Anatomy and Physiology I

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Studying Targets

  • Determine the elements of the integumentary system
  • Describe the layers of the pores and skin and the capabilities of every layer
  • Determine and describe the hypodermis and deep fascia
  • Describe the function of keratinocytes and their life cycle
  • Describe the function of melanocytes in pores and skin pigmentation

Though chances are you’ll not sometimes consider the pores and skin as an organ, it’s in actual fact fabricated from tissues that work collectively as a single construction to carry out distinctive and significant capabilities. The pores and skin and its accent constructions make up the integumentary system, which offers the physique with total safety. The pores and skin is fabricated from a number of layers of cells and tissues, that are held to underlying constructions by connective tissue (Determine 1). The deeper layer of pores and skin is properly vascularized (has quite a few blood vessels). It additionally has quite a few sensory, and autonomic and sympathetic nerve fibers making certain communication to and from the mind.

This illustration shows a cross section of skin tissue. The outermost layer is called the epidermis, and occupies one fifth of the cross section. Several hairs are emerging from the surface. The epidermis dives around one of the hairs, forming a follicle. The middle layer is called the dermis, which occupies four fifths of the cross section. The dermis contains an erector pilli muscle connected to one of the follicles. The dermis also contains an eccrine sweat gland, composed of a bunch of tubules. One tubule travels up from the bunch, through the epidermis, opening onto the surface a pore. There are two string-like nerves travelling vertically through the dermis. The right nerve is attached to a Pacinian corpuscle, which is a yellow structure consisting of concentric ovals similar to an onion. The lowest level of the skin, the hypodermis, contains fatty tissue, arteries, and veins. Blood vessels travel from the hypodermis and connect to hair follicles and erector pilli muscle in the dermis.

Determine 1. Layers of Pores and skin. The pores and skin consists of two important layers: the dermis, fabricated from intently packed epithelial cells, and the dermis, fabricated from dense, irregular connective tissue that homes blood vessels, hair follicles, sweat glands, and different constructions. Beneath the dermis lies the hypodermis, which consists primarily of unfastened connective and fatty tissues.

Studying: Layers of the pores and skin diagram

The pores and skin consists of two important layers and a intently related layer. View this animation to be taught extra about layers of the pores and skin. What are the essential capabilities of every of those layers?

The Dermis

The dermis consists of keratinized, stratified squamous epithelium. It’s made of 4 or 5 layers of epithelial cells, relying on its location within the physique. It doesn’t have any blood vessels inside it (i.e., it’s avascular). Pores and skin that has 4 layers of cells is known as “skinny pores and skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. Many of the pores and skin will be categorised as skinny pores and skin. “Thick pores and skin” is discovered solely on the palms of the arms and the soles of the toes. It has a fifth layer, known as the stratum lucidum, situated between the stratum corneum and the stratum granulosum (Determine 2).

Part A is a micrograph showing a cross section of thin skin. The topmost layer is a thin, translucent layer with irregular texture and areas where cells are sloughing off. The deepest layer is dark purple and extends into the third layer with finger like projections. The third light purple layer contains thin bands of fibers and small, dark cells. The fourth, and deepest layer, is darker than the third layer, but is still light purple. It contains thick fiber bands that are loosely packed. Part B is a magnified view of the epidermis of thick skin. It shows the topmost layer is five times thicker than the topmost layer of thin skin. The topmost layer of thick skin is also denser and less translucent than the topmost layer of thin skin.

Determine 2. Skinny Pores and skin versus Thick Pores and skin. These slides present cross-sections of the dermis and dermis of (a) skinny and (b) thick pores and skin. Observe the numerous distinction within the thickness of the epithelial layer of the thick pores and skin. From high, LM × 40, LM × 40. (Micrographs supplied by the Regents of College of Michigan Medical College © 2012)

The cells in all the layers besides the stratum basale are known as keratinocytes. A keratinocyte is a cell that manufactures and shops the protein keratin. Keratin is an intracellular fibrous protein that offers hair, nails, and pores and skin their hardness and water resistant properties. The keratinocytes within the stratum corneum are lifeless and often slough away, being changed by cells from the deeper layers (Determine 3).

