Skin, Hair, and Nails
Overview
The human body is an amazing and complex entity, renewing itself on an endless basis. Three of the more fascinating components of the body are the skin, hair and nails.
Skin
Very few of the body’s many parts renew themselves more quickly than the skin. The skin has two distinct, main layers. The outer layer is called the epidermis, whose main function is that of providing protection for the body. The underlying layer is called the dermis. Each and every month the body’s outer layer of epidermis is completely shed, at an amazing rate of some 30,000 dead cells every 60 seconds.
Thousands of sensors which are sensitive to touch are found in the dermis. Sweat glands and blood vessels are also contained in the dermis, playing an extremely vital role in regulating the body’s temperature. Directly under the dermis is a layer of subcutaneous fat, acting as a buffer and providing insulation for the body against extremes of both cold and heat.
The skin can be viewed as a mirror-image of one’s health, reflecting an individual’s lifestyle and diet. Research has shown that external factors as well as internal disorders and diseases can have a direct influence on the health of the skin, creating such disorders as sores, spots and rashes.
Skin growth can also be attributed to exposure to hazardous radiation, ultraviolet light, or toxic chemicals.
One of the largest organs of the human body, each individual’s total skin weighs in at approximately 3 to 5 kg, or 6 to 9 pounds. Typical surface area of a person’s skin is 2m squared, or 21 square feet. The skin is formed from several different types of cells, some of which produce hair and the tissue that becomes fingernails and toenails.
Many people believe the skin is merely an ultra-thin, waterproof covering for the body. Nothing could be farther from the truth. The skin is actually a very complex organ made up of a wide variety of highly specialized cells. Skin comes in varying thickness, from about 0.5mm on areas such as the eyelids to 5 mm or more on those areas which experience greater wear and tear, such as the soles of the feet.
Nails
Not much thought is typically given to how the body forms fingernails and toenails. However, this complex process is the result of hard “plates” being formed by the protein known as keratin. A fold of flesh called a cuticle is where the nail growth takes place, as the nail matrix continues to add keratinized cells to the root of the nail. The entire nail is continuously pushed upward along the bed of the nail toward the nail’s free edge. Typical growth for a nail is around 0.5mm each week, although fingernails do have a tendency to grow at a faster rate than toenails.
Hair
What is a hair? A hair is a rod of dead cells which is filled with keratin. The bulb of the hair (also called the “root”) is essentially buried in a pit called a follicle. The hair lengthens as more and more cells are added to the root. While the body has many different kinds of hair, hairs on the scalp grow about 0.33mm each day. After a period of three or four years, the follicles enter a phase of rest in which the hair may fall out. Some three to six months after entering the rest period, the follicle becomes active again and begins to produce new hair.
Other Functions
It is easy to understand that the skin is the body’s first line of defense to anything which may cause it harm. With its supple and “cushioning” qualities, the skin is well equipped to help prevent potential physical damage. Although the skin cells which form the outer layers are very tightly woven together, a certain degree of pliability does exist.
Each skin cell contains enough of the protein keratin to fend off attacks by many different types of chemicals which may come in contact with the skin. Millions of sebaceous glands, each tied to a hair follicle, secrete sebum, an oily substance which provides the skin with natural antibiotic and water repellant qualities. This secretion serves to inhibit the growth of some microorganisms and also prevents the hair on the body from becoming brittle.
Regulating a consistent temperature in the body is yet another function of the skin. In this important process, blood vessels in the dermis widen when the body is too hot, allowing extra blood flow so additional heat can leave the surface of the skin. Sweat glands also produce more sweat during times of fever, causing evaporation, which also draws away body heat.
When the body is too cold, the blood vessels in the skin constrict, minimizing sweating and heat loss. The arrector pili muscles also pull tiny hairs on the body to an upright position to trap an insulating layer of air, thus helping to preserve heat.
The dermis also controls another important bodily function – the sense of touch.
The nerve endings on very small nerve cells in the dermis are able to detect various physical changes, ranging from very light contact to intense or painful pressure. A patch of skin the size of a fingernail typically contains around 1,000 different receptors. The skin on the fingertips, however, contains more than 3,000 receptors, allowing an individual to feel the most delicate touch.
