2. So What Does The Skin Do?

3. 32.7 Vertebrate Skin— Example of an Organ System
Skin is the body’s interface with the environment
Sensory receptors, barrier against pathogens, internal temperature control, water conservation
Vertebrate skin is made up of all four tissue types arranged in two layers:
Outer epidermis contain keratinocytes
Deeper dermis contains nerves, blood and lymph vessels, hair follicles and glands

4. Epidermis – epithelial tissue
a. stratum germinativum – wavy ridges extend from dermis, stem cells regenerate skin takes ~ 14d
- as cells move outward they gain keratin
b. stratum corneum – dead outer layer (~ 14 d)
Skin Color – melanin & blood supply.

5. outer flattened epidermal cells
cells being flattened
Figure 32.13
(a) Skin structure. (b) Section through human skin. (c) Structure of a hair. It arises from a hair follicle derived from epidermal cells that have sunk into the dermis.
Figure It Out: How many polypeptide chains are in a keratin macrofibril?
Answer: Three
dividing cells
dermis
Fig b, p. 548

6. Dermis – contains accessory structures
a. Hair papilla at base of follicle adds keratin
- contains blood vessels and nerves (sensation)
- arrector pili makes hair stand on end
b. Sebaceous glands – sebum lubricates hair & inhibits bacteria. Activated at puberty.
- May clog & form acne
c. Sweat glands – secretes water, salt & substances that produce body odor

7. hair epidermis dermis hypodermis sensory neuron oil gland
Figure 32.13
(a) Skin structure. (b) Section through human skin. (c) Structure of a hair. It arises from a hair follicle derived from epidermal cells that have sunk into the dermis.
Figure It Out: How many polypeptide chains are in a keratin macrofibril?
Answer: Three
hypodermis
sensory neuron
oil gland
hair follicle
sweat gland
blood vessels
smooth muscle
Fig a, p. 548

10. keratin polypeptide chain
hair’s cuticle
one hair cell
keratin polypeptide chain
keratin macrofibril
Figure 32.13
(a) Skin structure. (b) Section through human skin. (c) Structure of a hair. It arises from a hair follicle derived from epidermal cells that have sunk into the dermis.
Figure It Out: How many polypeptide chains are in a keratin macrofibril?
Answer: Three
Fig c, p. 548

11. Sunlight and Human Skin
Melanocytes in skin make a brown pigment (melanin) which affects skin color and tanning
Melanin protects against UV radiation
A little UV promotes vitamin D production
A lot of UV damages DNA and promotes cancer

12. Nails – can be used as an indicator for circulation.
- WHAT IS CLUBBING?

13. 32.8 Farming Skin
Commercially grown skin substitutes are already in use for treatment of chronic wounds
Skin may be a source of stem cells that could be used to grow other organs

16. 32.7-32.8 Key Concepts A Closer Look at Skin
Skin is an example of an organ system
It includes epithelial layers, connective tissue, adipose tissue, glands, blood vessels, and sensory receptors
It helps protect the body, conserve water, control temperature, excrete wastes, and detect external stimuli