The outer layer of cells in this micrograph is the thinnest layer and stained deep purple due to full keratinization of dead cells. The next layer occupies one quarter of the micrograph, is lightly stained, and is a dense collection of cells. The third layer from the top is mostly white, with lightly stained, loosely-packed strands radiating in random directions. The bottom-most layer is densely-packed, with thick bands of highly organized muscle tissue that are darkly stained.

Determine 3. Dermis. The dermis is epithelium composed of a number of layers of cells. The basal layer consists of cuboidal cells, whereas the outer layers are squamous, keratinized cells, so the entire epithelium is commonly described as being keratinized stratified squamous epithelium. LM × 40. (Micrograph supplied by the Regents of College of Michigan Medical College © 2012)

View the College of Michigan WebScope at to discover the tissue pattern in better element. When you zoom on the cells on the outermost layer of this part of pores and skin, what do you discover concerning the cells?

Stratum Basale

The stratum basale (additionally known as the stratum germinativum) is the deepest epidermal layer and attaches the dermis to the basal lamina, beneath which lie the layers of the dermis. The cells within the stratum basale bond to the dermis by way of intertwining collagen fibers, known as the basement membrane. A finger-like projection, or fold, generally known as the dermal papilla (plural = dermal papillae) is discovered within the superficial portion of the dermis. Dermal papillae improve the power of the connection between the dermis and dermis; the better the folding, the stronger the connections made (Determine 4).

This illustration shows a cross section of the epidermis. The cells of the innermost layer, the stratum basale, are large and have a purple nucleus. The stratum basale curls around the dermis, which projects into the epidermis. The stratum basale contains four layers of large, triangle-shaped keratinocytes. Fibers are visible within the spaces between keratinocytes in the stratum basale. A melanocyte is also present in this layer. The melanocyte possesses finger-like projections extending from its main cell body. The projections branch through the extracellular spaces between nearby keratinocytes. Above the stratum basale is the stratum spinosum which consists of 8 layers of oval-shaped keratinocytes. The nucleus is present in these keratinocytes, but has faded to a lighter purple. The stratum granulosum contains five layers of keratinocytes, each containing spots in its cytoplasm, labeled the lamellar granules. The stratum lucidium contains 4 layers of diamond-shaped cells with no nucleus. The stratum corneum contains 9 layers of keratinocytes with no nucleus , nor cytoplasm. A few of the cells in the topmost layer of the stratum corneum are flaking off from the skin.

Determine 4. Layers of the Dermis. The dermis of thick pores and skin has 5 layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

The stratum basale is a single layer of cells primarily fabricated from basal cells. A basal cell is a cuboidal-shaped stem cell that may be a precursor of the keratinocytes of the dermis. All the keratinocytes are produced from this single layer of cells, that are continually going by means of mitosis to supply new cells. As new cells are fashioned, the prevailing cells are pushed superficially away from the stratum basale. Two different cell sorts are discovered dispersed among the many basal cells within the stratum basale. The primary is a Merkel cell, which capabilities as a receptor and is accountable for stimulating sensory nerves that the mind perceives as contact. These cells are particularly ample on the surfaces of the arms and toes. The second is a melanocyte, a cell that produces the pigment melanin. Melanin provides hair and pores and skin its shade, and likewise helps shield the dwelling cells of the dermis from ultraviolet (UV) radiation injury.

In a rising fetus, fingerprints kind the place the cells of the stratum basale meet the papillae of the underlying dermal layer (papillary layer), ensuing within the formation of the ridges in your fingers that you just acknowledge as fingerprints. Fingerprints are distinctive to every particular person and are used for forensic analyses as a result of the patterns don’t change with the expansion and ageing processes.

