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The Integumentary System
1. The Integumentary System
2. Integumentary System
• Only 1.5 to 4 mm thick but is body’s largestorgan
– 7% of body weight
• Provides protection
– Microbes
– Dehydration
– Mechanical damage
• Contains all four tissue types
3. Integument Composition
• Two basic layers– Epidermis
• External
• Stratified squamous epithelium
– Dermis
• Deeper
• Mostly dense irregular connective tissue
• Additional layer
– Hypodermis (subcutaneous)
• Connective tissue
• Not really part of integument, but nowhere else to put it!
4. Integument
EpidermisDermis
Subcutaneous layer
5. Layers of the Integument (Figure 6.1)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Hair shaft
Sweat pore
Epidermis
Epidermal ridge
Dermal papilla
Papillary
layer
Integument
Arrector pili muscle
Sebaceous (oil) gland
Dermis
Sweat gland duct
Reticular
layer
Merocrine sweat gland
Vein
Artery
Subcutaneous
layer
Adipose connective tissue
Hair follicle
Tactile
(sensory)
receptors
Areolar
Sensory
connective tissue nerve fiber
6. Epidermis
• Epithelial tissue arranged in 5 layers or strata– Cells divide in only in base layer and are pushed
outward
– Form a keratinized layer on surface
– Cell division is regulated by growth factor (EGF)
7. Epidermal Strata
• From deep to superficial– Stratum basale (base layer)
– Stratum spinosum (spiny layer)
– Stratum granulosum (grainy layer)
– Stratum lucidum (light layer or clear layer)
– Stratum corneum (horny layer)
8. Thick Skin High Magnification
EpidermisStratum
corneum
Stratum
lucidum
Stratum
granulosum
Stratum
spinosum
Dermis
Stratum
basale
9. Stratum Basale
• Single layer of cuboidal to low columnar cells attached to abasement membrane
• Include
– Keratinocytes
• Keratin is a tough, water-resistant protein
– Melanocytes
• Melanin is a brown protein pigment
• Transfer melanin to keratinocytes for protection against UV damage
• Skin color
– Tactile cells (Merkel cells)
• Touch receptors
10. Stratum Spinosum
• Cells are pushed up from below and become“squished” and look spiny on cross sectional
view
– Spiny appearance comes from connections
(desmosomes) between cells
– Cells are further from blood supply so alive, but
not dividing
• Epidermal dendritic cells
– Phagocytic immune cells
11. Stratum Granulosum
• Cells in this layer start to keratinize (fill withkeratin) and look grainy
– Keratohyalin- precursor to keratin
• As they go through the process, the organelles
in these cells disintegrate
• Cells die
12. Stratum Lucidum
• Keratinocytes with transforming keratohyaline– Keratohyaline transforms to clear substance
eleidin
– Found only in thick skin
– Dead cells
13. Stratum Corneum
• 20-30 layers of dead keratinocytes• Keratin now fully formed
• Cells are dead
– Keratinized stratified squamous epithelium
– Migration process from stratum basale about 2
weeks
– Remain in stratum corneum for about 2 weeks
and then are shed
14. Epidermal Strata (Figure 6.2)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Dead keratinocytes
Stratum corneum
Sweat gland duct
Sweat gland duct
Stratum lucidum
Stratum granulosum
Living keratinocyte
Stratum spinosum
Melanocyte
Epidermal dendritic cell
Stratum basale
Basement membrane
Dermis
Tactile cell
LM 25x
Sensory nerve ending
(a)
(b)
a: © Ed Reschke/Peter Arnold Images
15. Variations in the Epidermis
• Epidermis is not the same over all portions ofthe body or for all people
– Thick skin
• Soles of feet, fingers, toes
• Has all 5 layers, but no hair follicles or sebaceous glands
– Thin skin
• Rest of body
• Doesn’t have 5 layers, has hair follicles and sebaceous
glands
16. Thick Skin
Thin Skin17. Thick Skin High Magnification
EpidermisStratum
corneum
Stratum
lucidum
Stratum
granulosum
Stratum
spinosum
Dermis
Stratum
basale
18. Thin Skin High Magnification
EpidermisStratum
corneum
Stratum
granulosum
Stratum
spinosum
Dermis
Stratum
basale
19. Thin Skin Low Magnification
Stratum corneumEpidermis
Stratum granulosum
Dermis
Stratum spinosum
Dermal papillae
Duct of merocrine sweat
gland
Stratum basale