Anatomy & Physiology of Skin, Hair, and Nails

The skin, hair, and nails of the human body are not only complex, but also serve as the primary parts of the body that experiences the outside world firsthand. They are meant to protect the rest of the body from irritants and damage, as well as send signals to the brain concerning sensations and possible danger. While only the outer layers of the skin, hair, and nails are visible to the human eye, each has several sub layers that serve different functions.

Skin Anatomy & Physiology

Human skin is made up of several different layers, the first being the epidermis which contains the cells that make up skin pigment. This thin layer is what is visible to the eye, and is actually made up of three different subsections. The first is the stratum corneum, which is the part of human skin that sheds. This layer also includes the protein keratin, which protects the epidermis from damage. The second part of the epidermis is the keratinocytes layer, and the third is the basal layer, or the bottom part of the epidermis. This layer contains basal cells, which create keratin for the two top layers to replace what is shed from the surface.

Underneath the epidermis is the dermis. This layer of skin houses blood and lymph vessels as well as the body’s hair follicles and sweat glands. All of these are held together by collagen, which provide skin with its strength. As humans age, this collagen breaks down, making skin thinner and creating wrinkles. The dermis is also the part of the skin that contains pain and touch receptors. The subcutis is the bottom layer of skin. It acts as a sort of shock absorber, protecting organs from injury. It is comprised of both collagen and fat cells, which help to conserve and regulate the body’s heat.

Skin is meant to protect the rest of the body underneath it from damage, and it is the largest organ in the human body. While it is mainly meant to protect against heat and light damage, skin also protects the body from injury and infection. It is also the body’s primary means of storing water, fat and vitamin D, as well as the main way the body absorbs vitamin D from the sun. Outside of these functions, the human skin also allows for the sense of touch, and sends this information back to the brain for processing, allowing the body to determine what action needs to be taken for protection or stimulation.

  • Anatomy of the Skin: This page offers a brief description of the function of human skin as well as its makeup.
  • Skin Makeup: This page offers highly detailed information of every layer of the human skin.
  • Skin Visual: This site provides visual references for the makeup of skin.
  • Physiology of the Skin: This page provides detailed information on all of the functions of skin as well as visual aids.
  • Melanin: This provides a brief definition of this part of the skin that determines pigmentation.
  • Vitamin D: This article provides detailed information on this essential vitamin, as well as explains how the skin absorbs it from the sun.
  • Sense of Touch: This page provides detailed information on how the skin processes touch.
  • How Skin Acts as Protection: This article provides information on how the skin acts as a protective layer for the body, and how the skin protects itself.
  • Insulation: This article details how the skin protects the body, including how it acts as insulation and regulates temperature.
  • Collagen: This site provides detailed information on collagen and how it functions in the skin.
  • Infection: This article provides information on how the skin protects against infection and what happens when the skin’s protective layer is breached.

Hair Anatomy & Physiology

Hair begins in the dermis layer of the skin and pushes outward. It is made up primarily of the protein keratin. Unlike other portions of the body, the hair is only alive at the root, where the sebaceous gland produces oil to lubricate the hair. Strands of hair are made up of three parts. The cuticle is the outermost layer, and varies in thickness based on genetics. Underneath the cuticle is the cortex, which determines both the color and shape of the hair. The cortex is made up of mostly melanin, the same thing that determines skin pigment. The cortex is also the main portion of hair, making up the majority of its structure. Below all of this is the medulla, which is hollow. This serves mainly as a core for the cortex and cuticle, and is not present in every person’s hair. The diameter of the entire hair structure ranges from 0.00067 to 0.0071 in.

One of the primary functions of hair is the keep the body warm. As humans have developed other means of accomplishing this, the amount of hair on the human body has gradually decreased over time. Despite this, when a person becomes too cold, their hair will “stand on end”, creating a layer above the skin that is meant to trap heat, protecting the body from frost bite and hypothermia. It is also meant to protect delicate parts of the body, especially the eyes, from dirt, sweat and other irritants or dangers. Eyelashes in particular can sense when an irritant is near, sending a signal to the brain to close the eyes. Outside of these functional purposes, hair is also meant as a means for human’s to attract a mate. Research has shown that women with thick, lustrous hair naturally attract more male attention, as their hair signifies that they are fertile.

  • Hair Anatomy: This article details the anatomy of hair and where it is located on the human body.
  • What is Hair: This page provides a good description of what hair is and how it functions.
  • Purpose of Body Hair: This article briefly describes the purpose of body hair, focusing on the role it plays in human sexuality.
  • Why Hair Grows: This article describes why hair grows in different ways and lengths all over the body.
  • Mammals and Hair: This article provides information on the purpose of hair for mammals, including humans.
  • Hair Structure and Function: This document provides extremely detailed information, with visuals, on the structure and function of hair.
  • Human Hair: Provides extensive information on the various purposes of human hair.
  • Keratin: This site provides detailed information on what keratin is.
  • Keratin Makeup: This site provides information on the different parts of keratin and how it makes human hair.

Nail Anatomy & Physiology

A human nail is made up of three parts: the matrix, the plate, and the nail bed. The matrix acts as a base for the rest of the nail, containing nerves as well as lymph and blood vessels. The matrix creates the rest of the cells that make up the nail. The only part of the matrix that is visible to the naked eye is the white, crescent portion of the nail known as the lunula. On top of the matrix is the nail bed, which is made up of the dermis and epidermis. The visible portion of the nail, or the nail plate, is made up of keratin and amino acids. It is formed by the flattened, dead cells pushed up by the matrix, and the bone of the finger determines its shape.

Nails are meant to protect the fingertips and toes, as well as the tissues around them from injury. It also helps the fingers themselves function in a more accurate manner. The nails place slightly more weight on the finger tips, allowing for more precise movements. It also increase sensitivity in the fingertip. Despite the fact that the exposed part of the nail is comprised of dead cells, it is attached to a very sensitive portion of skin full of nerves. Any contact with the nail sends signals directly to these nerves, increasing sensitivity.

  • Nail Anatomy: This site details the makeup of human nails.
  • Healthy Nails: This article gives an overview of what unhealthy nails look like and how to keep nails healthy.
  • What Fingernails Say: This article describes how fingernails can show health issues in other areas of the body.
  • Nail Diagram: This page provides information and a diagram of a nail.
  • Nail Growth: This page provides a brief description of how nails grow.
  • Nail Injuries: This article details the different injuries that nails can endure and the possible treatment options for them.
  • Nail Fungus: This site offers information on the structure of nails and the possible infections they can encounter.