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BIO 1121 The Integumentary System, Chapter 5
The integumentary system consists of:
1. Cutaneous membrane
• Epidermis
• Dermis
2. Accessory structures
3. Subcutaneous layer
Integumentary system functions:
1. Protection
2. Temperature maintenance
3. Nutrient storage (adipose in hypodermis)
4. Vitamin D3 synthesis
5. Sensory detection
6. Excretion, Secretion
Epidermis
• The epidermis is composed of layers of keratinocytes
• Stratified squamous epithelium
• Thin skin = four layers (strata)
• Thick skin = five layers
The epidermis functions:
1. Provides mechanical protection
2. Prevents fluid loss
3. Keeps microorganisms from invading the body
4. Merkel cells – in basal layer – sense of touch
Layers of the epidermis:
1. Stratum germinativum
• Stratum basale – cells are dividing
2. Stratum spinosum
• Spiny layer (desmosomes)
• Some cell division
• Langerhans cells (immunity)
3. Stratum granulosum
• Keratin and kertohyalin (grnaules)
4. Stratum lucidum (only in thick skin)
• Translucent layer
5. Stratum corneum
• Outer layer of dead cornified (keratinized) cells
Keratinization
• Keratinocytes undergo keratinization as they move towards the surface
• Cells become full of keratin
BIO 1121; ch5 Page 1
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• Dehydration – no cytoplasm
• Dead cells
• Water resistant
Epidermal characteristics:
• Cells accumulate keratin and eventually are shed
• Fingerprints
o Epidermal ridges are interlocked with dermal papillae
o Improve gripping ability
• Langerhans cells (immunity) in s. spinosum
• Merkel cells (sensitivity) in s. germinativum
Skin color depends on:
• Blood supply (in dermis)
• Carotene – orange pigment that can accumulate in the skin
• Melanin
o Produced by melanocytes
o Different shades of melanin
o Can be stimulated to produce more by sun exposure
o Protects against harmful UV radiation
• Cyanosis – blue tinge caused by too little oxygen or poor circulation
Vitamin D
• Epidermal cells synthesize vitamin D3 (cholecalciferol) when exposed to UV
sunlight
• Modified cholesterol → Vitamin D
• Needed for the absorption of calcium
• Deficiency leads to impaired bone growth (rickets) and maintenance
Epidermal Growth Factor
• Found in saliva and intestinal juices
• Epidermal growth factor promotes:
o Growth
o Division
o Repair
Dermis
• Under epidermis
• True skin
• Has two layers:
1. Papillary layer
2. Reticular layer
Papillary layer
• Papillary layer contains dermal papillae
• Contains blood vessels, lymphatics, sensory nerves of epidermis
BIO 1121; ch5 Page 2
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BIO 1121 The Integumentary System, Chapter 5
The integumentary system consists of:
1. Cutaneous membrane
• Epidermis
• Dermis
2. Accessory structures
3. Subcutaneous layer
Integumentary system functions:
1. Protection
2. Temperature maintenance
3. Nutrient storage (adipose in hypodermis)
4. Vitamin D3 synthesis
5. Sensory detection
6. Excretion, Secretion
Epidermis
• The epidermis is composed of layers of keratinocytes
• Stratified squamous epithelium
• Thin skin = four layers (strata)
• Thick skin = five layers
The epidermis functions:
1. Provides mechanical protection
2. Prevents fluid loss
3. Keeps microorganisms from invading the body
4. Merkel cells – in basal layer – sense of touch
Layers of the epidermis:
1. Stratum germinativum
• Stratum basale – cells are dividing
2. Stratum spinosum
• Spiny layer (desmosomes)
• Some cell division
• Langerhans cells (immunity)
3. Stratum granulosum
• Keratin and kertohyalin (grnaules)
4. Stratum lucidum (only in thick skin)
• Translucent layer
5. Stratum corneum
• Outer layer of dead cornified (keratinized) cells
Keratinization
• Keratinocytes undergo keratinization as they move towards the surface
• Cells become full of keratin
BIO 1121; ch5 Page 1
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• Dehydration – no cytoplasm
• Dead cells
• Water resistant
Epidermal characteristics:
• Cells accumulate keratin and eventually are shed
• Fingerprints
o Epidermal ridges are interlocked with dermal papillae
o Improve gripping ability
• Langerhans cells (immunity) in s. spinosum
• Merkel cells (sensitivity) in s. germinativum
Skin color depends on:
• Blood supply (in dermis)
• Carotene – orange pigment that can accumulate in the skin
• Melanin
o Produced by melanocytes
o Different shades of melanin
o Can be stimulated to produce more by sun exposure
o Protects against harmful UV radiation
• Cyanosis – blue tinge caused by too little oxygen or poor circulation
Vitamin D
• Epidermal cells synthesize vitamin D3 (cholecalciferol) when exposed to UV
sunlight
• Modified cholesterol → Vitamin D
• Needed for the absorption of calcium
• Deficiency leads to impaired bone growth (rickets) and maintenance
Epidermal Growth Factor
• Found in saliva and intestinal juices
• Epidermal growth factor promotes:
o Growth
o Division
o Repair
Dermis
• Under epidermis
• True skin
• Has two layers:
1. Papillary layer
2. Reticular layer
Papillary layer
• Papillary layer contains dermal papillae
• Contains blood vessels, lymphatics, sensory nerves of epidermis
BIO 1121; ch5 Page 2
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