Integumentary system. Skin: Epidermis & Dermis. FuncIons of the Integumentary System. Structures of the Integumentary System 1/24/13

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1 1/24/13 Integumentary system Integument = the covering of an organism eg skin, shell, husk, rind Specialist: Dermatologist FuncIons of the Integumentary System Regulates body temperature Stores blood Protects from external environment Detects cutaneous sensaions Excretes & absorbs substances Synthesizes vitamin D Structures of the Integumentary System The Integumentary system consists of: Skin Epidermis Dermis Accessory structures Hair Oil Sweat glands Nails Sensory receptors Skin: Epidermis & Dermis Skin AKA cutaneous membrane Largest & heaviest organ (7%) 1-2mm on most of body. Thickness ranges from 0.5mm at eyelids to 4mm on heels. 2 main parts: Epidermis composed of Avascular epithelial 2ssue Dermis composed of Vascular connec2ve 2ssue. Hypodermis or subcutaneous layer consists of areola and adipose Issue and is not part of the skin. A\aches to underlying fascia of mm & bones 1

2 KeraInized straified squamous epithelium The Epidermis 0.1mm 4 or 5 strata of the THE EPIDERMIS 4 main cell types 90% Kera2nocytes make kerain protein. Tough, protecive, and water repelling sealant 8% Melanocytes make melanin pigment and transfer it to kerainocytes to shade nucleus Langerhans cells migrate from bone marrow to skin immune funcion Merkel cells make contact w sensory neurons 4 or 5 Layers of KeraInocytes Thin (hairy) skin has 4 layers Stratum corneum layers of dead cells Stratum granulosum 3-5 layers, undergoing apoptosis as far from dermis Stratum spinosum 8-10 layers of cells produce coarser kerain than basale Stratum basale cuboidal or columnar kerainocytes & stem cells that coninuously divide Thick (hairless) skin on palms & soles has 5 layers. Adds stratum lucidum fla\ened clear dead cells w lots of kerain and thickened plasma membrane New cells are formed by cell division in the stratum basale. As kerainocytes move from s. basale to the surface, they accumulate more kerain and become less metabolically acive. 4-6 wks from basale to sloughing off surface. Stratum basale kerainocytes divide more quickly w scrapes or burns of surface under influence of epithermal growth factor (EGF) Xs shedding of surface cells = dandruff. Increased rate of cell division and sloughing is psoriasis (7-10d) Growth of epidermis 2

3 Dense irregular connecive Issue w collagen & elasic fibers very strong, can stretch & recoil Thickness varies: Much thicker than epidermis. The Dermis Papillary & ReIcular regions THE DERMIS Cell types: Mostly fibroblasts. Some macrophages & adipocytes Embedded structures: hair, blood vessels, nerves, glands 2 regions: thin superficial papillary region & thick deeper re(cular region Papillary Region of the Dermis Thin collagen and fine elasic fibers Dermal papillae contain: Capillary loops Meissner s corpuscles: detect touch Free nerve endings: detect warmth, coolness, pain, Ickling, itching Fingerprints / epidermal ridges Epidermal ridge: downward projecion of epidermis into dermis. unique to each person. Increases surface area of epidermis Increases # of meissner s corpuscles thus sensiivity to touch Creates strong bond between dermis & epidermis protects against shear Inc surface area be\er grip More contact w capillaries in dermis for nutriion Sweat glands open at tops of ridges 3

4 ReIcular Region of the Dermis Region that is a\ached to the subq layer Protein: Thick collagen, coarse elasic fibers Cells: fibroblasts, some adipose, & wandering cells eg macrophages Structures: blood vessels, hair, sebaceous glands, sudoriferous glands occupy space between fibers Skin Color Melanin, Hemoglobin & carotene give skin its color # of melanocytes are same in all people Amount of melanin pigment determines skin color 2 forms of Melanin Pheomelanin- pale yellow to red (seen best in hair) Eumelanin - brown to black Skin color Synthesis of melanin Black skin White skin Melanin is made in melanosome from amino acid tyrosine Depends on tyrosinase enzyme UV light increases amount and darkness of melanin (tan) made Melanin absorbs UV light Tan is lost when kerainocytes containing melanin shed from stratum corneum Small amount of light exposure is needed to make Vit D 4

5 Hemoglobin & carotene Light skinned people have li\le melanin in the epidermis so it is translucent. Can see the hemoglobin in blood vessels below more oxygen a\ached to hemoglobin, redder skin Carotene yellow/orange pigment. Precursor of vita. Stored in stratum corneum & fat of dermis & subq. Can turn skin yellow/orange in light skinned individuals Hair, Nails, Sudoriferous, Sebaceous glands ACCESSORY STRUCTURES FuncIons of Hair Prevents heat loss from scalp Protects from sun Protects eyes from foreign objects Senses light touch w hair root plexus if hair is moved even slightly (On most skin except palms & soles) Hair Anatomy Medulla, cortex, cuicle along whole hair Shao above skin surface Root in dermis or subq Hair follicle surrounds the root Dermal root sheath Epithelial root sheath External root sheath Internal root sheath Bulb is the Bo\om of root which contains the: Dermal Papilla indentaion with blood vessels that feed the Hair Matrix were cell division / hair growth occurs 5

