d anatomy and physiology of the hair and skin
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Anatomy and Physiology of the Hair and Skin
Learning Objectives1.) Name the layers of the epidermis.2.) Name appendages within the dermis.3.) List the major functions of the skin.4.) Name components of the pilosebaceous
unit.5.) Name the three stages of hair growth.
Integumentary systemThe skin and its accessory organs
Sebaceous glandsSudoriferous glandsSensory perceptorsHairNails
Pilosebaceous unitThe hair follicle and its appendages
Internal and external root sheathsHair shaftDermal papillaSebaceous glandArrector pili muscle
Overall Look at SkinBody’s largest organ
Up to 20 square feet on the average personMade of epithelial tissue and connective tissue
Epithelial – forms thin protective layerConnective – binds, protects, cushions, & supports
3 main layersEpidermisDermisSubcutis or subcutaneous layer
Epidermis“Horny Zone”
Stratum CorneumStratum LucidumStratum
Granulosum“Germinal Zone”
Stratum SpinosumStratum
Germinativum
Cells divide in the lowest layer
Migrate up to replace dead cells that have been shed
As they move up, they are filled with keratin to protect against invasion (keratinization)
Stratum CorneumA.K.A – “horny layer”Outermost layer of dead skin cellsConstantly sheddingMostly bound by sebum
Sebum – fatty or oily secretion of sebaceous gland; serves as lubrication
Stratum LucidumBelow stratum corneumCells allow light to pass through themOnly present in palms of hands and soles of
feet, where epidermis is thickestPurpose unknown
Stratum GranulosumAKA – “granular layer”Cells are livingAs cells are pushed upward, lose nuclei and
dieGives skin opaque appearanceVaries in thickness
Persistent friction and pressure cause areas to thicken for protection and form calluses
Stratum SpinosumAKA – “Prickle cell layer”Made of living cellsAttached to each other by prickly shaped
fibers
Stratum GerminativumLowest layer of epidermisMitosis (cell division) occurs hereCells migrate up, replacing dead skin cells
that have been shedDesquamation (exfoliating dead skin cells)
takes about 28 daysStratum mucosum – single cell layer
Stratum GerminativumContains melanocytes
UV rays react with amino acid tyrosine found in melanocytes to produce melanin
MelaninDark pigment gives skin color and protects
dermis from UV radiation and sun damage
Skin ColorSkin color depends on melaninPeople have same number of melanocytes
Dark skin – melanocytes are more active, producing more melanin
DermisLiving layer or “true skin”Made of dense connective tissueDivided into two layers
Papillary layer Reticular layer
Papillary layerMade of fibers called papillae
Connects epidermis and dermisSuperficial capillaries looped around
papillaeNerve endings sensitive to touchThis layer forms the connective tissue
sheath around hair follicles.
Reticular LayerThickest layer of skinDense bundles of collagen fibers
Fibers are denser closer to papillary layer and thin as they near the fatty subcutaneous tissue
AppendagesArrector pili musclesBlood vesselsFat cellsHair folliclesLymph vesselsNerve endingsSebaceous glandsSudoriferous glands
Blood SupplyArteries and veins circulate into the dermis
and branch into smaller capillaries at the hair follicles, the hair papillae, and glands
Transports oxygen-rich blood and nutrients essential for:GrowthReproductionTissue repair
Lymph SupplyLymph glands produce lymph
Contains waste products, salts, nitrogenous wastes
Carried through vessels to lymph nodes and fluid is filtered for excretion
Sudoriferous GlandsSweat glandsFound deep in dermis
Tubular ducts going to pores in epidermisTwo kinds of sweat glands:
Apocrine Eccrine
Types of Sudoriferous GlandsApocrine
Found in genital area and armpits (axillae) Create body odor Believed to excrete pheromones
Eccrine Found all over body Increased numbers on forehead, palms,
soles of feet
Sebaceous GlandsFound all over skinMost often appendages to the hair follicles
and open into the shafts of the folliclesProduce waxy, oily substance called sebum
which lubricates skin Most active during puberty
Nerve EndingsCarry impulses to the brainFound at various levels, various shapes,