Stratum Spinosum

Because the title suggests, the stratum spinosum is spiny in look as a result of protruding cell processes that be a part of the cells by way of a construction known as a desmosome. The desmosomes interlock with one another and strengthen the bond between the cells. It’s fascinating to notice that the “spiny” nature of this layer is an artifact of the staining course of. Unstained dermis samples don’t exhibit this attribute look. The stratum spinosum consists of eight to 10 layers of keratinocytes, fashioned on account of cell division within the stratum basale (Determine 5). Interspersed among the many keratinocytes of this layer is a kind of dendritic cell known as the Langerhans cell, which capabilities as a macrophage by engulfing micro organism, overseas particles, and broken cells that happen on this layer.

This micrograph of the epidermis shows stratum corneum as a rough, darkened layer. The next layer, the stratum granulosum, contains white cells with areas of black in their cytoplasm, equal in thickness to the stratum corneum. The third layer, the stratum spinosum, contains large, grayish cells. The stratum spinosum is the thickest layer, occupying half of the micrograph. A hair follicle is embedded in this layer, which is a round structure with black, concentric spots. The fourth layer is the stratum basalis, which contains grayish cells with clear, dark nuclei, similar in thickness to the stratum corneum. The dermis is the deepest layer, and is lightly-colored with interspersed gray cells. A cross-section of a capillary is visible within the dermis.

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Determine 5. Cells of the Dermis. The cells within the totally different layers of the dermis originate from basal cells situated within the stratum basale, but the cells of every layer are distinctively totally different. EM × 2700. (Micrograph supplied by the Regents of College of Michigan Medical College © 2012)

View the College of Michigan WebScope to discover the tissue pattern in better element. When you zoom on the cells on the outermost layer of this part of pores and skin, what do you discover concerning the cells?

The keratinocytes within the stratum spinosum start the synthesis of keratin and launch a water-repelling glycolipid that helps stop water loss from the physique, making the pores and skin comparatively 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 look attributable to additional modifications to the keratinocytes as they’re pushed from the stratum spinosum. The cells (three to 5 layers deep) turn out to be flatter, their cell membranes thicken, and so they generate massive quantities of the proteins keratin, which is fibrous, and keratohyalin, which accumulates as lamellar granules inside the cells (see Determine 4). These two proteins make up the majority of the keratinocyte mass within the stratum granulosum and provides the layer its grainy look. The nuclei and different cell organelles disintegrate because the cells die, abandoning the keratin, keratohyalin, and cell membranes that may kind the stratum lucidum, the stratum corneum, and the accent constructions of hair and nails.

Stratum Lucidum

The stratum lucidum is a clean, seemingly translucent layer of the dermis situated simply above the stratum granulosum and beneath the stratum corneum. This skinny layer of cells is discovered solely within the thick pores and skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are lifeless and flattened (see Determine 4). These cells are densely full of eleiden, a transparent protein wealthy in lipids, derived from keratohyalin, which supplies these cells their clear (i.e., lucid) look and offers a barrier to water.

Stratum Corneum

The stratum corneum is probably the most superficial layer of the dermis and is the layer uncovered to the surface atmosphere (see Determine 4). The elevated keratinization (additionally known as cornification) of the cells on this layer provides it its title. There are often 15 to 30 layers of cells within the stratum corneum. This dry, lifeless layer helps stop the penetration of microbes and the dehydration of underlying tissues, and offers a mechanical safety in opposition to abrasion for the extra delicate, underlying layers. Cells on this layer are shed periodically and are changed by cells pushed up from the stratum granulosum (or stratum lucidum within the case of the palms and soles of toes). The whole layer is changed throughout a interval of about 4 weeks. Beauty procedures, corresponding to microdermabrasion, assist take away among the dry, higher layer and purpose to maintain the pores and skin wanting “contemporary” and wholesome.


