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Integumentary System (Skin) 12/14 Lab 4A BIO 105 1. Protection – Chemical • Low pH secretions (acid) retard bacterial activity – Physical/mechanical barriers • block most water & water- soluble substances • Limited penetration of skin by any substance 2. Body temperature regulation 3. Cutaneous sensations--temperature, touch, and pain 4. Metabolic functions – Synthesis of vitamin D precursor – Prevents dehydration 5. Excretion—nitrogenous wastes and salt in sweat BIOL 105 Lab 4A--Skin 1 Consists of three major regions 1. Epidermis—outermost region 2. Dermis—middle region 3. Hypodermis (superficial fascia)—deepest region • • not technically part of skin Mostly adipose tissue BIOL 105 Lab 5A--Skin 2 Epidermis • Keratinized stratified squamous epithelium with 4 different types of cells and 4-5 layers – Keratinocytes—main cell type; produce keratin (protein) – Melanocytes • Produce melanin pigment—gives skin its coloring– yellowblack – Langerhans cells—macrophages that help activate immune system – Merkel cells—tactile receptors – Nutrients reach epidermis by diffusing through tissue fluid BIOL 105 Lab 5A--Skin 3 Stratum corneum Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. •Stratum granulosum •Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of granules which release lipids and keratohyaline granules which surround keratin. Stratum spinosum •Several layers of keratinocytes. Cells contain thick bundles of intermediate filaments made of pre-keratin. • Stratum basale •Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and epidermal dendritic cells. BIOL 105 Lab 5A--Skin Figure 5.2b Layers of Epidermis: superficial deep Stratum Corneum (Horny Layer) • Outermost layer consisting of rows of dead, flat, keratinized membranous sacs (no nuclei seen in cells) – Dandruff from scalp or “dander” loose flakes that fall off dry skin • Makes up 3/4 of epidermal thickness • Functions o Protection from abrasion and penetration o Waterproofs o Forms a barrier against biological, chemical, and physical assaults—makes skin impermeable to most substances BIOL 105 Lab 5A--Skin 5 Stratum lucidum found in thick skin e.g. soles of feet, palms, fingertips; not seen in thinner skin. • Contains few rows of flat, dead, keratinocytes Stratum Granulosum or Granular Layer Skin layers superficial to this are made up of dying or dead cells; are too far from blood capillaries to get adequate nutrition and oxygen • Thin; 3-5 layers of flattened cells • Contains cells more resistant to destruction BIOL 105 Lab 5A--Skin 6 Stratum Spinosum • thickest layer of living cells. • cells start to flatten out • produce protein keratin and glycolipids that toughen and water-proof skin. BIOL 105 Lab 5A--Skin 7 Stratum Basale (Basal Layer) • Deepest epidermal layer • Firmly attached to dermis • Single row of stem cells • cells undergo rapid division –Takes ~25–45 days for cell to migrate from this layer to surface BIOL 105 Lab 5A--Skin 8 Dermis-thickest layer • Contains strong, flexible connective tissue • Only this layer is vascularized • Cells include fibroblasts, macrophages, and few mast cells and white blood cells • Has nerve fibers, blood vessels and lymphatic vessels • made up of 2 layers: – Papillary – outermost; contains areolar connective tissue; nerve endings for touch and pain – Reticular-innermost; dense irregular collagen, elastic and reticular fibers BIOL 105 Lab 5A--Skin 9 • Papillary layer of Dermis – Areolar connective tissue with collagen and elastic fibers and blood vessels – Looseness of connective tissue allows defensive cells to patrol the area for invaders – Makes dermal papillae which contain: • Capillary loops, Meissner’s corpuscles, Free nerve endings • Epidermal ridges on top dermal papillae make our fingerprints and allow us to grip items better BIOL 105 Lab 5A--Skin 10 • Reticular layer-Collagen fibers provide strength and resiliency • bind with water to keep skin hydrated – Elastic fibers provide stretch-recoil properties – Contains sebaceous