histology of the skin kelli a. hutchens, md, fcap director of dermatopathology assistant professor...
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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