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## Vitamin D Production - UV light causes skin to produce a precursor molecule of vitamin D. - Precursor is carried by blood to the liver where it is modified. - Next, it travels to the kidneys to be modified again to form active vitamin D. - Vitamin D can be ingested through fish oil, fortified...

## Vitamin D Production - UV light causes skin to produce a precursor molecule of vitamin D. - Precursor is carried by blood to the liver where it is modified. - Next, it travels to the kidneys to be modified again to form active vitamin D. - Vitamin D can be ingested through fish oil, fortified milk, eggs, and butter. - Vitamin D stipulates the intestine to absorb calcium and phosphate (bone growth and muscle function) ## Temperature Regulation - Body temperature should be 98.6 °C. - The rate of chemical reactions (metabolism) is altered by changes in temperature. ### To Cool the Body: - Blood vessels in the dermis dilate and heat is transferred from deep tissues to the skin. - Sweat is produced. ### To Heat the Body: - Blood vessels constrict to reduce blood flow to the skin, and heat is retained. ## Aging and the Integument - Blood flow decreases, and the skin becomes thinner due to a decreased amount of collagen. - Decreased activity of sebaceous and sweat glands makes temperature regulation more difficult. - Loss of elastic fibers causes skin to sag and wrinkle. ## Classification of Burns - **1st Degree:** damages only the epidermis - Redness, slight swelling, pain - Heals within 2-3 days - Usually no scar - Includes sunburns or exposure to cold. - **2nd Degree:** damages the epidermis and upper dermis - Redness, swelling, pain, blisters. - **3rd Degree:** Destroys the epidermis and dermis - Burned areas are cherry red to black. - Nerve endings are destroyed, thus the burned area is painful. - A skin graft might be necessary because regeneration is not possible.