Introduction to Drematology and Venereology

For Udergraduate Medical Students

Studying dermatology cannot be well understood without a basic knowledge of normal skin anatomy & physiology.

Basic knowledge of its structure & function is essential for proper understanding & correct management of its disorder

Basic structure of the skinBasic structure of the skinThe largest organ in our body…

◦ comprises about 15% of the body weight , 10% of total circulation

Human skin is composed of three layers: epidermis, dermis, and subcutaneous tissue (panniculus)

The epidermis, the outermost layer, is formed by an ordered arrangement of cells called keratinocytes

Their basic function is to synthesize keratin, a filamentous protein that serves a protective function.

The dermis is the middle layer. Its principal constituent is the fibrillar structural protein collagen.

The dermis lies on the panniculus, which is composed of lobules of lipocytes

There is considerable regional variation in the relative thickness of these layers:-

The epidermis is thickest on the palms and soles, measuring approximately 1.5 mm. It is very thin on the eyelid, where it measures less than 0.1 mm.

The dermis is thickest on the back, where it is 30 to 40 times as thick as the overlying epidermis.

The amount of subcutaneous fat is generous on the abdomen and buttocks compared with the nose and sternum, where it is meager.

Epidermis Epidermis The outermost part of the skinthickness from 0.1 to 1.5 mmcontinually renewing structure that

gives rise to derivative structures called appendages

The majority of cells in the epidermis are keratinocytes – 80%

Keratinocytes organized in to four layers

ectodermally derived cells

progressively differentiate from proliferative basal cells to the terminally differentiated, keratinized stratum corneum

Keratinocyte differentiation (keratinization) is a genetically programmed, carefully regulated & complex event

endpoint is a terminally differentiated, dead keratinocyte (corneocyte) that contains keratin filaments

resident cells — melanocytes, Langerhans cells, and Merkel cell

many regional differences

Layers of the EpidermisLayers of the EpidermisBasal Layerstratum germinativum contains

mitotically active, columnar-shaped keratinocytes

cells with proliferative potentials gives rise to the whole of the suprabasal cells

K5 and K14 attaches them to the basement membrane (hemidesmosomes)

Desmosomes – lateral attachments

stem cells, transit amplifying cells, and postmitotic cells

Transit time from the basal layer to the SC - 14days

Transit time thru the SC until desquamation - 14days

Spinous layerthe spine-like appearance of the

cell margins in histologic sections“spines” -- abundant desmosomesproduce organelles known as

lamellar granulesThe granules deliver precursors of

stratum corneum lipids into the intercellular space

Granular layerAbundant basophilic

keratohyalin granules Contains components of cornified

cell envelope - profilaggrin, keratin filaments, and loricrin

Stratum corneumanucleate, flattened cornified cellsmechanical protection and barrier

functiontwo-compartments - brick and

mortar - lipid - depleted, protein-enriched

corneocytes - extracellular lipid matrix

Stratum basaleStratum spinosumStratum granulosumStratum corneum

horny cell layer (10-20 layers

granular cell layer (2-3 layers)

suprabasal cell layer (5-10 layers)

basal cell layer (1 layer)

Other cells of the EpidermisMelanocytes -neural crest-derived, pigment-

synthesizing cells that reside in the basal layer

-produce melanin by the process called melanogenesis and inject it in to the Keratinocytes

Merkel cells - slow-adapting mechanoreceptors - hairy skin, skin of the digits, lips, the

oral cavity, and the outer root sheath of the hair follicle

Langerhans cells - immunne competent cells

- dendritic ,antigen processing and presenting cells

- they transport antigen to the regional lymph nodes

DermisDermisA structure below the epidermisVaries in thickness from 0.3mm on

the eyelid to 3.0mm on the backThe bulk of the skin

Elasticity Tensile strength Thermal regulation Water binding sensory function Different interaction

Composed of

CT matrixCells, nerve and vascular networkappendages

CT matrixCT matrixForms

Fibrous -collagen -elastic Filamentous -GP Amorphous -PG -GAG

Fibrous

CollagenElastic CT

CollagenMajor component75% of the dry wtTensile strength

aa → procollagen → collagen fibrils → filaments → network

Types I, III, V

Elastic CTElasticity4%

Elastic fibersElastin

Both are produced by fibrocytes Microfibrils + varing amount of elastin

d/t elastic fibers

OxytalanElauninMature elastic fibers

Amorphous and filamentous

Found b/n the fibrous matrix, on cell surface

PGs and GAG are of the ground substance

GP forms the filamentous

Major PG

Chondrotin sulphate, dermatan sulphate, heparan sulphate,

Determines lateral growth of fibrils

Hyaluronan major component of GAG

Regions of the dermisRegions of the dermisTwo regions papillary dermis PD reticular dermis RD

