ANP - Integumentary system PDF

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Integumentary system -

Integumentary system → skin + its derivatives (sweat and oil glands, hair, nails) - Roles of skin → Protection from infection, regulate body temp, repairs itself, skin grows with you( as you grow from infant to adult). Skin is an organ. - 2 layers of the skin → epidermis and dermis ● Epidermis → composed of epithelial cells, is the outermost protective shield of the body, superficial layer of skin, composed of keratinized stratified squamous epithelium, is not vascularized (therefore, not blood vessels run through it) ● Dermis → makes up the bulk of the skin, is a tough, leathery layer composed mostly of dense irregular connective tissue. Is underlying and better nourished due to being vascularized. - Only the dermis is vascularized. Nutrients reach the epidermis by diffusing through the tissue fluid from blood vessels in the dermis. - Skin: accounts for about 7% of total body weight in the average adult. Without our skin, we would quickly fall prey to harmful bacteria and perish from water and heat loss ● subcutaneous tissue → tissue deep to the skin, also called hypodermis or superficial fascia.not part of the skin, but it shares some of the skin’s protective functions. It consists mostly of adipose tissue with some areolar connective tissue. - Its roles: 1) stores fats 2) anchors the skin to the underlying structures (mostly to muscles), but loosely enough that the skin can slide relatively freely over those structures 3) Due to the fatty composition, it also acts as a shock absorber and an insulator that reduces heat loss. *Sliding skin protects us by ensuring that everyday bumps often just glance off our bodies ● The epidermis consists of four distinct cell types and four or five distinct layers. - The 4 cell types → keratinocytes, melanocytes, dendritic cells, and tactile epithelial cells. 1) Keratinocytes - Produce keratin

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Keratin → the fibrous protein that helps give the epidermis its protective properties. Is found in epidermis, hair and nails that makes those structures hard and water resistant (water proof). Precursor is kertaphayline Most epidermal cells are keratinocytes. Keratinocytes are tied together by desmosomes for strength and, in some layers, by tight junctions to hinder movement of water between cells arise in the deepest part of the epidermis from a cell layer called the stratum basale. stratum basale → undergo almost continuous mitosis in response to epidermal growth factor→ a peptide (hormone) produced by various cells throughout the body to cause mitosis Newly formed keratinocytes are pushed upward by the production of new cells beneath them, all the while making the keratin that eventually fills them. By the time the keratinocytes approach the skin surface, they are dead, scale-like flat sacs completely filled with keratin. A new epidermis every 25 to 45 days Where the skin experiences friction, both cell production and keratin formation are accelerated. Persistent friction (from a poorly fitting shoe, for example) causes a thickening of the epidermis called a callus

2) Melanocytes - Spider-shaped epithelial cells that synthesize the pigment melanin, found in the deepest layer of the epidermis - Melanin → gives color to skin and hair, made in membrane-bound granules called melanosomes and then melanosomes are transferred through the cell processes to nearby keratinocytes. So, basal keratinocytes contain more melanin than do the melanocytes themselves. - This melanin clusters on the superficial side of the keratinocyte nucleus, forming a pigment shield that protects the nucleus and DNA (so you don't get skin cancer) from the damaging effects of ultraviolet (UV) radiation in sunlight 3) Dendritic cells - Start shaped, arise from bone marrow and migrate to the epidermis, also called Langerhans cells in skin - Are protective cells that engulf antigens, migrate to lymph nodes and present antigen to T cells causing them to activate and mount an immune response, ingest foregin substances and key activators of immune system, take bacteria and present them so other cells can fight against the bacteria 4) Tactile epithelial cells - Also called Merkel cells - present at the epidermal-dermal junction / boundary

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Shaped like a spiky hemisphere have a disc like sensory nerve ending. The combination functions as a sensory receptor for touch (touch receptors)

