MHS1102 Lecture 2 Integumentary System PDF

MHS1102: LECTURE 2 INTEGUMENTARY SYSTEM  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin  Describe the structures that comprise the integumentary system  Outline the structure and cells of the layers of...

MHS1102: LECTURE 2 INTEGUMENTARY SYSTEM  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin  Describe the structures that comprise the integumentary system  Outline the structure and cells of the layers of the skin  Describe the appendages of the skin [hair & nails]  Name two types of sweat glands & describe the structure & function of each  Describe the types of cancers that can arise from cells of the skin  Discuss the healing process in skin following injury  THE INTEGUMENTARY SYSTEM  comprises skin & accessory organs [hair, nails & glands]  largest & heaviest organ of body  covers 1.5-2.0 m2 & 15% of body weight  thickness ranges from 0.5-6 mm Thick skin: palms of hands, soles of feet  sweat glands, but no hair follicles or sebaceous glands  epidermis 0.5 mm thick Thin skin covers rest of body  hair follicles, sebaceous glands & sweat Photos © McGraw-Hill Education glands  epidermis ± 0.1 mm thick  FUNCTIONS OF THE SKIN  Resistance to trauma & infection  keratin  acid mantle Other barrier functions  H2O barrier – prevents H2O getting in  H2O retention fostered by tight junctions between skin cells  helps prevent dehydration  UV radiation  harmful chemicals  Vitamin D synthesis  skin carries out first step  liver & kidneys complete process Photos © McGraw-Hill Education  FUNCTIONS OF THE SKIN  Sensation  extensive sense organ  receptors for temperature, touch, pain,  thermoregulation  vasoconstriction/vasodilation  perspiration b: © McGraw-Hill Education/Joe DeGrandis, photographer  Nonverbal communication Figure 6.2b  facial expression  importance in social acceptance & self image ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin √  Describe the structures that comprise the integumentary system  Outline the structure and cells of the layers of the skin  Describe the appendages of the skin [hair & nails]  Name two types of sweat glands & describe the structure & function of each  Describe the types of cancers that can arise from cells of the skin  Discuss the healing process in skin following injury  THE SKIN & SUBCUTANEOUS TISSUE  Three main layers  epidermis: outer, stratified squamous epithelium  dermis: middle, deeper connective tissue layer  hypodermis - deep, connective tissue layer below dermis (not considered part of skin, but associated with it)  EPIDERMIS  keratinized stratified squamous epithelium keratin – protein: cells at skin surface contain tough keratin protein stratified – layers or strata squamous – cells are flat epithelium – lining tissue ▪ main cell type - keratinocytes  lacks blood vessels - diffusion of nutrients from underlying connective tissue  nerve endings & receptors for touch & pain  LAYERS OF THE EPIDERMIS  Thin skin contains four layers [strata] & thick skin contains five strata Stratum basale (deepest epidermal layer)  single layer of stem cells & keratinocytes resting on basement membrane  stem cells divide & form keratinocytes - migrate to surface to replace lost cells  also contains some melanocytes & tactile cells Stratum basale  LAYERS OF THE EPIDERMIS Stratum spinosum  several layers of keratinocytes joined by desmosomes & tight junctions  named for appearance of cells after histological preparation (‘spiny’)  also contains some dendritic cells Stratum spinosum Photos © McGraw-Hill Education  LAYERS OF THE EPIDERMIS Stratum granulosum  three to five layers of flat keratinocytes  cells contain dark-staining keratohyalin granules Stratum granulosum Photos © McGraw-Hill Education  LAYERS OF THE EPIDERMIS Stratum lucidum  thin, pale layer found only in thick skin  keratinocytes packed with clear protein eleidin – converted to keratin at surface Stratum lucidum Photos © McGraw-Hill Education  LAYERS OF THE EPIDERMIS Stratum corneum (surface layer)  several layers (up to 30) of dead, scaly, keratinized cells  resists abrasion, penetration, water loss Photos © McGraw-Hill Education Stratum corneum  STRATA OF THE EPIDERMIS Figure 6.3 ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  