HISTOLOGY OF SKIN 22 şubat 2024.pdf

HISTOLOGY OF SKIN INTEGUMENTARY SYSTEM CUTIS ŞULE ÇETİNEL SKIN FUNCTIONS       IT ACTS AS A BARRIER IT PROVIDES IMMUNOLOGIC INFORMATION IT PARTICIPATES IN HOMEOSTASIS (BODY TEMP. AND WATER LOSS) IT CONVEYS SENSORY INFORMATION IT PERFORMS ENDOCRINE FUNCTIONS IT FUNCTIONS IN EXCRETION LAYERS OF...

HISTOLOGY OF SKIN INTEGUMENTARY SYSTEM CUTIS ŞULE ÇETİNEL SKIN FUNCTIONS       IT ACTS AS A BARRIER IT PROVIDES IMMUNOLOGIC INFORMATION IT PARTICIPATES IN HOMEOSTASIS (BODY TEMP. AND WATER LOSS) IT CONVEYS SENSORY INFORMATION IT PERFORMS ENDOCRINE FUNCTIONS IT FUNCTIONS IN EXCRETION LAYERS OF THE SKIN  EPIDERMIS  DERMIS  HYPODERMIS EPIDERMIS NO BLOOD VESSELS  KERATINIZED STRATIFIED SQUAMOUS EPITHELIUM  DERIVED FROM ECTODERM  CONSIST OF 5 LAYERS IN THICK SKIN  The epidermis forms the external surface of the skin and is mainly composed of keratinocytes which differentiate to form 4 or 5 layers: ACELLULAR KERATIN GRANULAR LAYER PRICKLE CELL LAYER LANGERHANS’CELL MELANOCYTES BASAL LAYER 5 EPIDERMIS LAYERS STRATUM CORNEUM 2. STRATUM LUCIDUM 3. STRATUM GRANULOSUM 4. STRATUM SPINOUSUM 5. STRATUM BASALE 1. A section of thick skin. Note the blood vessels in the dermal papillae improving the nutrition of the thick epithelium. The basal layer consists of 1 cell layer of cuboidal cells attached by hemi-desmosomes to a thin basement membrane which separates it from the underlying dermis the cells are interconnected by desmosomes and gap junctions. spinous or prickle cell layer due to the fine cell processes containing desmosomes attaching to another. (autoimmune disease pemphigusdesmosomes are damaged, epidermal cells become separated, acantholysis, and an intraepidermal blister results ) Active protein synthesis occurs in this layer, producing a fibrillar protein keratin which aggregates to form tonofibrils. These tonofibrils migrate to the granular layer to eventually become part of the keratin complex Stratum Granulosum: each keratinocyte contains keratohyalin granules. Stratum Corneumconsists of fully keratinized cells bound together by lipids synthesized in the granular layer. Cellular Components of the Epidermis Keratinocytes: The Basal keratinocyte is a mitotically active cell which differentiates from the basal (least keratin) to the cornified cells (most keratin). During migration upward, there is synthesis of keratin proteins, which constitute part of the protective interface between the body and the environment. keratinocytes mitotic in the stratum basale and malpighian layer once in stratum spinosum they are post-mitotic, differentiate and are pushed towards surface by inferior (lower) cell division and growth - differentiation includes accumulation of keratin filaments, aggregation of filaments into tonofibrils, synthesis of lamellar granules and release at cell surface - nuclei begin to degenerate in the outer layer of the stratum granulosum (apoptosis), release of lysosomal enzymes which degrade intracellular organelles - final result is a fibrillar meshwork of keratin filaments and interfibrillar matrix which give the keratin layer Epidermisin temel yapısı olan keratin üretirler. Epidermal su bariyerin oluşumunun bir parçasıdır. Bazal tabakadaki keratinositler bazofiliktir, serbest ribozomlar, golgi aygıtı, mitokondri ve 7-9nm. ara filamentler (keratin) içerirler. Daha sonra bu filamentler tonofilamentler olarak isimlendirilir. St. spinosuma ilerledikçe filamentler demetler halinde gruplaşır ve tonofibriller denir. St. granulosumda hücreler keratohiyalin granülleri içeren araçaptaki filamentlerle ilişkili proteinler ve glikolipid içeren lamellar cisimler içerir EPIDERMAL BARRIER 1- MULTİLAMELLİ LİPİD Lipidler epidermal permeabilite bariyerini oluşturmak için involukrin ile kovalent olarak bağlanır. Lipidler spinosum ve granulosum tabakalarında beliren lamellar cisimciklerden orjin alırlar. 2- Hücre kapsülü Keratinositlerin farklılaşmasının son fazına geldiklerinde plazma membranını güçlendirmek için özelleşmiş bir yapıdır. Keratin, filaggrin ve 3 protein (involukrin, küçük prolince zengin protein ve lorikrin) birbirlerine transglutaminaz enzimi ile çapraz bağlanır. 3-Keratin-filaggrin kompleks Keratin filamentleri filaggrin ile küme halindedir. Hücre zarını oluşturmak için plazma membranın iç tarafıyla etkileşimi vardır. 