skin zhong jie li (李仲杰), ph. d school of medicine,zhejiang university 20131017
TRANSCRIPT
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SkinSkin
• Zhong Jie Li (李仲杰) , Ph. D
• School of Medicine,Zhejiang University
• 20131017
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skin
epidermis
(dermis)
hypodermis
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General outlineGeneral outline
skin is the largest organ of the human body, it constitutes about 16% of body weight
is composed of epidermis , dermis and its appendages
its total surface area is about 1.2-2.2 m2
the function of the skin:
barrier and protection
sensory reception
excretion
body temperature regulation
absorbing some materials
remarkable regenertive capacity
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•Thick skin•Thin skin
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1. Structure of skin
---epidermis
---dermis
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1) Epidermis
---consist of keratinised cell and
non-keratinised cell
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①keratinised cell:
---from basal to surface, we can classify the cells into five layers
Keratinised stratified squamous epithelium
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stratum corneum ( C)
stratum lucidum ( L)
stratum granulosum ( G)
stratum spinosum
( S)stratum basale ( B)
Epidermis
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a. stratum basale ---structure: LM: -a layer of cuboidal or low
columnar cell with a large, pale nuclei
-basophilic cytoplasmEM: -free ribosome -keratin filament - desmosome---function: mitotic activity and
proliferation, for constant renewal of
epidermal cells.
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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 membrane- coated /contain phospholipid and steroid -intercellular bridges- Desmosome
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c. stratum granulosum---structure: LM: 3-5 layers flattened cell -nuclei begin to
degenerate-stained slightly -keratohyalin granules: basophilicEM: -keratohyalin granules: with
tonofilament insert into them -lamellated granules:
fused with cell membrane* keratohyalin + tonofilament =
keratin
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d. stratum lucidum---structure:LM: -3-4 layers of cell appear
homogeneous and transparent
-no nucleus and organella
-eosinophilic-keratohyalin -tonofilament embedded
in homogeneous matrix
lucidum
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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
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② non-keratinised cell: a. melanocyte: ---structure: LM: -large cell with long branches -located among stratum basale cells EM: -risosome -RER -Golgi complexes tyrosine -melanosome(tyrosinase) →↓ melanin ↓ melanin granules
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---function:
• responsible for skin color
• absorb ultraviolet light
• protect deep tissue
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b. Langerhans cell---structure: LM: -dark nucleus, light cytoplasms -among the spinous cell -dendritic-typed processes EM: -lysosome -Birbeck granule: /membrane-coated /characteristic racket-shape /15-30 nm long, 4 nm in D---function: • antigen presenting cell in skin• involve in immune reaction
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c. Merkel’s cell
located in basal layer
with short processes
contain many dense-core granules
chemical synapse: between Merkel’s cell and afferent N
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---function: not very clear, may be
• sensory epithelial cell
• neuroendocrine cell
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2) 2) Dermis:Dermis:
located beneath the epidermis
Reticular layer:
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)
•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.
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---papillary layer: dermal papillae-increase the junction between epi. and underlying CT
papillary layer
reticular layer
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Meissner’s corpuscle
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---reticular layer:
DCT, contains rough F ,CF, EF, RF
• large BV, LV• lamellar corpuscle• skin appendages:
including sweat gland, sebaceous gland and hair
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2. hypodermis: LCT and fat tissue
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Skin appendagesSkin appendages
hair
sebaceous gland
sweat gland
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Skin appendages
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HairHair
• 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
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papilla
hair root
hair bulb
hair follicle
Sturcture of Hair root
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•Hair root
•Hair follicle
•Hair follicle
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•Hair follicle•Hair root
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Sebaceous GlandsSebaceous 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.
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Sebaceous glands
Secretory portion:
in the central :
Large Polygonal shaped cells with many droplets fat in cytoplasm;
the basal layer : small cuboidal shaped cells ,dark staining .
Production: sebum
Arrector pili muscle
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Arrector pili
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•Arrector pili – smooth muscle of hair this muscle contracts– “goose pimple”
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Sweat GlandsSweat 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
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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
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