Exploring the body’s biggest organ

1. Exploring the body’s biggest organ • An organ is a portion of the body that has special functions to perform for the entire body. • When you think of an organ you may think of the heart, brain, or liver but the skin is also an organ and in fact is the largest organ. • The skin is connected to the rest of the body and it functions and communicates through nerves and three kinds of vessels, arteries, veins and lymphatics.

2. What the skin does • Protection • Against larger organisms - Lice, worms • Against smaller organisms - bacteria, viruses • Against powers and fluids - dirt, water, chemicals • Ultraviolet light • Controls body temperature • Makes Vitamin D for the body • Heals itself • Lasts for your entire life but changes with age • Acne, wrinkles, hair changes

3. Organisms that affect the skin come in different sizes- • Look in the louse box-and pick some lice (don’t worry not real – just celery seeds) and put on your skin. Use the surface microscope and compare the size of the “louse” with that of a hair. On the scalp lice lay eggs on hairs. These are the small grey nits that infected people may have. • The fake lice on your skin are approximately the same as a real louse that can be spread from person to person and causes infections and severe itching. • A bacterium is about 1/1000 the size of the louse and a large virus is about 1/10,000 the size of the louse.

4. Find sweat glands on the palms • Where on the palm can you see sweat glands must easily? • Their opening is seen along the ridges that form the fingerprints- • Use higher power-to see small glistening drops of sweat. • How regular is the distance between sweat glands on the skin ridges? • Do you see openings in the depressed portions between the ridges? • Try to see sweat glands on other parts of the body. • What are the functions that the ridges might have-think about the ridged soles on some sports shoes? • Sweat contains amino acids, the building blocks of proteins, and can be stained with special chemicals - this is used by crime scene intelligence agents.

5. Skin is essential for controlling the body’s temperature • Sweat glands, blood vessels and nerves for a system to control temperature. • Sweat glands deliver a watery fluid (‘sweat’) with small amounts of salt and amino acids to the skin surface. • The heat brought to the skin by large and small blood vessel evaporates the sweat on the skin surface and lowers the body temperature. • If sweat glands are lacking because of genetic diseases children get very hot and sick during a fever or exercise. Certain drugs can block sweating. Some drugs leave the body in the sweat. • Botox, a drug to decrease skin wrinkling is sometimes used when people have excess sweating on their hands, feet, or armpits.

6. Body Temperature • Sweats glands are over entire body except for special locations like the lips. • Sweat is formed in a coiled portion of the gland in the fatty layer from the glands that are close to small blood vessels. • Nerves near the blood vessels control blood flow and also release small chemicals that control sweating. • Sweat glands lie deep in the skin in the fatty layer-the subcutaneous layer, each gland has a duct that carries the sweat across the dermis of the skin and the duct crosses the epidermis to exit on the skin surface. Figure from: http://www.nature.com/milestones/skinbio/subjects/index.html

7. Sunlight- • Sunlight and the skin have important relationships- • The skin is the only part of the body that uses sunlight to make Vitamin D from a cholesterol-like chemical • Too much sunlight, or suntan beds, causes redness and pain in the skin, scaling, darkening of the skin color, wrinkling, aging and skin cancer. • The epidermis blocks the most dangerous shorter UV rays but longer UV enters the dermis (Layer II) and damaged the molecules collagen and elastin that form the bulk of the dermis and give skin its characteristic feel. These molecules require special electron microscopes to be seen.

8. Sunlight • Look at the skin the with scope on the outside and inside portions of the upper arm. • Which side is darker? • What might the reasons be? • Look at some freckles and see if someone has a mole. • What do you see in the mole? • Different structures such as globules and a netlike pattern are often seen.

9. Hair • Hair follicles are over the entire skin except for special locations like the lips and the palms and soles. • People used to think that hair on the palms was the skin of a werewolf. • Look at the hair under high magnification and look for an overlapping patterns of cells on the outside cuticle layer of the hair. • The hair is dead - what will happen if the hair is exposed to too damage or chemicals. • Look at the very fine hairs that are on the face. Acne starts when these hair follicles get blocked. • Hair follicles, if completely lost can not regrow, See if someone in your group has a scar and what that skin looks like.

10. Conclusion • Skin is the largest organ and serves many functions • You should now have a better understanding of how the skin protects us from bugs, the location and function of sweat glands, sun damage spots, and hair.