and sweat glands, pressure receptors BIOL 105 Lab 5A--Skin 11 Skin Color • Three pigments contribute to skin color: 1. Melanin • Yellow to reddish-brown to black, responsible for dark skin colors – darker skinned people produce melanocytes with more pigment and their keratinocytes retain color longer than lighter skinned people – Freckles and pigmented moles result from local accumulations of melanin 2. Carotene • Yellow to orange, most obvious in the palms and soles 3. Hemoglobin--not a skin pigment but gives the pinkish hue of skin because blood vessels are close to the skin surface BIOL 105 Lab 5A--Skin 12 Skin Appendages: Sweat Glands • Two main types of sweat (sudoriferous) glands 1. Eccrine or merocrine sweat glands—abundant on palms, soles, and forehead • • Sweat ducts connect to pores Function in temperature regulation BIOL 105 Lab 5A--Skin 13 2. Apocrine sweat glands—confined to axillary and anogenital areas (animals use smells from these to identify the opposite sex) • Secretion is sweat + fatty substances and proteins; odorless secretion but bacteria feed off it and make odor • Functional from puberty onward – Specialized “sweat” glands: • Ceruminous glands—in external ear canal; secretes cerumen or wax • Mammary glands—secrete milk BIOL 105 Lab 5A--Skin 14 Sebaceous (Oil) Glands • Widely distributed • Typically located near hair follicles-keep hair moist • Made up of branched alveolar glands • Become active at puberty – Secrete sebum, an oily secretion – Bactericidal – Softens hair and skin BIOL 105 Lab 5A--Skin 15 Specialized Receptors: • Pressure: – Meissner corpuscles— –light touch • In Papillary layer – Pacinian Corpuscles— –deep touch • In Reticular layer BIOL 105 Lab 5A--Skin 16 Nails • Scalelike modification of epidermis on distal, dorsal surface of fingers and toes BIOL 105 Lab 5A--Skin 17 Hair-• Consists of dead keratinized cells • Contains keratin which is tougher and more durable than soft keratin of skin • Root is in skin, shaft projects from the skin • Hair pigments: melanins (yellow, rust, brown, black) – Gray/white hair: decreased melanin production, increased air bubbles in shaft BIOL 105 Lab 5A--Skin 18 Hair • Functions – Alerts body to presence of insects on skin – Helps to keep us warm – Guards scalp against physical trauma, heat loss, and sunlight • Distribution – Entire surface except palms, soles, lips, nipples, and portions of external genitalia BIOL 105 Lab 5A--Skin 19 Hair Follicle • Extends from epidermal surface into dermis • Sensory nerve endings wrap around each hair bulb or root • Bending of hair stimulates these nerve endings; hair functions as a very sensitive touch receptor • Hair Bulb • Hair grows from the bulb which contains blood vessels and nerves BIOL 105 Lab 5A--Skin 20 Hair Follicle • Extends from epidermal surface into dermis • Two-layered wall: outer--connective tissue, inner-epithelial tissue • Deep end expands to form hair bulb • Sensory nerve endings wrap around each hair bulb or root • Bending of hair stimulates these nerve endings; hair functions as a very sensitive touch receptor Hair Bulb • Hair grows from the bulb which contains blood vessels and nerves BIOL 105 Lab 5A--Skin 21 • Arrector pili muscle – Smooth muscle attached to follicle – Responsible for “goose bumps” BIOL 105 Lab 5A--Skin 22 Hypodermis or superficial fascia (because it is superficial to the fascia which wraps the skeletal muscles) Not technically part of skin • Subcutaneous tissue deep to dermis • Consists mostly of adipose tissue – This area gets thicker with weight gain • What surgical procedure do some people have to get rid of this fat? • Anchors skin to underlying structures • Is shock absorber • Is an insulator BIOL 105 Lab 5A--Skin 23 LABWORK 1. List, identify, and describe the major regions of the skin. 2. List, identify, and describe the layers of the epidermis (Pacinian and Meissner’s Corpuscle slides may work best). 3. List, identify, and describe the structures found in the dermis (scalp and corpuscle slides may be best). BIOL 105 Lab 5A--Skin 24