Nerve impulses are generated due to deformation of the receptor’s layers, as well as contraction or expansion of the dermis due to changes in temperature. These impulses travel along the nerve fiber in the receptor, joining other bundles of nerve fibers in the layers below the dermis. Receptors typically “fire” their nerve signals on an infrequent basis when no stimulation is present, and increase the rate of nerve firings when the skin is touched.
References
- Marieb, E.N. & Hoehn, K. Human Anatomy & Physiology (8 edition), Pearson Education, Inc (2004)
- McCracken, T. & Walker, R. New atlas of human anatomy, London : Constable (2001)
- Parker, S. The Concise Human Body Book, Dorling Kindersley Limited (2009)
- Winston, R. et al. Human: The Definitive Visual Guide, DK Publishing, Inc (2004)
- Ullmann, H.F. Atlas of Anatomy, Elsevier GmbH, Munich (2009)
Posted in Skin, Hair, & Nails
Ask a Question Or Join a DiscussionSkin, Hair, & Nails Disorders
Burns
Burns are one of the most common types of at-home minor injuries. It’s much too easy to inadvertently grab a hot plate, or bump a wrist on the inside of the oven and end up with a red, painful injury. Burns can range from a minor pain that goes away shortly, to a severe burn which goes much deeper into the skin and leaves more damage behind. Thankfully, in part because humans have been getting burns since they were able to cook over a fire, many natural treatments can be used to help heal a burn and make it less painful.
Hair Loss
Few things are more distressing than hair loss for both men and women. Sometimes there is no specific explanation for this condition and it can strike at any time. Alopecia is the condition where a person begins losing his or her hair. This condition can affect a small patch of hair or the entire head. Although the cause behind alopecia is unknown, some health care professionals believe it is the result of a stressful event. Sometimes the hair will fall out in patches over a short period of time, but other alopecia victims lose all of their hair virtually overnight. Often the hair will grow back in a few weeks, but in the case of alopecia totalis, re-growth of the hair is highly unlikely.
Acne and Rosacea
Acne is considered to be a disease of the hair follicles (or pilosebaceious units – PSUs) which results in inflammation and then rupturing of the skin. While rosacea does not involve a rupture in the skin, it does result in chronic redness of the cheeks, nose, chin and forehead because of widening of the small blood vessels in the face. Both conditions can be significant enough to mar the appearance of the individual suffering from acne or rosacea.
Dandruff
Dandruff is a scalp condition which causes white, unsightly flakes to form in the scalp and the hair. This rather common condition is caused by seborrhea, a dermatitis (inflammation) of the scalp in which the white flakes are actually dead skin from the scalp.
Dermatitis
Dermatitis is the term most commonly used for a rash that is not caused by an infection. This name is given to a wide variety of adverse conditions of the skin, with the most common one being contact dermatitis. This condition is very widespread and can afflict people of all ages. It is often a temporary condition which is resolved without medical assistance or treatment. Some types of dermatitis are acute allergic reactions and others are chronic conditions.
Scabies & Lice
Scabies are tiny mites which tunnel under the skin to lay their eggs, frequently leaving a visible mark on the skin as they do so. Scabies are most commonly found on the hands, wrists, abdomen and genitals, but in very young children they can occur anywhere on the body. Lice are insects that feed on blood and lay their eggs, which are called nits, on the skin’s surface or on clothing. They are found most often on the scalp or in the pubic hair, but they can also be found anywhere on the body.
Psoriasis
Inflamed patches of the skin which are scaly and come and go could be psoriasis, a rather common skin condition which is chronic. Sometimes the patches itch and burn, and this condition can occur virtually anywhere on the body, although it is most commonly found on the elbows, knees, hands, lower back and on the scalp.
Eczema
Eczema is an inflammatory skin condition that causes discomfort and itching. Eczema affects about one in 12 people and is becoming increasingly common. This skin condition typically is first seen in childhood and frequently the symptoms ease as the child becomes older.
Herpes Virus
In today' s world, herpes is less publicized than AIDS but is far more prevalent, affecting in one form or another 80 percent of the American population. More than half of Americans are stricken with cold sores from time to time, the result of herpes simplex virus 1 (or HSV1).
Hives
Acute urticaria usually develops within a few hours of exposure to whatever has caused the condition. The few hours prior to the outbreak of hives should be carefully thought over for possible causes. A good way to discover the cause of hives is to keep a diary and record:
