Art Labeling Activity the Structure of the Epidermis (2022)

Learning Objectives

  • Identify the components of the integumentary system
  • Describe the layers of the skin 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 role of melanocytes in peel pigmentation

Although you may not typically call up of the skin as an organ, it is in fact made of tissues that work together as a unmarried construction to perform unique and critical functions. The skin and its accessory structures make upwardly theintegumentary system, which provides the body with overall protection. The peel is made of multiple layers of cells and tissues, which are held to underlying structures past connective tissue (Effigy 1). The deeper layer of pare 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.

Art Labeling Activity the Structure of the Epidermis (1)

Figure one.Layers of Pare.
The skin is equanimous of two master layers: the epidermis, made of closely packed epithelial cells, and the dermis, made of dense, irregular connective tissue that houses blood vessels, hair follicles, sweat glands, and other structures. Below the dermis lies the hypodermis, which is composed mainly of loose connective and fat tissues.

The skin consists of two principal layers and a closely associated layer. View thisblithenessto learn more about layers of the skin. What are the bones functions of each of these layers?

The Epidermis

Theepidermisis composed of keratinized, stratified squamous epithelium. Information technology is made of iv or five layers of epithelial cells, depending on its location in the body. It does non have any blood vessels within it (i.eastward., it is avascular). Peel that has 4 layers of cells is referred to equally “thin skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Most of the skin tin can be classified as sparse peel. “Thick skin” is institute only on the palms of the hands and the soles of the feet. It has a 5th layer, called the stratum lucidum, located between the stratum corneum and the stratum granulosum (Effigy 2).

Art Labeling Activity the Structure of the Epidermis (2)

Figure2.Thin Skin versus Thick Peel.
These slides evidence cross-sections of the epidermis and dermis of (a) sparse and (b) thick skin. Note the significant deviation in the thickness of the epithelial layer of the thick skin. From peak, LM × 40, LM × 40. (Micrographs provided by the Regents of University of Michigan Medical Schoolhouse © 2012)

The cells in all of the layers except the stratum basale are called keratinocytes. Akeratinocyteis a jail cell that manufactures and stores the protein keratin.Keratinis an intracellular fibrous poly peptide that gives pilus, nails, and peel their hardness and water-resistant properties. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced past cells from the deeper layers (Figure 3).

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Art Labeling Activity the Structure of the Epidermis (3)

Effigy 3.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 being keratinized stratified squamous epithelium. LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

View the Academy of Michigan WebScope at 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 observe about the cells?

Stratum Basale

Thestratum basale(also chosen 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 bond 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 strength of the connection between the epidermis and dermis; the greater the folding, the stronger the connections made (Figure 4).

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Effigy4.Layers of the Epidermis.
The epidermis of thick skin has v layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

The stratum basale is a single layer of cells primarily fabricated of basal cells. Abasal jail cellis a cuboidal-shaped stalk cell that is a precursor 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. As new cells are formed, the existing cells are pushed superficially away from the stratum basale. 2 other prison cell types are found dispersed among the basal cells in the stratum basale. The first is aMerkel jail cell, which functions equally a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. These cells are specially abundant on the surfaces of the hands and feet. The 2nd is a
melanocyte, a cell that produces the pigment melanin.Melaningives hair and pare its color, and also helps protect the living cells of the epidermis from ultraviolet (UV) radiation damage.

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In a growing fetus, fingerprints form where the cells of the stratum basale see 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 do not change with the growth and crumbling processes.

Stratum Spinosum

As the name suggests, thestratum spinosumis spiny in appearance due to the protruding prison cell processes that join the cells via a structure chosen adesmosome. The desmosomes interlock with each other and strengthen the bond between 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 do not exhibit this characteristic appearance. The stratum spinosum is composed of eight to 10 layers of keratinocytes, formed every bit a result of prison cell segmentation in the stratum basale (Figure5). Interspersed amid the keratinocytes of this layer is a type of dendritic cell called theLangerhans prison cell, which functions as a macrophage by engulfing bacteria, strange particles, and damaged cells that occur in this layer.

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Figurefive.Cells of the Epidermis.
The cells in the different layers of the epidermis originate from basal cells located in the stratum basale, even so the cells of each layer are distinctively different. EM × 2700. (Micrograph provided past the Regents of University of Michigan Medical School © 2012)

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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 department of skin, what do you lot detect almost the cells?

