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The Integumentary System Skin, Hair, Nails, and Glands
Do Now: • Calculate the weight of your skin: • For average adult skin accounts for 7% of body weight!
Where in the body is your skin the thinnest (~1.5mm)? • Lips • Palmar region • Lower eyelids • Cervical region • Popliteal region
Where in the body is your skin the thickest (4mm)? • Calcaneal region • Abdominal region • Buccal region • Otic region
Integumentary Structure • 2 Components: • Cutaneous Membrane • Epidermis • Dermis • Hypodermis • aka subcutaneous layer • Superficial fascia • Accessory Structures • Hair • Nails • Exocrine Glands
Integumentary Function • Protection • Temperature maintenance • Synthesis and storage of nutrients • Sensory reception • Excretion and secretion
Epidermis • Avascular& Keratinized • Thick skin – 5 layers • Thin skin – 4 layers • New epidermis every 25-45 days • Cells: • Keratinocytes(90% cells) – produce keratin • Tightly connected by desmosomes • Callus – accelerated keratin formation • Melanocytes – (8% cells) spider shaped, produce melanin • Melanin taken in by keratinocytes • Shields nucleus from UV • Langerhans’ cells – star shaped phagocytes • Merkel cells – sense skin curvature
Layers of Epidermis • Layers (starting from basement membrane): • Stratum Germinativum (Basale) • 3 Intermediate layers • Stratum Spinosum • Stratum Granulosum • Stratum Lucidum** • Stratum Corneum (superficial)
Stratum Germinativum (aka stratum basal) • Newly synthesized keratinocytes attached to basement by hemi-desmosomes • Forms ridge contours at interface of epidermal ridges and papillae of underlying dermis creating a strong bond, and increasing grip • Ridge contours are developmentally determined in 3rd month of fetal development and visible in palmer, plantar, and digits • 1 layer of Stem cells or germinative cells dominate the stratum germintivum • Undergoing mitosis • 10-25% melanocytes, some merkel cells • Receives nourishment from dermis
What is Psoriasis? • Autoimmune disease • Fungal infection • Increased rate of mitosis • Contagious
Very common between 15-35 • Autoimmune disease • increased rate of mitosis despite same rate of shedding • Non-contagious • Treated w/topically or phototherapy
Intermediate Strata • Stratum Spinosum • spiny or prickly layer • Newly synthesized keratinocytes (8-10 layers) • Cells continue to divide • Langerhans cells abundant • Stratum Granulosum • 3-5 flattened grainy cell layers • Stopped dividing, undergo apoptosis, nuclei & organelles break down • Produce keratin (durable, water resistant protein) becomes more apparent • Produce glycolipids –reduces water loss • Stratum Lucidum** • Thin tough clear layer • Found in thick skin • 4-6 layers of densely packed cells filled with keratin
Stratum Corneum • Most Superficial layer • ¾ of epidermis • 20-30 (up to 50) layers of flat dead keratinized or cornifiedcells • Held tightly together by desmosomes • Relatively dry (prevents microorganism growth) • Lasts about 2 weeks before shed • Avg person sheds 40lbs of skin in a lifetime!
Pigmentation:Skin Color • Melanin (yellow, brown or black pigment) • Produced by melanocytes in epidermis • Production increases in response to sun exposure • Prevents skin damage by absorbing UV rays • All humans have same number of melanocytes • Freckles & moles are areas of heavy melanin production • Carotene (orange-yellow pigment) • Converted to vitamin A for epithelial maintenance • Accumulates in stratum corneum • Dermal Circulation • Oxygenated Hemoglobin - reddish tint • Constricted blood vessels – pale • Cyanosis– Sustained constriction bluish color in Caucasian, only visible in nail beds of dark skin
What causes wrinkled leathery skin? • Clumping of elastic fibers • Thymine dimers in DNA • Disruption of collagen fibers • 1&3 • All of the above
What is the most common form of cancer? • Breast cancer • Lung cancer • Malignent melanomas • Basal Cell carcinoma
Sun Exposure • UV stimulates production of vitamin D3 • D3 is modified by liver and converted to calcitrol by kidneys • Calcitrol essential for absorption of calcium and phosphorus • Too much UV clumps elastin fibers causing leathery appearance • UV destroys folate needed for DNA synthesis • Too much UV can also cause chromosomal damage in stem cells of stratum germinativum causing skin cancer
Skin Cancer • Most common form of cancer (and most preventable) • Basal Cell Carcinoma – originates in stratum germanitivum • Squamous Cell Carcinomas – superficial layers • Malignant Melanomas • Extremely dangerous • Begins as a mole • Melanocytes grow rapidly and metastasize through lymphatic system Know the ABCD rule!
