Skin is the largest organ of your body. It is made up of three layers: epidermis, dermis, and the fatty layer
1. Epidermis – the outer, thinnest layer. These outermost cells are dead and water repellent. These cells are constantly replaced.
2. Dermis – is located directly below the epidermis. This layer is the thickest and contains blood vessels, nerves, muscles, oil glands, and sweat glands
3. Fatty Layer – is below the dermis and is where most fat is deposited when a person gains weight.
Melanin – epidermis cells produce melanin. It is a pigment that protects your skin and gives it color. The more melanin you have, the darker your skin appears. (Melanin also acts as a natural sunblock. The more you have the more your skin blocks UV rays. The downside is that it also blocks Vitamin D production. *I am in no way telling anyone that they should or should not wear sunblock*)
**The most important function of the skin is protection.** It protects against physical and chemical injury. Other important functions of the skin are: sensory response (touch – nerve cells detect and relay information to the brain), formation of vitamin D, regulation of body temperature (sweat), and ridding the body of waste (sweat).
When skin is injured (scratched, burned, ripped, etc…) it is exposed to harsh conditions and disease causing organisms can enter the body and cause infections. When skin is damaged the epidermis produces new cells and the dermis repairs the tears in the skin.
Different amounts of melanin give humans a variety of skin colors (shades).
Muscles
Muscles help make our daily movements possible. Voluntary muscles are muscles that you are able to control like you hand, arm, and leg muscles. Involuntary muscles are muscles that you can't control consciously like your cardiac (heart) muscles and the muscles that help you breathe and digest food.
** Trivia ** It takes 13 muscles to smile and 43 muscles to frown
Humans have three types of muscle tissue: skeletal, smooth, and cardiac.
Your skeletal system is made up of 206 bones. Without it, you would be a blob of skin and organs on the floor. It's two most important functions are protection and to assist with locomotion.
Your bones provide protection for your organs and tissue like your heart and ribs. When your muscle is attached to your bones you are able to move. Locomotion is movement.
There are many different types of bones: long bones, short bones, flat bones, and irregular bones but what connects those bones together is a tissue known as cartilage. This flexible yet strong tissue is found in your earlobe, at the end of your nose, and between joints like your knees and elbows. In the early stages of development, your skeletal system is mostly cartilage and then hardens into bone in the early infant stages of life. This is known as ossification.