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By: dr. Susianti, M.Sc.

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GENERAL FEATURES

The largest and heaviest organ

Protects:Microorganism, toxic substances,dehydration, UV, impact, frictionSensory receptorExcretionVit D metabolismRegulation of blood pressure and body temperature

A. General Functions

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2 type :Thin skin (epidermis 75-150 m)Thick skin (epidermis 400-600 m)

Consist of:

EpidermisDermis

B. General Organization

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1. EpidermisOuter layer of skin, from ectodermKeratinized stratified squamous epithelium

Avascular

Innervation is by uncapsulated nerve endings5 layers:

Stratum corneumStratum lucidum

Stratum granulosumStratum spinosumStratum basale

superf ic ia l

deep

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2. Dermal-epidermal junction

The stratum basale is underlying by a basementmembrane

Epidermal ridgesDermal papillae

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4. Hipodermis/ subcutaneous

fasciaNot a part of the skin

Derive from mesodermLoose connective and adipose tissueVariety of thickness depending on: nutritionalstatus, level of activity, body region, gender

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Glands (sebaceous & sweat)

HairsNails

C. Structures Associated with the skin

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EPIDERMIS

Two major cell populations:KeratinocytesMelanocytes

Two minor cell populations: Langerhans Merkels

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A. Keratinizing System

Keratinocytes make up most of the epidermisContinous turnover (renewal) of the skin surface

by passing through 4 overlapping processes:Cell renewal/ mitosisDifferentiation/keratinizationCell death

ExfoliationEntire process take 15-30 days

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2. Stratum spinosum

Cuboidal/polygonaluntill slightlyflattened

Several layers Tonofibril spiny

appearance

Malphigian layers

Mitotic rate is lowerthan stratum basale

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3. Stratum Granulosum

3 5 layers Flattened polygonal

Basophilickeratohyalingranules

Ovoid/ rodlikelamellar granules

releaseglycosaminoglycansand phospholipids

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4. Stratum Lucidum

5. Stratum Corneum

Acidophilic Translucent Without nuclei and organelles Dense cytokeratin embedded in matrix (from keratin

granules), sometimes called eleidin

Dead cells Plate like

No nucleus Thickened plasma membrane Mature keratin / scleroprotein

L

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B. Pigmentation System

Factors affecting skin color:Melanin andcarotene,number of blood vessels,blood color,thickness of dermis

1. MELANINS- Skin, eye, hair color- Synthesized by melanocytes- Eumelanins (dark brown) & pheomelanins (red)

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Diagram of a melanocyte (shown in color). Its arms extend upward into the intersticesbetween keratinocytes. The melanin granules are synthesized in the melanocyte, migrate

to its arms, and are transferred into the cytoplasm of keratinocytes. Ribosomes, Golgicomplex, rough endoplasmic reticulum and mitochondria are also present.

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2. MELANOCYTES

- Derive from the neural crest- Scattered among the keratinocytes of the

stratum basale

- Have round cell bodies, central nuclei andlong cytoplasmic processes- Melanosomes: in which melanin is

synthesized- Dark- and lightly- skinned races: the same

number of melanocytes

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3. MELANIN SYNTHESIS

Tyrosinase Tyrosinase

Tyrosin DOPA Dopaquinone Melanin

4. FATE OF MATURE MELANIN GRANULES-Mature melanin granules injected into keratinocytes

-Melanin granules accumulate over the nuclei ofdividing keratinocytes to protect nuclei.

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5. MELANIN FUNCTION

- Melanins major protective effect from freeradicals

6. SOME FACTORS AFFECTING MELANINSYNTHESIS:- Exposure to UV rays- Melanocytes- Stimulating Hormones- ACTH Addisons disease - Albinism- Hydroquinone

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C. Langerhans Cells

Star shaped cells in the stratum spinosumRodlike or racket shaped cytoplasmic granules

(Birbecks granules) As a macrophage and antigen- presentingcells

Also occur in oral and vagina epithel

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LANGERHANS CELL

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D. Merkels Cells

In the stratum basaleMost numerous in thick skin

Resemble basal keratinocytesFree nerve ending form a dislike expansion(Merkels disk) that covers the basal surface ofeach Merkels cell

as sensory mechanoreceptors

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DERMIS

Contain:Hair folliclesSebaceous glandsSweat glands

Consist of 2 layers of vascular connective tissue:Papillary layer

Reticular layer

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A. Papillary LayerLoose connective tissueRich in elastic fibersDermal papillae interdigitate with epidermal ridges