FIVE CELLS TYPES OF THE EPIDERMIS (i) Stem cells - undifferentiated cells that give rise to keratinocytes  in deepest layer of epidermis (stratum basale) Figure 6.3  CELLS OF THE EPIDERMIS (ii) Keratinocytes - majority of epidermal cells - synthesise keratin  produced by mitosis of stem cells in stratum basale  mitosis requires abundant O2 & nutrients - once cells migrate away from blood vessels of dermis, mitosis cannot occur  new keratinocytes push older cells towards surface  flatten, produce more keratin & membrane-coating vesicles  in 30-40 days a keratinocyte makes its way to skin surface & exfoliates  process slower in old age - faster in injured or stressed skin  calluses or corns  CELLS OF THE EPIDERMIS (iii) Melanocytes - synthesize pigment melanin - shields DNA from UV radiation  occur only in stratum basale but branched processes spread upwards & among keratinocytes & distribute melanin  CELLS OF THE EPIDERMIS (iv) Dendritic cells - macrophages, originate in bone marrow ▪ guard against pathogens  in stratum spinosum & stratum granulosum (v) Tactile cells - touch receptor cells associated with dermal nerve fibers  in basal layer of epidermis  SKIN DISORDERS Ichthyosis ▪ genetically inherited [may be acquired] ▪ shedding process inhibited – build-up of dead cells ▪ can result in overheating Eczema ▪ chronic, inherited, inflammatory skin condition with symptoms including areas of dry, itching and reddened skin Exfoliative dermatitis ▪ excessive shedding if skin  DERMIS Connective tissue layer beneath epidermis  0.2 mm (eyelids) to 4 mm (palms, soles)  mainly collagen  rich in blood vessels, sweat glands, sebaceous glands & nerve endings  contains hair follicles & nail roots  attachment for skeletal muscles of facial expression & emotion  DERMIS  forms wavy boundary with the epidermis  dermal papillae - upward, finger-like extensions of dermis  epidermal ridges - downward waves of epidermis  prominent waves on fingers produce friction ridges of fingerprints  DERMIS Two layers Papillary layer ▪ superficial zone  thin areolar tissue in & near the dermal papilla  allows mobility of leukocytes & other defense cells Reticular layer ▪ deeper, thicker layer Figure 6.5 ▪ dense, irregular connective tissue ▪ stretch marks (striae) - tears in collagen fibres due to stretching of skin  SKIN OF FINGER Photos © McGraw-Hill Education Epidermis Dermis Thin skin Thick skin Distal phalynx Middle phalynx Proximal phalynx  HYPODERMIS  subcutaneous tissue  more areolar & adipose tissue than in dermis  pads body & binds skin to underlying tissues  abundant blood vessels - common site of drug injection  Subcutaneous fat  energy reservoir  thermal insulation  thicker in women  thinner in infants, elderly  STRUCTURE OF THE SKIN & SUBCUTANEOUS TISSUE Figure 6.1 Copyright © McGraw-Hill Education. Permission required for reproduction or display.  SKIN COLOR Melanin produced by melanocytes, accumulates in keratinocytes  Two forms of the pigment:  eumelanin - brownish black  pheomelanin - reddish yellow (sulfur-containing) Different skin colors have same number of melanocytes  darker skinned people produce greater quantities of melanin  melanin granules more spread out in keratinocytes  melanised cells seen throughout the epidermis  lighter skinned people  melanin clumped near keratinocyte nucleus  little melanin seen beyond stratum basale  VARIATIONS IN SKIN PIGMENTATION Figure 6.6a,b a: © McGraw-Hill Education/Dennis Strete, Photographer; (girl): © Tom & Dee Ann McCarthy/Corbis; b: © McGraw-Hill Education/Dennis Strete, photographer; (boy): © Creatas/PunchStock RF ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  SKIN COLOR  exposure to UV light stimulates melanin secretion & darkens skin  colour fades as melanin is degraded & old cells are exfoliated Other pigments can influence skin color  haemoglobin - pigment in red blood cells - reddish to pinkish hue to skin  carotene - yellow pigment acquired from egg yolks & yellow/orange vegetables  concentrates in stratum corneum & subcutaneous fat  SKIN COLOURS OF DIAGNOSTIC VALUE  cyanosis - blueness due to oxygen deficiency  albinism - pale skin & blue-gray eyes due to genetic lack of melanin synthesising