Hair, skin and nails

Definitions & Key takeaways

The hair, skin, and nails are all made up of protein. The main protein in the hair is called keratin. Keratin is also present in the skin and nails. The hair, skin, and nails function includes protection against microbes, temperature regulation, and environmental interaction. They also provide clinicians with information regarding clients' health status.

Chapters:

Watch video only

Introduction0:00–0:42

Hair, skin glands (including oil and sweat glands), and nails are all considered skin appendages, and they help with regulating body temperature and protection from the environment.
These appendages are found in a layer of skin called the dermis which is a layer sandwiched between two other layers called the epidermis and hypodermis.
The epidermis is the thin outermost layer of skin, the dermis is the thicker layer that lies below that, and the hypodermis is the lowest layer that’s made of fat and connective tissue and anchors the skin to the underlying muscle.
Hair is found on nearly every part of skin except the palms of the hands, soles of the feet, and the lips. Every strand of hair is composed of the shaft, root, and bulb that sits in a pouch like structure called the hair follicle.

Hair0:42–4:04

The hair follicle is epidermal tissue that dips down into the dermis, and is associated with other structures like apocrine glands, sebaceous glands, the arrector pili muscle, and nerve receptors.
Inside the bulb lies the hair matrix which serves as the active site of hair growth and gives hair its color. It contains two different cell types - follicular keratinocytes and melanocytes, and these cells receive blood from a small cluster of capillaries called the papilla.
Similar to the epidermal keratinocytes in the skin, follicular keratinocytes in the hair replicate rapidly and die in a process called keratinization.
During this process, keratinocytes produce keratin. Keratin is a long filamentous protein that comes in many different forms depending on the type of keratinocytes producing it, but it is generally divided into soft and hard keratin; where soft keratin is produced by skin and hard keratin is produced by hair and nails.
Hard keratin is much denser than the soft keratin produced by epidermal keratinocytes in the epidermis, which gives hair and nails their durability.During keratinization, the hard keratin fills up the entire cell, causing the organelles to flatten out.
Eventually, these follicular keratinocytes die - turning into compact little brick-like cells as they slowly get pushed further and further up into the hair follicle.
As this process continues different parts of the hair strand are made including the hair root and hair shaft that projects from the surface of skin.
Meanwhile, follicular keratinocytes at the bulb of the hair replicate only a set number of times, and once they have reached the maximum number, the hair follicle stops growing and falls out, which leads to baldness.
Now, melanocytes produce melanin, which is a protein pigment, or coloring substance, that gives each strand of hair its color.
Melanin is actually a broad term that constitutes several types of melanin found in people of differing skin color. These subtypes of melanin range in color from black to reddish yellow and their relative quantity define a person’s skin color and hair color.
Melanocytes move melanin into small sacs called melanosomes, and these get taken up by newly formed follicular keratinocytes--giving hair its color.
Over time these melanocytes stop producing melanin, which is why hair turns white as people age.Looking at some of the structures in the follicle, we can see nerve receptors that wrap around the hair bulb, and these get stimulated when the hair shaft is moved like when a tiny bug walks over our forearm.
There’s also the arrector pili muscle that pulls on the hair making them stand up during cold weather or when you’re frightened - creating what are called goosebumps.
For many mammals - this was an evolutionary trick to make an animal look larger than it really is to scare away predators.
Sort of like when a cat gets scared and all of it’s hair stand up tall! Now, sebaceous glands, or oil glands, are located in the dermis layer of the skin and they’re found everywhere on the skin except on the palms, soles of the feet, and lips.

Sebaceous Glands4:04–5:08

Sebaceous glands secrete an oily substance called sebum onto a nearby hair follicle or through pores that extend directly to the skin surface.
As it turns out, arrector pili muscles surround the sebaceous glands, so when these tiny muscles contract, sebum gets squeezed out.
Sebum softens the hair shaft preventing it from becoming brittle. Sebum also prevents moisture loss from the skin and is slightly acidic, which helps to deter pathogens.
Now, during puberty, there’s an increase in androgen hormones and that causes more sebum to be produced. Unfortunately, that excess sebum can block pores and plug up hair follicles, creating tiny little enclosures that allow infections like acne and folliculitis to develop.
And since there are more sebaceous glands in the face and scalp, those are the most commonly affected areas. Now, there are two main types of sweat glands - eccrine glands and apocrine glands.

Sweat Glands5:08–6:50

Eccrine glands are found everywhere except the lips, ear canal, clitoris, and glans of the penis. They’re coil shaped structures located in the dermis and have a duct that opens up into a pore on the skin surface.
Sweat is hypotonic relative to blood, and contains mostly water with small amounts of electrolytes like sodium and waste products like ammonia.
Sweat also contains dermcidin which is a secreted protein that helps destroy bacteria. But the main purpose of sweat is to help cool the body by taking the heat energy from the skin and helping it dissipate into the air by evaporating.
The sympathetic nervous system activates sweat glands during heavy cardiovascular activity like when you’re working out, or during the fight or flight response like when you run into a bear.
And in those situations, sweating begins on the forehead and proceeds downward. Another trigger for sweating is fear or anxiety, like when giving a speech, but in those situations sweating starts on the palms and soles.
Apocrine glands are similar to eccrine glands, but they’re bigger and fewer in number, and the secretions contain more lipids and proteins.
Apocrine glands are located in the dermis layer, in regions of the body like the armpit and the genitals. Bacteria love to dine on nutrients from the apocrine secretions and that gives those body regions their distinct odor.
Finally, there are also some modified apocrine glands that serve really unique roles - like ceruminous glands in the ear which produce earwax, and mammary glands in the breast which secrete milk.
Finally, there are the nails which grow from proximal to distal or near to far on the tips of our fingers and toes. Now, looking at the nail from above, there are nail folds along each side of the nail, which are where the skin seals of the edges of the nail, as well as proximally by the the eponychium.

Nails6:50–8:06

The eponychium, is a another nail fold, that gives rise to the cuticle, which is the semi-circular layer of dead skin keratinocytes that covers the junction where the nail enters the skin so that pathogens can’t enter.
Now, let’s look at a cross section of the finger. There’s the nail matrix, which can be seen as the lunule, which is the small, proximal white part of the nail at the near end.
The nail matrix creates the nail plate, which is the hard part of nail we can see as well as the free edge that hangs over the skin.
The nail matrix is special epidermal tissue that dips down into the dermis, which contains nerves, lymphatics, and blood vessels that support the nail.
Additionally, the nail matrix contains modified keratinocytes that replicate and undergo the process of keratinization - similar to what happens in the skin and hair.
The youngest keratinocytes are in the nail matrix, and older cells die and keratinize, and become part of the nail plate.
Alright, as a quick recap, the appendages of skin include hair, nails, as well as oil and sweat glands. The function of these accessory structures includes protection from microbes, temperature regulation, as well as heightened sensation and interaction with our environment.

Review8:06–8:29

They serve as important gateways for multiple physiologic functions and ultimately can tell a
Hair, skin and nails: Video, Anatomy, and Function | Osmosis