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Integumentary system General outline skin (Integument) is the largest organ of the human body, it constitutes about 16% of body weight, its total surface area is about 1.2-2.2 m2 Skin -- 2 layers: epidermis and dermis, attaching to underlying structure via hypodermis. Appendages -- hair, nails, sebaceous glands, sweat glands. the function of the skin: barrier and protection sensory reception excretion body temperature regulation absorbing some materials remarkable regenertive capacity skin epidermis (dermis) hypodermis 1. Structure of skin ---epidermis ---dermis 1) Epidermis ---consist of keratinised cell and non-keratinised cell Keratinised stratified squamous epithelium ①keratinised cell: ---from basal to surface, we can classify the cells into five layers Epidermis stratum corneum (C) stratum lucidum (L) stratum granulosum (G) stratum spinosum(S) stratum basale (B) a. stratum basale structure: LM: a layer of cuboidal or low columnar cell with a large, pale nuclei, basophilic cytoplasm. EM: free ribosome, keratin filament function: mitotic activity and proliferation, for constant renewal of epidermal cells. b. stratum spinosum structure: LM: 4-10 layers polygonal cell with large round nucleus,spinous processes, slight basophilic cytoplasm EM: -tonofibrils -lamellated granules: /100-300nm membranecoated /contain phospholipid and steroid -intercellular bridgesDesmosome c. stratum granulosum structure: LM: 3-5 layers flattened cell -nuclei begin to degeneratestained slightly ---keratohyalin granules: basophilic EM: keratohyalin granules: with tonofilament insert into them -lamellated granules: fused with cell membrane * keratohyalin + tonofilament = keratin d. stratum lucidum ---structure: LM: 3-4 layers of flattened, acidophilic and transparent cells. Nuclei and organelles disappear lucidum e. stratum corneum structure: LM: 15~20 layers horny cell ---died cell- no nucleus and organella ---eosinophilic ---keratin • desquamation: surface keratin will shed from outer surface due to abrasion corneum lucidum ② non-keratinised cell: a. melanocyte: ---Location:--located among stratum basale cells ---structure: LM: -large cell with long branches EM: ---risosome ---RER ---Golgi complexes tyrosine ---melanosome(tyrosinase) →↓ melanin ↓ melanin granules ---function: • responsible for skin color • absorb ultraviolet light • protect deep tissue b. Langerhans cell ---Location:-among the spinous cell ---structure: LM: -dark nucleus, light cytoplasms -dendritic-typed processes EM: -lysosome -Birbeck granule: /membrane-coated /characteristic racket-shape ---function: • antigen presenting cell in skin • involve in immune reaction c. Merkel’s cell ---Location: located in basal layer ---structure with short processes contain many dense-core granules chemical synapse: between Merkel’s cell and afferent N ---function: not very clear, may be • sensory epithelial cell • neuroendocrine cell 2) Dermis: located beneath the epidermis Papillary layer: a thin layer of LCT which increase the total contact surface between the dermis and epidermis, contain capillary network and nerve ending (tactile corpuscle) Reticular layer: under the papillary layer; consists of irregular DCT; contain large blood vessels, appendages of skin, nerves (lamellated corpuscle). The elastic network is responsible for the elasticity of the skin. ---papillary layer: dermal papillaeincrease the junction between epi. and underlying CT papillary layer reticular layer Meissner’s corpuscle(tactile corpuscle) ---reticular layer: 1.Dense connective tissue 2.Contains blood vessels, lymphatics, nerves and lamellated corpuscles and appendages of skin. skin appendages: including sweat gland, sebaceous gland and hair 2. hypodermis: LCT and fat tissue Skin appendages hair sebaceous gland sweat gland Skin appendages Hair • Hair is a thorny thread-like • • • structure. Hair shaft is the part that extends above the surface and hair root is part that is embedded in the skin Hair resides in a hair follicle. Hairs differ in length, thickness and color according to their position on the body hair follicle hair root hair bulb papilla Sturcture of Hair root Hair follicle Hair root Hair follicle Hair follicle Hair root Sebaceous Glands • Associated with the hair follicles • Produce oily substance, which is act as a • lubricant to make the skin soft and protects both skin and the hair from drying out. Oil released to outside via the hair follicle. If passage becomes blocked, cause acne. Sebaceous glands Cell features: in the central : Large Polygonal shaped cells with many droplets fat in cytoplasm; at periphery : small cuboidal shaped cells ,dark staining . Production: sebum Arrector pili muscle Arrector pili – smooth muscle of hair this muscle contracts– “goose pimple” Sweat Glands • Sweat glands are distributed over most of the body. • Simple tubular glands that transverse from the dermis to the surface of the epidermis. Merocrine sweat glands are found on most of the body and produce a thin watery solution and function in heat regulation. Apocrine sweat glands are found in axilla, mammary areolae, and circumanal region produce much thicker secretion that is odor producing. Often become activated at puberty A sweat gland is divided into two parts: Secretory portion: is composed of pyramidal secretory cells Duct: lined by two layers of cuboidal epithelial cells Secretory portion duct