histology of the skin
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DESCRIPTIONHistology 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. Objectives. - PowerPoint PPT Presentation
Histology of the Skin Kelli A. Hutchens, MD, FCAPDirector of DermatopathologyAssistant ProfessorLoyola University Medical CenterAssistant Director of Mechanisms of Human DiseaseLoyola Stritch School of Medicine
Objectives Identify the epidermis, dermis, and subcutis of the skinName and label the layers five layers of the of the epidermisCompare and contrast the anatomic and histologic differences between thick and thin skinIdentify (when possible) / or know the location of the following cells: KeratinocyteMelanoycteMerkel cellLangerhan cellDescribe the general function and location of the following components of the dermal epidermal junction and intercellular space.HemidesmosomesBasement membraneBasal layer keratinocytesAnchoring fibrils DesmosomesName and identify the two regions of the dermisIdentify and classify the following: Eccrine glandSebaceous glandApocrine glandCompare and contrast the histologic appearance, function, and location of Pacinian corpuscles versus Meissners corpuscles.
Overview of the SkinDermisSubcutisEpidermis
EpidermisMost superficial layer of the skinComposed of multiple layers of keratin containing epithelial cells = keratinocytes with Melanocytes, merkel cells, and Langerhans dispersed throughoutMajor functions:Maintenance of fluid and electrolyte balanceProtection from ultraviolet lightSensory and immune function
Epidermis : LayersCancel Lab Get Some BeerStratum CorneumStratum GranulosumStratum SpinosumStratum BasaleStratum LucindumStratum LucidumThin SkinThick SkinRete ridge
Differences between thin & thick skinThin SkinPalms of hands and soles of feet = acral skin5 layers thick stratum corneum with increased granular layerMore sensory receptorsLack sebaceous glands and increased eccrine glandsNo hair follicles Thick SkinEntire body except thick skin areas.Less than 5 layers of stratum corneum with no stratum lucidumHair 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 cellsFrom basal cell to cornified cell takes about 25 daysShorter maturation periods seen in inflammatory conditions such as psoriasisKeratin 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 Dariers Disease.
Epidermis Basement MembraneCell to Cell AdherenceZona adherens: Ca++ dependent cadherins that connect to actinZona occludens: tight junctions prevent diffusion across cellsMacula adherens: Made of desmosomesGap junctions: communication for electric / metabolic functionHemidesmosomes: connect cells to BM
Epidermis Desmosome = Intercellular Bridges
Epidermis: MelanocytesMelanocytes: clearish cells in basal layer with dark nuclei ; ratio of 1: 10. Langerhanss 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 JunctionConnects the epidermis and dermisIt is composed of proteins which provide a firm connection Hemidesmosome: connects basal keratinocytes to basement membraneBasement membraneLamina lucida = collagen types XVII, XIII, laminin 5 & 6Lamina densa = collagen type VIIAnchoring fibrils attach the basement membrane to the dermis hooking on to collagen VII and collagen I.
