Hair, skin and nails

00:00 / 00:00



Hair, skin and nails

Integumentary system


Hair, skin and nails


0 / 6 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

6 pages


Hair, skin and nails

of complete


USMLE® Step 1 style questions USMLE

of complete

A pathologist is reviewing skin biopsy slides under a microscope. She identifies a neural crest cell derivative that produces pigment to shield the body from ultraviolet radiation. Within which layer of the skin is this cell type located?  

External References

First Aid








Clubbing (nails)


glomus tumors under p. 490


clubbing p. 58

glomus tumors under p. 490

External Links


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.

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.


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.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Keratin: Structure, mechanical properties, occurrence in biological organisms, and efforts at bioinspiration" Progress in Materials Science (2016)
  6. "The skin: an indispensable barrier" Experimental Dermatology (2008)

Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.