L3 Histology Skin I 2025 PDF

Histology of integument system I Skin Netter’s Essential Histology, 3nd Edition pp 263-273 1 1  Objectives Describe the type...

Histology of integument system I Skin Netter’s Essential Histology, 3nd Edition pp 263-273 1 1  Objectives Describe the types of skin and their distribution Compare and contrast the morphological features of major layers of the skin Compare and contrast location, structure, and function of the four cell types of the epidermis Describe melanin synthesis and distribution Describe the skin’s blood supply and sensory components in terms of structure, function, and location 2 2  Integument Composed of skin and skin appendages Protects deeper tissues from injury, drying and invasion by foreign organisms Play important roles in thermoregulation, limited role in excretion and absorption Absorbs ultraviolet light Metabolizes vitamin D Contains peripheral endings of sensory nerves 3 3 Integument Structure https://www.ck12.org/book/ck-12-biology/section/21.4/ 4 4  Skin http://www.histology-world.com/photoalbum/displayimage.php?pid=1209&fullsize=1 5 5  Two types of skin Thick skin Ø Glabrous Ø Palms, soles and flexor surfaces of the digits Ø Thick cornified layer (stratum corneum) Thin skin Ø Hirsute Ø Majority of skin Ø Thin cornified layer (stratum corneum) 6 6  Comparison of skin http://clinicalgate.com/skin-and-its-appendages/ 7 7  Two types of skin Which is which https://www.histologyguide.com/slideview/MH-090-thin-skin/11-slide-1.html 8 https://www.histologyguide.com/slideview/MHS-235-thick-skin/11-slide-1.html 8  Epidermis Outer layer of skin Outer layer of keratin that is protective and waterproof Cells: Keratinocytes, melanocytes, Langerhans’ cells and Merkel cells Stratified squamous epithelium containing keratinocytes in 4 layers: inner basal, squamous, granular and outer cornified Rete ridges: Undulating forms of epidermis and dermal papillae at dermoepidermal junction - flattens with aging Keratinization takes 30 - 45 days Alterations in pattern and speed cause dermatoses, hyperkeratosis or parakeratosis 9 9  Layers of epidermis https://courses.lumenlearning.com/wm-biology2/chapter/epidermis/ 10 10  Stratum basale Deepest epidermal layer Mitotically active, produces other keratinocytes Separated from dermis by continuous basal membrane Keratinocytes attached to basement membrane by hemidesmosomes Contains melanocytes https://www.ouhsc.edu/histology/Glass%20slides/44_06.jpg 11 http://www.lab.anhb.uwa.edu.au/mb140/corepages/integumentary/integum.htm 11  Stratum spinosum AKA prickle or malpighian layer Several layers of cells, larger than basal layer Become flat and eosinophilic towards surface due to an increase in keratin and reduction in ribosomes Attached to each other by spiny bridges with central dot-like desmosomes (Bizzozero’s nodule) Loss of spiny bridges causes acantholysis 12 http://www.iupui.edu/~anatd502/Labs.f04/integument%20lab/s31.100x.i2.jpg 12 Stratum spinosum Intercellular bridges Attached to each other by spiny bridges with central dot-like desmosomes (Bizzozero’s nodule) Character of squamous differentiation 13 http://class.kmu.edu.tw/~wags/Biology/Wags/histopage/colorpage/cep/cepib.GIF 13  Stratum granulosum 1 - 3 layers of flattened cells Contain intensely basophilic keratohyalin granules Generate large amounts of the keratin, and keratohyalin, which accumulates as lamellar granules http://www.dartmouth.edu/~anatomy/Histo/lab_4/skin/DMS033/popup.html 14 14  Stratum lucidum Translucent layer of the epidermis Located between the stratum granulosum and the stratum corneum ONLY in the thick skin of the palms, soles, and digits Composed of dead and flattened keratinocytes http://www.histologyguide.com/slideview/MHS-235-thick-skin/11-slide-1.html 15 15  Stratum corneum Also called horny layer Basket weave pattern of multiple layers of polyhedral cells without nuclei Thicker and more compact in acral region http://www.histologyguide.com/slideview/MH-090-thin-skin/11-slide-1.html 16 http://www.histologyguide.com/slideview/MHS-235-thick-skin/11-slide-1.html 16  Normal keratinocyte turnover https://www.researchgate.net/figure/5602580_fig1_General-structure-of-the-epidermis-See-Introduction-for-details 17 17 Desmosome, a strong intercellular adhesion structure 18 18  Desmosome, a strong intercellular adhesion structure http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab11_micrograph.html 19 19  Hemidesmosome, a strong adhesion structure between keratinocytes and basement membrane http://classes.kumc.edu/som/cellbiology/connections/intermediate/tut3.html 20 20  Hemidesmosome, a strong adhesion structure between keratinocytes and basement membrane Hemidesmosomes (HD), lamina densa (LD); anchoring filaments (AF), cross-banded anchoring fibrils (AFb) and in the lower dermis collagen fibres (Col) https://www.researchgate.net/figure/13095752_fig1_Figure-1-Electron-microscopy-study-showing-the-basal-cell-surface-of-a- 21 human 21  Disruption of desmosome or hemidesome causes vesicular dermatosis Robbins and Cotran Pathological Basis of Disease, 9th Edition, p 1167 22 22  Disruption of desmosome or hemidesome causes vesicular dermatosis Subcorneal vesicle https://www.pathologyoutlines.com/topic/skinnontumoragep.html 23 23  Disruption of desmosome or hemidesome causes vesicular dermatosis Intraepidermal and suprabasal vesicle https://www.consultant360.com/articles/pemphigus-vulgaris 24 24  Disruption of desmosome or hemidesome causes vesicular dermatosis Subepidermal vesicle https://www.pathologyoutlines.com/topic/oralcavitypemphigoid.html 25 25  Epidermal melanocytes Neural crest origin In basal epidermis, hair follicles, most squamous mucous membranes, leptomeninges Produce melanin from tyrosine, transfer it (via cytocrinia) to adjacent epithelial cells to protect against ultraviolet rays https://ohiostate.pressbooks.pub/vethisto/chapter/7-additional-cells-of-the-epidermis/ 26 26  Epidermal melanocytes Contain dendrites, delicate cytoplasmic processes that extend between keratinocytes Peripheral clearing due to retraction, smaller nuclei, uniform chromatin, indented nuclear contour, no nucleoli http://flylib.com/books/en/2.953.1.6/1/ 27 27  Ultrastructure of melanocyte Filopodia: Long, slender, tapering processes Melanosomes: Membrane-bound organelles containing tyrosinase, etc http://intranet.tdmu.edu.ua/data/kafedra/internal/histolog/classes_stud/en/med/lik/ptn/2/16%20Adrenal%20gla 28 nds%20and%20diffuse%20endocrine%20system.%20Skin%20and%20its%20appendages..htm 28  Melanosome maturation Stage I: Round melanosomes with granular to filamentous material in the vesicle periphery Stage II: Ovoid melanosomes containing parallel filaments Stage III: Ovoid melanosomes with melanin deposition obscuring the filaments Stage IV: Large oval melanosomes (or mature melanin granules) completely filled with melanin 29 29  Melanogenesis http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0365-05962013000100076 30 30  Two type of melanin Eumelanin Ø Brown to black Ø Epidermis, iris, brown and black hair Pheomelanin Ø Yellow to red Ø Skin, lips, nipples, genital area, and red hairs http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0365-05962013000100076 31 31  Skin pigmentation Melanin produced by melanocytes but transferred to keratinocytes Color of skin depends on amount of melanin in keratinocytes, NOT number of melanocytes http://eliasandwilliams.com/pigmented-skin-more-acidic/ 32 32  Melanogenesis regulation Factors that INCREASE melanin production: Ø Increased UV exposure (i.e. tanning) Ø Melanocyte-stimulating hormone (MSH): Placental MSH increases maternal skin pigmentation, etc Ø Pituitary ACTH (α-MSH peptide sequence): Addison’s disease can result in hyperpigmentation due to excess ACTH production Factors that DECREASE melanin production: Ø Genetic defects in melanin synthesis: Albinism results from mutation in tyrosinase Ø Destruction of melanocytes (ex: vitiligo) Ø Hydroquinone creams http://eliasandwilliams.com/pigmented-skin-more-acidic/ 33 33  Chronic sun exposure: a risk for skin cancers, including melanoma http://www.intechopen.com/books/research-on-melanoma-a-glimpse-into-current-directions-and-future- trends/ultraviolet-light-as-a-modulator-of-melanoma-development 