enzyme  SKIN COLOR  erythema - redness due to increased blood flow to skin  jaundice - yellowing due to bilirubin in blood (e.g. compromised liver function)  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin √  Describe the structures that comprise the integumentary system √  Outline the structure and cells of the layers of the skin √  Describe the appendages of the skin [hair & nails]  Name two types of sweat glands & describe the structure & function of each  Describe the types of cancers that can arise from cells of the skin  Discuss the healing process in skin following injury  SKIN APPENDAGES: HAIR & NAILS  composed of mostly dead, keratinized cells  pliable soft keratin makes up stratum corneum of skin  compact hard keratin comprises hair & nails  tougher & more compact due to numerous cross-linkages between keratin molecules  HAIR Photos © McGraw-Hill Education  HAIR  slender filament of keratinized cells growing from tube/follicle in skin  covers most of the body  not found on palms or soles, nor lateral surfaces & distal segments of digits  limbs & trunk have 55-70 hairs per cm2  face has about 10 times as many  100,000 hairs on average scalp  STRUCTURE OF THE HAIR & FOLLICLE Hair is divisible into three zones along its length (i) bulb: a swelling at the base of the hair follicle where hair originates in dermis  only living hair cells are in or near bulb (ii) root: the remainder of the hair in the follicle (iii) shaft: the portion above the skin surface  HAIR Keratinocytes Hair shaft Photos © McGraw-Hill Education  STRUCTURE OF THE HAIR & FOLLICLE  hair matrix - region of mitotically active cells immediately above papilla  hair’s growth center  dermal papilla - bud of vascular connective tissue encased by bulb  only source of nutrition for hair  STRUCTURE OF THE HAIR & FOLLICLE  hair receptors - sensory nerve fibers entwining follicles  piloerector muscle (arrector pili) - smooth muscle attaching follicle to dermis  contracts to make hair stand on end (goose bumps)  HAIR GROWTH & LOSS  lose± 50-100 hairs daily  hair growth - scalp hairs grow 1 mm per 3 days  alopecia - thinning of the hair or baldness  pattern baldness - hair lost from select regions  baldness allele is dominant in males - expressed when testosterone levels are high  testosterone causes terminal hair on top of scalp to be replaced by thin hair  hirsutism – excess hair in areas that are not usually hairy  SKIN APPENDAGES: NAILS  Fingernails & toenails - clear, hard derivatives of stratum corneum  composed of thin, dead cells packed with hard keratin  Functions:  assist with grooming, picking apart food, other manipulations  provide counterforce to enhance sensitivity of fleshy fingertips to tiny objects  Nail plate - hard part of the nail  free edge: overhangs fingertip  nail body: visible attached part of nail  nail root: extends proximally under overlying skin  NAILS  nail fold - surrounding skin rising above nail  nail groove - separates nail fold from nail plate  nail bed - skin underlying the nail plate  hyponychium - epidermis of nail bed  nail matrix - growth zone (mitotic) of stratum basale at proximal end of nail  1 mm per week in fingernails, slightly slower in toenails  lunule - opaque white crescent at proximal end of nail due to thickness of matrix  eponychium (cuticle) - narrow zone of dead skin overhanging proximal end of nail  NAILS Free edge Nail body Eponychium - cuticle Nail matrix Nail root Photos © McGraw-Hill Education CONDITIONS AFFECTING NAILS  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin √  Describe the structures that comprise the integumentary system √  Outline the structure and cells of the layers of the skin √  Describe the appendages of the skin [hair & nails] √  Name two types of sweat glands & describe the structure & function of each  Describe the types of cancers that can arise from cells of the skin  Discuss the healing process in skin following injury  GLANDS OF THE SKIN: SWEAT GLANDS  Two kinds of sweat (sudoriferous) glands: apocrine & merocrine (i) Apocrine sweat glands  locations: groin, anal region, axilla, areola, beard area in men  inactive until puberty  ducts lead to nearby hair follicles  produce sweat that is milky & contains