2. Structure of the Skin Epidermal growth and repair
Turnover or regeneration time refers to time required for epidermal cells to form in the stratum basale and migrate to the skin surface—about 35 days
Shortened turnover time will increase the thickness of the stratum corneum and result in callus formation
Normally 10% to 12% of all cells in stratum basale enter mitosis daily
Each group of 8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes is called an epidermal proliferating unit, or EPU

3. Structure of the Skin Dermal-epidermal junction
A definite basement membrane, specialized fibrous elements, and a polysaccharide gel serve to “glue” the epidermis to the dermis below
Functions of the junction
“Glue” the two layers together
Provide mechanical support for the epidermis
Partial barrier to the passage of some cells and large molecules

4. Structure of the Skin Dermis (corium) Sometimes called “true skin”
Much thicker than the epidermis and lies beneath it
Gives strength to the skin
Serves as a reservoir area for storage of water and electrolytes
Dermis on the ventral surface and over the appendages is generally thinner than on the dorsal surface
Somatic sensory receptors process information such as pain, pressure, touch, and temperature

5. Structure of the Skin Dermis (cont.) Contains various structures:
Arrector pili muscles and hair follicles (Figure 6-1)
Sensory receptors (Figure 6-3)
Sweat and sebaceous glands
Blood vessels
Rich vascular supply plays a critical role in temperature regulation

8. Structure of the Skin Dermis (cont.) Papillary layer
Composed of dermal papillae that project into the epidermis
Contains fine collagenous and elastic fibers
Contains the dermal-epidermal junction
Forms a unique pattern that gives individual fingerprints

9. Structure of the Skin Dermis (cont.) Reticular layer
Contains dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable
When processed from animal skin, produces leather

11. Structure of the Skin Dermal growth and repair
The dermis does not continually shed and regenerate itself as does the epidermis
Wound healing
Fibroblasts begin forming an unusually dense mass of new connective fibers
If not replaced by normal tissue, this mass remains a scar
Cleavage lines (Figure 6-4)
Patterns formed by the collagenous fibers of the reticular layer of the dermis
Also called Langer’s lines

13. Structure of the Skin Hypodermis
Also called subcutaneous layer or superficial fascia
Deep to the dermis, forming connection between the skin and other structures
Not part of the skin

14. Skin Cancer Three major types of skin cancer Basal cell carcinoma
Most common
Begins in stratum basale
Rarely metastasize
Squamous cell carcinoma
Also arises in epidermis
Sun-exposed areas
Not likely to mestastisize
Malignant melanoma
Most deadly
Sometimes develops from a pigmented nevus (mole)
ABCD rule: assymetry, border, color, diameter

15. Quick Check
What is the name of the gluelike layer separating the dermis from the epidermis?
Which layer of the dermis forms the bumps that produce ridges on the palms and toes?
Which layer is vascular: the epidermis or dermis?