Anatomy of the SkinAnatomy of the Skin

The Epidermis IIThe Epidermis IIDr Mesfin HunegnawDr Mesfin Hunegnaw

Consultant Dermatologist & VenerologistConsultant Dermatologist & Venerologist

AAU, Medical facultyAAU, Medical faculty

Dept. of DermtovenerologyDept. of Dermtovenerology

Epidermal Dynamics and KineticsEpidermal Dynamics and Kinetics According to experimental dataAccording to experimental data

- 10% of basal keratinocytes act as new foci os - 10% of basal keratinocytes act as new foci os

epidermis or “STEM CELLS”epidermis or “STEM CELLS”

- 50% of basal cells undergo further division serving as - 50% of basal cells undergo further division serving as

“ “TRANSIENT AMPLIYFING POPULATION”TRANSIENT AMPLIYFING POPULATION”

- 40% are Postmitotic- 40% are Postmitotic

Epidermal...Epidermal... KineticsKinetics

- Turnover Time: time for whole cell population to renew - Turnover Time: time for whole cell population to renew

itself which is dependant on cell cycle (time taken for itself which is dependant on cell cycle (time taken for

individual cells to divide) and growth fraction (proportion individual cells to divide) and growth fraction (proportion

of basal cells dividing). of basal cells dividing).

Turnover Time Normal(days) Psoriatic(days)Turnover Time Normal(days) Psoriatic(days)

Germinative 12 – 19 1.5Germinative 12 – 19 1.5

Stratum corneum 14 2Stratum corneum 14 2

Total Epidermis 52 – 75 8 - 10Total Epidermis 52 – 75 8 - 10

Epidermal RegulationEpidermal Regulation In the normal state epidermal thickness and population size is In the normal state epidermal thickness and population size is

maintained at a constant.maintained at a constant. This control of epidermal homeopoiesis maintained by This control of epidermal homeopoiesis maintained by

by a balance of stimulatory and inhibitory signal. by a balance of stimulatory and inhibitory signal. StimulatorsStimulators

- Epidermal Growth Factor (EGF)- Epidermal Growth Factor (EGF)

- Transforming Growth Factor alpha from keratinocytes- Transforming Growth Factor alpha from keratinocytes

- Keratinocyte Growth Factor from Dermis- Keratinocyte Growth Factor from Dermis Inhibitors Inhibitors

- Transforming Growth Factor beta- Transforming Growth Factor beta

- Pentapeptide- Pentapeptide

- Alpha and Gamma Interferon and Tumor Necrosis Factor.- Alpha and Gamma Interferon and Tumor Necrosis Factor.

Non Keratinocytes of Epidermis Non Keratinocytes of Epidermis The MelanocyteThe Melanocyte

- dendritic pigment synthesizing cells of the basal layer.- dendritic pigment synthesizing cells of the basal layer.

- cells derived from the neural crest and and enter to the - cells derived from the neural crest and and enter to the

epidermis around 7 week.epidermis around 7 week.

- distribute themselves in non random fashion with the help of - distribute themselves in non random fashion with the help of

integrin receptors.integrin receptors.

- characterized by pale cytoplasm, ovoid nucleus and the - characterized by pale cytoplasm, ovoid nucleus and the

pigment containing melanosomes.pigment containing melanosomes.

- organizational and functional interaction with keratinocyte- organizational and functional interaction with keratinocyte

- ‘Melanocyte – Epidermal Unit’- ‘Melanocyte – Epidermal Unit’

- 36 keratinocytes to 1 melanocte- 36 keratinocytes to 1 melanocte

- transfer of pigment ? cytoplasmic communication- transfer of pigment ? cytoplasmic communication

? phagocytosis of dendrite? phagocytosis of dendrite

Non Keratinocytes....Non Keratinocytes.... - Regulation: Paracrine, Hormonal and Extrinsic factors.- Regulation: Paracrine, Hormonal and Extrinsic factors.- bFGF: powerful melanocyte mitogen from keratinocytesbFGF: powerful melanocyte mitogen from keratinocytes- IL – 1alphaIL – 1alpha- IL – 6IL – 6- TNF alphaTNF alpha- Melanocyte Stimulating HormoneMelanocyte Stimulating Hormone- Sex HormonesSex Hormones- Vitamin D3Vitamin D3- Inflammatory MediatorsInflammatory Mediators- UVBUVB

N eu r a l C r e st

M elan ob la st

E y e

In n er ear

M en in g e s

Non Keratinocytes...Non Keratinocytes... Langerhans CellLangerhans Cell - dendritic pigment free cells of the epidermis.- dendritic pigment free cells of the epidermis.