Do Now: What are Stretch Marks? • Damage to the dermis (collagen & elastin fibers) due to rapid stretching of the skin due to rapid growth or weight gain • Appear reddish- purple at first then fade to a lighter color over time • Tend to occur in regions of the body where fat is stored • Hormonal changes, genetics, and diet can all affect development of stretch marks
Dermis “hide” • Dermis – contains network of blood vessels, lymph vessels, and nerve fibers • Papillary Layer (thin superficial) • Loose connective tissue • fibroblasts, macrophages, mast cells • Dermal Papillae indent epidermis • Supports and nourishes epidermis • Capillaries and nerves • Meissnerscorpsucles – touch receptors • Reticular Layer (80% of dermis) • Meshwork of dense irregular connective tissue • Elastic fibers provide stretch & recoil • Collagen fibers provide rigidity & strength • BV, sweat and oil glands • Phagocytes • Striae – stretch marks • Blisters
Mechanoreceptors of Skin • Merkel’s disk • Skin Curvature • Meissner Corpuscle • Light Touch • Free Nerve Endings • Pain • Chemicals • Ruffini’s ending • Heat • Stretch • Pacinian Corpuscle • Deep Pressure • Vibrations
What causes a decubitus ulcer or bed sore? Caused by an interruption of blood supply to a tissue causing necrosis. These develop in patients that have been bed ridden for long periods of time. They are caused by the weight of the body on the skin overlying a bony area compressing the blood supply.
Do Now: List & describe layers of the Integument • Epidermis • Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum germanitivum (Basale) • Dermis • Papillary Layer • Reticular Layer • Hypodermis
Subcutaneous Layer • Not actually part of integument, blurred boundary • Anchors skin to muscles, but loosely so it can slide • Loose connective tissue with many adipocytes • Fat distribution changes as grow and mature (shock absorption & insulation) • Females thighs & breasts • Males abdomen “beer belly” • Contains no vital organs and few capillaries • Subcutaneous injection useful method of administering drugs with hypodermic needle
Burns • Burns • 1st degree – kills superficial epidermal cells, injures papillary dermis • 2nd degree – kills epidermis and possible some dermis, injures reticular dermis\ • 3rd degree – kills all epidermal and dermal cells, injures hypodermis and deeper tissues • Skin Gun: http://www.youtube.com/watch?v=eXO_ApjKPaI
Do Now: What is alopecia? • Hairs not replaced as fast as they are shed, begins anteriorly and progresses posteriorly • Male pattern baldness – sex linked trait by delayed action gene that when turned on changes response to testosterone • Until recently, only cure inhibits testosterone production
Accessory Structures: Hair and Hair Follicles • 2.5 million hairs on human body!! • Hair Growth Cycle • Hair grows for 2-5 years about .3mm per day then pushed to surface to be shed for new cycle to begin (scalp 6-10 yr cycle, eyebrows 3-4 months) • Function • Protect scalp from UV, cushion head, and insulate skull • Prevent entry of foreign particles in nostrils, ears, and eyes • Respond to stress or cold • Arrectorpilismooth muscle in dermis forces hair to stand up
Hair Structure • Walls of follicle contain cells of epidermis • Hair Papilla – peg of connective tissue containing capillaries and nerves, cell division occurs • Hair Root – anchors hair in to skin • Hair Shaft – 3 layers of dead keratinized cells • Medulla – core of hair (soft keratin) • Absent in fine hair • Cortex – surrounds medulla (hard keratin) • Cuticle – surface single layer made of overlapping shingles of cells
Hair Texture • Oval – silky & wavy • Flat & ribbonlike – curly • Round – straight • Conditioners – smooth out rough cuticles making it shiny • Split ends – cuticle wears away at ends
Hair Types: • Cuticle • Coronal • Crown like (stacked paper cups) • Small rodents & bats • Spinous • Petal or triangular shaped • Mink, cats and seals • Imbricate • Flattened, overlapping scales • Humans and other animals • Medulla • Fragmentary (trace) • Discontinuous (broken) • Continuous • Cortex • Human pigment granules distributed by cuticle (except red-hair) • Cattle, dogs and some humans have ovoid bodies
Hair Color • Genetically determined by type and amount of pigment produced by melanocytes • Brown – true melanin • Blond - sulfur • Red - iron • Gray - Pigment production decreases • White air bubbles within hair shaft
Human Hairs vs. Animals • Consistent color & pigmentation throughout shaft (see banding in animals) • Animal pigmentation is centrally located • Humans 2 types of hair: • Vellus hair – fine body hair • Terminal hair – coarser, darker hair (increased testosterone increases growth)
Write an analogy for our skin…. • Human skin is like __________ because _______________.