Basement MembraneLamina LucidaLamina DensaBasal layer keratinocytes of epidermisBasement MembraneHemidesmosomesCollagen type XVII, XIIILaminins 5 & 6 Collagen Type VIIAnchoring FibrilsDermisCollagen type I
DermisEverything below the dermal epidermal junction / basement membraneConnective tissue layer with contains blood vessels, nerves, sensory receptors, adnexal structures
DermisTwo layers Papillary dermis = includes the dermal papilla which project into the epidermisThe increases contact area preventing epidermal detachmentAlso 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 Meissners corpuscles.Reticular dermis = area between the papillary dermis and subcutis
Papillary Dermis Papillary DermisCapillaries
Dermis The dermis is composed of two major types of fibers:Type I CollagenElastic fibers: three types based on microfiber and elastin content
Reticular DermisSebaceous GlandsErector Pili muscleHair Follicle
Dermal AppendagesHair FolliclePilar Muscle Sebaceous GlandsEccrine Glands
Sebaceous GlandsUsually associated with hair folliclesSimple branched acinar glandsSeveral acini that empty into single ductHolocrine secretion Empty sebum into hair follicle
Hair FollicleOuter Root SheathInner Root SheathHair CuticleHair MedullaHair Cortexcross section(above the level of the bulb)PapillaBulbMatrixConnective Tissue Sheath
Eccrine Glands Merocrine sweat glandsRelease to adjust body temperatureThree cell typesDark cells: pyramid shaped with secretory granules line lumen of tubuleClear cells: located toward basement membraneMyoepithelial cells: spindle shaped contractile cells
Apocrine GlandsApocrine glandsSimilar to eccrine glands but larger lumens and ducts empty onto superficial regions of hair follicleRelease product by shedding of part of cytoplasm = apocrine snoutingInfluenced by hormones (sexual scent glands) Only found on axilla, areola, perianal and genital area
Subcutis Pacinian CorpuscleSubcutis Area deep to the dermisIncludes 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
Welcome to basic histology of the skin*We will begin with an overview of the skin. On the left is a cartoon and on the right is a full thickness punch biopsy of the skin, stained with hemotoxlin and eosin, aka h&e,. From superficial to deep the major regions of the skin are the epidermis, dermis, and subcutis. You can see the epidermis stains purple/blue while the collagen of the underlying dermis stains a pinkish hue. The remainder of this tutorial will focus on the important histologic points of each of these regions. *The epidermis is the superficial layer of the skin and is composed mainly of epthelilial cells called keratinoocytes. Amongst the keratinocytes three other types of cells reside. Melanocytes, merkel cells, and Langerhans cells. Together these cells act as a both a barrier to external assault such as the radiating effects of ultraviolet light, dynamic membrane insuring fluid and electrolyte balance is maintained, and an immune organ and sensory organ. *The keratinocytes of the epidermis are organized into 4 or 5 layers depending on the regional location. The layers can be easily remembered with the pneumonic cancel lab get some beer. From superficial to deep the layers on thick skin are the strum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and the basal most layer the stratum basale. Proliferation of these basal layer cells into the epidermis can result in the common neoplasm, basal cell carcinoma. The section of thin skin on the left has all the same layers in the same order with the exception of the stratum lucidum. Both types of skin have a relatively flat surface with a convolted underside due to the papillary dermis insertion into the epidermis. The finger like projections of epidermis that extend into the dermis are called rete ridges. *The differences between thin skin and thick skin are summarized on this chart. The major differences are the antomic location and the increased thickness of thick skin due to the addition of the stratum lucidum and the thickend corneal layer. Thick skin is only found on the palms of the hands and soles of the feet. Another name for thick skin is acral skin as it is found on these acral surfaces. Additional histologic differences listed here include variation in the adnexal structures of the dermis such as increased sensory strutures and a lack of hair follicles on thick skin which is why we dont have hairy palms, most of us at least. We will discuss these changes again when we look more closely at the adenexal components of the dermis. *The layers of the epidermis are not static but contantly being replaced through the maturation of cells from the basal layer to the cornified layer. This process is called desquamatization. It takes about 25 days fro a cell to move from the basal layer to the cornified layer. Cells move upward to calcium signalling which results in changes in keratin production and subsequent maturation of the cells. Cells of the basal layer make keratins 5 and 14 while cells of the spinous layer make keratins 1 and 10. *The keratinocytes of the epidermis are connected to one another and the basement membrane by specialized attachement proteins. Some of the most clinically important are the desmosomes which are found inbetween keratinocytes. Desmosomes are composed of various types of desmolgliens. When the desmogleins, specifically desmoglien type 3, are attacked by a persons own immune system in diseases such as pemphigus vulgaris the cells will separate from one another and roll up in balls. This process is called acantholysis and results in crusted and blistered skin lesions. Also clinically important are the hemi