This micrograph shows layers of skin in a cross section. The papillary layer of the dermis extends between the downward fingers of the darkly stained epidermis. The papillary layer appears finer than the reticular layer, consisting of smaller, densely-packed fibers. The reticular layer is three times thicker than the papillary layer and contains larger, thicker fibers. The fibers seem more loosely packed than those of the papillary layer, with some separated by empty spaces. Both layers of the dermis contain cells with darkly stained nuclei.

Determine 6. Layers of the Dermis. This stained slide reveals the 2 elements of the dermis—the papillary layer and the reticular layer. Each are fabricated from connective tissue with fibers of collagen extending from one to the opposite, making the border between the 2 considerably vague. The dermal papillae extending into the dermis belong to the papillary layer, whereas the dense collagen fiber bundles beneath belong to the reticular layer. LM × 10. (credit score: modification of labor by “kilbad”/Wikimedia Commons)

The dermis is likely to be thought of the “core” of the integumentary system (derma- = “pores and skin”), as distinct from the dermis (epi- = “upon” or “over”) and hypodermis (hypo- = “beneath”). It incorporates blood and lymph vessels, nerves, and different constructions, corresponding to hair follicles and sweat glands. The dermis is fabricated from two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts (Determine 6).

Papillary Layer

The papillary layer is fabricated from unfastened, areolar connective tissue, which implies the collagen and elastin fibers of this layer kind a unfastened mesh. This superficial layer of the dermis initiatives into the stratum basale of the dermis to kind finger-like dermal papillae (see Determine 6). Throughout the papillary layer are fibroblasts, a small variety of fats cells (adipocytes), and an abundance of small blood vessels. As well as, the papillary layer incorporates phagocytes, defensive cells that assist battle micro organism or different infections which have breached the pores and skin. This layer additionally incorporates lymphatic capillaries, nerve fibers, and contact receptors known as the Meissner corpuscles.

Reticular Layer

Underlying the papillary layer is the a lot thicker reticular layer, composed of dense, irregular connective tissue. This layer is properly vascularized and has a wealthy sensory and sympathetic nerve provide. The reticular layer seems reticulated (net-like) attributable to a good meshwork of fibers. Elastin fibers present some elasticity to the pores and skin, enabling motion. Collagen fibers present construction and tensile power, with strands of collagen extending into each the papillary layer and the hypodermis. As well as, collagen binds water to maintain the pores and skin hydrated. Collagen injections and Retin-A lotions assist restore pores and skin turgor by both introducing collagen externally or stimulating blood stream and restore of the dermis, respectively.


The hypodermis (additionally known as the subcutaneous layer or superficial fascia) is a layer immediately beneath the dermis and serves to attach the pores and skin to the underlying fascia (fibrous tissue) of the bones and muscular tissues. It isn’t strictly part of the pores and skin, though the border between the hypodermis and dermis will be tough to tell apart. The hypodermis consists of well-vascularized, unfastened, areolar connective tissue and adipose tissue, which capabilities as a mode of fats storage and offers insulation and cushioning for the integument.

On a regular basis Connection: Lipid Storage

The hypodermis is residence to many of the fats that issues individuals when they’re making an attempt to maintain their weight underneath management. Adipose tissue current within the hypodermis consists of fat-storing cells known as adipocytes. This saved fats can function an power reserve, insulate the physique to forestall warmth loss, and act as a cushion to guard underlying constructions from trauma.

The place the fats is deposited and accumulates inside the hypodermis depends upon hormones (testosterone, estrogen, insulin, glucagon, leptin, and others), in addition to genetic components. Fats distribution modifications as our our bodies mature and age. Males are likely to accumulate fats in numerous areas (neck, arms, decrease again, and stomach) than do ladies (breasts, hips, thighs, and buttocks). The physique mass index (BMI) is commonly used as a measure of fats, though this measure is, in actual fact, derived from a mathematical system that compares physique weight (mass) to peak. Subsequently, its accuracy as a well being indicator will be known as into query in people who’re extraordinarily bodily match.

