Chapter 5 - The Integumentary System

Integumentary System

• largest organ system of the body

  • accounts for 16% of body weight

• composed of

  • skin

  • exocrine glands

  • hair, nails

Cutaneous Membrane

Epidermis - superficial epithelium

Dermis - connective tissues

• Papillary

• Reticular

Epidermis

Stratified Squamous Epithelium

• protects dermis, tissues, organs

• excretion of salts, water, organic wastes through glands

• maintenance of body temp (insulation & evaporation)

• prevents water loss & entry of pathogens

• production of melanin & keratin

• synthesizes vitamin D3

• storage of lipids

• sensory receptors detect touch, pressure, pain, temp

Keratinocytes

• contain large amounts of keratin

• most abundant ells in epidermis

Melanocytes

• containing pigment melanin

• contribute to skin color

• protect underlying tissues

Papillary Layer

• nourishes and supports epidermic from blood

• areolar tissue

• contains capillaries, lymphatics & sensory neuron endings

• dermal papillae project between epidermal ridges

Reticular Layer

• dense irregular connective tissue

• has sensory receptors that detect touch, pressure, pain, vibration, temp

• blood vessels assist in thermoregulation

• contains larger blood vessels, lymphatics & nerve fibers

• composed of collagen & elastic fibers

  • provides skin with flexibility & resilience properties

Cutaneous Membrane

Epidermis - superficial epithelium

Dermis - connective tissues

Subcutaneous Layer (Hypodermis)

• elastic areolar & adipose connective tissue

• provides stability for skin

• site of subcutaneous injection

Types of Skin

• depends of # of epidermal layers

Thin

• covers most of the body

• 4 layers of keratinocytes

Thick

• covers palms of hands & soles

• 5 layers of keratinocytes

Layers of Thick Skin

• Stratum Corneum

• Stratum Lucidum

• Stratum Granulosom

• Stratum Spinosum

• Stratum Basale

Layers of Thin Skin

• Stratum Corneum

• Stratum Granulosom

• Stratum Spinosum

• Stratum Basale

Stratum Basale

• attached to basement membrane by hemidesmosomes

• strong bond between epidermis & dermis

• forms epidermal ridges (basis of fingerprints)

• dermis forms dermal papillae (tiny mounds)

  • increases surface area of basement membrane

  • provides added strength between epidermis and dermis

Cells of Stratum Basale

• keratinocytes

• basal cells (germinative or stem)

• Merkel cells

  • found in hairless skin

  • respond to touch

• melanocytes

  • produce melanin

Stratum Spinosum

aka “spiny layer”

• produced by stratum basale stem cell division

• 8-10 layers of keratinocytes bound by desmosomes

• cells shrink untill cytoskeleton protrudes

• contains dendritic (Langerhans) cells

Stratum Granulosum

aka “grainy layer”

• keratinocytes stop dividing

• begin to produce protein fibers

  • keratin - tough, fibrous protein

  • keratohyalin - dense granules, cross-link keratin fibers

• dehydrated & dies

• form tightly interlocked layer of keratin surrounded by keratohyalin

Stratum Ludicum

aka “clear layer”

• found only in thick skin

• translucent cell layer

Stratum Corneum

aka ‘horn layer”

• exposed surface of skin

• 15-30 layers of keratinized cells

• water resistant

• shed & replaced about every 2 weeks

Keratinization (Cornification)

• formation of a layer of dead, protective cells packed with keratin

• relatively dry layer that is moistened by sebaceous glands

• occurs on all exposed skin surfaces except eyes

• takes up to 7-10 days for newly generated cells to migrate form stratum basale to stratum corneum

Types of Perspiration

Insensible - interstitial fluid lost by evaporation through stratum corneum

Sensible - water excreted by sweat glands

Dehydration of Skin

• damages stratum corneum

• increases insensible perspiration

  • particularly dangerous for burn victims

Hydration of Skin

• replenishes tissues

Pigments in Skin Color

Carotene

• orange-yellow pigment

• found in orange veggies (ex: carrots)

• accumulates in epidermal cells & dermal fatty tissue

• can be converted to vitamin A

Melanin

• yellow-brown or black pigment

• produced by melanocytes in stratum basale

• melanosomes are transferred to keratinocytes

RBC

Melanocytes

• found associated with stratum basale

• long process extend from melanocyte into stratum spinosum

• melanin is transferred to keratinocytes by means of pigment-carrying melanosomes

  • travels up via transcytosis

Contribution to Skin Color

• melanin protects skin from sun damage

• melanosomes shield nucleus of keratinocytes

Melanocyte Contribution:

• level of melanin

• melanin isoform expression

• equivalent #s of melanocytes

RBC Contribution:

• skin reddens when heat causes blood vessels to dilate

• skin turns pale as blood flow decreases

• skin developed bluish tiny due to severe reduction in blood flow or oxygenation

Jaundice

• build-up of bile produced by the liver

• yellowing of the skin

Pituitary Tumor

• skin darkening due to excess MSH (melanocyte-stimulating hormone)

