CHAPTER 5
The Integumentary System
1
INTRODUCTION
• Integument = skin & accessory structures
• Functions:
– Guards body’s physical & biochemical integrity
– Maintains constant body temperature
– Provides sensory information about surrounding environment
2
STRUCTURE OF THE SKIN
• Cutaneous membrane
• Superficial portion = epidermis
– composed of epithelial tissue
• Deeper layer of skin = dermis
– primarily connective tissue
• Deep to dermis = subcutaneous layer (hypodermis)
– not a part of skin
– areolar & adipose tissue
– fat storage
– area for blood vessel passage
– area of pressure-sensitive nerve endings
3
Principle Cells In Epidermis
• Keratinocytes (90% of epidermal cells)
– keratin: protect skin & underlying tissue from heat, microbes,
& chemicals
– lamellar granules: produce waterproof sealant
• Melanocytes (8% of epidermal cells)
– produce melanin
•contributes to skin color
•absorbs damaging ultraviolet (UV) light
– sensitive to UV light
4
Principle Cells In Epidermis
• Langerhans cells (small % of epidermal cells)
– derived from bone marrow  immune response
– extremely sensitive to UV light
• Merkel cells (least numerous cells)
– contact flattened sensory neuron (Merkel disc)
– function in sensation of touch
5
Layers of the Epidermis
• Four or five layers, depending upon degree of friction &
mechanical pressure applied to skin
• From deepest to most superficial, the layers of the epidermis are:
–
–
–
–
–
stratum basale (stratum germinativum)
stratum spinosum
stratum granulosum
stratum lucidum (only in palms and soles)
stratum corneum
6
Stratum Basale
• Also called stratum germinativum
• Deepest layer of epidermis
– Single layer of cuboidal or columnar keratinocytes
– Merkel cells, melanocytes, & Langerhans cells
– Tonofilaments eventually will form keratin in superficial layers
– Desmosomes & hemi-desmosomes attach cells to each other & to
basement membrane
– Rapidly dividing layer
• When destroyed, new skin cannot regenerate without a skin graft
7
Stratum Spinosum
• Superficial to stratum basale
• 8-10 layers of keratinocytes
• Tonofilaments & desmosomes
provide strength & flexibility
• Langerhans cells & melanocytes
also found in this layer
8
Stratum Granulosum
• 3-5 layers of flat apoptotic keratinocytes
• Tonofilaments more apparent
• Lamellar granules release lipid that repels water
• Keratohyalin converts tonofilaments into keratin
• Keratinocytes die
• **Transition between the metabolically active strata &
dead superficial layer**
9
Stratum Lucidum
• 3-5 layers of clear, dead, flattened keratinocytes
• Present ONLY in fingertips, palms & soles  ‘thick
skin’
• Large amounts of keratin
• Thickened plasma membranes
10
Stratum Corneum
• 25 to 30 layers of flattened, dead keratinocytes
• Continuously shed & replaced
• Barrier to light, heat, water, chemicals & bacteria
– Lamellar granules repel water
• Callus = abnormal thickening of stratum corneum
– from constant exposure to friction
11
Keratinization & Epidermal Growth
• Stem cells in stratum basale divide to produce keratinocytes
• Keratinocytes slowly pushed towards surface  accumulate keratin @
each step
•keratinization
– occurs as cells move to skin surface (deep to superfic)
– about 4 weeks from beginning to end
• Epidermal growth factor (EGF) and other hormone-like proteins
regulate epidermal growth
• Psoriasis
– Premature shedding of keratinocytes (7-10d)
– Treated with UV light & topical ointment
12
Dermis
• Connective tissue layer composed of collagen & elastic fibers,
fibroblasts, macrophages & fat cells
• Contains hair follicles, glands, nerves & blood vessels
• Two major regions:
– papillary region
– reticular region
13
Dermis - Papillary Region
• Top 20% of dermis
• Mostly areolar CT
– contains fine elastic fibers
• Dermal papillae = finger-like projections
– anchors epidermis to dermis
– capillary loops feed epidermis
– contains Meissner’s corpuscles & free nerve endings
•touch sensations (Meissner’s)
•heat, cold, pain, tickle, and itch
14
Dermis - Reticular Region
• Attached to subcutaneous (sub-Q) layer
• Dense irregular connective tissue
– interlacing collagen bundles
– coarse elastic fibers
• Some adipose, oil glands, sweat glands, & hair follicles
