They are formed due to the abrasion on the skin as a result of an elliptical-type motion. The papillary layer is made up of areolar connective tissue and the underlying reticular layer is composed of dense irregular connective tissue.
This dermal part of the skin organ is vasculated has blood vessels and is innervated has nerves. As described earlier, the dermis is sparsely populated with fibroblasts that produce collagen and elastin fibers in the extracellular matrix.
This leads to a strong and elastic tissue structure. The matrix can also contain mast cells involved in allergic reactions. The fibroblasts are dispersed within the collagen and elastin fibers of the areolar tissue loose connective tissue of the papillary layer. This forms a loose mat, which contains an abundance of small blood vessels.
The dermal papillae with blood capillaries interdigitate become interlocked with the epidermal ridges of the stratum basale. In addition, the papillary layer contains phagocytes — defensive cells that help fight bacteria or other infections that have breached the skin. This layer is also interspersed with lymph vessels and sensory receptors. Fibrocytes form the bundles of collagen that extend into the papillary layer and the hypodermis, making these layers hard to distinguish. The flexible collagen provides structure and strength, while elastin lends limited elasticity to the skin.
Collagen also binds with water, keeping the skin hydrated. Dehydration causes a loss of turgor; if the skin of a dehydrated person is pinched it remains domed and does not immediately flatten out. Collagen injections and Retin-A creams help restore skin turgor by introducing collagen externally in the former case or by stimulating blood flow and repair of the dermis in the latter case.
The hypodermis also called the subcutis or subcutaneous layer functions to connect the integument epidermis and dermis to the underlying muscles and organs.
The hypodermis is not considered part of the skin, but has several important functions. Like the dermis, the hypodermis is made up of areolar tissue, collagen, and elastic fibers, providing it with some elasticity. Additionally, it contains adipose tissue, which functions as a mode of fat storage. The hypodermis is vascular and contains arteries, veins, and blood capillaries. Adipose tissue present in the hypodermis accumulates fat, which serves as an energy reserve, insulates the body, and prevents heat loss.
The fat distribution changes as our bodies mature and age. It is also hormone-dependent. Men tend to accumulate fat in different areas neck, arms, lower back, and abdomen than do women breasts, hips, thighs, and buttocks. Physical inactivity due to a lack of exercise and sedentary jobs, combined with the consumption of high-calorie foods, has resulted in the highest rates of obesity ever seen in our country.
While accumulation of fat provided an evolutionary advantage to our ancestors, who experienced unpredictable bouts of famine, it is now considered a major health threat. Improved diet and increased exercise are the best ways to control body fat accumulation, especially when it gets to levels that increase the risk of heart disease.
Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. Although these structures appear to be part of the dermis, they are actually derived from the epidermis.
The hair shaft is made of dead, keratinized cells and gets its color from melanin pigments. Nails are also keratinized and protect the extremities of our fingers and toes from mechanical damage. Sweat glands and sebaceous glands produce sweat and sebum, respectively.
Each of these fluids has a role to play in maintaining homeostasis. Sweat helps the body remove excess fluids and electrolyte wastes and also cools down the body surface when it gets overheated. Sebum acts as a natural moisturizer of the dead, flaky outer keratin layer of skin and hair. Sebum is also known for its microbicidal and microbiostatic properties. Privacy Policy. Langerhans cells are smaller than keratinocytes , with relatively clear cytoplasm, usually located within the stratum spinosum or stratum basale.
Langerhans cells are dendritic cells , with extensive cytoplasmic processes extending between keratinocytes to sample intruding antigens throughout the epidermis. Merkel cells named after Friedrich Merkel , b. Their function has long been uncertain, but they seem to be involved in neural development and tactile sensation. Recent evidence supports a role for Merkel cells in light touch, "suggesting that these cells form an indispensible part of the somatosensory apparatus" Science , ; also see The Journal of Neuroscience 32 10 : , doi: Some uncommon skin cancers derive from Merkel cells.
The dermis consists of dense, fibrous connective tissue whose predominant connective tissue component is collagen. Like ordinary connective tissue throughout the body, connective tissue of the dermis serves several distinct functions. Clinical note : Lines of tension in the dermis, called Langer's lines after Karl Langer , b. Cuts across the lines tend to pull apart, with concommitant tendency toward tissue distortion and scarring, more so than do cuts parallel to the lines. The ground substance of the dermis serves as the substrate for diffusion of nutrients and wastes to and from various other tissue components.
Mast cells , lymphocytes and macrophages in the connective tissue carry out surveillance for the immune system. Finally, the dermis together with its associated blood vessels and nerves is capable of active response to injury, yielding the defensive reaction of inflammation , followed by the healing processes of growth and repair. Within the dermis are embedded several other structures, including epidermal appendages sweat glands and hair follicles as well as blood vessels and nerve endings.
The connective tissue of the dermis grades into hypodermis , without a sharp transition or distinct boundary. Over most of the body, hypodermis is characterized by adipocytes and may comprise a thick layer of adipose tissue.