depending on purposeMost superficial are responsible for touchClose to surface is pain receptor
Below that are receptors for heat and coldDeeper in dermis are pressure receptors
Hair AKA – pilosebaceous unit Found all over body except palms of hands
and soles of feet Most is invisible to naked eye
Denser on head and limbs, after puberty in groin area and axillae (armpits)
Hair growth influenced by hormones and genetic inheritance
Subcutaneous LayerLocated at base of dermisLayer of fatty tissueAKA – subcutis; adipose tissueSeparates dermis from muscles and helps
skin to move over themContains arteries, veins, lymph, nerve
endings, fat cells
Structure of Hair – Follicular Canal and Sheaths
Follicular canal – depression in the skin that houses the hair
External root sheath – inner side of canal
Hair ShaftLined with epidermal tissue extends through
dermis into subcutaneous tissueEpidermal cells produce follicle and hair
matrixBase of follicle widens into hair follicle bulb
Bulb – where hair grows; contains hair matrix which is where cell division occurs
Hair matrix produces the hair and external and internal root sheath
Internal Root SheathInnermost layer of
the follicleCan sometimes
see on tweezed hair Looks like clump
of petroleum jellyProtects hair up as
far as sebaceous gland
Dermal Papilla and PapillaeDermal papilla – located at base of bulb
Layer of dermal tissue that attaches itself to the epidermis with papillae
Papillae contain blood vessels – needed for nutrients and hormones for growth
Arrector Pili MuscleAttaches to the underside of the hair at the
dermal papilla and the hair shaftResponsible for lifting the hair, trapping a
layer of air on the skin’s surface assisting in heat regulation fear and cold stimulate contraction causes “goose bumps”
Sebaceous GlandAttached to hair follicle and opens into
shaftSecretes sebum
Lubricates hair to prevent dryness and breakage
Lubricates epidermis to prevent dryness and to prevent bacteria and germs from entering
Layers of the Hair3 layers compose the hair:
1.) Cuticle2.) Cortex3.) Medulla
CuticleOutermost layerPurpose: protect inner layers of the hair
CortexBelow the cuticleContains pigment that gives hair its colorGives hair its strength and elasticity
MedullaInnermost layerAKA – pith or marrowFine hair lacks medullaCan be found in all wavy hair
General rule: curlier the hair, the stronger the medulla
3 Types of Hair1.) Lanugo2.) Vellus3.) Terminal
LanugoAKA – fetal hairSoft, downy hair on fetuses in utero and
infants at birth, covering bodies and scalpMay contain pigment, light or darkSheds a few weeks after birthPermanent hair begins to grow in
Vellus – “peach fuzz”Confused with lanugo; difference is vellus is
present through adulthoodFine, short, often no pigment or medullaWomen believed to have 55% more vellus
hair than men
TerminalLonger, coarser hair that covers scalp, arms,
legs, groin area, axillae, and on faces, chests, and backs of men
Hair follicles can produce vellus or terminal hair.
Affected by:AgeGeneticsHealthHormonal changes of puberty, pregnancy,
and menopause
Stages of Hair Growth1.) Growing - Anagen
2.) Transitional - Catagen
3.) Resting – Telogen
**ACT
Anagen: The Growing PhaseHair follicle at its deepestHair matrix active, surrounding the dermal
papillaCan be affected by health of the individualOnce hair reaches full length it can remain
there, depending on location, for varying amounts of time.
Catagen: The Transitional PhaseFollicle separates from dermal papilla and
shrinks to 1/3 of sizeThin cord of epidermal tissue attaching
follicle to dermal papilla retracts upward with the dermal papilla
Shortest hair growth stage
Telogen: The Resting StageFollicle is 1/3 of original sizeBase looks like clubBulb is usually whiteDermal papilla is separated from hair
follicle and attached by thin cord of epidermal cells; will be released by end of phase
Hair GrowthIncomplete scienceThings we know:
Hair grows faster in the summerGood health improve hair growthYoung people experience more hair growthIncrease in number of telogen hairs during
illness, after childbirth, and when experiencing stress.
