integumentary system

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. 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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