The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid that helps forbid h2o loss from the body, 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

Thestratum granulosumhas a grainy appearance due to further changes to the keratinocytes equally they are pushed from the stratum spinosum. The cells (3 to five layers deep) become flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is fibrous, andkeratohyalin, which accumulates as lamellar granules within the cells (run acrossEffigy iv). These two proteins make up the majority of the keratinocyte mass in the stratum granulosum and give the layer its grainy appearance. The nuclei and other cell organelles disintegrate every bit the cells die, leaving backside the keratin, keratohyalin, and cell membranes that will form the stratum lucidum, the stratum corneum, and the accompaniment structures of hair and nails.

Stratum Lucidum

Thestratum lucidumis a polish, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer of cells is constitute simply in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened (seeFigure iv). These cells are densely packed witheleiden, a clear poly peptide rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.due east., lucid) appearance and provides a bulwark to water.

Stratum Corneum

Thestratum corneumis the most superficial layer of the epidermis and is the layer exposed to the outside environment (run acrossEffigy 4). The increased keratinization (likewise chosen cornification) of the cells in this layer gives it its proper name. There are unremarkably 15 to thirty 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 than delicate, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed upwardly from the stratum granulosum (or stratum lucidum in the example of the palms and soles of anxiety). The entire layer is replaced during a period of about 4 weeks. Cosmetic procedures, such as microdermabrasion, help remove some of the dry out, upper layer and aim to proceed the skin looking “fresh” and salubrious.

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Dermis

Art Labeling Activity the Structure of the Epidermis (6)

Effigy 6.Layers of the Dermis.This stained slide shows the ii components of the dermis—the papillary layer and the reticular layer. Both are made of connective tissue with fibers of collagen extending from i to the other, making the border between the ii somewhat indistinct. The dermal papillae extending into the epidermis belong to the papillary layer, whereas the dense collagen fiber bundles below vest to the reticular layer. LM × x. (credit: modification of work by “kilbad”/Wikimedia Eatables)

Thedermismight be considered the “core” of the integumentary organization (derma– = “skin”), as singled-out from the
epidermis
(epi– = “upon” or “over”) and
hypodermis
(hypo– = “below”). It contains claret and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands. The dermis is made of ii layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts (Figure 6).

Papillary Layer

Thepapillary layeris made 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 form finger-similar dermal papillae (seeFigure vi). Inside the papillary layer are fibroblasts, a small number of fatty 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 have breached the pare. This layer also contains lymphatic capillaries, nerve fibers, and touch receptors chosen the Meissner corpuscles.

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Reticular Layer

Underlying the papillary layer is the much thickerreticular 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 fibersprovide some elasticity to the skin, enabling movement. Collagen fibers provide structure and tensile forcefulness, with strands of collagen extending into both the papillary layer and the hypodermis. In addition, collagen binds water to keep the pare hydrated. Collagen injections and Retin-A creams help restore skin turgor by either introducing collagen externally or stimulating blood menstruum and repair of the dermis, respectively.

Hypodermis

Thehypodermis(also called the subcutaneous layer or superficial fascia) is a layer direct beneath the dermis and serves to connect the skin to the underlying fascia (fibrous tissue) of the bones and muscles. It is not strictly a part of the skin, although the border betwixt 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 fatty storage and provides insulation and cushioning for the integument.

Everyday Connectedness: Lipid Storage

The hypodermis is home to most of the fat that concerns people when they are trying to keep their weight nether control. Adipose tissue present in the hypodermis consists of fatty-storing cells called adipocytes. This stored fat can serve as an energy reserve, insulate the body to prevent estrus loss, and deed every bit 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), besides as genetic factors. Fat distribution changes equally our bodies mature and age. Men tend to accrue fat in different areas (cervix, artillery, lower back, and belly) than practise women (breasts, hips, thighs, and buttocks). The body mass alphabetize (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 tiptop. Therefore, its accuracy as a health indicator can be called into question in individuals who are extremely physically fit.

