The Integumentary System

1. The Integumentary System

2. Integumentary System

• Only 1.5 to 4 mm thick but is body’s largest
organ
– 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

Epidermis
Dermis
Subcutaneous layer

5. Layers of the Integument (Figure 6.1)

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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

Epidermis
Stratum
corneum
Stratum
lucidum
Stratum
granulosum
Stratum
spinosum
Dermis
Stratum
basale

9. Stratum Basale

• Single layer of cuboidal to low columnar cells attached to a
basement 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 with
keratin) 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 of
the 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 Skin

17. Thick Skin High Magnification

Epidermis
Stratum
corneum
Stratum
lucidum
Stratum
granulosum
Stratum
spinosum
Dermis
Stratum
basale

18. Thin Skin High Magnification

Epidermis
Stratum
corneum
Stratum
granulosum
Stratum
spinosum
Dermis
Stratum
basale

19. Thin Skin Low Magnification

Stratum corneum
Epidermis
Stratum granulosum
Dermis
Stratum spinosum
Dermal papillae
Duct of merocrine sweat
gland
Stratum basale

20. Dermis