In some sites e. Hair follicles and sweat glands may extend into hypodermis. The appearance of the skin can have considerable clinical significance. The skin is readily accessible for examination no invasive procedures needed , and its color and texture can reveal much about underlying physiology. Color: Skin is moderately transparent. Light which penetrates the skin is reflected back from varying depths by epidermal cells, by collagen, and by blood.
Recent research: "Shedding light on skin color," Science If the epidermis is not heavily pigmented, light readily penetrates into the dermis. Collagen scatters light from the dermis without altering its color. Hence, the whiteness of "white" skin is primarily a reflection of collagen. Hemoglobin in red blood cells scatters red light and is responsible for the pinkness of unpigmented skin. The relative amount of pink in any given patch of skin reflects how closely blood approaches the base of the epidermis i.
Each of these elements contributes to the apparent color of skin. Variations in skin color in different parts of the body see regional differences are based on variations in these elements, most especially the amount of pigment , the thickness of dermis , and the degree of perfusion in dermal capillaries. Perhaps most significantly, blood flow through the dermis is highly variable and is regulated in response to many conditions heat, pain, fluid balance, inflammation, emotional reaction.
Resulting variations in pinkness can provide indicators of underlying physiology, both locally and systemically. Obvious examples include inflammation , overheating , dehydration , shock , and even embarrassment i. Texture: Skin texture is affected the thickness and smoothness of the epidermis, by the quality of fibers in the dermis, and by the amount of fluid in dermal connective tissue. Because the epidermis is continually being replenished by cell divisions among basal keratinocytes and because this tissue is exposed to a variety of insults, the epidermis is especially prone to disturbances of growth.
See any pathology book for examples. The connective tissue fibers of the skin are permanent, enduring without replacement except by repair after injury throughout life. Although collagen is quite durable, elastin commonly deteriorates with age and especially with repeated exposure to sunlight and loses its elasticity. This is easily demonstrated by a "pinch test. Elderly skin commonly remains in its deformed position, returning more slowly if at all.
Both edema accumulation of excess fluid in connective tissue and dehydration can dramatically alter the appearance of skin. Skin includes several specialized structures , including epidermal appendages sweat glands , hair follicles , nails as well as blood vessels and nerve endings which travel through the dermis. Epidermal appendages play an especially important role in recovery from superficial scrapes and burns. Third-degree burns are so serious precisely because tissue damage extends deep enough into the dermis to destroy these sources of replacement cells.
Sweat glands are simple tubular glands lined by cuboidal epithelium. The secretory portion of the gland lies deep in the dermis, where the tubule is twisted into a fairly compact tangle.
A duct communicates outward through the overlying dermis and the epidermis. The secretory portion is comprised of larger cells than the duct. These cells form a simple cuboidal epithelium , along with interspersed myoepithelial cells which can expel sweat by contraction.
Cells comprising the duct, or conducting portion of the tubule, usually form a two-layered stratified cuboidal epithelium. These cells are usually stained more intensely than those comprising the secretory portion of the tubule.
Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and skin cancer. They also tend to be 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 Figure. Neither albinism nor vitiligo directly affects the lifespan of an individual.
Other changes in the appearance of skin coloration can be indicative of diseases associated with other body systems. 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. A sudden drop in oxygenation can affect skin color, causing the skin to initially turn ashen white.
This happens when the oxygen supply is restricted, as when someone is experiencing difficulty in breathing because of asthma or a heart attack. This ABC video follows the story of a pair of fraternal African-American twins, one of whom is albino. Watch 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?
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 by 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 by cells formed from the basal layer. The stratum basale also 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. 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 skin, is the connective tissue that connects the dermis to underlying structures; it also harbors adipose tissue for fat storage and protection.
The skin consists of two layers and a closely associated layer. 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 notice about the cells?
Figure These cells do not 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 about them? Figure These cells have desmosomes, which give the cells their spiny appearance. The papillary layer of the dermis is most closely associated with which layer of the epidermis? What determines the color of skin, and what is the process that darkens skin when it is exposed to UV light?
The pigment melanin, produced by melanocytes, is primarily responsible for skin color. Melanin comes in different shades of brown and black. Individuals with darker skin 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 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 as the cells die, leaving behind the keratin, keratohyalin, and 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. Skip to content The Integumentary System. Learning Objectives By the end of this section, you will be able to: 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 skin pigmentation.
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, hair follicles, sweat glands, and other structures.
Beneath the dermis lies the hypodermis, which is composed mainly of loose connective and fatty tissues. The Epidermis The epidermis is composed of keratinized, stratified squamous epithelium. Thin Skin versus Thick Skin. These slides show cross-sections of the epidermis and dermis of a thin and b thick skin.
Note the significant difference in the thickness of the epithelial layer of the thick skin. 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 often described as being keratinized stratified squamous epithelium. 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.
Layers of the Epidermis. The epidermis of thick skin has five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. Stratum Spinosum As the name suggests, the stratum spinosum is spiny in appearance due to the protruding cell processes that join the cells via a structure called a desmosome. 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 different.
Stratum Granulosum The stratum granulosum has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum.
Stratum Lucidum The stratum lucidum is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. Stratum Corneum The stratum corneum is the most superficial layer of the epidermis and is the layer exposed to the outside environment see 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 one to the other, making the border between the two somewhat indistinct.
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