the skin. This layer also contains lymphatic capillaries, nerve fibers, and impact receptors chosen 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-like) due to a tight meshwork of fibers. Elastin fibers provide some elasticity to the pare, enabling movement. Collagen fibers provide structure and tensile strength, with strands of collagen extending into both the papillary layer and the hypodermis. In add-on, collagen binds water to keep the skin hydrated. Collagen injections and Retin-A creams assist restore skin turgor past either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively.

Hypodermis

The hypodermis (also 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 non strictly a part of the skin, although the border between the hypodermis and dermis tin can exist 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 Connexion

Lipid Storage
The hypodermis is domicile to well-nigh of the fat that concerns people when they are trying to keep their weight under command. Adipose tissue present in the hypodermis consists of fat-storing cells called adipocytes. This stored fat can serve as an free energy reserve, insulate the body to prevent heat loss, and human activity 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 equally our bodies mature and historic period. Men tend to accumulate fat in dissimilar areas (neck, artillery, lower back, and abdomen) than practice women (breasts, hips, thighs, and buttocks). The body mass alphabetize (BMI) is often used as a measure of fat, although this mensurate is, in fact, derived from a mathematical formula that compares body weight (mass) to height. 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 pattern of storing excess calories as fatty to exist used in times when nutrient is non readily available. In much of the developed world, insufficient exercise coupled with the set up availability and consumption of loftier-calorie foods accept resulted in unwanted accumulations of adipose tissue in many people. Although periodic accumulation of backlog fat may have provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, information technology is now condign chronic and considered a major health threat. Recent studies bespeak that a distressing percentage of our population is overweight and/or clinically obese. Not but is this a trouble for the individuals afflicted, but information technology likewise has a severe impact on our healthcare arrangement. Changes in lifestyle, specifically in diet and practise, are the best ways to command body fatty aggregating, especially when information technology reaches levels that increase the risk of heart disease and diabetes.

Pigmentation

The colour of skin is influenced by 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 chosen a melanosome ([link]).

Skin Pigmentation

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

Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red color. Dark-skinned individuals produce more melanin than those with stake skin. Exposure to the UV rays of the sunday or a tanning salon causes melanin to be manufactured and built upwards in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the Dna of epidermal cells from UV ray damage and the breakup of folic acid, a food necessary for our wellness and well-being. In contrast, too much melanin 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 available sunlight and folic acrid devastation, and protection from UV radiation and vitamin D production.

Information technology requires about x days after initial sun exposure for melanin synthesis to acme, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially. Dark-skinned individuals can besides get sunburns, only are more protected than are pale-skinned individuals. Melanosomes are temporary structures that are eventually destroyed by fusion with lysosomes; this fact, forth with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.

Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular construction of the skin, and in severe cases, tin crusade sufficient Deoxyribonucleic acid 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 virtually are benign, they should be monitored for changes that might bespeak the presence of cancer ([link]).

Moles

Moles range from beneficial accumulations of melanocytes to melanomas. These structures populate the mural of our peel. (credit: the National Cancer Institute)

Disorders of the…

Integumentary Arrangement
The first thing a clinician sees is the skin, and so the exam of the skin should exist part of whatsoever thorough physical exam. Near peel disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, bear on the appearance of the peel and its accessory organs. Although neither is fatal, it would exist hard to claim that they are benign, at least to the individuals and so afflicted.

Albinism is a genetic disorder that affects (completely or partially) the coloring of peel, pilus, and eyes. 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 pare and hair. Recall 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 than decumbent to sunburns and peel cancer. They also tend to exist more sensitive to light and have vision problems due to the lack of pigmentation on the retinal wall. 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 ([link]). Neither albinism nor vitiligo directly affects the lifespan of an private.

Vitiligo

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

Other changes in the advent of peel coloration 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 peel appearing xanthous or jaundiced (jaune is the French word for "yellowish"). 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. Similarly, Addison'southward 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 bear on skin color, causing the pare to initially turn ashen (white). With a prolonged reduction in oxygen levels, dark red deoxyhemoglobin becomes dominant in the blood, making the skin appear blueish, a condition referred to as cyanosis (kyanos is the Greek give-and-take for "blue"). This happens when the oxygen supply is restricted, every bit when someone is experiencing difficulty in animate because of asthma or a eye attack. However, in these cases the effect on pare colour has nothing practice with the skin's pigmentation.

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

Chapter Review

The skin is composed of two major layers: a superficial epidermis and a deeper dermis. The epidermis consists of several layers beginning 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 expressionless cells that shed periodically and is progressively replaced by cells formed from the basal layer. The stratum basale also contains melanocytes, cells that produce melanin, the paint 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 force and elasticity due to the presence of collagen and elastin fibers. It has only two layers: the papillary layer with papillae that extend into the epidermis and the lower, reticular layer composed of loose connective tissue. The hypodermis, deep to the dermis of pare, is the connective tissue that connects the dermis to underlying structures; it also harbors adipose tissue for fatty storage and protection.

Interactive Link Questions

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

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

[link] If you zoom on the cells at the outermost layer of this section of skin, what practise you lot discover well-nigh the cells?

[link] These cells do not have nuclei, so you can deduce that they are dead. They announced to exist sloughing off.

[link] If you lot zoom on the cells of the stratum spinosum, what is distinctive nearly them?

[link] These cells have desmosomes, which requite the cells their spiny appearance.

This ABC video follows the story of a pair of fraternal African-American twins, 1 of whom is albino. Sentinel this video to learn nearly the challenges these children and their family face. Which ethnicities practise y'all recollect are exempt from the possibility of albinism?

In that location are none.

Review Questions

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

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

D

Langerhans cells are ordinarily found in the ________.

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

A

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

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

C

Collagen lends ________ to the skin.

1. elasticity
2. structure
3. colour
4. UV protection

B

Which of the following is non a function of the hypodermis?

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

C

Disquisitional Thinking Questions

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

The pigment melanin, produced past melanocytes, is primarily responsible for pare color. Melanin comes in unlike shades of brown and black. Individuals with darker pare have darker, more abundant melanin, whereas blanched 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 as they become integrated into the different layers of the epidermis.

As the cells move 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 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 die, leaving behind the keratin, keratohyalin, and cell membranes that grade 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 skin, in which there is no melanin production

basal prison cell

blazon of stem cell plant in the stratum basale and in the hair matrix that continually undergoes 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, composed 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 protein elastin that increase the elasticity of the dermis

eleiden

clear poly peptide-spring lipid found in the stratum lucidum that is derived from keratohyalin and helps to prevent water loss

epidermis

outermost tissue layer of the pare

hypodermis

connective tissue connecting the integument to the underlying bone and muscle

integumentary organisation

skin and its accessory structures

keratin

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

keratinocyte

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

keratohyalin

granulated protein found in the stratum granulosum

Langerhans jail cell

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

melanin

pigment that determines the color of hair and skin

melanocyte

cell constitute in the stratum basale of the epidermis that produces the paint 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

papillary layer

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

reticular layer

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

stratum basale

deepest layer of the epidermis, made of epidermal stem 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, found only in thick pare roofing the palms, soles of the feet, and digits

stratum spinosum

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

vitiligo

peel condition in which melanocytes in certain areas lose the power to produce melanin, possibly due an autoimmune reaction that leads to loss of color in patches

Source: http://pressbooks-dev.oer.hawaii.edu/anatomyandphysiology/chapter/layers-of-the-skin/

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