6 Hair Arrector Pili & Hair Root Plexus Arrector pili extends from dermal root sheath covering hair to superficial dermis Autonomic nerves simulate to contract under physiological or emoional stress or exciiaion Makes hair stand on end goose bumps. Retains body heat Hair root plexus generates nerve signals if hair is moved. Detects light touch Hair Growth Cycle Growth 2-6yrs. cells of matrix divide. New cells arise at the base. Old cells pushed up, become kerainized and die Regression 2-3wks. matrix stops dividing. Hair stops growing. Follicle atrophies Res2ng 3mo. Nl hair loss hairs/day. Incr. w low calorie/low protein diets, 3-4 mo aoer childbirth, age, stress, illness. Lanugo fetus. Nonpigmented, downy Shed in utero before birth, lanugo become: Terminal hairs- eyebrow, eyelashes, scalp Vellus hairs rest of body (short, fine, barely visible) Types of hairs 6

7 Depends on amount & type of melanin Dark hair eumelamin Blond & red hair pheomelanin Grey hair less melanin White hair no melanin + air bubbles in medulla Hair Color Sebaceous glands = oil glands Branched acinar gland Mostly connected to hair follicles where sebum keeps hair from drying, skin soo, and partly anibacterial Sebum = triglycerides, cholesterol, proteins, inorganic salts On lips, glans penis, labia minora, eyelids, sebacous glands open directly onto skin surface. Absent on palms and soles 2 types: eccrine & apocrine Eccrine - forehead, palms, soles Sweat consists of water, ions (Na, Cl) urea, uric acid, ammonia, amino acids, glucose, lacic acid. Opens into pores Thermoregulatory & emoional sweat Apocrine axilla, groin, breast areolae, male face (bearded region) Sweat has same components as eccrine plus lipids & proteins so appears milky or yellow. opens onto hair follicle Only funcion aoer puberty NO thermoregulaion. EmoIonal sweaing only Sudoriferous glands = sweat glands Thermoregulatory vs EmoIonal sweaing Thermoregulatory sweat forms on forehead & scalp first, then rest of body, & last on palms & soles. (eccrine, not appocrine) EmoIonal sweaing (cold sweat) is in response to emoion & appears first on palms, soles & axillae, then spreads to rest of body 7

8 Nails Tightly packed, dead, kerainized epidermal cells. Free edge, nail body, Nail root is under the skin Lunula has thick epidermis under so looks white CuIcle is a band of epidermis Nail matrix is deep to the nail root. Nail grows from cell division at matrix. Rate of mitosis/ nail growth is 1mm/wk but varies with age, season, Ime of day, nutriion, environmental temp FuncIons of Skin Blood reservoir ThermoregulaIon ProtecIon Cutaneous sensaion ExcreIon & absorpion Synthesis of vitamin D FuncIon as protecion for fingerips & counterpressure to palmar surface of finger Ip to enhance percepion & grasp of small objects Blood reservoir ThermoregulaIon The dermis blood vessels carry 8-10% of total blood flow in a resing adult Skin acts as a blood reservoir 2 mechanisms of thermoregulaion: 1. AdjusIng flow of blood in the dermis. Blood vessels in skin dilate to release heat & constrict to retain heat 2. Sweat in response to heat from environment or exercise, eccrine glands produce swet. EvaporaIon of sweat cools body 8

9 1/24/13 4 phases of Deep Wound Healing Epidermal Wound healing Epidermal wounds = abrasions, minor burns When epidermis is injured, stratum basale cells divide & migrate to fill the hole MigraIon stops with contact inhibiton ie when a cell is contacing other epidermal cells on all sides Cutaneous sensaions Wound is down to dermis or subq + scar Issue results (fibrosis) Inflamma(on Blood clot forms. VasodilaIon & leaky capillaries. PhagocyIc white blood cells engulf bacteria. Heat, redness, pain. Migra(on clot becomes scab. epithelial cells (fibroblasts) migrate to wound. make granula2on 2ssue (collagen & glycoproteins) to bridge the wound. Blood vessels begin to regrow. Prolifera(on much deposiion of collagen & growth of blood vessels Matura(on scab sloughs off, fibroblasts decrease. Collagen organizes. Blood vessels normalize ExcreIon & AbsorpIon Insensible perspiraion evaporates before it can be seen. ( about 600mL sweat /day from eccrine glands) Sensible perspiraion sweat that can be seen increases with acivity. Few substances can be absorbed: not water- soluble substances but gasses, or lipid soluble substances can pass through eg steroids, hormones, vit ADEK 9

10 Vitamin D First step of vitamin D synthesis occurs in skin Provitamin D3 (7- dehydrocholesterol) is found mainly in stratum basale and stratum spinosum Upon exposure to UV- B, it is transformed into Vitamin D3 10