1. Seven Functions of Skin
Mechanical/Chemical damage – keratin toughens cells; fats cells cushion blows; and pressure receptors measure damage
Bacterial damage – skin secretions are acidic and inhibit bacteria.
Ultraviolet radiation – melanin produced to protect from UV damage

2. Thermal control – regulates body temperature
Heat loss: sweat to cool the skin
Heat retention: prevents blood from losing heat & shivering
Waterproofing – contains lipids to prevent drying out
Excretion of waste – urea and uric acid secreted in sweat
Makes vitamin D – changes cholesterol molecules in skin and converts it to vitamin D

3. Skin Structure Epidermis — outer layer Dermis – middle layer
Subcutaneous tissue – deepest layer
also referred to as the ‘hypodermis’

4. A cell takes 40 – 56 days from creation to sloughing off
Epidermis
Summary of layers from deepest to most superficial:
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
A cell takes 40 – 56 days from creation to sloughing off

5. Layers of the Epidermis
Stratum basale
Deepest layer of epidermis
Cells actively undergoing cell division
New cells push older cells upward until they
eventually fall off
Cells are mostly keratinocytes and some melanocytes

6. Keratinization
Keratin is a protein that helps harden skin cells, makes them tougher and helps prevent water loss by the body.
Keratinocytes are responsible for making keratin
Keratin makes the skin waterproof
Keratin is found in cells of the basale and spinosum strata

7. Stratum spinosum – Made of keratinocytes
Some cells grow projections that connect to other cells making the cell layer stronger
Prickle Cells with long projections
Stratum granulosum – mostly flattened keratinocytes that have lost nuclei and organelles
Death zone of keratinocytes

8. Vitamin D Production Cells of stratum spinosum and basale: Vitamin D:
UV energy + cholesterol = Vitamin D
Vitamin D:
used by kidney to make the hormone calcitriol
Calcitriol:
necessary to signal small intestine to absorb calcium from the blood
No Vitamin D  no calcitriol 
no calcium absorption 
weak bones

9. Stratum lucidum
Formed from dead cells of the deeper layers
Occurs only in thick, hairless skin of the palms of hands and soles of feet
Stratum corneum
Outermost layer of epidermis
Scale-like dead cells are filled with keratin which is a strengthening protein also preventing water loss from skin

10. Layers of Skin
No Lucidum Layer

11. Melanin Pigment (melanin) produced by melanocytes
Melanocytes are mostly in the stratum basale
Color is yellow to red to brown to black

12. Melanocytes: Cells deep in the epidermis and dermis that produce a pigment called melanin which protects the cells from UV damage
Skin color determined by the size and quantity of melanin granules in the tissue

13. What’s your color?
Determined by genetic, environmental, and physiological factors
Your DNA determines how much MELANIN is produced
UV radiation increases melanin production
Circulation, vitamin deficiencies, physical ailments (liver failure)

14. Why the Spots…?
Large amounts of melanin occur in some regions like freckles, moles, and nipples.
Caused by uneven distribution of melanin
Less melanin occurs in the lips, hands, and soles of the feet.

15. Albinism
A single gene mutation can cause a deficiency or complete absence of melanin.
Albinos have fair skin, white hairs, and unpigmented eyes (eyes appear red)

16. Fingerprints
The up and down border between the dermis and epidermis helps bond the layers together
In thick skin, epidermal ridges show on the surface as fingerprints:
Function – enhance gripping

17. Dermis – the middle layer
Papillary layer:
Thin (20%)
Consists:
Contains dermal papillae
Capillaries, sensory neurons
Function: feed epidermis
Reticular Layer:
Thick (80%)
Elastic and Collagen fibers
Sweat and oil glands
Deep pressure receptors
Function: provide strength and flexibility

18. Dermal Papillae
small, nipple-like extensions of the dermis into the epidermis
Blood vessels nourish all hair follicles and bring nutrients and oxygen to the lower layers of epidermal cells

19. What makes us stay young looking?
Elastic fibers
gives skin elasticity
fibers can stretch up to 1.5x their length and snap back to their original length when relaxed
Collagen fibers
gives skin support/firmness
~ one quarter of the human body is collagen
support the skin’s mechanical strength and texture

20. Sensory Perception in Skin
Skin is highly sensitivity to touch because of large amounts of sensory structures found in dermis

21. Sensory Perception in Dermis
Merkel cells: deep layers of epidermis
superficial touch
Free Nerve Endings: superficial dermis
pain and temperature
Meissner’s Corpuscles: superficial dermis
light touch
Pacinian Corpuscles: deep dermis
- pressure and vibrations

22. Skin Structure Subcutaneous tissue (hypodermis) is deep to dermis
Not part of the skin
Anchors skin to underlying organs, bones and muscles
Contains half of the body’s fat; acts as padding and insulation.