Anchoring fibrils (special collagen fibers)The tips of dermal papillae contain Meissners

corpuscles

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B. Reticular LayerThicker layer of dense irregular connective tissue

Richly vascularized: Arterioanastomoses/shuntRichly supply of nerves free and encapsulatedendings (Eg: Pacinian corpuscles)

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BLOOD SUPPLY

Skin receive blood supply through the dermalblood vessels (4.5 % of the body total bloodvolume)

1. Arterial plexuses2. Papillary capillaries3. Venous plexuses4. Arteriovenous anastomoses (shunts)

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HAIR

Only in thin skinIts color, size, shape and distribution varyaccording to race, age, sex, and body regionStructures that form and maintain: hair follicles

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A. Follicle and Hair Development

1. FOLLICLES

- In the third month of human development:local epidermal thickenings form invadethe dermis dermal papila invades

epidermal down growth- Differentiation: hair bulb hair follicle +

sebaceous gland

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2. HAIRS

- Fifth or sixth month of gestation: fine hair(lanugo).

- Before birth: Lanugo shed, except: scalp,

eyebrows, eyelashes- A few month after birth:* lanugo coarser mature terminal hair ,* rest of body fine short hair (vellus)

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- Puberty: coarse terminal hairs replace vellus in specific

body areas

axilla, pubic region, face, over the restof the body

axilla, pubic region

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B. Follicle andHair Structure

1. Germinal matrix2. Hair shaft layers : medulla,

cortex, cuticle3. Root sheats : Internal root

sheath, external rootsheath, glassy membrane,connective tissue sheath

4. Associated structures :Sebaceous glands,arrector pili muscles

DP:Dermalpapilla

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Hair Follicle

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C. Keratinization of Hair

Different with epidermis:- Keratin is harder- Keratinized hair cells remain tightly attached,

not sloughed- Keratinization is intermittent and restrict in the

bulb- Differ in structure and function depending on

hair position

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D. Hair Growth

Not continous, but cyclesGrowing phase: Proliferation and differentiation

Resting phase: germinal matrix becomeinactive

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NAILS

The end of the third month of the embryonic

development : Narrow plate of epidermis invadesunderlying dermisNail grooveNail matrix Differentiate nail plate, nail bed

A. Nail Develpoment

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Nail plate (nail body, nail root)

Nail matrix

Nail bed

Eponychium (or cuticle)

Hyponychium (distal)

Lunula (whitish, opaque,crescent shaped region on

the proximal nail body)

B. Nail Complex Structure

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SEBACEOUS GLANDS

Exocrine gland in the thin skinOften in association with hair follicleMost numerous: face, forehead, scalp

Acinar secretory contain many large lipid

A. Structures and Location

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Containing a mixture of triglycerides, waxes,squalene, and cholesterol and its esters.

Mixture + Cell debris: Sebum

Holocrine secretion

Lubricates the skin, have antibacterial or antifungal

effects

B. Function

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Sweat glands

Two types:

Eccrine (merocrine) Apocrine

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- Distribution, occur most of the body, except, glanspenis, clitoris, lips

- Structure :1. Duct : coiled, simple to stratified cuboidal

epithelium2. Secretory portion (pyramidal+myoepithelial)3. Secretory product : watery secretion (NaCl,

urea, ammonia, uric acid)- Excreting products of protein metabolism- Evaporation of water reduces body

temperature

A. Eccrine (merocrine) Sweat Glands

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B. Apocrine Sweat Glands

B. Apocrine sweat glands- Distribution : axilla, pubic and anal regions, areola of the

breasts

- Structure : simple coiled tubular- Duct : Coiled ducts + low cuboidal epithelium

- Secretory portions : in dermis, wide lumen, cuboidal to

columnar cells + myoepithelial

- Secretory products : viscous, odorless fluid

Apocrine: secretory cells released their apical

cytoplasm.