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Anatomy and Physiology I BIOL 2401 Chapter 5 Integumentary System Integumentary system: • Skin • Accessory structures – glands, hair, nails, sensory receptors Functions of the Skin • • • • • Protection – Stratified epidermis…protects from abrasions – Sweat and sebum…protects from bacterial infections – Keratin…water proofing – Melanin…protects from UV – WBC in dermis…immunity Temperature regulation – Sweat…evaporates to cause cooling – Blood vessels…vasoconstriction/vasodilation to regulate heat loss from warm blood in the skin – Arrector pili…goose bumps Sensation – Nerves to sense touch, temperature and injury (pain) Excretion – Sweat…salts, lactic acid, urea Synthesis of vitamin D – For absorption of calcium Skin Two parts/layers: • Epidermis • Dermis *Subcutaneous layer attaches the skin to underlying muscles Skin - Epidermis Stratified squamous epithelium Composed of 4-5 layers: • Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum basale Four Principle Cells of the Epidermis • keratinocytes produce the protein keratin, which helps protect the skin and underlying tissue from heat, microbes, and chemicals, and releases a waterproof sealant • Melanocytes produce the pigment melanin which contributes to skin color and absorbs damaging ultraviolet (UV) light • Langerhans cells- derived from bone marrow – participate in immune response • Merkel cells contact a sensory structure called a tactile (Merkel) disc and function in the sensation of touch Skin Epidermis Stratum corneum: • Top layer with flat, dead cells • Packed with keratin • Continuously shed as dander Stratum lucidum: • Dead keratinocytes • Present only in thick skin (palm, sole) Stratum granulosum: • Keratinocytes making keratin • Degenerating nucleus…dying cells Stratum spinosum: • Live, non-dividing keratinocytes • Phagocytize melanin from melanocytes present in S basale Stratum basale: • Deepest layer • Actively dividing cuboidal cells • Produce new cells that are pushed upwards to become keratinocytes of S spinosum • Have melanocytes (make melanin) and Merkel cells (touch sensation) Skin - Dermis Connective tissue layer • collagen & elastic fibers • fibroblasts, macrophages & fat cells Contains • hair follicles • glands • nerves • blood vessels Two major regions • papillary region • reticular region Skin - Dermis Papillary region: • Areolar (loose) connective tissue • Upper region of dermis • Has finger like projections dermal papillae • Contains capillaries that feed epidermis • Contains Meissner’s corpuscles (touch) & free nerve endings for sensations of heat, cold, pain, tickle, and itch • Dermal papillae reflect on the surface as epidermal ridges and fingerprints – increase friction for grasping objects Skin - Dermis Reticular region: • Dense connective tissue • Lower region of dermis • Has glands, hair follicles and fat tissue • Specific arrangement of collagen fibers reflect on the surface as cleavage lines and wrinkle lines • Provides strength and ealsticity to the skin Skin - Hypodermis Also referred to as: Subcutaneous layer Superficial fascia Made of adipose tissue (loose connective tissue) Attaches skin to the underlying muscle layers Skin Color Three main factors affecting skin color: 1. Melanin: Brown pigment Gives brown color to the skin Made by melanocytes in S basale layer Pigment phagocytized by keratinocytes of upper layers of epidermis Amount of pigment is controlled by: • Genetics • UV exposure • Hormone 2. Carotene: – Yellow pigment (also found in yellow fruits and vegetables) – Used to make vitamin A – Gives yellow hue to the skin 3. (Hemoglobin) Blood capillaries: – Network of capillaries varies in dermis – Gives reddish color to the skin Skin color clues: • Jaundice - yellowish color to skin and whites of eyes due to the buildup of yellow bilirubin in blood from liver/blood disease • Cyanosis - bluish color in the nails and skin due to oxygen circulation deficiencies • Erythema: redness of skin due to dilation of blood capillaries in the dermis, caused by inflammation, infection, allergy or burns Albinism: melanocytes are present but melanin gene is mutated little or no melanin made no color in the skin, hair and eyes Vitiligo: partial or complete loss of melanocytes patchy skin Accessory Structures of the Skin Formed by the epidermis Hair - Hair follicle • Glands – Sudoriferous gland – Sebaceous gland • Nails Accessory Structures of the Skin - Hair Hair parts: • Shaft • Root Made of: • medulla, cortex & cuticle Hair follicle: • Jacket that surrounds hair root • Made by pushing in of the S basale and S spinosum of the epidermis • Base of the follicle – Bulb • Surrounded by touch sensitive nerves – hair root plexus • blood vessels • germinal cells in papilla for hair growth Arrector pili: • Smooth muscle band - attaches follicle to epidermis • Contracts goose bumps Accessory Structures of the Skin - Hair Hair Color, Growth and Function Hair color depends upon amount and type of melanin: • Dark hair – a lot of melanin • Red and blonde hair – different type of melanin • Gray hair – decrease in melanin production (decreasing tyrosinase) • White hair – absence of melanin and presence of air bubbles in hair medulla Hair growth cycle: • Growth stage – lasts for 2 to 6 years – matrix cells at papilla of hair root producing cells • Resting stage – lasts for 3 months – cells accumulate keratin & follicle atrophies Old hair falls out and growth stage begins again Normal hair loss is 70 to 100 hairs per day Growth and replacement cycle affected by illness, diet, high fever, surgery, blood loss, severe emotional stress, and gender (hormones). Chemotherapeutic agents affect the rapidly dividing matrix hair cells resulting in hair loss. Function: protects from sun, prevents heat loss, and provides touch sensitivity Glands of the Skin Exocrine glands: • Sebaceous (oil) glands • Sudiferous (sweat) glands • Ceruminous (wax) glands • Mammary (milk) glands • • • • Glands of the Skin - Sebaceous Gland Usually connected to hair follicles Absent in the palms and soles Located in the dermis Exocrine gland – produce sebum • contains cholesterol, proteins, fats & salts – secretions are stimulated by hormones at puberty • Function: • moistens hairs • waterproofs and softens the skin • inhibits growth of bacteria & fungi (ringworm) Acne – bacterial inflammation of glands Glands of the Skin - Sudoriferous Gland • • • Located in the dermis Duct opens on to the surface of the skin Function: – regulates body temperature through evaporation (perspiration) – help eliminate wastes such as urea Sweat: water, salts, urea, lactic acid, ammonia…. Eccrine sweat glands Apocrine sweat glands 1. Located all over the body, more in the palm and soles limited in distribution to the skin of the axilla, pubis, and areolae 2. Secretory portion is in dermis with duct to surface secretory portion in dermis duct that opens onto hair follicle 3. Active right after birth Active after puberty 4. Secretion is commonly referred to as “sweat” secretions are more viscous, and have a distinct odor. 5. regulate body temperature through evaporation (perspiration) help eliminate wastes such as urea. Glands of the Skin – Other Glands Ceruminous (wax) glands: • • • • Present in the skin lining the external canal of the ear Modified sudoriferous gland Secretes a waxy liquid (cerumen) Function: Protection against moisture and insect entry into the ear canal Mammary (milk) glands: • • • • Located between the pectoralis major muscle and the skin Modified sudoriferous gland Secretes milk Function: Nutrition for the newborn Nails • • • • • Made of thick, keratinized epidermis Divided into: • Nail body - visible part • Nail root – embedded into the skin Lunula: white region of the nail body…thickened stratum basale Eponychium (cuticle): stratum corneum layer that projects over the nail body Nail growth: in the nail matrix surrounding the nail root Thick vs. Thin Skin Mostly refers to differences in epidermis of the skin Thin Skin • Skin is thin and smooth • Most regions of the body • Epidermis has four layers: – S corneum – S granulosum – S spinosum – S basale • • • • S corneum is thinner Sebaceous glands are present Fewer sudoriferous glands Fewer sensory receptors • • • • • • • Thick Skin Skin is thicker and rougher Specific regions – palm and sole Epidermis has five layers: – S corneum – S lucidum – S granulosum – S spinosum – S basale S corneum is thicker Seceous glands are absent More sudoriferous glands More sensory receptors Skin Wound Healing Two types of injuries: • Superficial wounds – Such as abrasions and superficial burns – Healing may take 24 – 72 hours • Deep wounds – Such as deep lacerations or surgical incisions – May take days to months Skin Wound Healing – Superficial Wound Healing Stratum basale cells from the periphery of the wound migrate towards the center divide to make new epidermal cells replace the lost tissue cells become keratinized and pick up melanin skin becomes normal Skin Wound Healing – Deep Wound Healing • • • • Inflammatory phase – Bleeding is stopped by a clot; WBC migrate to clean up Migratory phase – Clot dries to form scab; S basale cells of epidermis migrate under the scab; Fibroblasts of the dermis migrate to form new fibers Proliferative phase – Extensive activity of epidermal cells to make new epidermis; Continued addition of fibers to form new dermis; New blood vessels grow in Maturation phase – The scab comes off; New skin appears from underneath; Scar tissue is lighter and may lack accessory structures Skin Burns: Clinical Applications Caused by: Fire, electricity, radiations, and chemicals Effects on the body: Dehydration, lowered body temperature, decreased blood pressure, decreased or no urine production (kidneys shut down), infections • First degree burn – epidermis is damaged erythema, pain, flaking and peeling • Second degree burn – epidermis and part of the dermis is damaged erythema, blister formation, pain, partial loss of skin functions and some scarring • Third degree burn – epidermis, dermis and accessories lost marble white area surrounded by redness, major scarring Skin Graft: • Autograft – skin from one area to another area of the same individual • Isograft – skin from an identical twin…matching MHC antigens • Homograft – temporary graft skin from another person (donor, cadaver, foreskin) • Heterograft – temporary grafts from another animal • Synthetic skin – artificial skin, temporary use only. Skin Cancer • 1 million cases diagnosed per year • 3 common forms of skin cancer – basal cell carcinoma (rarely metastasize) more than 70% cases – squamous cell carcinoma (may metastasize) approx 25% cases – malignant melanomas (metastasize rapidly) approx 5% cases • most common cancer in young women • arise from melanocytes ----life threatening • key to treatment is early detection watch for changes in symmetry, border, color and size • risks factors include-- skin color, sun exposure, family history, age and immunological status Clinical Applications Psoriasis: more rapid division of the stratum basale thicker S corneum dry scales and flakes on the surface Callus and Corns: frequent friction on skin over a bone thicker S corneum painful thickening Stretch marks: due to sudden stretching of the reticular region of the dermis Tattoos: special pigments used to permanently color the dermis Aging and Integumentary System • Number of fibroblasts and fibers decrease – Skin looses it’s elasticity and attachment to underlying layers • WBC (macrophages) does not protect – Infections • Loss of subcutaneous fat – Skin becomes thinner • Decrease in activity of sebaceous and sudoriferous glands – Skin dries, cracks and gets infected • Decrease in melanocyte number and activity – Skin color becomes patchy