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In lots of animals, there’s a sample of storing extra energy as fats for use in occasions when meals just isn’t available. In a lot of the developed world, inadequate train coupled with the prepared availability and consumption of high-calorie meals have resulted in undesirable accumulations of adipose tissue in many individuals. Though periodic accumulation of extra fats could have supplied an evolutionary benefit to our ancestors, who skilled unpredictable bouts of famine, it’s now turning into persistent and regarded a significant well being risk. Latest research point out {that a} distressing proportion of our inhabitants is chubby and/or clinically overweight. Not solely is that this an issue for the people affected, nevertheless it additionally has a extreme affect on our healthcare system. Modifications in way of life, particularly in eating regimen and train, are the very best methods to regulate physique fats accumulation, particularly when it reaches ranges that improve the chance of coronary heart illness and diabetes.


The colour of pores and skin is influenced by plenty of pigments, together with melanin, carotene, and hemoglobin. Recall that melanin is produced by cells known as melanocytes, that are discovered scattered all through the stratum basale of the dermis. The melanin is transferred into the keratinocytes by way of a mobile vesicle known as a melanosome (Determine 7).

This figure consists of two diagrams side by side. The right diagram shows development of light colored skin; the left shows development of dark-colored skin. In both, a brown melanocyte sits at the border between the dermis and epidermis. The melanocyte has a large nucleus and six finger-like extensions. These reach between cells of the stratum basalis. Sections of the extensions detach and travel through the skins. These are melanosomes. In the left diagram, both the melanocyte and melanosomes contain melanin particles, shown as dark dots. Melanosomes travel upwards to outer skin layers, releasing melanin. As a result, keratinocytes in the left diagram contain several melanin particles that darken skin color. In light colored skin, the melanocyte contains no melanin. It still releases melanosomes into upper layers of the skin; however, these melanosomes contain no melanin. Therefore, the skin does not darken and remains light.

Determine 7. Pores and skin Pigmentation. The relative coloration of the pores and skin relies upon of the quantity of melanin produced by melanocytes within the stratum basale and brought up by keratinocytes.

Melanin happens in two major kinds. Eumelanin exists as black and brown, whereas pheomelanin offers a crimson shade. Darkish-skinned people produce extra melanin than these with pale pores and skin. Publicity to the UV rays of the solar or a tanning salon causes melanin to be manufactured and constructed up in keratinocytes, as solar publicity stimulates keratinocytes to secrete chemical substances that stimulate melanocytes. The buildup of melanin in keratinocytes leads to the darkening of the pores and skin, or a tan. This elevated melanin accumulation protects the DNA of epidermal cells from UV ray injury and the breakdown of folic acid, a nutrient vital for our well being and well-being. In distinction, an excessive amount of melanin can intervene with the manufacturing of vitamin D, an vital nutrient concerned in calcium absorption. Thus, the quantity of melanin current in our pores and skin relies on a steadiness between obtainable daylight and folic acid destruction, and safety from UV radiation and vitamin D manufacturing.

It requires about 10 days after preliminary solar publicity for melanin synthesis to peak, which is why pale-skinned people are likely to undergo sunburns of the dermis initially. Darkish-skinned people also can get sunburns, however are extra protected than are pale-skinned people. Melanosomes are short-term constructions which might be finally destroyed by fusion with lysosomes; this reality, together with melanin-filled keratinocytes within the stratum corneum sloughing off, makes tanning impermanent.

An excessive amount of solar publicity can finally result in wrinkling as a result of destruction of the mobile construction of the pores and skin, and in extreme instances, may cause adequate DNA injury to end in pores and skin most cancers. When there may be an irregular accumulation of melanocytes within the pores and skin, freckles seem. Moles are bigger plenty of melanocytes, and though most are benign, they need to be monitored for modifications which may point out the presence of most cancers (Determine 8).

