1. Bellwork:

2. Skin – the integumentary system.
Section 32.3

3. What are the main functions of the integumentary system?
The integumentary system includes skin, hair and nails
As a system it serves as a barrier against infection and injury, helps regulate body temperature, removes waste from the body, gathers information and produces vitamin D
The skin acts as a physical barrier, blocking out pathogens and debris, preventing the body from drying out
Also protects from UV radiation
Nails are also produced by the skin
The skin regulates body temperature by releasing excess heat generated by working cells
Hair also works in preventing heat loss
Small amounts of sweat are continuously released from your sweat glands
The Skin contains numerous sensory receptors
Vitamin D is produced in your skin, and is required for the absorption of calcium and phosphorous from the small intestine
Sunlight drives this chemical reaction

4. What is the role of the epidermis?
The epidermis is the outer layer of the skin, and it has two layers
The outer layer (part you can see) is made up of dead cells
The inner layer is made up of living cells (including stem cells)
These cells divide rapidly
As older cells move upwards, they flatten, organelles disintegrate, and they begin to produce keratin ( a tough protein)
When the older cells die they produce a tough, flexible, waterproof surface. Once every four to six weeks a new layer of dead cells replaces an old layer
Epidermis also contains melanocytes – cells that produce a dark brown pigment called melanin, which absorbs UV rays from the sun
Skin color is related to amount of melanin (people with darker skin produce more melanin).

5. What is the role of the dermis?
The dermis is directly beneath the epidermis, and contains the protein collagen, blood vessels, sensory receptors, smooth muscles and hair follicles
This is what interacts with other body systems to help maintain homeostasis
How do structures in the skin work to maintain body temperature?
On a cold day, blood vessels constrict, preventing heat from escaping. On a hot day the opposite happens
Sweat also aids temperature regulation - how?
Skin also secrets Sebum from sebaceous glands. What does Sebum do?
Sebum helps keep the skin flexible and waterproof, and as it is acidic, can help kill bacteria.

6. Why are hair and nails important?
Both are made from keratin, which also makes bull horns, reptile scales, bird feathers, porcupine quills!
Hair on head can help protect scalp from UV radiation and acts as insulation from the cold
Hair in ear, nose, around eyes helps protect dirt and other particles from entering the body
Hair is produced by a hair follicle – a pocket of epidermal cells that extend into the dermis.
They contain stem cells that help renew skin and heal wounds
They are large columns of cells that have filled with keratin and then died
Nails grow from the nail root – an are of rapidly dividing cells
During Cell division, the cells of nail root fill with keratin
They grow at an average of 3mm per month, and fingernails grow faster than toenails.

7. What is acne?
Skin can develop a series of issues due to constant interaction with the environment
Acne develops when sebum and dead skin cells form plugs in hair follicles
Bacteria become trapped, leading to infection and inflammation
85% of people experience it some form during adolescence
One suggestion is that high hormone levels are linked with high levels of sebum production
There are many treatments ranging from over the counter remedies, to prescription drugs

8. What are hives?
Allergic reactions to food or medicine often display themselves as hives
With an allergic reaction, a chemical called histamine is released
This causes small blood vessels to widen, and fluid oozes from blood vessels into surrounding tissue
This causes swelling, leading to hives

9. What causes skin cancer?
Excessive exposure to Ultraviolet radiation (from sunlight or from tanning beds) can lead to abnormal growth in cells of the skin
There are many different types
Over 60,000 people are diagnosed with melanoma (the most serious type) every year, and as many as 8,000 people die from it
Sunblock ( at last SPF 15), clothing, hats, and avoiding tanning salon’s all help prevent skin cancer

10. Key concepts What are the main function of the integumentary system?
What organs and tissues make up the integumentary system?
What structures are found in the epidermis? What structures are found in the dermis?
How does skin help to remove excess heat from the body?
How can you minimize your risk of developing skin cancer?
What causes acne? How can it be treated?