- distributed in all layers except the coneal layer but - distributed in all layers except the coneal layer but usually found in the suprabasal layers.usually found in the suprabasal layers. - comprise 2 – 8 % of cells in epidermis.- comprise 2 – 8 % of cells in epidermis. - pale staining cytoplasm with convoluted nuclei well - pale staining cytoplasm with convoluted nuclei well developed ER, golgi complex and lack melanosomes.developed ER, golgi complex and lack melanosomes. - contain vimentin intermediate filaments and unique- contain vimentin intermediate filaments and unique Langerhan cell granules/Birbeck BodiesLangerhan cell granules/Birbeck Bodies - primary cells in epidermis for recognition, uptake, processing - primary cells in epidermis for recognition, uptake, processing

and persentation of skin antigens: reticuloepithelial trap.and persentation of skin antigens: reticuloepithelial trap. - APC derived from the bone marrow- APC derived from the bone marrow - CD4, CD45, HLADR- CD4, CD45, HLADR

Non Keratinocytes...Non Keratinocytes... Langerhan cells... continuedLangerhan cells... continued

- Involved in allogenic and autogenic antigen specific T cell - Involved in allogenic and autogenic antigen specific T cell activation, Cytotoxic T cell response, Contact hypersenstivity,activation, Cytotoxic T cell response, Contact hypersenstivity,

sensitivity involved in rejection of skin allografts.sensitivity involved in rejection of skin allografts.- impaired function by UV radiation.impaired function by UV radiation.- ?reason for PUVA therapy?reason for PUVA therapy

Non Keratinocytes...Non Keratinocytes... Merkel Cells Merkel Cells - slow adapting mechanoreceptors located in sites of high - slow adapting mechanoreceptors located in sites of high tactile sensitivity.tactile sensitivity. - found among basal keratinocytes from which they recieve - found among basal keratinocytes from which they recieve stimuli as the keratinocyte is deformed and closely associated stimuli as the keratinocyte is deformed and closely associated with a neurite.with a neurite. - hairy and glaborous skin of digits, oral cavity, outer root - hairy and glaborous skin of digits, oral cavity, outer root sheath of hair follicle.sheath of hair follicle. - pale staining cytoplasm, lobulated nucleus and cytoplasmic - pale staining cytoplasm, lobulated nucleus and cytoplasmic ‘ ‘spines’ spines’ - contain keratin K18/K8/K19- contain keratin K18/K8/K19 - first appear at 11 weeks of gestation- first appear at 11 weeks of gestation - originate most likely from the epidermis itself.- originate most likely from the epidermis itself. - ?Neurite and Merkel cell function as a Synapse- ?Neurite and Merkel cell function as a Synapse

Histologic CorrelatesHistologic Correlates AcantholysisAcantholysis

- loss of cohesion between keratnocytes due to breakdown of - loss of cohesion between keratnocytes due to breakdown of intercellular bridgesintercellular bridges

- seen in disease states like pemphigus and variants, - seen in disease states like pemphigus and variants,

Darier’s disease transient or persistent acantholytic dermatosisDarier’s disease transient or persistent acantholytic dermatosis

AcanthosisAcanthosis

- increase in the number of cells of the prickle cell layer- increase in the number of cells of the prickle cell layer

- distinct from pseudoacanthosis (cell enlargement)- distinct from pseudoacanthosis (cell enlargement)

- naevoid conditions and localized benign epidermal tumours - naevoid conditions and localized benign epidermal tumours like keratodermas epidermal naevi.like keratodermas epidermal naevi.

- virally induced papillomatosis like viral wart or molluscum.- virally induced papillomatosis like viral wart or molluscum.

-secoundary to inflammatory conditions like pruigo. cronic -secoundary to inflammatory conditions like pruigo. cronic eczema. eczema.

Histologic...Histologic... HyperkeratosisHyperkeratosis - increased thickness of the stratum corneum.- increased thickness of the stratum corneum. - there may be associated acanthosis.- there may be associated acanthosis. - can occur in keratodermas and some icthyotic disease- can occur in keratodermas and some icthyotic disease

ParakeratosisParakeratosis - retention of keratinocyte nuclei in the horny cell layer- retention of keratinocyte nuclei in the horny cell layer - commonly seen in conditions like psoriasis and subacute - commonly seen in conditions like psoriasis and subacute

eczemaseczemas

SpongiosisSpongiosis - intercelllar edema and widening of space between - intercelllar edema and widening of space between

keratinocytes due to fluid accumulation.keratinocytes due to fluid accumulation. - seen in acute and subacute eczemas- seen in acute and subacute eczemas