BIOL 210 Lecture 2 - The Integumentary System (Qs) PDF

Lecture 2: The Integumentary System BIOL 210 Dr. K  Objectives Explain organization and functions of integumentary system Describe histological organization of layers of epidermis Describe histological organization of dermis Analyze structure of subcuta...

Lecture 2: The Integumentary System BIOL 210 Dr. K  Objectives Explain organization and functions of integumentary system Describe histological organization of layers of epidermis Describe histological organization of dermis Analyze structure of subcutaneous layer (hypodermis) and its importance Compare and contrast anatomy and functions of skin’s accessory structures: hair, glands and nails Explain how skin responds to injuries and repairs itself Summarize effects of aging on skin  The Integumentary System Integument = skin Largest system of body Made up of 2 parts: 1. Cutaneous membrane a. Epidermis- superficial epithelium b. Dermis- underlying connective tissue with blood supply 2. Accessory structures a. Hair b. Nails c. Exocrine glands Sweat/sebaceous glands Functions of the Integumentary System Protection First line of defense against Bacteria Viruses Protects underlying structures from Ultraviolet (UV) radiation Dehydration Vitamin D production Needed for calcium absorption from digestive tract Sensation Sensory receptors Body temperature regulation If too hot Dermal blood vessels dilate Vessels carry more blood to surface so heat can escape If too cold Dermal blood vessels constrict Prevents heat from escaping Excretion Small amounts of waste products are lost through perspiration  Structure of Skin Epidermis Superficial portion of skin Composed of stratified squamous epithelial tissue Dermis Deep layer of skin Composed of dense connective tissue proper Hypodermis (subcutaneous layer or superficial fascia) Deep to dermis NOT part of skin Consists of subcutaneous tissue- loose connective tissue proper and adipose tissue Fat storage, an area for blood vessel passage and an area of pressure-sensing nerve endings  The Epidermis Avascular stratified squamous epithelium Cells in epidermis Keratinocytes Most abundant cells Produce tough protein, keratin Helps protect skin and underlying tissue from heat, microbes and chemicals Migrate superficially towards surface of skin while producing and accumulating keratin Cells die and are called corneocytes (resistant to dehydration and friction) Melanocytes Produce skin pigment, melanin Contributes to skin color and absorbs damaging ultraviolet (UV) light Merkel cells Sensory cells Langerhans (dendritic) cells Wandering macrophages  The Epidermis 4-5 layers of epidermis, depending upon degree of friction and mechanical pressure applied to skin Thin skin Covers most of body 4 layers of keratinocytes Thick skin Covers palms of hands and soles of feet 5 layers of keratinocytes  Layers of Epidermis 5 layers of keratinocytes in thick skin Deep to superficial: 1. Stratum Basale 2. Stratum Spinosum 3. Stratum Granulosum 4. Stratum Lucidum (only in palms and soles) 5. Stratum Corneum Come Lets Get Sun Burnt  Stratum Basale Deepest layer; 1-cell layer thick Cells: Keratinocytes Melanocytes Produce melanin Basal (stem) cells Undergo mitosis to form new keratinocytes and migrate upward Replace superficial keratinocytes that are shed at surface Merkel cells Specialized epithelial cell found in skin surfaces that lack hair Most abundant where sensory perception is most acute – fingertips and lips Respond to touch Forms dermal ridges Extend into dermis, increasing contact between epidermis and dermis Projections from dermis toward epidermis = dermal papillae Ensure secure grip on objects Form fingerprints  Stratum Spinosum “Spiny layer” Keratinocytes bound together by desmosomes Associated with tonofibrils Protein filaments in each keratinocyte Provides strength and flexibility to skin Langerhans (dendritic) cells Active in immune response against epidermal cancer cells and pathogens During slide preparation, cells shrink but desmosomes and tonofibrils between cells remain intact → cells with spiny outline  Stratum Granulosum “Grainy layer” with darker cells Transition between dividing strata and dead cells of superficial strata Most superficial layer in which cells still have a nucleus As keratinocytes move superficially, they synthesize more keratin and keratohyalin Keratin Makes up hair and nails Reduces water loss Keratohyalin In dense granules Forms a water-resistant layer around cells Promotes cross-linking of keratin fibers Increased friction against skin, increases synthesis → thickening skin → callus  Stratum Lucidum “Clear layer” Cells do not stain well Found only in thick skin (palms of hands and soles of feet) Thin, transparent layer of cells Lack organelles and nuclei Filled with keratin filaments  Stratum Corneum “Horn layer” Most superficial layer Contains interlocking, flattened, dehydrated dead cells Lack organelles and nuclei Filled with keratin Cells shed and replaced every 2 weeks Cells also accumulate yellow-orange pigment, carotene Precursor for Vitamin A  The layer of epidermis that contains cells undergoing cell division is the _____. a) stratum spinosum b) stratum granulosum c) stratum basale d) stratum corneum  The layer of epidermis that contains cells undergoing cell division is the _____. a) stratum spinosum b) stratum granulosum c) stratum basale d) stratum corneum  Which of the following layers is found only in thick skin such as the palms of the hands or the soles of the feet? a) stratum basale b) stratum lucidum c) stratum corneum d) stratum spinosum  Which of the following layers is found only in thick skin such as the palms of the hands or the soles of the feet? a) stratum basale b) stratum lucidum c) stratum corneum d) stratum spinosum  The Dermis Located between epidermis and subcutaneous layer Anchors epidermal accessory structures (hair follicles, sweat glands) and Dermis contains fibroblasts, macrophages and fat cells 2 major regions: Superficial papillary layer Deep reticular layer  Dermal Organization Papillary layer: Superficial portion of dermis Consists of loose connective tissue with collagen and elastic fibers Fingerlike projections into epidermis (dermal papillae) Anchors epidermis to dermis Contains capillaries that supply epidermis Contain small sensory receptors for light touch = tactile corpuscles  Dermal Organization Reticular layer: Deep to papillary layer Contains dense irregular connective tissue Has meshwork of thick bands of collagen fibers Penetrated by hair follicles, sweat glands and sebaceous glands from epidermis Contain sensory receptors that detect deep pressure and vibration = lamellated corpuscles  Dermis Dermal strength and elasticity Collagen fibers Very strong, resist stretching Easily bent or twisted Limit flexibility to prevent tissue damage Elastic fibers Permit stretching and then recoil to original length Provide flexibility Fibers and water provide flexibility and resilience Known as skin turgor  Dermis Skin damage (wrinkles, stretch marks) Loss of skin turgor is caused by Dehydration (reversible) Aging Hormones UV radiation Excessive distortion of dermis from pregnancy or excessive weight gain Elastic and collagen fibers break Skin does not recoil Skin wrinkles and creases → stretch marks Tretinoin (Retin-A)- derivative of vitamin A Increases blood flow to dermis and stimulates dermal repairs Rate of wrinkle formation decreases and existing wrinkles become smaller  Dermal Blood Supply Cutaneous plexus Deep network of arteries and veins at junction between reticular layer of dermis and subcutaneous layer Subpapillary plexus Network of small arteries in papillary layer Capillary loops along epidermal-dermal boundary drain into small veins that lead to larger veins in subcutaneous layer  The Hypodermis Subcutaneous layer Lies below integument Not part of integumentary system Stabilizes position of skin Composed primarily of adipose tissue Superficial region contains large arteries and veins, remaining areas contain few capillaries Site of subcutaneous injections using hypodermic needles  Which layer of skin is made of stratified squamous epithelium and is therefore avascular? a) hypodermis b) subcutaneous c) dermis d) epidermis  Which layer of skin is made of stratified squamous epithelium and is therefore avascular? a) hypodermis b) subcutaneous c) dermis d) epidermis  Skin Color Due to: Dermal blood supply Reduction in blood flow → pale color Sustained reduction in blood flow → cyanosis Most apparent in thin skin – lips and beneath nails Various concentrations of carotene and melanin Carotene Derived from carrots, corn and squash Converted to vitamin A Synthesis of visual pigments in photoreceptors of eyes Melanin Produced and stored in melanosomes within melanocytes Vesicles transferred to keratinocytes Cells in more superficial layers of epidermis have less melanin and are lighter in color Creates natural skin color and tan Protects skin against UV radiation Within each keratinocyte, melanosomes are most abundant around nucleus, absorbing UV radiation before it can damage DNA Exposure to UV light increases rate of