• Provides strength, extensibility & elasticity to skin
– stretch marks = dermal tears from extreme stretching (striae)
• Epidermal ridges form in fetus as epidermis conforms to dermal
papillae  fingerprints
– genetically determined
– increase grip of hand
15
Skin Pigments
• Melanin produced in epidermis by melanocytes
– tyrosinase converts tyrosine to melanin
•UV light increases melanin production
– differences in skin color determined by **AMOUNT** of
pigment present
• Clinical observations
– freckles or liver spots = accumulation of melanocytes
– mole = benign overgrowth of melanocytes
– albinism = inherited lack of tyrosinase; no pigment
– vitiligo = autoimmune loss of melanocytes in areas of skin
produces white patches
• Three pigments in dermis yield variety of skin colors
– range from yellow to red & tan to black
16
Skin Pigments
• Melanin
– Pheomelanin (yellow to red)
– Eumelanin (brown to black)
– Increased synthesis results in “tan”  protects from further
damage (within limits)
• Carotene in dermis
– yellow-orange pigment (precursor of vitamin A)
– found in stratum corneum & dermis
• Hemoglobin
– red, oxygen-carrying pigment in blood cells
– epidermis is translucent so if other pigments not present,
pinkness will be evident
17
Skin Color as a Diagnostic Tool
• Color of skin and mucous membranes can provide clues for
diagnosing certain problems
– Jaundice
•yellowish color to skin and whites of eyes
•buildup of yellow bilirubin in blood from liver disease
– Cyanosis
•bluish color in nail beds and skin
•hemoglobin depleted of oxygen looks purple-blue
– Erythema
•redness of skin due to enlargement of capillaries in dermis
•caused by inflammation, infection, allergy or burns
– Pallor = paleness of skin resulting from shock or anemia
18
Accessory Structures of Skin
• Develop from embryonic epidermis
• Cells sink inward during development to form:
– hair
– oil glands
– sweat glands
– nails
19
HAIR (PILI)
• Present on all skin surfaces except palms, soles, & palmar/plantar
surfaces of the digits
• Eyebrows & lashes protect from foreign particles
• Sense light touch
• Anatomy
– shaft
– root
– hair follicle
• New hairs develop from cell division of matrix in the bulb
20
Structure of Hair
• Shaft = superficial (visible) portion
• Root = below the surface
• 3 concentric layers
– medulla
•2-3 rows of irregularly. shaped cells
– cortex
•elongated cells
– cuticle
•single layer of thin, flat cells
•heavily keratinized
21
Structure of Hair
• Follicle surrounds root
– Epithelial root sheath
• external root sheath
• internal root sheath
• Dermal root sheath
• surrounds follicle
• Bulb = base of follicle
• blood vessels (in papilla)
• germinal cell layer (matrix)
– arise from str. basale
– **site of cell division**
– gives rise to internal root sheath
22
Hair-Related Structures
• Arrector pili
– smooth muscle associated w/ hair
– contraction causes goosebumps as hair is pulled vertically
• Hair root plexus
– surrounds follicle
– touch-sensitive dendrites
•detect hair movement
23
Hair Growth
• Growth cycle = growth stage & resting stage
– Growth stage
• lasts for 2 to 6 years
• matrix cells at base of hair root divide  length
– Resting stage
• lasts for 3 months
•matrix cells inactive & follicle atrophies
•Old hair falls out as growth stage begins again
– normal hair loss is 70 to 100 hairs per day
• Rate of growth & replacement can be altered by illness, diet, blood loss,
severe emotional stress, & gender
• Chemotherapeutic agents affect rapidly dividing matrix cells
25
ACCESSORY STRUCTURES: Glands
Specialized exocrine glands found in dermis:
• Sebaceous (oil) glands
• Sudiferous (sweat) glands
• Ceruminous (wax) glands
• Mammary (milk) glands
27
Sebaceous glands
•
•
•
•
Usually connected to hair follicles
Absent in palms and soles
Secretory portion of gland is located in the dermis
Produce sebum
– lipid-rich, oily substance
– moistens hairs
– waterproofs and softens the skin
– inhibits growth of bacteria & fungi
• Acne
– bacterial inflammation of sebaceous glands
– caused by increased production of sebum
28
Sudoriferous glands
• Simple, coiled tubular glands
• Eccrine sweat glands (merocrine) = most common