Bases CT organization Cell density Nerve and vascular pattern

The subpapillary plexus separates the PD from RD

The change from fibrous to adipose CT separates the RD from HD

Papillary DermisPapillary DermisSuperficialArea of interaction with the epidermisUp to the subpapillary plexus

small-diameter collagen fibrils and immature elastic fibers

Many fibroblastic cells – rapid proliferation

More resident cellsCapillaries that extend from

the subpapillary plexus accompanying venules and lymphatics

Reticular dermis Reticular dermis Beneath the subpapillay plexusThe bulk of the demis and the skin

large-diameter collagen fibrils large fiber bundles

Mature, bandlike elastic fibers

Cells of the dermis Cells of the dermis Regular cellsFibroblasts

◦synthesis and degradation of CTMacrophages, dermal dendritic

cells◦highly phagocytic and presents Ag

Mast cells◦Takes part in allergic reactions

In inflammation -more lymphocytes -leukocytes and other

inflammatory cells

Vasculature Vasculature Skin richly supplied More than needed Nutrition, Temprature regulation,

immunologic

Organization arterioles/terminal arterioles

precapillary sphincters arterial and venous capillarie postcapillary venules collecting venules

Lymphatics follow the vascular pattern but started as blind ends

Nerves Nerves Composd of

Sensoryautonomic fibers

Sensory -free nerve endings -specialized receptorsMediates touch, pain, pressure,

temperature, itchAutonomic -in innervates the sweet glands,

vascular SM, arrector pili muscleCutaneous innervations parallels

the vasculature

DEJDEJThe epidermis & dermis are attached by a

special band like structure called the dermo-epidermal junction.

The DEJ is important for the structural integrity of the skin

it provides mechanical support for the epidermis & acts as a partial barrier against exchange of cells & large molecules

Its components can be attacked by immune reactants and their genetic defect is expressed by skin fragility

Subcutaneous TissueSubcutaneous TissueComposed of adipocytes and the

connective tissue septa Important for supporting blood

vessels, nerves & lymphatics to the dermis

Absorbs pressureInvolves in thermoregulation

Hair follicles / other appendages Hair follicles / other appendages

Comprise pockets of epithelium that are continuous with the superficial epidermis

Hair follicles undergo intermittent activity throughout life called hair cycle (growing, involution, resting phases)

Sebaceous glands, arrector pilli muscle and apocrine sweet glands (some areas) are parts of the pillosebaceous unit

Also derived from the epidermis

& opening directly to the skin surface are the eccrine sweat glands present in every region of the body

Sweat glands Eccrine-Originate in

dermis and open on skin surface directly

Apocrine- Large, deep in dermal layer. Open through a hair follicle. Mostly in axillae and groin.

                                                                            

Nail◦consists of

horny “dead” product the nail plate and four specialized epithelia: the proximal

nail fold, the nail matrix, the nail bed, and the hyponychium

◦functions protecting the distal phalanges tactile discrimination pick up small objects natural weapon.

Functions of the SkinFunctions of the SkinMechanical functionThermoregulation Sensory and autonomic functionImmunologic functionVitamin D synthesisExertionSociosexual function

Mechanical functionPhysical barrier - two way - almost by the epidermis - cornified material + IC cement

(lipid) - ceramides, cholesterol, FFAUV protection -melanin mainly- absorbs and

scatters UVThermal and chemical protectionResistance to mechanical forces - provided by the dermis

Thermoregulation Thermal homeostasis -vasoconstriction/vasodilatation -piloerection present/absent -metabolism

increased/decreased -panniculus

Sensory and Autonomic function sensory – free nerve endings - specialized sensory

receptors◦touch, temperature, pain, pressure,

vibration, itch

autonomic – sympathetic and parasympathetic

Immunologic functionFirst barrier to microbial invasionImmune seveillanceTakes part both in innate and

adaptive immunity

Innate immunityPhysical barrier – PH, Secretions…Cells- macrophages, neutrophilsSoluble molecules – complement,

AMPPattern recognition receptors - TLRAdaptive immunityLangerhans and DDC

Vitamin D synthesisIn the presence of UVBIn the keratinocytes of the basal

epidermis7-dehydrocholesterol (provitamin

D3 ) Previtamin D3 Vitamin D3 vitamin D (1,25-hydroxyvitamin D, calcitriol).

Sociosexual functionThe visual appeal, smell and feel

of the skin has importance in social and sexual communication!!!

