INTEGUMENTARY SYSTEM

Introduction to the SKIN!Integumentary System

Skin (aka- cutaneous membrane)NailsHair FolliclesSkin Glands

The skin is the largest organ by weightFunctions:

Protective coveringSlows water lossRegulates body temperatureHouses sensory receptorsExcretes small amounts of wasteHelps in vitamin D formation

Tissues of the Skin- Into to Layers2 distinct layers

Epidermis Outer layer Stratified squamous epithelium

Dermis Inner layer Connective tissue Smooth muscle tissue Nervous tissue Blood

Layers are separated by a basement membrane

Tissues of the Skin- HypodermisSubcutaneous layer

Aka- hypodermisNot part of the skinAreolar and adipose tissuesBinds skin to underlying organsHelps insulateContains blood vessels that supply the skin

The dermis and hypodermis lack a sharp boundary

Tissues of the Skin- InjectionsIntradermal injections

Injected into the skinSubcutaneous injections

Injected into the hypodermisAdministered through a hollow needleAlso called hypodermic injections

Transdermal patchesDrug passes into the epidermis through a

permeable membraneMotion sickness, chest pain, blood pressure,

smoking cessation

The Epidermis- Characteristics and FunctionsLacks blood vesselsThickest on palms and soles (0.0-1.4 mm)Other body regions average 0.07-0.12 mmProduction of new epidermal cells balances loss of dead

cells in healthy skinSkin does not completely wear awayCell division increases where skin is rubbed/pressed

regularly Leads to calluses and corns

Protective FunctionsShields against water lossPrevents injuryProtects against harmful chemicalsKeeps out pathogens

The Epidermis-Layers4 main layers:

Stratum corneum Outermost layer Keratinized, dead epithelial cells Keratinization- hardening of cells, waterproof keratin

proteins made and stored in the cellsStratum granulosumStrantum spinosumStratum basale

Deepest layer Able to divide and grown Receive nutrients from dermis Contains melanocytes

The Epidermis- PigmentationThe epidermis contains melanocytes

Produce the pigment melaninFound in the stratum basale

MelaninProvides skin colorAbsorbs UV radiation

Effect of Environmental FactorsSunlight, UV light, X rays

Rapidly darken melanin Stimulate melanocytes to produce more pigment Pigment is transferred to nearby cells

Effect of BloodWell oxygenated blood is bright red

Light-complexioned people may appear pinkDilated vessels redden the skin

Overheated, embarrassed, under the influence of alcohol

Constriction of vesssel cause loss of color Low body temperature, frightened/anxious person

Human Skin ColorDetermined by heredity and environmental &

physiological factorsAll people have ~same number of melanocytesDifferences in skin color result from different

amounts of melanin produced Controlled by several genes More melanin = darker skin

The Dermis- General CharacteristicsThe boundary between the epidermis and dermis

is unevenDermal papillae extend from dermis into ridges

of the epidermisIncreases surface areaMost abundant in hands and feetForm fingerprints

Genes determine general patterns Fetal movement forms distinct characteristics

The dermis binds epidermis to underlying tissuesThickness ranges from 0.5 mm to 3.0 mm

The Dermis- LayersPapillary Layer

Upper layerAreolar connective tissue

Reticular LayerLower layerDense irregular connective tissueGive skin toughness and elasticity

The Dermis- Additional Components

Smooth muscle fibersCan wrinkle the skin (testes)Associated with hair follicles and glands

Skeletal muscle fibersVoluntary movements (facial expressions)

Nerve cellsCarry impulses to dermal muscles and glandsCarry sensory impulses away from sensory

receptors Lamellated corpuscles

In deep dermis Respond to heavy pressure

Tactile corpuscles In upper dermis Sense light touch and texture

Accessory Structures (blood, hair follicles, glands)

Accessory Structures of the Skin-NailsProtective coveringsComponents:

Nail plateNail bed

Skin surfaceLunula

Most actively growing region Produces keratinized, dead cells

Wears away with normal useAnalogous to hoofs and claws of other animals

Accessory Structures of the Skin- Hair FolliclesHair is present on all surfaces except: palms,

soles, lips, nipples and parts of external reproductive organsNot well developed on other surfaces (forehead)

Originates in epidermisNourished by dermisGrow, divide and push older cells toward

surfaceCells become keratinized and dieCreate the hair shaft

Average hair loss is 20-100 hairs a dayA single hair grows 2-6 years and is then

replaced by a completely new hairGenes determine hair color

direct the type and amount of pigment produced by melanocytes

Arrector pili muscles attaches to each hair follicleContraction causes hair to stand upCauses goose bumps

Accessory Structures of the Skin- GlandsSebaceous glands

Associated with hair folliclesOil glandsProduce sebum (oil and cell fragments)Ducts usually empty into hair folliclesActivated by hormonesKeep hairs and skin soft, pliable and

waterproofNot on palms or soles

Sweat glands~2 million per personWidespreadOriginates in deep dermisEccrine glands

Most numerous Abundant on forehead, neck, back Palms and soles

Respond to elevated body temperature Also respond to emotional stress

Apocrine glands Develop a scent as they mix with skin bacteria Activated at puberty React to emotional upset, fright, pain, sexual arousal Most unmberous in axillary regions and groin

Specialized sweat glandsCeruminous glands- ear waxFemale mammary glands- milk