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Integumentary System

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Integumentary System • Dermatology – scientific study and medical treatment of the integumentary system. • Integumentary System – consists of the skin and its accessory organs – hair, nails, and cutaneous glands • skin is the most vulnerable organ • skin is the most vulnerable organ – exposed to radiation, trauma, infection, and injurious chemicals • body’s largest and heaviest organ Skin and Subcutaneous Tissue • consists of two layers: – epidermis – stratified squamous epithelium – dermis – connective tissue layer – hypodermis • another connective tissue layer below the dermis • not part of the skin contains fat tissue (for insulation), blood vessels and nerves • thick skin – on palms and sole, and corresponding surfaces on fingers and toes – has sweat glands, but no hair follicles or sebaceous (oil) glands • thin skin – covers rest of the body – possesses hair follicles, sebaceous glands and sweat glands Functions of the Skin • resistance to trauma and infection – keratin (mechanical protection) – acid mantle (prevents bacterial from entering body) – macrophages –“reach out and touching each other to detect bacteria” • other barrier functions – waterproofing – resists dehydration UV radiation – harmful chemicals • vitamin D synthesis – skin is first step of synthesis – liver and kidneys complete process • sensation – skin is our most extensive sense organ • thermoregulation – thermoreceptors – vasoconstriction (when cold)/ vasodilation (when hot) • transdermal absorption – administration of certain drugs steadily through thin skin Structure of the Skin Cell Types and Layers of the of the Epidermis Hair Follicle Hair Follicle Epidermis • keratinized stratified squamous epithelium – dead cells at the surface packed with tough protein – keratin – lacks blood vessels depends on the diffusion of nutrients from underlying connective tissue -dermis – contains nerve endings for touch and pain Five Types of Cells of the Epidermis – stem cells

• undifferentiated cells that give rise to keratinocytes • in deepest layer of epidermis (stratum basale) – keratinocytes (stratified squamous epithelial cells) • great majority of epidermal cells • synthesize keratin “As keratinocytes mature and move further away from the basal skin they are dying.

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Their cytoplasm and organelles are being replaced by the protein called keratin.

Will become dead shells filled with keratin. ” – melanocytes occur only in stratum basale • synthesize pigment melanin through secretion vesicles that shields DNA from ultraviolet radiation (protection) “Melanin will accumulate above the nucleus of the cell for protection” • branched processes spread melanin among keratinocytes – tactile (merkel) cells • in basal layer of epidermis • touch receptor cells associated with dermal nerve fibers – merkel disk- ends like a cup – attributes to sensation along with merkel cell “if someone touches your skin and compresses your cells into your merkle disks that allows us the sensation of being touched” – dendritic (langerhans) cells macrophages originating in bone marrow (originate from blood tissue) that guard against pathogens • found in stratum spinosum and granulosum • stand guard against toxins, microbes, and other pathogens that penetrate skin “Their processes stretch out and touch each other’s prcesses creating a net through our entire skin that nothing can penetrate without being detected. It will either attack the pathogen or call out bigger troops”

• thick skin – 5 layers of skin (extra layer- stratum lucidum) on palms and sole, and corresponding surfaces on fingers and toes – has sweat glands, but no hair follicles or sebaceous (oil) glands • thin skin – 4 layers of skin – covers rest of the body – possesses hair follicles, sebaceous glands and sweat glands Stratum Basale “lowest layer/ mitotic layer” • a single layer of cuboidal to low columnar stem cells – stem cells produce keratinocytes resting on the basement membrane – melanocytes and tactile cells are scattered among the stem cells and keratinocytes • stem cells of stratum basale divide – give rise to keratinocytes that migrate toward skin surface – replace lost epidermal cells 4 Cell types: stem cells, melanocytes (pigment-producing cells), dentritic (Langerhans) cells (immune cells), and Merkel cells (touch receptors) Stratum Spinosum • consists of several layers of keratinocytes (8-10 layers) • thickest stratum in most skin – in thick skin, exceeded by stratum corneum • deepest cells remain capable of mitosis – cease dividing as they are pushed upward “not really going through cell division but still alive” • produce more and more keratin filaments which causes cell to flatten – higher up in this stratum, the flatter the cells appear When put on slide, cells shrink and produce spiny appearance” • dendritic cells found throughout this stratum Stratum Granulosum • consists of 3 to 5 layers of flat keratinocytes • contain coarse dark-staining keratohyalin granules (melanin accumulation) / lamellar granules (water proofing-fatty deposit) • transitional layer of living to dead skin layers Stratum Lucidum • seen only in thick skin (only soles feet and palms of hands) “when exposed to friction, it increases in thickness” • thin translucent zone • cells have no nucleus or other organelles

Stratum Corneum • up to 25-30 layers of dead, scaly, keratinized cells “All cytoplasmic contents have been replaced” • resistant to abrasion, penetration, and water loss (lots of lamella granules) – surface cells flake off (exfoliate) keratinocytes • keratinocytes are produced deep in the epidermis by stem cells in stratum basale – some deepest keratinocytes in stratum spinosum also multiply and increase their numbers • mitosis requires an abundant supply of oxygen and nutrients – deep cells acquire from blood vessels in nearby dermis once epidermal cells migrate more than two or three cells away from the dermis, their mitosis ceases • newly formed keratinocytes push the older ones toward the surface • in 30 – 40 days a keratinocyte makes its way to the skin surface and flakes off – slower in old age – faster in skin injured or stressed • calluses or corns – thick accumulations of dead keratinocytes on the hands or feet Epidermal Water Barrier • forms between stratum granulosum and stratum spinosum • consists of: – lipids secreted by keratinocytes tight junctions between keratinocytes – thick layer of insoluble protein on the inner surfaces of the keratinocyte plasma membranes Dermis (vascular)

• connective tissue layer beneath the epidermis • well supplied with blood vessels, sweat glands, sebaceous glands, and nerve endings • hair follicles and nail roots are embedded in dermis • smooth muscle>> (piloerector muscles) associated with hair follicles – contract in response to stimuli, such as cold, fear, and touch – goose bumps The Dermis Structure Layers in Dermis: papillary layer – superficial zone of dermis (just bellow epidermis) – thin zone of areolar tissue in and near the dermal papilla – rich in small blood vessels • dermal papillae – upward fingerlike extensions of the dermis – friction ridges on fingertips that leave fingerprints – flection lines- lines between creases on hands • reticular layer – deeper and much thicker layer of dermis – consists of dense, irregular connective tissue – stretch marks (striae) – tears in the collagen fibers caused by stretching of the skin Hypodermis (NOT PART OF SKIN) • The hypodermis is not part of “skin”, it’s below the “skin”! subcutaneous tissue • more areolar and adipose than dermis • pads body • binds skin to underlying tissues • drugs introduced by injection – highly vascular & absorbs them quickly • subcutaneous fat – energy reservoir – thermal insulation Skin Color • melanin – most significant factor in skin color – produced by melanocytes – accumulate in the keratinocytes of stratum basale and stratum spinosum – eumelanin – brownish black – pheomelanin – a reddish yellow sulfur-containing pigment • people of different skin colors have the same number of melanocytes – dark skinned people • produce greater quantities of melanin

Other Factors in Skin Color • hemoglobin – red pigment of red blood cells – adds reddish to pinkish hue to skin • carotene – yellow pigment acquired from egg yolks and yellow/orange vegetables – concentrates in stratum corneum and subcutaneous fat Abnormal Skin Colors • cyanosis – blueness of the skin from deficiency of oxygen in the circulating blood – airway obstruction (drowning or choking) – lung diseases (emphysema or respiratory arrest) – cold weather or cardiac arrest • erythema – abnormal redness of the skin due to dilated cutaneous vessels – exercise, hot weather, sunburn, anger, or embarrassment pallor – pale or ashen color when there is so little blood flow through the skin that the white color of dermal collagen shows through – emotional stress, low blood pressure, circulatory shock, cold, anemia • albinism – genetic lack of melanin that results in white hair, pale skin, and pink eyes • jaundice – yellowing of skin and sclera (white of eye) due to excess of bilirubin in blood – cancer, hepatitis, cirrhosis, other compromised liver function • hematoma – (bruise) mass of clotted blood showing through skin Skin Markings Friction ridges- finger prints

Flexion lines (flexion creases)- are the lines on the flexor surfaces of the digits, palms, wrists, elbows, and other places Freckles- are flat melanized patches that vary with heredity and exposure to the sun mole (nevus)- elevated patch of melanized skin, often with hair hemangiomas- are patches of skin discolored by benign tumors of the blood capillaries Hair • hair, nails, and cutaneous glands are accessory organs of the skin • hair and nails are composed of mostly of dead, keratinized cells – pliable soft keratin makes up stratum corneum of skin – compact hard keratin makes up hair and nails tougher and more compact due to numerous cross-linkages between keratin molecules Distribution of Human Hair • hair is a slender filament of keratinized cells that grows from an oblique tube in the skin called a hair follicle • hair is found almost everywhere on the body except – palms and soles – ventral and lateral surface of fingers and toes – distal segment of the finger – lips, nipples, and parts of genitals • limbs and trunk have the most hair • differences in appearance due to texture and pigmentation of the hair • pilus – another name for hair • pili – plural of pilus Types of Human Hair Three kinds of hair grow over the course of our lives – lanugo – fine, downy, unpigmented hair that appears on the fetus in the last three months of development – vellus – fine, pale hair that replaces lanugo by time of birth • two-thirds of the hair of women • one-tenth of the hair of men • all of hair of children except eyebrows, eyelashes, and hair of the scalp – terminal – longer, coarser, and usually more heavily pigmented

• forms eyebrows, eyelashes, and the hair of the scalp • after puberty, forms the axillary and pubic hair • male facial hair and some of the hair on the trunk and limbs Structure of Hair and Follicle Hair is divisible into three zones along its length – bulb – a swelling at the base where hair originates in dermis or hypodermis • only living hair cells are in or near bulb – root – the remainder of the hair in the follicle – shaft – the portion above the skin surface • dermal papilla – bud of vascular connective tissue (dermis) encased by bulb – provides the hair with its sole source of nutrition • hair matrix – region of mitotically active cells immediately above papilla – hair’s growth center • follicle – diagonal tube that dips deeply into dermis and may extend into hypodermis • hair receptors nerve fibers that entwine each follicle – respond to hair movement • piloerector muscle (arrector pili) – bundles of smooth muscle cells – extends from dermal collagen to connective tissue around hair root – goose bumps Hair Color • color due to pigment granules (eumelanin and/or pheomelanin) in the cells of the cortex – brown and black hair is rich in eumelanin – red hair has a slight amount of eumelanin but a high concentration of pheomelanin – blond hair has an intermediate amount of pheomelanin and very little eumelanin – gray and white hair results from scarcity or absence of melanin and the presence of air in the medulla

Hair Growth • alopecia – thinning of the hair or baldness • pattern baldness – the condition in which hair loss from specific regions of the scalp rather than thinning uniformly – combination of genetic and hormonal influence – baldness allele is dominant in males and expressed only in high testosterone levels – testosterone causes terminal hair in scalp to be replaced by vellus hair • hirsutism (hyperpertuism)– excessive or undesirable hairiness in areas that are not usually hairy (e. g. upper lip on a woman) Functions of Hair most hair on trunk and limbs is vestigial – reminisce from ancestors • hair receptors alert us of parasites crawling on skin • scalp helps retain heat • scalp protects against sunburn • guard hairs (vibrissae) – guard nostrils and ear canals Nails • fingernails and toenails – clear, hard derivatives of the stratum corneum • composed of very thin, dead cells packed with hard keratin • flat nails allow for more fleshy and sensitive fingertips – tools for digging, grooming, picking apart food, and other manipulations • nail plate – hard part of the nail free edge – overhangs the finger tip – nail body – visible attached part of nail – nail root – extends proximally under overlying skin

• nail fold – surrounding skin rising a bit above the nail • nail bed – skin underlying the nail plate • hyponychium – epidermis of the nail bed • nail matrix – growth zone of thicken stratum basale at the proximal end of nail – mitosis here accounts for nail growth • lunule – an opaque white crescent at proximal end of nail (tissue is thicker there) • eponychium (cuticle) – narrow zone of dead skin commonly Cutaneous Glands he skin has five types of glands – merocrine (eccrine) sweat glands – apocrine sweat glands – sebaceous glands – ceruminous glands – mammary glands Sweat Glands (Sudoriferous) • two kinds of sweat (sudoriferous) glands – merocrine (eccrine) sweat glands • are present from birth • most numerous skin glands • are simple tubular glands that secrete watery secretion • watery perspiration that helps cool the body • they react in response to stimulation by sympathetic nervous system and squeeze perspiration up the duct • involved in thermoregulation apocrine sweat glands • develop at puberty – present with secondary sex characteristic • produce sweat that is thicker, milky, and contains fatty acids • occur in groin, anal region, axilla, areola, bearded area in mature males • scent glands that respond to stress and sexual stimulation • pheromones – chemicals that influence the physiology of behavior of other members of the species • bromhidrosis – disagreeable body odor produced by bacterial action on fatty acids

Sweat – release lots of potassium ions, urea, lactic acid, ammonia, and some sodium chloride remain in the sweat, most sodium chloride reabsorbed by duct – some drugs are also excreted in sweat – on average, 99% water, with pH range of 4 to 6 (acid)

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Integumentary System. (2016, Oct 14). Retrieved from https://graduateway.com/integumentary-system/

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