melanin formation (tanning begins) Repeated exposure to UV light → Long-term epidermal and dermal damage Abnormal connective tissue structure Premature wrinkling Epidermal skin cancer Thickness of stratum corneum  Skin Color Illness and skin color Jaundice Buildup of bile produced by liver Skin and whites of eyes may turn yellow Pituitary tumor Excess MSH increases production of melanin Addison’s disease Causes pituitary gland to release excess ACTH, which has an effect similar to MSH Vitiligo Loss of melanocytes causing loss of color  Vitamin D3 Cholecalciferol Produced by epidermal cells in presence of UV radiation Liver and kidneys together convert vitamin D3 into calcitriol Essential for absorption of calcium and phosphate ions by small intestine Insufficient vitamin D3 can cause rickets in children and osteomalacia in adults Sources of Vitamin D3  Accessory Structures of the Skin Develop from embryonic epidermis= epidermal derivatives Cells sink inward during development to form: Hair Oil glands Sweat glands Nails Exposed on surface of skin and project deep into dermis  Hair Present on most skin surfaces except Palms, palmar surfaces of digits Soles and plantar surfaces of digits Lips Portions of external genitalia Functions: Protect from UV light and insulate Guard openings from particles and insects Serve as sensory receptors Movement of hair sends impulses via nerves to brain (presence of root hair plexus) Such as when a bug is crawling on your arm Hair consists of: Hair papilla Hair bulb Hair root that penetrates dermis and subcutaneous layer Hair matrix (keratinized) Hair shaft  Hair Hair follicles Organs that produce nonliving hairs Located deep in dermis Base is surrounded by sensory nerves (root hair plexus) Arrector pili Involuntary smooth muscle attached to each hair follicle Contraction causes hairs to stand up Produces “goose bumps” when we are cold  Regions of Hair Hair root Embedded deep in a hair follicle Anchors hair to skin Begins at hair bulb and extends distally, halfway to skin surface Hair shaft Upper part of hair Extends from skin surface Not attached to integument Formed by keratinization of hair cells above matrix, which causes them to harden and die  Hair Structure Hair bulb Epithelial cells at hair follicle base Surrounds a hair papilla Connective tissue containing nerves and capillaries At base of bulb is hair matrix Living, proliferative epithelial layer of hair Undergo mitosis and daughter cells push up and out, elongating hair (it “grows”) Consists of: Medulla Inner, central core Flexible soft keratin Cortex Intermediate layer Hard keratin Stiffness of hair Cuticle Outer surface layer Single layer of dead, keratinized cells that coats hair  Hair Follicle Structure Beginning at hair cuticle and moving outward, cells of follicle wall arranged in 3 concentric layers: 1. Internal root sheath Surrounds hair root Produced by cells at periphery of hair matrix 2. External root sheath Extends from skin surface to hair matrix Includes all cell layers found in superficial epidermis 3. Glassy membrane Clear, thick layer wrapped in connective tissue sheath Hair Follicle Structure  Hair Types: 1. Terminal hairs a. Thick, heavy hairs on scalp, eyebrows and eyelashes 2. Vellus hairs a. Lightly pigmented and distributed over much of skin b. Soft, fine hairs (“peach fuzz”) 3. Lanugo hairs a. Unpigmented, fine hair that develops after 3 months of embryonic development b. Most shed before birth Hair color Due to: Variation in melanin production by melanocytes at hair matrix More melanin = darker hair Decreased production = gray hair Lack of melanin and presence of air bubbles within medulla of hair shaft = white hair Influenced by: Genetics Hormones Environmental factors  Exocrine Glands in Skin Sebaceous (oil) glands Holocrine glands Discharge lipid secretion (sebum) into hair follicles Lubricates and protects hair shaft Inhibits growth of bacteria Sweat (sudoriferous) glands Apocrine sweat glands Ceruminous glands Mammary glands Eccrine sweat glands Gland function Lubricates epidermis Excretes waste Assists in thermoregulation  Sebaceous (Oil) Glands Connected to hair follicles Secretory portion of gland in dermis Produces sebum (waxy, oily lipid) Via holocrine secretion Coats hair shafts and epidermis to reduce brittleness and prevents excessive drying Inhibits growth of bacteria (antibacterial) Absent in palms of hands and soles of feet If ducts become blocked Acne or furuncle (boil) may develop Sebaceous follicles Large sebaceous glands NOT associated with hair Discharge sebum directly onto skin