4- Sıkı bağlantılar Permeabilite bariyerin Komponentlerinden olan st. granulosumdaki sıkı bağlan ılar claudin-1 içerirler. Blood Flow Skin temperature is highly dependent on skin blood flow. Contraction or dilation of the dermal blood vessels results in vast changes in blood flow. Under the control of the sympathetic nervous system ("flight or fright"), arteriovenous anastamoses shunts blood to the superficial venous plexus to cause heat loss by convection and radiation. KERATIN LAYER EPIDERMIS PAPILLARY DERMIS SEBACEOUS GLAND RETICULAR DERMIS HAIR FOLLICLE CUTANEOUS PLEXUS ECCRINE GLAND APOCRINE GLAND SUBCUTIS SUBCUTANEOUS PLEXUS THIN SKIN (ARM PIT) THICK SKIN (SOLE) ARCHITECTURE OF THE SKIN Blood Flow Skin temperature is highly dependent on skin blood flow. Contraction or dilation of the dermal blood vessels results in vast changes in blood flow. Under the control of the sympathetic nervous system ("flight or fright"), arteriovenous anastamoses shunts blood to the superficial venous plexus to cause heat loss by convection and radiation. STRATUM CORNEUM Stratum corneum is made up of corneocytes, which are anucleated keratinocytes that have reached the final stage of keratinocyte differentiation. Corneocytes retain keratin filaments within a filaggrin matrix, and the cornified lipid envelope replaces the keratinocyte plasma membrane. Cells on the soles are completely replaced every month PSORIASIS Psoriasis kronik epidermal-dermal bir hastalıktır. 1-anormal hücre çoğalması ile epidermisin kalıcı hiperplazisi 2- dermisin kapiller pleksusun anormal sirkulasyonu St. corneum daki hücrelerin nukleusları Epidermis içine nötrofillerin göçü Epidermisdeki mikroabses Dermal papillada kapiller halkalar venülle dönüşümü Dermiste lenfositlerin bulunması St. Corneumun kalınlaşması Epidermiste Mikroskobik abse STRATUM LUCIDUM    appears only on palms & soles protectıon from uv lımıted to thıck skın STRATUM GRANULOSUM 2-4 cells thıck granules of keratohyalıne (ıntensely staınıng) keratınızatıon begıns ın thıs layer STRATUM SPINOSUM spınes ( characterıstıc lıght microscopic appearance) prıckle cell layer actıve proteın sentesıs langerhans’ cells ( role ın ımmune response ) STRATUM BASALE STRATUM GERMINATIVUM (MITOTICALLY ACTIVE CELLS - STEM CELLS OF EPIDERMIS )  REST ON BASAL MEMBRANE  SINGLE LAYER OF COLUMNAR CELLS  UNDERGOES CELL-DIVISION  MERKEL CELL (MECHANORECEPTOR)  MELANOCYTES (PRODUCES MELANIN )  DESMOSOME LAMINA LUCIDA LAMINA DENSA BASAL CELL HEMIDESMOSOME FIBRONECTIN ANCHORING FIBRILS ELASTIC FIBER MİCROFIBRIL DERMAL COLLAGEN CELLS OF THE EPIDERMIS  KERATINOCYTES  MELANOCYTES  LANGERHANS’ CELLS  MERKEL’S CELLS MERKEL CELLS MELANOCYTES LANGERHANS’ CELLS Thin skin. The stratum corneum is thinner than that in thick skin, and the keratinized plates are organized in a more compact way. Stratum spinosum of the skin from the sole of the foot (thick skin) showing the spiny projections that strongly bind the cells of this layer together to resist abrasion. Keratin Filaments -dense cytoplasmic bundles -crosslinked by filaggrin to form large aggregates -concentrated at cell periphery in projections that terminate at desomosomal junctions -crucial for structural integrity, stability, and continuity of the epithelium In junctional EB, there is a defect in the genes inherited from both parents (autosomal recessive) that normally promote the formation of anchoring filaments (thread-like fibers) or hemidesmosomes. These structures anchor the epidermis to the underlying basement membrane. The defect leads to tissue separation and blistering in the upper part of the basement membrane. Papillary dermis DERMIS 1-Papillary d 2-Reticular d Reticular dermis What is the difference ? Components of the dermis: Cellular Fibroblasts(synthesize collagen, elastin, and reticulin), histiocytes, endothelial cells, perivascular macrophages mast cells, smooth musce, Fibrous collagen (Type I collagen) and reticulin (Type III collagen), which provide tensile strength. Elastic fibers Ground substance consists largely of glycosaminoglycans: hyaluronic acid, chondroitin sulfate, and dermatan sulfate Thin Skin Poorly developed rete ridge system Keratin layer Well developed ridge system Thick Sole Skin G Fingertip skin G: Glomus Body Adipose tissue Blood vessel Subcutaneous tissue: Dense fibrocollagenous layer Several types of sensory skin nerve endings. What are the differences ? Nasıl acı duyarım Tüylerim diken diken oldu…..nasıl olur EPIDERMAL SKIN APPENDAGES  HAIR FOLLICLES AND HAIR  SEBACEOUS GLANDS  SWEAT GLANDS  NAILS i)cuticle: outermost layer, thin, fish-scale appearing with free-end facing the same direction as hair growth, heavily keratinized ii) cortex: middle layer, keratinized iii) medulla: pigmented, nonkeratinized Anagen: hair growth, duration of this phase determines hair length Catagen: regression, cell division ceases in the bulb, the papilla shrinks, and the shaft and inner root sheath detach from the dermal papilla and are pulled/pushed up the follicle by programmed cell death, the follicle shrinks but a strand of the external root sheath remains