Layers of epidermis from deep to superficial→ stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum - Variation in epidermal thickness determines if skin is thick or thin. - Thick skin : covers areas subject to abrasion—the palms, fingertips, and soles of the feet—the epidermis consists of five layers, or strata - Thin skin : covers the rest of the body, the stratum lucidum is absent and the other strata are thinner 1) Stratum basale (basal layer) - deepest epidermal layer, also called the stratum germinativum (germinating layer) - attached to the underlying dermis along a wavy borderline - consists of a single row of stem cells—a continually renewing cell population—representing the youngest keratinocytes. Have a row of actively dividing mitotic stem cells - The many mitotic nuclei seen in this layer reflect the rapid division of these cells. Each time one of these basal cells divides, one daughter cell is pushed into the cell layer just above to begin its specialization into a mature keratinocyte. The other daughter cell remains in the basal layer to continue the process of producing new keratinocytes. - 10–25% of the cells in the stratum basale are melanocytes, and their branching processes extend among the surrounding cells, reaching well into the more superficial stratum spinosum layer. - Main role : The stratum basale undergoes almost continuous mitosis to replace cells lost by abrasion 2) Stratum Spinosum (Prickly Layer) - several cell layers thick. - This layer gets its name from the many spinelike extensions of its keratinocytes as seen under a microscope. - However, these spines do not exist in living cells: They are artifacts created during tissue preparation because the cells shrink while holding tight at their many desmosomes. Meaning, several layers of keratinocytes are unified by desmosomes - Cells of the stratum spinosum contain thick bundles of intermediate filaments, made of pre-keratin. These intermediate filaments resist tension in the cell and are anchored to the desmosomes.

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Scattered among the keratinocytes are dendritic cells, which are most abundant in this epidermal layer.

3) Stratum Granulosum (Granular Layer) - consists of one to five cell layers in which keratinocyte appearance changes drastically and the process of keratinization (in which the cells fill with keratin) begins. - Has 5 layers of flattened cells,, cytoplasm is full of lamellar granules and keratohyalin granules - These cells flatten, their nuclei and organelles begin to disintegrate, and they accumulate two types of granules: a) keratohyalin granules → help to form keratin in the upper layers b) lamellar granules → contain a water-resistant glycolipid that is secreted into the extracellular space. Together with tight junctions, the glycolipid plays a major part in slowing water loss across the epidermis. -

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Proteins within the keratinocytes and lipids deposited outside them make these cells tough and water resistant. This is why the outermost layers of skin are strong and water-tight. Like all epithelia, the epidermis relies on capillaries in the underlying connective tissue (the dermis in this case) for its nutrients. Above the stratum granulosum, the epidermal cells are too far from the dermal capillaries to survive. In addition, the glycolipids coating their external surfaces cut them off from nutrients. As a result, they die. Where cells don't get enough oxygen so therefore die

4) Stratum Lucidum (Clear Layer) - found only in thick skin, found in palms of hands and soles of feet or areas where we expose in physical trauma and abrasion,gives more sturdiness - visible through a light microscope as a thin translucent band just above the stratum granulosum - consists of a few rows of clear, flat, dead keratinocytes. Electron microscopy reveals that its cells are identical to those at the bottom of the next layer, the stratum corneum. 5) Stratum Corneum (Horny Layer) - This outermost epidermal layer is a broad zone 20 to 30 cell layers thick (of dead cells) that accounts for up to three-quarters of the epidermal thickness. Most superficial layer. - Keratin consists of the pre-keratin intermediate filaments embedded in a “glue” from the keratohyaline granules -

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Flat membranous sacs filled with keratin. Glycolipids in extracellular space. Keratin and proteins that accumulate just inside the plasma membrane of cells in this stratum protect the skin against abrasion and penetration. The glycolipid between its cells helps keep this layer nearly waterproof. The cells of the stratum corneum are shed regularly. These cells are the dandruff shed from the scalp and the flakes that come off dry skin. If dead cells of the stratum corneum did not shed from your body, but rather stuck to it and continued to accumulate, problems that occur are:

a) You would either be unable to grow, or there would be big cracks in the stratum corneum as you grew. b) The thickness of the skin would impede joint movement so it would be hard to move. c) You would not be able to lose heat through your skin as effectively as you do now. d) Your skin would be very heavy to carry around after a while.

