Histology of the Skin

Kelli A. Hutchens, MD, FCAPDirector of Dermatopathology

Assistant ProfessorLoyola University Medical Center

Assistant Director of Mechanisms of Human DiseaseLoyola Stritch School of Medicine

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

Dermis

Subcutis

Epidermis

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

Epidermis : Layers• Cancel Lab Get Some Beer

Stratum Corneum

Stratum Granulosum

Stratum Spinosum

Stratum Basale

Stratum Lucidum

Thin Skin Thick SkinRete ridge

Differences between thin & thick skin

Thin 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

Thick 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

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

Basement Membrane

Cell to Cell Adherence

Zona adherens: Ca++ dependent cadherins that connect to actin

Zona occludens: tight junctions prevent diffusion across cells

Macula adherens: Made of desmosomes

Gap junctions: communication for electric / metabolic function

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.

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

Lamina Lucida

Lamina Densa

Basal layer keratinocytes of epidermis

Basement Membrane

Hemidesmosomes

Collagen type XVII, XIIICollagen type XVII, XIII

Laminins 5 & 6 Laminins 5 & 6

Collagen Type VIICollagen Type VII

Anchoring FibrilsAnchoring FibrilsDermis

Collagen type ICollagen 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

Papillary Dermis

Capillaries

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

Hair FolliclePilar Muscle

Sebaceous Glands

Eccrine Glands

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

Hair Follicle

Outer Root SheathInner Root Sheath

Hair Cuticle

Hair Medulla

Hair Cortex

cross section(above the level of the bulb)

Papilla

Bulb

Matrix

Connective Tissue Sheath

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

Pacinian Corpuscle

• 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

Hair bulb in the subcutis of the scalp.

Adipocytes