Five photos of moles. The three upper photos show moles that are small, flat, and dark brown. The bottom left photo shows a dark black mole that is raised above the skin. The bottom right photo shows a large, raised, reddish mole with protruding hairs.

Determine 8. Moles vary from benign accumulations of melanocytes to melanomas. These constructions populate the panorama of our pores and skin. (credit score: the Nationwide Most cancers Institute)

Key Takeaways

Problems of the Integumentary System

The very first thing a clinician sees is the pores and skin, and so the examination of the pores and skin ought to be a part of any thorough bodily examination. Most pores and skin issues are comparatively benign, however just a few, together with melanomas, will be deadly if untreated. A few the extra noticeable issues, albinism and vitiligo, have an effect on the looks of the pores and skin and its accent organs. Though neither is deadly, it could be arduous to assert that they’re benign, at the very least to the people so troubled.

This photo shows the back of a man’s neck. There is a large, discolored patch of skin at the base of his hairline. The discolored area extends over the ears onto the cheeks, toward the front of the face. The man’s head and facial hair are mostly gray, but white patches of hair are seen above the discolored skin.

Determine 9. Vitiligo. People with vitiligo expertise depigmentation that leads to lighter coloured patches of pores and skin. The situation is very noticeable on darker pores and skin. (credit score: Klaus D. Peter)

Albinism is a genetic dysfunction that impacts (utterly or partially) the coloring of pores and skin, hair, and eyes. The defect is primarily as a result of lack of ability of melanocytes to supply melanin. People with albinism have a tendency to look white or very pale as a result of lack of melanin of their pores and skin and hair. Recall that melanin helps shield the pores and skin from the dangerous results of UV radiation. People with albinism have a tendency to want extra safety from UV radiation, as they’re extra susceptible to sunburns and pores and skin most cancers. Additionally they are typically extra delicate to gentle and have imaginative and prescient issues as a result of lack of pigmentation on the retinal wall. Therapy of this dysfunction often entails addressing the signs, corresponding to limiting UV gentle publicity to the pores and skin and eyes. In vitiligo, the melanocytes in sure areas lose their potential to supply melanin, presumably attributable to an autoimmune response. This results in a lack of shade in patches (Determine 9). Neither albinism nor vitiligo immediately impacts the lifespan of a person.

Different modifications within the look of pores and skin coloration will be indicative of ailments related to different physique programs. Liver illness or liver most cancers may cause the buildup of bile and the yellow pigment bilirubin, resulting in the pores and skin showing yellow or jaundiced (jaune is the French phrase for “yellow”). Tumors of the pituitary gland may end up in the secretion of huge quantities of melanocyte-stimulating hormone (MSH), which ends up in a darkening of the pores and skin. Equally, Addison’s illness can stimulate the discharge of extra quantities of adrenocorticotropic hormone (ACTH), which may give the pores and skin a deep bronze shade. A sudden drop in oxygenation can have an effect on pores and skin shade, inflicting the pores and skin to initially flip ashen (white). With a protracted discount in oxygen ranges, darkish crimson deoxyhemoglobin turns into dominant within the blood, making the pores and skin seem blue, a situation known as cyanosis (kyanos is the Greek phrase for “blue”). This occurs when the oxygen provide is restricted, as when somebody is experiencing issue in respiration due to bronchial asthma or a coronary heart assault. Nonetheless, in these instances the impact on pores and skin shade has nothing do with the pores and skin’s pigmentation.

This ABC video follows the story of a pair of fraternal African-American twins, one among whom is albino. Watch this video to be taught concerning the challenges these youngsters and their household face. Which ethnicities do you assume are exempt from the opportunity of albinism?

Self-Verify Questions

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Learn extra: What Is My Pores and skin Kind?

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