Hair (types, function, growth) – Human Body

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Hair is a defining characteristic of all mammals. It is a protein that grows from the body through your skin or epidermis.

Human hair can grow in most areas of the body, but is predominantly found on your head, face, armpits, and pubic regions.

Types of Hair

The body produces two types of hair: vellus and terminal.

Vellus hair is grown in childhood and covers most of your body. These hairs are short, light, and very fine.

Terminal hair is also called androgenic hair. These hairs are the hairs that most of us refer to as “our hair.” Terminal hair replaces vellus hair in several regions of the body as the body matures.

Keratin Scales

Parts of Hair

Hair can be broken up into three parts lengthwise, as well as three parts crosswise.

Lengthwise the parts of hair are: bulb, root, and shaft. The bulb is found at the base of the hair. The root is the hair that is found beneath the skin’s surface, and shaft is the hair that is above the skin’s surface.

Crosswise the parts of hair are: medulla, cortex, and cuticle. The medulla is the core of hair and it is made up of loose cells and air. The cortex is the main body of hair and it is made up of densely packed protein. The cuticle is the outermost layer of hair.

How Hair Grows

The only “living” part of hair is found at the follicle. This is where hair begins. Blood feeds the bulb that creates more cells. As the cells are created they push older cells up and through your skin.

Before the hair breaks through the skin it passes through oil glands. These oil glands cause the hair to be shiny and soft.

The hair on your head grows at a rate of 0.4 millimeters a day. The cells die before they break through your skin which is why you can’t feel your hair.

Every day about 50 to 100 hairs will fall out of your scalp. The follicles in some people will stop growing hair as they get older. Therefore as people get older their hair may be thinner, or they may go bald.

Hair Root

The Purpose of Hair

Different hairs on your body serve different purposes. The hair on your head has two purposes: it protects you from UV rays from the sun and keeps heat within your body.

Eyebrows and eyelashes protect your body from dirt. Eyebrows are also used as a form of nonverbal communication, displaying emotions like anger and surprise.

The specific purpose of other hairs is still debated among scientists.

Cross section of hair

Interesting Facts:

  • The protein in hair is called keratin
  • Hair doesn’t grow on your lips, the palms of your hands, or the soles of your feet
  • There are about 100,000 follicles on your scalp
  • Facial hair grows faster than any other hair on your body

Biology

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