– secretory portion is deep in dermis
– excretory duct terminates as pore at surface of epidermis
– regulate body temp thru evaporation (perspiration)
– help eliminate wastes such as urea
29
Sudoriferous glands
• Apocrine sweat glands
– limited distribution in body
•found in armpit & groin regions
– secretory portion in subcutaneous layer
•secrete via exocytosis (merocrine manner)
– excretory duct opens into hair follicle
– more viscous sweat includes lipids & proteins
– begin functioning @ puberty
– responsible for cold sweats
30
Ceruminous Glands
• Modified sudoriferous glands in external ear
– produce waxy substance called cerumen
– secretory portion in subcutaneous layer
– excretory ducts open into ear canal or sebaceous gland
– secretions = combination of oil & wax glands
•sticky barrier against foreign substances
• Impacted cerumen
– abnormal amount of cerumen in external auditory meatus or
canal
– prevents sound waves from reaching ear drum
31
ACCESSORY STRUCTURES: Nails
• Tightly packed, dead keratinized cells
• Nail body
– pink, visible portion
• Free edge
– extends past distal end of finger
• Nail root
– portion buried in fold of skin
• Lunula
– crescent-shaped area near proximal end
• Hyponychium (nail bed)
– secures nail to fingertip
• Eponychium (cuticle)
– stratum corneum layer
• Nail matrix = growth region of nail
32
FUNCTIONS OF SKIN
• Thermoregulation
– Liberation of sweat lowers body temperature
– Adjusts blood flow in dermis
•Constriction of vessels = warming effect
•Dilation of vessels = cooling effect
– During exercise
•moderate exercise: more blood brought to surface to lower
temperature
•extreme exercise: blood shunted to muscles & body
temperature rises
• Blood reservoir
– extensive network of blood vessels
– 8-10% total blood flow in adult
34
FUNCTIONS OF SKIN
• Protection
–
–
–
–
–
physical, chemical & biological barriers
keratin & tight cell junctions prevent bacterial invasion
lipids retard evaporation
pigment protects somewhat against UV light
Langerhans cells alert immune system to presence of microbes,
etc.
• Cutaneous sensations
–
–
–
–
touch
pressure
vibration
tickle
35
FUNCTIONS OF SKIN
• Synthesis of Vitamin D
– UV light activates precursor molecule in skin
– enzymes in liver & kidneys modify activated molecule to
produce active form of vitamin D
– necessary for absorption of calcium in the GI tract
• Excretion/Absorption
– 400 mL of water/day
– 200 mL/day as sweat (for sedentary person)
•excrete NH3, urea, salts via sweat
– minimal absorption of fat-soluble vitamins
36
Transdermal Drug Administration
• Method of drug absorption across epidermis & into blood vessels
of dermis
– drug contained in adhesive skin patch
– drug absorption most rapid in areas of thin (scrotum, face and
scalp)
• Examples:
– nitroglycerin (prevention of chest pain from coronary artery
disease)
– scopolamine (motion sickness)
– estradiol (estrogen replacement therapy)
– nicotine (stop smoking alternative)
37
Age-Related Structural Changes
• Most age-related changes occur in dermis
– Collagen fibers decrease in number & stiffen
– Elastic fibers lose elasticity & thicken
– Fibroblasts decrease in number
•decreased production of collagen & elastic fibers
•wrinkles
• Decrease in number of melanocytes (gray hair, blotching)
• Decrease in Langerhans cells (decreased immune responsiveness)
• Reduced number and less-efficient phagocytes
• Dermal blood vessels thicken
– decreased nutrient availability
– loss of subcutaneous fat
45
Photodamage
• Ultraviolet light (UVA and UVB) both damage the skin
• Acute overexposure causes sunburn
• DNA damage in epidermal cells can lead to skin cancer
• UVA produces oxygen free radicals that damage collagen
and elastic fibers and lead to wrinkling of the skin
47
Skin Cancer
• 1 million cases diagnosed per year
• 3 common forms of skin cancer
– basal cell carcinoma (metastasis rare)
– squamous cell carcinoma (may metastasize)
– malignant melanomas (rapid metastasis)
•can result in death within months of diagnosis
•key to treatment is early detection
– ‘ABCD’ acronym
•risks factors: skin color, sun exposure, family history, age
& immunological status
48