What are comedones? • Acne is caused by blocked sebaceous duct, forming a sebum plug • Affects over 85% of adolescents and young adults. • Secretions accumulate causing inflammation and possible bacteria infection • Blackheads – open comedones, melanin oxidizes turning black • Whiteheads – closed comedones • Hormonal changes can cause increased oil production • Try not to squeeze, scratch, pick, or rub the pimples. Although it might be tempting to do this, it can lead to skin infections and scarring.
Accessory Organs: Nails • Protect exposed finger tips and limit distortion when exposed to mechanical stress • Tools – pick up or scratch itch • Free Edge • Nail body – dead keratinized cells • Nail bed – epidermis covered by nail body • Nail root – anchors nail body • Nail matrix – nail growth occurs • Cuticle – portion of stratum corneum extending over nail • Lunula – pale crescent (area of obscured blood vessels)
Accessory Structures: Sebaceous Glands • Holocrine oil glands • Arrectorpili muscle contracts squeezes the sebaceous gland forcing oily secretion out • Sebum (oily secretion) lubricates hair and skin and inhibits bacteria growth, slows water loss from skin • Glands are sensitive to androgens (sex hormones) • Cradle Cap – overactive sebaceous glands
Accessory Structures: Sudoriferous (sweat) Glands • About 3 million per person! • Merocrine (eccrine) Sweat Glands • Secreted directly onto surface of skin via exocytosis • 99% water w/electrolytes, vitamin C, antibodies, metabolic wastes and drugs, pH of 4-6 • Cools surface of skin and lowers body temp • Too much perspiration may lead to dehydration • Flushes microorganisms from surface • ApocrineSweat Glands • sweat glands that secrete products into hair follicles in armpits, nipples, and groin • Sticky, cloudy secretion released at puberty • Odorous as bacteria break it down as food
ID structure A • Sweat Gland • Sebaceous Gland • Epidermal Ridges • Adipocytes • Arrector Pilli muscle • PacinianCorpsucle
ID structure B • Hair Papilla • Sebaceous Gland • Hair shaft • Hair root • Arrector Pilli muscle • PacinianCorpsucle
ID structure C • Sweat Gland • Sebaceous Gland • Epidermal Ridges • Paciniancorpsucle • Hair Papilla • Hair shaft • Hair root
ID structure D • Merocrine Gland • Sebaceous Gland • Epidermal Ridges • Arrector Pilli muscle • PacinianCorpsucle • Apocrine Gland
ID structure E • Sweat Gland • Sebaceous Gland • Epidermal Ridges • Adipocytes • Arrector Pilli muscle • PacinianCorpsucle
ID structure F • Stratum basal • Stratum spinosum • Epidermal Ridges • Stratum lucidum • Stratum granulosum • Stratum corneum
ID structure G • PacinianCorpsucle • Merkels discs • Ruffinis endings • Free Nerve endings • Adipocytes • Meissnerscorpsucle
Injury and Repair of Skin Inflammatory response • triggered by mast cells increase blood flow to area • Scab (fibrin proteins) forms at surface to restrict entry of microorganisms • Cells divide rapidly to replace missing cells • Macrophages and phagocytes clear debris and patrol area for pathogens Deeper wounds • Scar tissue – lots of collagen fibers and few blood vessels • Fetuses don’t scar • Keloid– thickened area of scar tissue with shiny smooth surface (tend to form in adults with dark skin) • Damaged hair follicles, sebaceous and sweat glands, muscle cells and nerves are rarely repaired