surface Located on face, back, chest, nipples and external genitalia If follicles become inflamed due to bacteria = folliculitis  Sweat Glands Scattered throughout dermis of most of integument Secrete watery solution into sweat ducts leading to skin surface or to hair follicles Consist of myoepithelial cells Contractions squeeze gland and discharge secretions Under ANS and hormonal control 2 types: 1. Eccrine (merocrine) sweat glands 2. Apocrine sweat glands  Sweat Glands Eccrine (merocrine) glands: Apocrine glands: Coiled tubular glands Coiled tubular glands Found all over body Found in axillae, nipple High concentrations on palms and soles and groin regions Produce a clear secretion = Produce a thick, cloudy, sweat (sensible perspiration) odorous secretion into directly onto surface of ducts that open onto hair epidermis follicle Via merocrine secretion 99% water, NaCl, metabolites Begin secreting at puberty and wastes (urea) May also contain Thermoregulation Sweat absorbs body heat and pheromones evaporates from skin, cooling Deeper in dermis than skin surface and decreasing eccrine glands body temperature NOT associated with hair follicles  Which of the following glands release their secretions into hair follicles of the axillae, around the nipples and in the groin? a) ceruminous glands b) sebaceous glands c) eccrine sweat glands d) apocrine sweat glands  Which of the following glands release their secretions into hair follicles of the axillae, around the nipples and in the groin? a) ceruminous glands b) sebaceous glands c) eccrine sweat glands d) apocrine sweat glands  Which of the following glands function in thermoregulation, excretion, and protection? a) ceruminous glands b) sebaceous glands c) eccrine sweat glands d) apocrine sweat glands  Which of the following glands function in thermoregulation, excretion, and protection? a) ceruminous glands b) sebaceous glands c) eccrine sweat glands d) apocrine sweat glands  Nails Structure of nails: Protect dorsal surface of tips of fingers and toes Consists of tightly packed keratinized dead cells Metabolic disorders can change nail structure (e.g. clubbing due alcohol poisoning, koilonychia due to iron- deficiency anemia)  Structure of a Nail Nail body Visible portion pink due to underlying blood vessels Protects underlying nail bed Bordered by lateral nail grooves and lateral nail folds Lateral edges of nail Free edge of nail body Extends over a thickened stratum corneum = hyponychium Nail root Epithelial fold at base of nail not visible from surface Where new nail growth occurs Eponychium (cuticle) Portion of stratum corneum of nail fold that extends over exposed nail near root Proximal nail fold Portion of skin near eponychium Lunula (pale crescent) Whitish portion near root where blood vessels are obscured  Skin/Tissue Repair Skin regenerates effectively because stem cells persist in epithelial and connective tissues 4 phases: 1. Inflammatory phase Damage of skin leads to inflammatory response by mast cells 2. Migration phase Scab (dried blood clot) stabilizes and protects area Macrophages clean area Cells of stratum basale divide and migrate along edges of wound Fibroblasts and endothelial cells divide, producing granulation tissue Fragile, vascularized 3. Proliferative phase Fibroblasts form collagen fibers and ECM Migrating epithelial cells form new epidermis beneath scab 4. Scarring phase Scab is shed, new epidermis is thin with shallow depression Fibroblasts continue forming scar tissue Inflexible, fibrous and avascular (fibrosis)  Which is the initial phase of repair after injury to the skin? a) proliferation phase b) migration phase c) inflammation phase d) scarring phase  Which is the initial phase of repair after injury to the skin? a) proliferation phase b) migration phase c) inflammation phase d) scarring phase  Effects of Aging on Skin Epidermis becomes thinner Basal cell activity decreases More prone to injury and skin infections Number of Langerhans cells decreases Vitamin D3 production declines Muscle weakness and weaker bones Melanocyte and glandular activities decline Decrease in melanin production → pale Decrease in sebum production → dry and scaly skin Impaired perspiration → overheating Blood supply to dermis is reduced Inability to dissipate heat Function of hair follicles declines Thinner, finer hairs Dermis becomes thinner and elastic fiber network shrinks Breakdown of collagen and elastic fibers → sagging, wrinkling skin Sex-specific hair and body fat distribution fades Decrease in sex hormones Skin repair slows down Effects of Aging on Skin