Functions of the SkinLargest sensory organMultiple functions:
ProtectionHeat regulationExcretion – discharging waste materialSecretion – producing and discharging substances
from glandsAbsorption – uptake of one substance into anotherSensationSynthesis of Vitamin D
Hair plays important role in these functions.
ProtectionSkin protects the body against the
environment and invasion of bacteria.Skin is usually NOT sterile and is covered
by bacteria Noninvading and nonpathogenic bacteria
Built-in protective aid, ACID MANTLE
Acid MantlepH of 5 to 5.6Created by the combined activity of sweat
and sebaceous glandsPerspiration is acidic and acts as bactericide
(inhibits growth of bacteria)NOT TRUE of areas of higher perspiration
(groin and axillae), skin is softer and less acidity in excessive perspiration
Protection continuedWhen organism does invade skin, reactions
(inflammation, swelling, welts) occur.Leucocytes are released and destroy the
invading organism.Reactions help to prevent spread of
infection to surrounding tissue.
Protection continuedHorny layer acts as barrierSkin is waterproof (thanks in part to sebum)Sebum prevents drying and cracking →
prevents bacteria and germs from enteringWhen intact, skin prevents harmful fluids from
entering and prevents water, blood, and lymph from leaving.
Protection continuedStratum germinativum protects by containing
melanocytes which produce melaninMelanin – the body’s own sunscreen which protects
from harmful UV radiationDark skin get better protection, few incidences of
skin cancer
Protection continuedAdipose tissue – cushions the body from
falls, protects against minor trauma, and provides source of energy
Protection by Lymphatic SystemLymphatic fluid and lymphocytes are
produced in lymph nodes.Lymphocytes transported through lymph
vesselsEngulf bacteriaCarried back to lymph nodesFiltered and drained of waste products
Heat RegulationHealthy body temperature of 98°F or 37°CSkin helps body to adjust and maintain a
safe temperatureEvaporationPerspirationRadiationInsulation
Heat Regulation – Evaporation and PerspirationEvaporation of perspiration produces
cooling (AKA thermoregulation).
Heat Regulation - RadiationRadiation from constriction or dilation of
capillaries affect body temperature.Dilation (expansion) causes surface heat of
body to be reduced through radiation. Causes flushed appearance.
Constriction (contraction) slows blood flow, preserving heat. Gives skin bluish tint.
Heat Regulation - InsulationArrector pili muscle contracts, lifts hair,
trapping a layer of insulating air on skin’s surface. (Air is the best insulator!)
Sebum lubricates hair, preventing it from breaking; allows hair to do its job.
Adipose tissue acts as effective insulator, keeping body warm.
Secretion and ExcretionSebaceous glands – secrete sebum, skin’s
natural lubricantSudoriferous glands – excrete salt, urea,
and other waste material during perspiration.
SensationExperience heat, cold, pain, pressureDamage to nerves can leave the skin
numb, once tissue has healed.
Absorption and PenetrationSkin can absorb oil- and fat-based
substancesPharmaceutical creams and lotions
penetrate the dermis and absorb into the blood supplyRequire medical guidance and physicians’
prescriptions to be obtained
Absorption and PenetrationCosmoceuticals contain NO drugs or
medications but could cause drug reactions.May have deeper absorption qualities than
over-the-counter cosmetics.Obtained from and require professional
guidance of dermatologist, plastic surgeon, or skin-care professional.
1.) What are the three main layers of the skin?
Epidermis, dermis, and subcutis or subcutaneous layer.
2.) Into which two zones is the epidermis divided?
Horny zone and germinal zone.
3.) Name two layers of the epidermis.
Stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum germinativum.
4.) In which layer are melanocytes found?
Stratum germinativum
5.) What are the two layers of the dermis?
Papillary layer and reticular layer
6.) What is a sudorific gland?
A sweat gland, or gland that excretes salt, urea, and other waste material.
8.) Where is the hair matrix?In the hair follicle bulb
9.) What are the three stages of hair growth?
Anagen, catagen, and telogen
10.) Name at least five functions of the skin.
Protection, heat regulation, excretion, secretion, absorption, sensation, synthesis of Vitamin D.