Thanks

BREAKBREAK

Approach to Dermatologic patients Approach to Dermatologic patients

Not d/t from the general clinical Dx, but it is more focused to the skin

It begins by taking Hx, P/E & lab Ix when needed

HistoryIdentificationPast illnessNutritional historyChief compliantPresent illness medicationSystemic review

Physical examinationV/SAnthropometric measurementsOther systemsMore focus on the SKIN mucus membranes nails hair

Dermatologists vary in whether they prefer to take a history before, during, or after performing a physical examination. In practice, many perform a brief examination initially, obtain some history, then return to a more focused examination.

visual specialty

complete cutaneous examination scalp, eyelids, ears, genitals,

buttocks, perineal area, and interdigital spaces; the hair; the nails; and the mucus membranes of the mouth, eyes, anus, and genitals

Ideal conditions for the complete skin examination

-excellent lighting, bright – natural -fully undressed, a gown -remove makeup or eyeglasses -examining table at a comfortable

height -gynecologic stirps -comfortable room temperature -chaperone

Recommended toolsA magnifying tool such as a loupe,

magnifying glass, or dermatoscope.A bright focused light such as a flashlight

or penlight to sidelight lesions.Glass slides or a hand magnifier for

diascopy.Alcohol pads to remove scale or surface

oil.Gauze pads or tissues with water for

removing makeup.

Gloves to be used for examination when scabies or another highly infectious condition (secondary syphilis) is suspected, when examining mucus membranes, vulvar and genital areas, and when performing any procedure.

A ruler for measuring lesions.Number 15 and number 11 scalpel blades for

scraping or incising lesions, respectively.A camera for photographic documentation.A Wood's lamp (365 nm) for highlighting

subtle pigmentary changes.

History - itching, burning, rash, generalized/localized eruption,

pain, pigmentary changes, swelling, ulceration etc are

presenting symptoms.

- elaborating enquiries are made about complaints

in terms of onset, duration, progression, distribution,

treatments taken etc

- Hx of similar illness previously or in the family, self &/or

family Hx of atopic Dss & other illness should be

enquired

- occupational & social Hx

Physical Examination - At present gross morphology in the form of

skin lesions remains the hard core of dermatological Dx.

- skin lesions are visible to the naked eye - using the same general principle of clinical

Dx makes the Dx of skin ds. - A proper skin examination should be

performed in good light preferably in daylight. Ideally the whole skin should be examined.

While describing skin lesions, the following features should be identified:-

Four cardinal features◦Type of lesion:◦Shape of individual lesions: ◦Arrangement of multiple lesions: ◦Distribution

Extent of involvement Pattern

Four cardinal features

◦ Type of lesion: macule, papule, nodule, vesicle, etc.

◦ Shape of individual lesions: annular, iris, arciform, linear, round, oval, umbilicated, etc.

◦ Arrangement of multiple lesions: isolated, scattered, grouped, linear, herpetiform, zosteriform, etc.

◦ Distribution (be sure to examine scalp, mouth, palms, and soles) Extent of involvement: circumscribed,

regional, generalized, universal? What percentage of the body surface is involved?

Pattern: symmetry, exposed areas, sites of pressure, intertriginous areas?

“He who studies skin diseases and fails to study the lesion first will never learn dermatology.”

Siemens(1891-1969)

Description of LesionsDescription of Lesions

Primary LesionsPrimary Lesions

Macule

-flat normal surface size <0.5cm in diameter

-area of color different from the surrounding skin or mucous membrane

Patch

-similar to a macule but size >0.5cm

Papule

-a solid, elevated lesion less than 0.5 cm in size

Plaque

-solid plateau-like elevation

-width >> height diameter > 0.5 cm

Nodule -a solid, round or

ellipsoidal, palpable lesion that has a diameter larger than 0.5 cm.

-depth of involvement and/or substantive palpability

Vesicle

-a fluid filled cavity size <0.5cm

Bulla/blister

-a fluid filled cavity size >0.5cm

Pustule

-a vesicle filled with pus

Cyst -an encapsulated

cavity or sac lined with a true epithelium that contains fluid or semisolid material (cells and cell products such as keratin

Secondary LesionsSecondary Lesions

Erosion -loss of a

portion or all of the viable epidermal or mucosal epithelium

-heals without scaring

Ulcer

-full thickness loss of epidermis & some dermis,

-heals with scaring

Atrophy -depression of

the surface due to thinning of

the epidermis or dermis. There are often fine

wrinkles & the blood vessels easily seen

under the skin

Fissure

-linear split in the epidermis or dermis at an orifice( angle of the mouth or anus) over a joint or along a skin crease.

Surface features - Scale : dry/flaky surface due to abnormal

stratum corneum with accumulation of or increased shedding of keratinocytes

-Crust : serum, blood or pus that has dried/ accumulated on the surface

-Excoriations : are surface excavations of epidermis that result from scratching

- Lichenification : thickening of the epidermis with increased skin markings due to persistent scratching.

THE ENDTHE END