fatty acids  respond to stress & sexual stimulation  secrete pheromones - chemicals that can influence behavior of others  bromhidrosis - body odour produced by bacterial action on sweat from apocrine glands  myoepithelial cells - contract in response to stimulation by sympathetic nervous system - squeeze perspiration up duct to surface  APOCRINE SWEAT GLAND: LOW & HIGH MAGNIFICATION Epithelium Lumen Myoepthelial cells Lumen Epithelial cells Photos © McGraw-Hill Education  SWEAT GLANDS (ii) Merocrine (eccrine) sweat glands  most numerous skin glands - 3 to 4 million in adult skin  especially dense on palms, soles & forehead  simple tubular glands  watery perspiration that helps cool the body  also have myoepithelial cells  MEROCRINE SWEAT GLAND: LOW & HIGH MAGNIFICATION Epidermis Merocrine sweat gland and duct Dermis Merocrine sweat gland Hypodermis Duct Photos © McGraw-Hill Education  DUCT OF SWEAT GLAND: HIGH MAGNIFICATION Dermis Epidermis Photos © McGraw-Hill Education Duct of sweat gland  SWEAT GLANDS Sweat:  protein-free filtrate of blood plasma produced by deep secretory portion of gland  some NaCl & other small solutes remain in sweat & some reabsorbed by duct  some drugs are excreted in sweat  ±99% H2O, with pH range of 4-6 – acid mantle that inhibits bacterial growth  insensible perspiration - 500 mL/day  does not produce visible wetness of skin  diaphoresis - sweating with wetness of the skin  exercise - may lose 1 L sweat per hour  SEBACEOUS GLANDS  flask-shaped & have short ducts opening into hair follicles  holocrine secretion  sebum - oily secretion of sebaceous glands  keeps skin & hair from becoming dry, brittle & cracked  lanolin - sheep sebum  Sebaceous Gland: High Magnification Sebaceous gland Basal cell of sebaceous gland Duct of sebaceous gland Secretory cells Photos © McGraw-Hill Education Hair follicle  MAMMARY GLANDS  milk-producing glands  develop only during pregnancy & lactation  modified apocrine sweat glands  rich secretion released through ducts opening at nipple  mammary ridges or milk lines  two rows of glands in most mammals  primates only two glands – some individuals have additional nipples along milk line (polythelia)  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin √  Describe the structures that comprise the integumentary system √  Outline the structure and cells of the layers of the skin √  Describe the appendages of the skin [hair & nails] √  Name two types of sweat glands & describe the structure & function of each √  Describe the types of cancers that can arise from cells of the skin  Discuss the healing process in skin following injury  SKIN CANCER  most cases caused by UV rays of sun damaging skin cell DNA  most frequent on head, neck & hands  most common in fair-skinned people & elderly  one of most common, easily treated cancers  one of highest survival rates if detected & treated early  Three types of skin cancer named for epidermal cells in which they originate:  basal cell carcinoma  squamous cell carcinoma  malignant melanoma  BASAL CELL CARCINOMA ▪ most common type & least dangerous - seldom metastasizes ▪ forms from cells in stratum basale ▪ lesion is small, shiny bump with central depression & beaded edges Figure 6.12a  SQUAMOUS CELL CARCINOMA ▪ arises from keratinocytes of stratum spinosum ▪ lesions usually on scalp, ears, lower lip, or back of hand ▪ raised, reddened, scaly appearance later forming a concave ulcer ▪ chance of recovery good with early detection and surgical removal ▪ tends to metastasize to lymph nodes - may become lethal Figure 6.12a Copyright © McGraw-Hill Education. Permission required for reproduction or display. b: © Biophoto Associates/Science  MELANOMA ▪ cancer that arises from melanocytes - < 5% of skin cancers - most deadly form ▪ can be successfully removed if caught early, but if metastasizes it is usually fatal ▪ greatest risk factor: familial history of malignant melanoma ▪ highest incidence in men, redheads & people who had severe sunburn as a child Figure 6.12c Copyright © McGraw-Hill Education. Permission required for reproduction or display. c: © James; Stevenson/SPL/Science Source  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin √  Describe the structures that