Addison’s Disease

• skin darkening due to excess ACTH (adrenocorticotropic hormone)

Vitiligo

• loss of color in patches of melanocyte populations

Vitamin D3 (aka Cholecalciferol)

• produced in response to UV radiation or obtained from diet

• converted to calcidiol by liver

• converted to calcitriol by kidney

  • resulting in absorption of Ca + P

• deficiency causes Rickets (weak & flexible bones)

Epidermal Growth Factor (EGF)

• potent peptide growth factor

• produced through glandular secretions

  • submaxillary glands & glands in small intestine

• promotes division of stratum basale stem cells

• accelerates keratin production

• stimulates epidermal repair & glandular secretion

Dermatitis

• inflammation of papillary layer

• caused by infection, radiation, chemicals, mechanical stimulation

• symptoms include itch and pain

Skin Damage

• reduction in skin elasticity caused by

  • dehydration, age, hormones, UV exposure

• stretch marks

  • thickened tissue caused by excessive stretching

Cleavage / Tension / Langer Lines

• collagen and elastic fibers arranged in parallel bundles

• arrangement enables resistance of forced from specific directions

• cut or incision parallel to bundles remain closed and heals well

• cuts perpendicular to bundles causes wound to pull open and often results in scarring

Blood Supply to the Dermis

Cutaneous Plexus - network of arteries along reticular layer

Subpapillary Plexus - capillary network arising from small arteries in papillary layer

Venous Plexus - capillary return deep to papillary plexus

Contusion - damage to blood vessels resulting in blood leaking into dermis, leaving bruising

Nerve Fibers in Skin Control…

• blood flow

• glandular secretions

• sensations

  • light touch - tactile (Meissner’s) corpuscles in dermal papillae

  • deep pressure & vibration - lamellated (Pacinian) corpuscles in reticular layer

  • pain & temp - sensory endings in epidermal & dermal layers

Accessory Structures

• derived from embryonic epidermis

• located in dermic

• project through skin surface

Functions of Accessory Structures

Hair Follicles

• protect skull

• provides delicate touch sensations on general body surface

Exocrine Glands

• assist in temp regulation & waste excretion

Nails

• protect & support tips of fingers & toes

Hair

• dead, keratinized epithelial tissue

• are active organs of skin

  • located in fermis

  • extends from epidermal surface to dermis (even to hypodermis)

  • epithelial cells wrap a dense connective tissue sheath

  • sensory nerve endings surround follicle base

Some regions are hairless

• palm, sole, sides of fingers & toes, lips, portions of external genatalia

Arrector Pili

• bundle of involuntary smooth muscle

• extends from papillary layer of dermis to connective tissue sheath of follicle

Sebaceous Glands

• lubricates hair

• conditions epithelial layers

• inhibits bacterial growth

Apocrine Sweat Glands

• coiled, tubular glands found in armpits, around nipples, pubic region that begin secreting at puberty

• secret by apocrine secretion into hair follicles

• produce sticky, cloudy secretions

• breakdown of bacteria causes odors

• surrounded by myoepithelial cells

  • squeeze gland, forcing secretion onto surface of skin

  • regulated by neural and endocrine systems

Merocrine (Eccrine) Sweat Glands

• widely distributed on body surface

  • concentrated on pamls & soles

• coiled, tubular gland

• watery discharge directly onto skin

• responsible for sensible perspiration

• lose water, salt, & organic material

• thermoregulation

  • maintains sensible perspiration

  • integrated nervous & cardiovascular system

• flushes microorganisms & harmful chemicals from skin

• controlled independent of other glands

• localized stimulation of sweating

Ceruminous Glands

• produce cerumen (earwax)

• protects eardrum

Autonomic Nervous System (ANS)

• involuntary control of sebaceous & apocrine sweat glands

• all glands effected concurrently

Repairing the Integument

• injury occurs with bleeding & inflammatory response is triggered

• blood clotting occurs, scab stabilizes & protects wounded area

• stem cells migrate around wound

• macrophages clean area

• fibroblasts & endothelial cells migrate to area

  • producing granulation tissue (scar tissue)

  • inflammation decreases, clot disintegrates

  • raised keloid may form

4 Phases of Repairing the Skin

Inflammation Phase

• bleeding occurs at site immediately after injury

• mast cells in region trigger inflammatory response

Migratory Phase

• scab will form after several hours, cells of stratum basal are migrating along edges of wound

• phagocytic cells remove debris, and more arrive due to enhanced circulation of area

• clotting around edges of affected area particularly isolates region

Proliferation Phase

• after a week, scab has been undermined by epidermal cells migrating over collagen fiber meshwork produced by fibroblast proliferation & activity

• phagocytic activity around site has almost ended

• fibrin clot is dissolving

Scarring Phase

• after several weeks, scab shed and epidermis is complete

• shallow depression marks injury sit, but fibroblasts in dermis continue to create scar tissue that will gradually elevate overlying epidermis