in association with the papilla - Telogen: rest, the proximal terminus of the hair shaft has migrated to just below the sebaceous gland and the proximal hair terminus is club-shaped instead of bulb shaped - Exogen: exit of hair shaft from follicle, Hair follicle. The follicle has a bulbous terminal expansion with a dermal papilla. The papilla contains capillaries and is covered by cells that form the hair root and develop into the hair shaft. The central cells (A) produce large, vacuolated, moderately keratinized cells that form the medulla of the hair. The cells that produce the cortex of the hair are located laterally (B). Cells forming the hair cuticle originate in the next layer (C). The peripheral epithelial cells develop into the internal and external root sheaths. The external root sheath is continuous with the epidermis, whereas the cells of the internal root sheath disappear at the level of the openings of the sebaceous gland ducts (not shown). H I E G melanocytes Transverse section H:Hair shaft E:External root sheath I:Internal root sheath G:Glassy membrane Longitudinal section Relationships between the skin, hair follicle, arrector pili muscle, and sebaceous and sweat glands. The arrector pili muscle originates in the connective tissue sheath of the hair follicle and inserts into the papillary layer of the dermis, where it ends. sebum Sebaceous gland: Precursor cells Sebaceous cells Apocrine gland (from axillary ) Eccrine gland Cuboidal eosinophilic lining cell Lumen Flat myoepithelial cell Axillary skin (Apocrine glands and hair follicles) Development of skin and hair The multipotent epithelial cells in the surface ectoderm subsequently become the embryonic epidermal basal layer of the stratifying epidermis, which giv es rise to all structures of the future epidermis. The formation of the embryonic basal layer is accompanied by the dev elopment of the basement membrane, produced by the basal layer cells. The basement membrane separates the epidermis from the dermis and prov ides epidermal basal cells with growth factors. Basal cells attach to the basement membrane through focal adhesions and hemidesmosomes composed of integrins. A layer of tightly adhered cells called the periderm transiently ov erlays the ectoderm during embryonic dev elopment (days 9–12 of gestation in mice, and weeks 4–8 of gestation in humans. The periderm is thought to protect the dev eloping epidermis from amniotic fluid,2 and is shed once the epidermis has stratified. In order to successfully differentiate and stratify, cells must escape the basement layer. Recent studies in mouse embryos have suggested that during stratification, basal cells change mitotic spindle orientation, allowing them to generate both a committed suprabasal cell as well as an undifferentiated basal cell. As cells in the basal layer proliferate, they form an ‘intermediate layer’ of cells under the periderm. This intermediate layer is transient and only exists in embryonic skin, it divides and matures into spinous cells. Both intermediate layer and spinous cells express K1, whose expression is induced by Notch signaling. Notch signaling directs spinous cells to continue to differentiate, mature, and migrate towards the surface of the skin to form the granular layer and cornified layer. In stage 0, a single basal layer of multipotent epithelial cells is established. In stage 1, continual interactions between mesenchymal cells and the epithelium result in the formation of hair placodes, which first appear in the underlying dermis. Placodes are areas of thickening epithelium that will give rise to hair follicles. In stage 2, the hair placode elongates downwards towards the dermiş while dermal fibroblasts that have aggregated under the placode condense and become more evident. In stage 3, the epidermal cells form a hair peg, a multi-layered and elongated column, and the aggregated dermal fibroblasts form a spherical dermal papilla adjacent to the hair peg. In stage 4, the hair peg thickens at the lower end to form a hair bulb, half enclosing the elongated dermal papilla. The inner root sheath forms above the dermal papilla. During stage 5, the inner root sheath extends up the hair follicle and the bulge becomes visible. In stage 6, the downward growth of the hair follicle reaches the subcutis and the inner root sheath forms a hair shaft at the upper end. The dermal papilla becomes thinner and is fully enclosed. The sebaceous gland forms at the upper end of the hair follicle. In stage 7, the tip of the hair shaft leaves the inner root sheath and enters the hair canal. Finally, in stage 8, the hair shaft protrudes above the skin surface and the hair follicle reaches its maximum length.