Hair and Nails

Functions of Hair

The hair on your headRounded proximal end that fits into the acetabulum of the hip bone. is called terminal hairThick, coarse hair found on the scalp, eyebrows, and other areas after puberty. whereas the hair on your body is called vellus hair. These hair types are structured similarly. However, they differ in the depth to which they penetrate the cutaneous membrane. They also differ in the length of the hair on the outside. I want to highlight something subtle on this diagram. The thin purple layer of the epidermisThe outermost layer of the skin, made of stratified squamous epithelium. dips down. It covers the entire hair that penetrates the skinThe body’s largest organ, providing protection and regulation.. Hair almost seems external to your body. This perception exists despite hair having its own free nerve ending and blood vessel.

Some facts: Your hair can grow about 1 cm per month.  This means that it grows 1 inch per 2-3 months.  Now, at any given moment, the hairs on your head are not the hairs that were there yesterday.  You are constantly shedding hair.  Ninety hairs per day!  That number just seems like a lot to me.  This also means that 90 new hairs are growing too, depending on your health and your diet.  You can put all the keratin-containing shampoos you want onto your hair. If you want more hair, you have to start with your diet. If you want it to be stronger and thicker, you have to start with your diet. 

Pregnant women do not shed their 90 hairs per day.  The hormone progesteroneA hormone that supports pregnancy and regulates the menstrual cycle. maintains a high level for 9 months.  While it does, hair is not shed, weight is gained, and anything else that helps the baby is done.  At the end of the 9 months of pregnancy, the progesterone levels drop. All the hairs that should have been shed during the 9 months are then shed over the weeks after delivery. 

Arrector Pili

Arrector pili are little muscles that are on each hair.  These muscles contract and pull the hair erect. This is the same mechanism at work when cats fluff their fur.  Side note, my cat has an abnormally short tail and legs. She was confined to a cage for the first 18 months of her life.   She was scared of other kitties at the pound.  But when we brought her home, everything scared her and she would fluff her stubby tail.  It was just look so funny. 

The stuff about my cat is not important. What IS important is that these muscles are smooth muscles. This means they are involuntarily controlled.  These arrector pili also all act together.  Each hair is controlled by a different free nerve ending. Yet, every single nerve and hair will coordinate to erect their hair simultaneously.  We call this multi-unit smooth muscle control..

When you are scared, you might say that you got goosebumps or that the hairs on your neckNarrow region just below the head; common fracture site. stood up.  Same thing.  Both these actions are the result of your arrector pili.  There are many theories about why humans have retained the ability to do this. However, that is the topic of another class I teach.

Structure of a Nail

I don’t have much to say about nailsHard, keratinized structures that protect the fingertips and enhance fine motor skills.. Anxiety causes me to chew mine until they bleed.  I think the one thing I’d like to point out about nails is the lunuleThe white, crescent-shaped area at the base of the fingernail.. This is the lighter shade of your nail that exists where the nail meets the skin.  Lunules expand with malnourishment.  It’s an easy way to tell if a child is getting the nutrition they need. It can also be a good indicator of Crohn’s or Celiac disease.  These two diseases affect the small intestine’s ability to absorb food.  So, food is passing through, but you are not getting any nutrition out of it.  Speaking about disease indicators, nails change significantly with auto-immune diseases.  They become ridged and brittle in diseases such as psoriasis. Psoriasis is a skin disease. It usually comes with hair, nails, and arthritic issues.  I have PSA or psoriatic arthritis.  Sometimes, I sausage fingers and they are so swollen and painful that I can’t type.  Don’t tell me to use talk-to-text. Have you ever used it?  It’s frustrating.

The lunule is also the site of the nail bedThe skin beneath the nail plate, rich in blood supply. that generates and grows the nail.  Damage to the nail bed can result in the inability to grow a smooth, correctly shaped nail.