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In many animals, there is a pattern of storing excess calories as fatty to exist used in times when food is not readily bachelor. In much of the developed world, insufficient exercise coupled with the ready availability and consumption of high-calorie foods take 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, it is now becoming chronic and considered a major health threat. Contempo studies bespeak that a distressing per centum of our population is overweight and/or clinically obese. Not merely is this a problem for the individuals affected, but it also has a astringent impact on our healthcare system. Changes in lifestyle, specifically in diet and practice, are the best ways to control body fatty aggregating, peculiarly when information technology reaches levels that increase the risk of heart disease and diabetes.

Pigmentation

The color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recollect that melanin is produced by cells called melanocytes, which are institute scattered throughout the stratum basale of the epidermis. The melanin is transferred into the keratinocytes via a cellular vesicle called amelanosome(Figure seven).

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Effigy 7.Peel Pigmentation.
The relative coloration of the peel depends of the amount of melanin produced by melanocytes in the stratum basale and taken upwards past keratinocytes.

Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red colour. Dark-skinned individuals produce more melanin than those with pale peel. Exposure to the UV rays of the sun or a tanning salon causes melanin to exist manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The aggregating of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the Deoxyribonucleic acid of epidermal cells from UV ray harm and the breakdown of folic acid, a food necessary for our health and well-being. In contrast, likewise much melanin can interfere with the product of vitamin D, an important food involved in calcium absorption. Thus, the corporeality of melanin nowadays in our pare is dependent on a balance between available sunlight and folic acid devastation, and protection from UV radiation and vitamin D production.

It requires about ten days after initial sunday 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. 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.

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Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular construction of the skin, and in astringent cases, can crusade sufficient DNA damage to result in skin cancer. When there is an irregular accumulation of melanocytes in the skin, freckles announced. Moles are larger masses of melanocytes, and although almost are benign, they should be monitored for changes that might indicate the presence of cancer (Figure 8).

Art Labeling Activity the Structure of the Epidermis (8)

Effigy 8. Moles range from benign accumulations of melanocytes to melanomas. These structures populate the landscape of our skin. (credit: the National Cancer Institute)

Key Takeaways

Disorders of the Integumentary System

The first thing a clinician sees is the peel, and then the exam of the pare should be office of any thorough physical exam. Nigh skin disorders are relatively beneficial, only a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the peel and its accessory organs. Although neither is fatal, information technology would exist hard to claim that they are benign, at least to the individuals and so affected.

Art Labeling Activity the Structure of the Epidermis (9)

Figure 9.Vitiligo.
Individuals with vitiligo feel depigmentation that results in lighter colored patches of skin. The condition is particularly noticeable on darker skin. (credit: Klaus D. Peter)

Albinismis a genetic disorder that affects (completely or partially) the coloring of peel, hair, and eyes. The defect is primarily due to the disability 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 pilus. Recall that melanin helps protect the skin from the harmful furnishings of UV radiation. Individuals with albinism tend to need more protection from UV radiation, as they are more than prone to sunburns and skin cancer. They also tend to be more sensitive to light and accept vision problems due to the lack of pigmentation on the retinal wall. Handling of this disorder unremarkably involves addressing the symptoms, such as limiting UV light exposure to the skin and optics. Invitiligo, 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 (Figure 9). Neither albinism nor vitiligo directly affects the lifespan of an individual.

Other changes in the advent of skin coloration can be indicative of diseases associated with other torso systems. Liver affliction or liver cancer can cause the accumulation of bile and the yellow pigment bilirubin, leading to the pare appearing yellow or jaundiced (jauneis the French word for “yellow”). Tumors of the pituitary gland can result in the secretion of big amounts of melanocyte-stimulating hormone (MSH), which results in a darkening of the skin. Similarly, Addison’due south disease can stimulate the release of excess amounts of adrenocorticotropic hormone (ACTH), which can give the skin a deep bronze colour. A sudden drop in oxygenation can touch on skin color, causing the skin to initially plough ashen (white). With a prolonged reduction in oxygen levels, night red deoxyhemoglobin becomes dominant in the blood, making the pare appear blue, a condition referred to equally cyanosis (kyanosis the Greek word for “blue”). This happens when the oxygen supply is restricted, as when someone is experiencing difficulty in breathing because of asthma or a heart assail. Yet, in these cases the result on peel color has nothing do with the skin’s pigmentation.

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Self-Check Questions

Accept the quiz below to check your understanding of the Layers of the Skin:

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