● Cells of dermis are found in the fibroblasts, macrophages, and occasional mast cells and white blood cells. - Its semifluid matrix, embedded with collagen, elastin and reticular fibers - Richly supplied with nerve fibers , blood and lymphatic vessels. Also hair follicles, oil and sweat glands - It is your “hide” and corresponds to animal hides used to make leather. ● The 2 layers of dermis → the papillary and reticular - Epidermis is not vascularized, so they do not get oxygen and they die. Dermis is vascularized. 1) Papillary dermis - Is thin and superficial, uppermost layer of dermis - areolar connective tissue in which interlacing collagen and elastic fibers form a mat with blood vessels. - The looseness of CT allows phagocytes and other defensive cells to wander freely as they look for bacteria that have penetrated the skin. - dermal papillae → Peglike projections which contain capillary and nerve endings for touch and pain and indent the overlying epidermis. bring blood vessels closer to epidermis - Other dermal papillae have free nerve endings (pain receptors) and touch receptors called tactile corpuscles or Meissner’s corpuscles - In thick skin, these papillae lie atop dermal ridges, to give epidermal ridges known as friction ridges

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friction ridges (fingerprints), may enhance our ability to grip certain kinds of surfaces, contribute to our sense of touch by enhancing vibrations detected by the large lamellar corpuscles (receptors) in the dermis. Cleavage lines → represent the lines between underlying collagen bundles in the reticular dermis, run circulatory around the trunk and longitudinally in the limbs, surgical incisions parallel to cleavage lines heal better than those made across them Flexure lines form where the dermis is closely attached to the underlying structures Friction ridges consist of epidermal ridges that lie on top of dermal ridges. Sweat duct openings on friction ridges help makes fingerprints Friction ridge patterns are genetically determined and unique to each of us.

2) Reticular dermis - accounting for ~ 80% of the thickness of the dermis - Coarse, dense irregular connective tissue. Has thick bundles of collagen fibers. Is the sturdiness part of the dermis. - The network of blood vessels that nourishes this layer, the dermal vascular plexus, lies between this layer and the subcutaneous tissue - The collagen fibers run in various planes, but most run parallel to the skin surface. Separations, or less dense regions, between these bundles form cleavage (tension) lines (in the skin) → invisible lines, tend to run longitudinally in the skin of the limbs and in circular patterns around the neck and trunk. - Cutting in between the collagen fibers will cause healing to occur more rapidly. They define the orientation of bundles of collagen fibers and what would be the best way to orient the cut. - Cleavage lines are important to surgeons because when an incision is made parallel to these lines, the skin gapes less and heals more readily. - Role of collagen fibers of dermis → give skin strength and resiliency that prevent minor jabs and scrapes from penetrating the dermis and maintain skin hydration. Elastic fibers provide the stretch-recoil properties of skin. - Flexure lines → dermal folds that occur at or near joints where the dermis is tightly secured to deeper structures, since the skin cannot slide easily to accommodate joint movement in such regions the dermis folds and deep skin creases form, flexure lines are also visible on the wrists, fingers, soles, and toes. Found in places where bending occurs.

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Striae → commonly called stretch marks, due to extreme stretching of the skin, such as during pregnancy or due to rapid growth, change in diet, can tear the dermis, leaving silvery white scars. Not enough dermis and epidermis

to recover quickly so it takes time. Short-term but acute trauma (ex: a burn) can cause a blister, a fluid-filled pocket (fluid accumulation) that separates the epidermal and dermal layers. Questions 1) Stefan’s front bike tire slipped on a patch of gravel as he rode to work. He needed five stitches to close the cut above his left eye. The split skin ran along a cleavage line. Is Stefan likely to have a major scar or is the wound likely to heal cleanly? Explain. Answer: Because Stefan’s wound runs along a cleavage line, it is likely to heal much more cleanly than it would if it ran perpendicular to the cleavage lines.

Melanin → - polymer made of an amino acid called tyrosine - Its two forms range in color from reddish yellow to brownish black. - is transported from melanocytes to the basal keratinocytes - Then lysosomes break down the melanosomes, so melanin pigment is found only in the deeper layers of the epidermis. - distribution of skin colors is not random—populations of darker-skinned people tend to be found nearer the equator (where greater protection from the sun is needed), lightest skin is found closer to the poles. - humans have the same # of melanocytes - Differences in skin color due to the type and amount of melanin made and retained. Darker skin = they produce more melanin. - Melanocytes of black- and brown-skinned people produce more darker melanosomes than fair-skinned people, and their keratinocytes retain it longer. Freckles and pigmented nevi (moles) are local accumulations of melanin. - When we are in the sun, keratinocytes secrete chemicals that stimulate melanocytes. Prolonged sun exposure causes a substantial melanin buildup, which helps protect the DNA of skin cells from UV radiation by absorbing the rays and dissipating the energy as heat. So out in the sun = more melanin is produced and skin turns a little darker. Melanin is produced to resist UV rays from going to the skin. - The initial signal for speeding up melanin synthesis seems to be a faster repair rate of DNA that has suffered photodamage. In all but the darkest-skinned people, this defensive response causes skin to darken visibly (tanning occurs) Carotene →

