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Download Integumentary System
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Integumentary System Integumentary System • Largest organ • Seen everyday • Spend a great deal of time on it • Problems can often be seen here first Integumentary System • 2 major components • cutaneous membrane –skin • accessory structures –hair –nails –exocrine glands Cutaneous Membrane • outer epidermis • underlying dermis • accessory structures begin in the dermis & protrude through epidermis to skin surface • deep to dermis is loose connective tissue in subcutaneous layerhypodermis Functions • Protection – abuse, abrasions, microorganisms, irradiation & chemicals – first line of protection against these irritants • Excretion – exudes salts, water & organic wastes • Maintains body temperature – insulates & cools • Vitamin D3 synthesis – essential for Ca++ metabolism • Storage – stores lipids in adipose tissue in dermis & subcutaneous layers • Detection – contains sensory receptors for touch, pain, pressure & temperature Epidermis • stratified squamous epithelium • protective barrier against ultra-violet light, bacteria, chemicals & abrasion • 4 cell types located in 4-5 layers • 4 layers-thin skin • 5 layers-thick skin Layers of Thick & Thin Skin Stratum Basale/Stratum Germinativium – separates epidermis from dermis – dermal papillae-extend between adjacent epidermal ridges – one row of cuboidal to columnar shaped-large, basal or germinative cellsdividereplace superficial keratinocytes – 10-25% cells are melanocytes – have long branching processes that extend, reaching into stratum spinosum – Merkel cells • sensitive to touch Stratum Spinosum • main cell typekeratinocyte • cells may continue to divide – Langerhans’ (epidermal dendritic) ells – participate in immune response Stratum Granulosum – – – – grainy layer cells do not divide begin to secrete keratin as cells are pushed upward, away from source of nutrition, they gradually diebecome keratinized – as keratin fibers develops cells become thinner & flatter – nuclei & other organelles disintegratecell dies – further dehydration produces a tightly interlocked layer of cells made of keratin fibers surrounded by keratohyalin Stratum Lucidum • clear layer • cells appear clearbecause of an accumulation of a keratin precursor • found only in thick skin-soles & palms • cells are flattened, densely packed & filled with keratin Stratum Corneum • • • • • • • • • • • outermost layer dead, flat, keratinized cells 25-30 layers sloughed off Keratinization or cornification – formation of protective, superficial layers of cells filled with keratin dry & more or less waterproof-resists surface evaporation-prevents excessive water loss layer is found on all exposed surfaces except anterior surface of eyes dead cells are connected by desmosomes-so tight-shed in groups takes 15-30 days for cell to move from s. germinativium to s. corneum dead cells remain in s. corneum 2 weeks before being shed surface maintained by coating it with lipid secretions from sebaceous glands Dermis • Between epidermis & hypodermis • Dense, irregular connective tissue • Stretches & recoils • Thicker than epidermis • Divided into papillary & reticular layers Dermis • Papillary layer – closest to epidermis – areolar tissue • Reticular layer – deeper & thickest layer – dense irregular connective tissue – contains thick bundles of interlacing collagen & elastic fibers – collagen give strength & ability to stretch – elastic stretch & recoil to original length Dermis • dermal papilla are found here • project into epidermis • some contain touch receptors-Meissner’s Corpuscles • some have free nerve endings • detect pain, coolness, itching and tickling Hypodermis not a part of the skin stabilizes skin’s position while allowing for independent movement consists of adipose tissue & areolar tissue protective functionsstores fat, helps prevent heat loss & acts as a shock absorber contains sensory endings for touchPacinian or lamellatedcorpuscle for deep pressure Skin Color Skin Color • Epidermal Pigmentation –Melanin –Carotene • Dermal Circulation Epidermal Pigmentation • Epidermis – contains 2 pigments – Carotene • orange-yellow pigment which accumulates in epidermal cells • most apparent in s. corneum – Melanin • brown, yellow-brown or black pigment – made by melanocytes in s. germinativium – travels in melanocyte processes & is transferred to keratinocytes – protects epidermis & dermis from UV radiation – melanocytes respond to UV exposure by increasing their activity – after UV exposure, melanin synthesis accelerates slowly peaking about 10 days after initial exposure – difference in skin color is due the amount made Dermal Circulation • blood contains RBCs which contain hemoglobin-a red pigment • binds & transports O2 • when bound to O2bright red • blood vessels in dermis take on a reddish tint-when dilated • circulatory system decreasesskinpale-may turn white • sustained reduction in circulatory system-tissue O2 decreases hemoglobin releases O2turns darker red-seen from surfacebluish-cyanosis Accessory Structures • • • • • Hair Sweat Glands Sebaceous Glands Nails Teeth Enamel – located in dermis & project through epidermis to surface Hair • projects above surface of skin • almost everywhere except sides & soles of feet & palms, sides of fingers, toes & lips • first appears-5 months prenatally – larugo-fine, unpigmented & shed before birth • replaced by vellus or terminal hair – Vellus-fine body hair – Terminal-coarser, heavy, deeply pigmented hair found on the scalp, eyebrows, etc • Primary function-protection Hair • produced in hair follicle – bag which extends into dermis • where it expands formshair bulb • hair root – anchors hair into skin, beginning at base of the hair at the bulb • hair shaft – projects from surface • cuticle consists of a layer of dead keratinized cells which overlap like shingles on a roof • Medulla – core-2-3 rows of cells containing pigment, air spaces & soft keratin • extension of dermal tissue at base-papilla protrudes inside the hair bulb – contains capillaries & nerves. • associated with each hair follicle is a tiny band of smooth musclearrector pili Skin Glands • specialized epithelial cells • Exocrine • secrete sweat, oil & wax Sweat Glands Sudoriferous glands coiled tubes in dermis with ducts leading to surface Apocrine armpits & anogenital area sticky, cloudy, potentially odorous secretion begins secreting at puberty Eccrine more numerous &widely distributed Functions cools surface of skin helps regulate body temperature prevents overheating protects from environmental hazards dilutes harmful chemicals discourages microorganism growth Types of Sweat Sensible Perspiration – felt as moisture Insensible Perspiration evaporates before being felt Thermoregulatory Sweating Emotional Sweating Cold sweat Sebaceous Glands • oil glands • secrete sebum (seb = oil) – mixture of triglycerides, cholesterol, proteins & electrolytes – usually secreted into hair follicle in a few regions-lips & mammary papilla & directly secreted onto skin surface of face, back & chest • Holocrine – entire gland dies when it secretes • Functions – inhibits bacterial growth – lubricates – protects keratin – conditions skin
