1. Skin & The Integumentary System
Chapter 6
Learning Targets:
By the end of this lecture, you should be able to:
List functions of skin.
Describe the various layers of the skin.
Explain the physiology behind skin and hair color.
List and describe the various accessory organs of the skin.
Hypertrichosis

2. The Skin
Organs are body structures composed of two or more different tissues.
The skin and its accessory organs make up the integumentary system.
Skin is also known as the cutaneous membrane
Cutis – skin in Latin
Cutaneous – anything relating to the skin

3. SHAPES The Skin Sensation (housing sensory receptors)
Functions of the skin include:
Sensation (housing sensory receptors)
Heat regulation (maintains homeostasis)
Absorption (certain chemicals/ medications)
Protecting underlying tissues
Excreting wastes
Synthesizing certain chemicals & vitamins

4. Skin Layers The skin consists of: Epidermis Dermis
Epithelial tissue
Dermis
Connective tissue
Smooth muscle tissue
Nervous tissue
Blood
Subcutaneous layer (hypodermis)
Loose connective tissue
Adipose Tissue

5. Epidermis Lacks blood vessels
As cells divide and grow, older cells are pushed away from the dermis
Farther the cells move, poorer their nutrient supply becomes, and in time, they die and are shed
In humans, it is thinnest on the eyelids at 0.05 mm (0.0020 in) and thickest on the palms and soles at 1.5 mm (0.059 in).

6. Epidermis
Keratinization - cytoplasm of older cells fills with keratin protein (tough and waterproof) as they move to the outer layers
Normally, production of epidermal cells is balanced with the loss of dead cells (so skin doesn’t wear away)
Where skin is rubbed or pressed regularly, cell division increases… causes calluses
Life span of a typical epidermal cell is about 2-4 weeks

7. Skin Color
Melanocytes - specialized cells in epidermis produce melanin
Melanin - a dark pigment that absorbs UV radiation & prevents mutations in DNA of skin cells
Melanin is produced because of UV light exposure
Melanocytes found in deepest portion of epidermis, cellular extensions pass between epidermal cells

8. Skin Color Largely due to melanin
All people have the same number of melanocytes
Differences result from amount of melanin produced and size of pigment granules

9. Skin Color
More pigment located near equator to protect from UV radiation
More pigment near the equator to protect from UV radiation which damages B-vitamin, folate, needed for DNA synthesis and cell division.
Less pigment away from the equator needed to help our bodies make more vitamin D for health and reproduction.

10. Tanning
As your body is exposed to UV light, your melanocytes produce more melanin to block the UV light.
The melanin moves outside of the melanocytes to protect you, tanning your skin or making it freckle in the process.

11. Tanning
Sunburn results when your skin cannot produce melanin quickly enough to prevent UV rays from injuring blood vessels near kin’s surface

12. Melanoma Most deadly type of skin cancer
Uncontrolled production of melanocytes
Usually starts on or near a mole
For women, most common on legs; for males, on the back
Click image for 4 min video

13. Melanoma

14. Dermis
Boundary with epidermis is uneven because epidermal ridges project internally
Dermal papillae then extend into spaces
Fingerprints - determined by genes and changes slightly as fetus moves during pregnancy (so identical twins usually don’t have exact same fingerprints)

15. Dermis
Composed of dense connective tissue with fibers that give the skin toughness and elasticity
Dermal blood vessels supply nutrients to all skin cells and help regulate body temperature
Nerve cells and sensory receptors also present
Hair follicles, sebaceous (oil-producing), and sweat glands also present

16. How do tattoos work? Ink is injected into dermis
Tattoo visible through epidermis
Tattoo wouldn’t work on epidermis because it would shed quickly
Click image for 1 min video

17. Dermal Growth & Repair Dermis doesn’t shed like epidermis
It can regenerate when injured
Starts to produce new tissue (has different texture and quality than surrounding tissue)
Will become a scar
Stretch marks are caused by rapid growth and tearing of elastic tissue; causes scarring

18. Subcutaneous Layer (Hypodermis)
Binds skin to underlying organs
No sharp boundary between dermis and hypodermis
Adipose tissue for insulation
Blood vessels supply nutrients

19. Accessory Organs of the Skin
Nails
Protective coverings on ends of digits
The whitish, thickened, half-moon shaped region (lunula) covers the most actively growing region
Cells here divide and become keratinized; pushes nail plate forward
Thumbnail grows slowest; middle nail fastest
Nails & Hair are dead cells filled with keratin
Hair pigment = melanin
Both nails & hair are derived from epidermal cells

20. Accessory Organs of the Skin
Hair
Present on all skin surfaces except palms, soles, lips, nipples and parts of external reproductive organs
Each hair develops from a group of epidermal cells called hair follicles
As the epidermal cells divide and grow, older cells are pushed up
These cells become keratinized and die (remains are hair)
Hair= dead epidermal cells
Nails & Hair are dead cells filled with keratin
Hair pigment = melanin
Both nails & hair are derived from epidermal cells

21. Hair A bundle of smooth muscle cells attaches to each hair follicle
 called the arrector pili muscle
The muscle is positioned so that a short hair w/in the follicle stands on end when the muscle contracts
If person is emotionally upset or cold, nerve impulses may stimulate the arrector pili muscles to contract, causing goose bumps
Nails & Hair are dead cells filled with keratin
Hair pigment = melanin
Both nails & hair are derived from epidermal cells

22. The Origin of Hair
Humans have as many hair follicles per square inch of skin as a chimpanzee
All of the 5 million hair follicles form during the 5th month of prenatal development
Perhaps humans evolved to have less hair for hunting(could run for longer times); perhaps to avoid parasites.
Click for video on Hypertrichosis..6 min

23. Hair Color
Genes determine hair color by directing amount of pigment melanocytes produce
A lot of melanin= darker hair
No melanin= white

24. Accessory Organs of the Skin
Sebaceous Glands
Associated with hair follicles
Secrete sebum to keep hair and skin soft, pliable and waterproof
Sweat Glands
Lined with sweat- secreting epithelial cells

25. Sweat Glands Eccrine Glands Apocrine Glands Modified sweat glands
Most numerous
Forehead, neck, back
Produce sweat
Water, Salt and Waste (Urea and Uric Acid)
Apocrine Glands
Responsible for natural body odor
Become active at puberty
Axillary regions and groin
Usually connect to hair follicles
Modified sweat glands
Mammary glands secrete milk
Ceruminous glands secrete ear wax
T-shirt mate selection video ~3min - pbs
Click image for t-shirt mate selection video—3 min