Histology of the Skin

Kelli A. Hutchens, MD, FCAP Director of Dermatopathology Assistant Professor Loyola University Medical Center Assistant Director of Mechanisms of Human Disease Loyola Stritch School of Medicine

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Objectives

Identify the epidermis, dermis, and subcutis of the skin Name and label the layers five layers of the of the epidermis Compare and contrast the anatomic and histologic differences between thick and thin skin Identify (when possible) / or know the location of the following cells: – Keratinocyte – Melanoycte – Merkel cell – Langerhan cell Describe the general function and location of the following components of the dermal epidermal junction and intercellular space.

– Hemidesmosomes – Basement membrane – Basal layer keratinocytes – Anchoring fibrils – Desmosomes Name and identify the two regions of the dermis Identify and classify the following: – Eccrine gland – Sebaceous gland – Apocrine gland Compare and contrast the histologic appearance, function, and location of Pacinian corpuscles versus Meissner’s corpuscles.

Overview of the Skin

Epidermis Dermis Subcutis

Epidermis

• • • Most superficial layer of the skin Composed of multiple layers of keratin containing epithelial cells = keratinocytes with Melanocytes, merkel cells, and Langerhans dispersed throughout Major functions: – Maintenance of fluid and electrolyte balance – Protection from ultraviolet light – Sensory and immune function

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Epidermis : Layers

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Stratum Corneum Stratum Granulosum Stratum Spinosum Stratum Lucidum Stratum Basale

Thin Skin Rete ridge

Stratum Lucindum

Thick Skin

Differences between thin & thick skin

Thin Skin

• • • Entire body except thick skin areas.

Less than 5 layers of stratum corneum with no stratum lucidum Hair follicles present except lips, labia minora, and glans penis • • • • •

Thick Skin

Palms of hands and soles of feet = acral skin 5 layers thick stratum corneum with increased granular layer More sensory receptors Lack sebaceous glands and increased eccrine glands No hair follicles

Epidermis

• Desquamatization: – Layers of epidermis represent vertical maturation from undifferentiated basal cells to fully differentiated cornified cells – From basal cell to cornified cell takes about 25 days • Shorter maturation periods seen in inflammatory conditions such as psoriasis • Keratin production also changes as the cell matures and disruption in the mechanism can effect the integrity of the keratinocytes such as in Haily-Haily and Darier’s Disease.

Epidermis

Cell to Cell Adherence Zona occludens: tight junctions prevent diffusion across cells Zona adherens: Ca++ dependent cadherins that connect to actin

Macula adherens: Made of desmosomes

Gap junctions: communication for electric / metabolic function Basement Membrane

Hemidesmosomes: connect cells to BM

Epidermis

Desmosome = Intercellular Bridges

Epidermis: Melanocytes

Melanocytes: clearish cells in basal layer with dark nuclei ; ratio of 1: 10. Langerhans’s Cells: dendritic cells of the epidermis. Sit in the mid-spinous. Not visible by light microscopy.

Merkel Cells: located in the stratum basale. Also not visible by light microscopy. They are receptor cells that establish synaptic contacts with sensory nerves and contain granules of neurotransmitters.

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Dermal-Epidermal Junction

Connects the epidermis and dermis It is composed of proteins which provide a firm connection – Hemidesmosome: connects basal keratinocytes to basement membrane – Basement membrane • Lamina lucida = collagen types XVII, XIII, laminin 5 & 6 • Lamina densa = collagen type VII – Anchoring fibrils attach the basement membrane to the dermis hooking on to collagen VII and collagen I.

Basement Membrane

Hemidesmosomes Collagen Type VII Lamina Lucida Lamina Densa Basal layer keratinocytes of epidermis Laminins 5 & 6

Basement Membrane

Collagen type XVII, XIII

Dermis

Anchoring Fibrils Collagen type I

Dermis

• Everything below the dermal epidermal junction / basement membrane – Connective tissue layer with contains blood vessels, nerves, sensory receptors, adnexal structures

Dermis

– Two layers • Papillary dermis = includes the dermal papilla which project into the epidermis – The increases contact area preventing epidermal detachment » Also results in an undulating pattern which vary by anatomic location and individual resulting in grooves in the epidermis =dermatoglyphics (fingerprints) – Capillaries, free nerve endings and encapsulated sensory receptors called Meissner’s corpuscles.

• Reticular dermis = area between the papillary dermis and subcutis

Papillary Dermis

Capillaries Papillary Dermis

Dermis

• The dermis is composed of two major types of fibers: – Type I Collagen – Elastic fibers: three types based on microfiber and elastin content

Reticular Dermis Sebaceous Glands Erector Pili muscle Hair Follicle

Dermal Appendages

Sebaceous Glands Eccrine Glands Pilar Muscle Hair Follicle

Sebaceous Glands

• • • • Usually associated with hair follicles Simple branched acinar glands – Several acini that empty into single duct Holocrine secretion Empty “sebum” into hair follicle

cross section (above the level of the bulb)

Hair Follicle

Connective Tissue Sheath Outer Root Sheath Inner Root Sheath Hair Medulla Hair Cortex Hair Cuticle Papilla Matrix Bulb

Eccrine Glands

• • Merocrine sweat glands Release to adjust body temperature • Three cell types – Dark cells: pyramid shaped with secretory granules line lumen of tubule – Clear cells: located toward basement membrane – Myoepithelial cells: spindle shaped contractile cells

Apocrine Glands

• Apocrine glands – Similar to eccrine glands but larger lumens and ducts empty onto superficial regions of hair follicle – Release product by shedding of part of cytoplasm = apocrine snouting – Influenced by hormones (sexual scent glands) – Only found on axilla, areola, perianal and genital area

Subcutis

• Subcutis – Area deep to the dermis – Includes the hypodermis • Loose connective tissue containing adipose tissue, nerves, sensory receptors, arteries and veins • Provides a flexible attachment to the underlying muscle and fascia Adipocytes Pacinian Corpuscle Hair bulb in the subcutis of the scalp.