Skin and Its Functions: Layers, Pigments, Glands, and More

HUMAN ANATOMY AND PHYSIOLOGY LECTURE CHAPTER 5 - INTEGUMENTARY SYSTEM INTEGUMENARY SYSTEM DERMIS • • • • • • • • • • Integument - covering Components o Skin o Hair o Nails o Glands Functions o Protection - water loss, microbes, UV light o Sensation - hot, cold, pain, pressure o Temperature regulation - helps maintain homeostasis o Excretion - removes waste o Vitamin D production - UV light stimulates production Skin o Weighs 9 lbs. o Used to determine body fat o 2 main regions: epidermis and dermis • • • • • • • • • • EPIDERMIS 1st major skin region (outside) Composed of stratified squamous epithelium Keratinization o process in which new cells (with keratin) push old cells to surface o 940-56 days for new cells to reach surface Strata of Epidermis o Stratum corneum ▪ outermost layer of epidermis ▪ 20-30 layers of dead squamous cells filled with keratin ▪ accounts for 75% of epidermal thickness ▪ dandruff is this layer flaking off scalp o Callus - forms when stratum corneum has frequent friction o Stratum basale o deepest layer of epidermis o single layer of cells o firmly attached to dermis 2nd major skin region Dense connective tissue Contains collagen and elastic fibers Contains fibroblasts, nerve endings, smooth muscle, glands, blood vessels, and hair follicles Cleavage lines o area where skin is most resistant to stretching o due to orientation of collagen fibers o important in scarring Layers of Dermis o Papillary layer - thin connective tissue layer that contains blood vessels ▪ Dermal papillae • projections that extend up into epidermis • remove waste and help regulate body temp. • ridged on hands and feet (fingerprints) • pattern is genetically determined o Reticular layer o deepest layer of dermis o accounts for 80% of dermis HYPODERMIS Below dermis Foundation of skin Attaches skin to underlying muscle and bone Contains loose and adipose tissue Contains ½ of body’s fat Body fat for females 20-23%, males 13-25% SKIN CLOR AND VARIATIONS • • • Determined by: o pigments o genetics o blood circulation o thickness of stratum corneum Melanocytes of darker skinned people produce more and darker melanin than fairer skinned people All races have same number of melanocytes SKIN PIGMENTS • • • • • Melanin o produced by melanocytes o ranges from yellow to reddish-brown to black o responsible for hair and eye color o provides protection against UV light o amt. produced determined by genetics, UV light, hormones o freckles - accumulation of melanin o albinism - absence of melanin Carotene o yellow-orange pigment found in plants o accumulates in stratum corneum Hemoglobin o gives pinkish-red color o found in red blood cells Tanning and Sunburns o Exposure to UV light stimulates melanocytes to increase production of melanin o Melanin builds up to help protect skin against UV radiation (tan) o A sunburn is the skin reacting to UV exposure o UV light causes elastic fibers to clump and become leathery o UV light can alter DNA in cells causing them to mutate (cancer) Skin Color and Disease o Redness - fever, hypertension, inflammation, allergies o Pallor - anemia or low blood pressure o Jaundice - liver disorder (yellow) o Bronzing - Addison’s disease (kidney disease) o Bruising - broken blood vessels • • • • How is hair produced? o Hair is produced in hair bulb o Hair bulb rests on blood vessels to supply it with nutrients o Hair grows longer as cells are added to base of hair bulb Hair Facts o Testosterone and good nutrition promote hair growth o Growth occurs in cycles: active and resting o Scalp hair grows for 3 years and rests for 1 year o Eyelashes grow for 30 days and rest for 105 days o We lose about 90 scalp hairs/day o Grey hair is the loss or fading of melanin o Male pattern baldness is from the loss of the hair follicle Hair Muscles o Arrector Pili: ▪ smooth muscle that surrounds each hair follicle ▪ contracts and hair stands on end (goose bumps) Glands o Sebaceous glands ▪ connected to hair follicle ▪ sebum - oily substance that lubricates hair and skin to prevent drying o Eccrine sweat glands ▪ all over body and open into sweat pores ▪ water and salt secretions o Apocrine sweat glands: ▪ open into hair follicle ▪ only in armpits and genitalia ▪ thick, rich secretions ▪ become active during puberty and cause body odor NAILS HAIR • • • • • Hair/shaft - flexible strands of keratinized cells Root - below skin (scalp) Hair Bulb - base of root; where hair is produced Hair Folliclegroup of cells that surround root and bulb; gives hair different shapesfgh • thin plate with layers of dead stratum corneum cells with hard keratin Nail Structure o Nail body - visual part o Nail root - covered by skin o Cuticle - stratum corneum that extends into nail body o Nail matrix - continuation of nail root; gives rises to most of nail o Nail bed - attaches to nail and is distal to nail matrix o Lunula - part of nail matrix; whitish, crescent shaped area; base of nail VITAMIN D PRODUCTION 1. 2. 3. UV light causes skin to produce a precursor molecule of vitamin D Precursor is carried by blood to liver where it is modified Next to kidneys where it is modified again to form active vitamin D • Vitamin D o can also be ingested through fish oils, fortified milk, eggs, and butter. o stimulates intestine to absorb calcium and phosphate (bone growth and muscle function) • • • TEMPERATURE REGULATION • • • • Body temp. should be 98.6oC Rate of chemical reactions (metabolism) is altered by changes in temp. To cool body: o blood vessels in dermis dilate and heat is transferred from deep in tissues to skin and sweat is produced Too heat body: o blood vessels constrict to reduce blood flow to skin and heat is retained AGING AND THE INTEGUMENT • • • Blood flow decreases and skin becomes thinner due to decreased amounts of collagen Decreased activity of sebaceous and sweat glands make temperature regulation more difficult Loss of elastic fibers cause skin to sag and wrinkle BURNS • • • 1st degree: o damages only epidermis o redness, slight swelling, pain o heals within 2-3 days (usually no scar) o includes sunburns or exposure to cold 2nd degree: o damages epidermis and upper dermis o redness, swelling, pain, blisters o heals in 2 weeks with some scarring 3rd degree: o destroys epidermis and dermis o burned areas are cherry red to black o nerve endings are destroyed o skin graft might be necessary SKIN CANCER • • • • • • Most common cancer Mainly caused by UV light exposure Fair-skinned people more prone Prevented by limiting sun exposure and using sunscreens UVA rays cause tan and is associated with malignant melanomas UVB rays cause sunburns • Sunscreens should block UVA and UVB rays Basal cell carcinoma: o cells in stratum basale affected o cancer removed by surgery Squamous cell carcinoma: o cells above stratum basale affected o can cause death Malignant melanoma: o arises from melanocytes in a mole o rare type o can cause death