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Yellow to orange pigment that accumulates in the stratum corneum epidermis layer and in fatty tissue of the subcutaneous tissue found in certain plant products such as carrots. In the body, carotene can be converted to vitamin A → needed for normal vision and epidermal health. The pinkish hue of fair skin reflects the crimson color of hemoglobin in the red blood cells circulating through the dermal capillaries. Because light-skinned people have less melanin, the epidermis is nearly transparent and allows hemoglobin’s color to show through. Cyanosis is when people look bluish due to less oxygen attached to hemoglobin.

Questions 1) Melanin and carotene are two pigments that contribute to skin color. What is the third and where is it found? Answer: The third pigment that contributes to skin color is hemoglobin, the pigment contained in red blood cells found in blood vessels of the dermis

Along with the skin itself, the integumentary system includes a number of associated structures. These skin appendages include hair and hair follicles, nails, sweat glands, and sebaceous (oil) glands. Each plays a unique role in maintaining body homeostasis. Although they all derive from the epithelial cells of the epidermis (i.e., they are epidermal derivatives), they all extend into the dermis. Hair -

Some roles: Its main function in humans is to sense insects on the skin before they bite or sting us. Hair on the scalp guards the head against physical trauma, reduces heat loss, and sunlight. Eyelashes shield the eyes, and nose hairs filter large particles like lint and insects from the air we inhale. Protects against sunburn on top of head.

● Structure - flexible strands produced by hair follicles and consist largely of dead, keratinized cells. - Hard keratin (hair and nails have this) that dominates hairs and nails has two advantages over the soft keratin found in typical epidermal cells: (1) It is tougher and more durable, and (2) its individual cells do not flake off. - Important regions of hair : root and shaft - Root → part embedded in the skin , shaft → part that projects above the skin’s surface - According cross section: if shaft is flat and ribbonlike → hair is curly, oval shaft → silky and wavy hair, round shaft → straight and coarse hair

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Shape determines if hair is straight, curly and size determines if you have thick or thin hair A hair has three concentric layers of keratinized cells: the medulla, cortex, and cuticle

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Medulla → consists of large cells and air spaces Only part of hair that contains soft keratin, is absent in fine hairs Cortex → The bulky layer surrounding the medulla consists of several layers of flattened cells (kernatiocutes). The pigment is here. 3) Cuticle → - formed from a single layer of cells overlapping one another. This arrangement helps separate neighboring hairs so the hair does not mat. - It is the most heavily keratinized part of the hair, providing strength and keeping the inner layers tightly compacted. - subjected to the most abrasion and damage (like when heating hair) so the cuticle tends to wear away at the tip of the hair shaft. This allows keratin fibrils in the cortex and medulla to frizz, creating “split ends.” - Gray hair due to not enough pigment. Hair pigment is made by melanocytes at the base of the hair follicle and transferred to the cortical cells. Diff conc of melanin produces hair color from blond to brown to black. Red hair is colored by pheomelanin. When melanin production decreases and air bubbles replace melanin in the hair shaft, hair turns gray or white. Hair follicle - Structure with outer and inner root sheath extending from the epidermal surface into dermis and from which new hair develops - fold down from the epidermal surface into the dermis (and sometimes into the subcutaneous tissue). - The deep end of the follicle, located about 4 mm (1/6 in.) below the skin surface, expands to form a hair bulb → where growing of hair occurs. - A knot of sensory nerve endings called a hair follicle receptor, or root hair plexus, wraps around each hair bulb. - Bending the hair stimulates these endings. Consequently, our hairs act as sensitive touch receptors. -

A papilla of a hair follicle (or hair papilla) is a dermal papilla that protrudes into the hair bulb. contains a knot of capillaries that supplies nutrients to the gr...