comprise the integumentary system √  Outline the structure and cells of the layers of the skin √  Describe the appendages of the skin [hair & nails] √  Name two types of sweat glands & describe the structure & function of each √  Describe the types of cancers that can arise from cells of the skin √  Discuss the healing process in skin following injury  BURNS  leading cause of accidental death  fires, kitchen spills, sunlight, ionizing radiation, strong acids or bases, or electrical shock  deaths result primarily from fluid loss, infection & toxic effects of eschar (burned, dead tissue)  debridement: removal of eschar  BURNS  Classified according to depth of tissue involvement  first-degree burns: involve only epidermis  redness, slight edema & pain  heal in days  second-degree burns: partial-thickness burn; involves part of dermis  may appear red, tan, or white; blistered & painful  two weeks to several months to heal & may leave scars  third-degree burn: full-thickness burn; involves epidermis, all of dermis & often some deeper tissues  often requires skin grafts  needs fluid replacement, infection control, supplemental nutrition  DEGREES OF BURN INJURIES Figure 6.13 Copyright © McGraw-Hill Education. Permission required for reproduction or display. a: © Sonda Dawes/The Image Works; (b,c) © John Radcliffe/Science Source  STAGES IN THE HEALING OF A SKIN WOUND  Healing of a cut in the skin:  severed vessels bleed into cut  mast cells & damaged cells release histamine  histamine dilates blood vessels & makes capillaries more permeable  Blood plasma seeps into wound carrying:  antibodies  clotting proteins 1) Bleeding into the wound Figure 5.34 (1) ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  STAGES IN THE HEALING OF A SKIN WOUND  Blood clot forms  knits edges of cut together  inhibits spread of pathogens  forms scab that temporarily seals wound & blocks infection  macrophages phagocytise & digest tissue debris 2) Scab formation & macrophage activity Figure 5.34 (2) ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  STAGES IN THE HEALING OF A SKIN WOUND  new capillaries sprout from nearby vessels  deeper portions of clot become infiltrated by capillaries & fibroblasts  transforms into soft mass called granulation tissue  macrophages remove blood clot  fibroblasts deposit new collagen  begins 3–4 days after injury & lasts up to 2 weeks 3)Formation of granulation tissue (fibroblastic phase of repair) Figure 5.34 (3) ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  STAGES IN THE HEALING OF A SKIN WOUND  epithelial cells multiply & migrate beneath scab (tissue regenerates)  underlying connective tissue undergoes fibrosis  scar tissue may or may not show through epithelium  remodeling (maturation) phase begins several weeks after injury & may last up to 2 years 4)Epithelial regeneration & connective tissue fibrosis (remodeling phase of repair) Figure 5.34 (4) ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.  SCARRING ▪ normal outcome of mammalian tissue repair ▪ in developed world 100 million patients annually acquire scars ▪ some cause considerable issues – aesthetic & social ▪ 55 million elective operations ▪ 25 million operations after trauma ▪ estimated 11 million keloid scars & 4 million burn scars - 70% in children  SCARRING ▪ skin healing without scars possible in early mammalian embryos ▪ complete regeneration occurs in lower vertebrates [salamanders & invertebrates] ?humans ▪ optimised for speed of healing under non-sterile conditions ▪ rapid inflammatory response allows injury to heal quickly ▪ prevents infection & future wound breakdown ▪ individuals with pigmented skin are more prone to severe skin scarring  LEARNING OUTCOMES  By the end of this lecture you should be able to:  Discuss the major functions of the skin √  Describe the structures that comprise the integumentary system √  Outline the structure and cells of the layers of the skin √  Describe the appendages of the skin [hair & nails] √  Name two types of sweat glands & describe the structure & function of each √  Describe the types of cancers that can arise from cells of the skin √  Discuss the healing process in skin following injury √  NEXT LECTURE: CARDIOVASCULAR SYSTEM 1