34 34  Melanocytic Nevus Hyperpigmentation due to melanocytic proliferation Either flat (junctional) or nodular (intradermal, compound) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3965271/ 35 35  Vitiligo Partial or complete loss of pigment producing melanocytes within the epidermis Usually hands / wrists, axilla, perioral, periorbital, anogenital skin https://medlineplus.gov/ency/imagepages/2673.htm 36 36  Epidermal Langerhans cells Bone marrow origin, monocyte-derived dendritic cells Scattered in upper squamous layer and in the dermis Express langerin (CD207) and CD1a Communicate with each other through E-cadherin Phagocytic and antigen-processing and antigen-presenting http://www.frontiersin.org/files/Articles/158763/fimmu-06-00534-HTML/image_m/fimmu-06-00534-g002.jpg 37 37 Epidermal Langerhans cells Ultrastructure Characteristic Birbeck granules (rod shaped structure with zipper-like striations, often with bulbous end) http://pathresidents.com/usapathology/em-handbook/diagn-organelles-section/organelle-pages/birbeck-granules.html 38 38 Epidermal Langerhans cells Functions Capture, process and present antigen Migrate to regional lymph node Activate downstream immune response http://www.cmaj.ca/content/170/13/1933/F5.expansion.html 39 39  Merkel cells Specialized receptor neuron Has no axon, relies on a secondary sensory neuron for signal transduction Concentrated in skin of digits, finger pads, proximal nail folds, palms, dorsum of feet, lips, hard palate More common in outer root sheath of hair follicles and tactile hair discs http://biology.stackexchange.com/questions/24349/why-are-merkel-cells-innervated-by-an-axon-and-not-a-dendrite 40 40  Dermis Contains collagen and elastic fibers Also contains adnexa, nerves and blood vessels Degenerates with age and sunlight Usually thicker on back https://gcps.desire2learn.com/d2l/lor/viewer/viewFile.d2lfile/6605/48061/The%20Integumentary%20System/The%20 Layers%20of%20the%20Skin%20Dermis%20and%20Hypodermis/TheLayersoftheSkinDermisandHypodermisANAT1U3L 41 3_print.html 41  Dermis Two parts: Papillary dermis: Superficial, contains dermal papillae between rete ridges and periadnexal dermis Reticular dermis: Deeper, contain sensory receptors, collagen and elastic fibers (strength & stretchiness), muscles attaching http://www.entwellbeing.com.au/skincare/skin-basics/what-is-skin/ 42 42  Blood supply Arteries deep in the hypodermis Subpapillary plexus: Beneath the dermal papillae, supplying the capillaries in the dermal papillae Cutaneous plexus: Dermal/hypodermal junction Arteriovenous anastomoses in the dermis, thermoregulation https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/integumentary- 43 system-5/functions-of-the-integumentary-system-66/blood-supply-to-the-epidermis-405-5030/images/the-dermis/ 43  Innervation 44 http://faculty.pasadena.edu/dkwon/chap10_A/chap%2010_A%20accessible_files/textmostly/slide14.html 44  Meissner's corpuscle ‘Coiled spring'-like, encapsulated sensory nerve ending One or more axon endings surrounded by sheath of modified Schwann cells and/or fibroblasts Fine touch receptor 45 http://www.dartmouth.edu/~anatomy/Histo/lab_3/neuro/DMS033/popup.html 45  Pacinian corpuscle Centrally-located unmyelinated axon and associated Schwann cells, multiple layers of supporting cells (modified fibroblasts) Detect deep pressure and vibration 46 http://www.dartmouth.edu/~anatomy/Histo/lab_3/neuro/DMS033/popup.html 46  Peripheral neuropathy Acquired or hereditary condition Characterized by nerve damage Results in abnormal sensation, such as numbness, pain, etc Commonly seen in diabetes, vitamin B12 deficiency, etc 47 47  Subcutis Also called subcutaneous Contains lobules of mature adipose tissue and thin connective tissue septa 48 http://stratum-lucidum.tumblr.com/post/25458872410/hypodermis 48  Functions of skin Protection: Against UV light, mechanical, thermal and chemical stresses, dehydration and invasion by micro-organisms. Sensation: Touch, pressure, pain and temperature. Thermoregulation: Sweat glands, hair, and adipose tissue. Metabolic functions: Production of vitamin D, and triglycerides 49 49