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.