The Basics of Human Skin, Nails and Hair
ByThe skin protects the body against physical injury, infection and the weather. The outer part, the epidermis, is made of dead flattened cells which are constantly produced by the underlying layer. Each cell lives for about twenty-eight days before being shed. Epidermal cells called melanoblasts make the brownish-black pigment melanin that gives skin its colour. The amount of melanin is determined by inherited factors, but ultraviolet rays in sunlight stimulate melanin production, so darkening or tanning the skin.
Beneath the epidermis is the thicker dermis. This contains a protein, collagen, and elastic fibres which make it tough, pliable and supportive. Skin has a very rich nerve supply and can sense touch, pain and temperature. It’s also responsible for making vitamin D from sunlight.
The body is cooled by the evaporation of sweat from the sweat glands, which lie in the dermis. Sweat contains natural antiseptics and waste substances. The palms of the hands and soles of the feet have the most sweat glands, and these are especially active during stress. Sweat doesn’t usually develop its characteristic smell until around puberty.
Hairs are rooted in small sacs in the dermis called follicles. Sebaceous glands supply sebum (oil) to the hairs and skin, and muscles attached to the hair shafts can lift the hairs slightly up from the skin. This latter action traps warm air next to the skin when it’s cold, causing the raised skin bumps known as goose pimples. The colour and thickness of the hair, the number of hairs and their degree of curl are largely inherited. A hair grows from its root in the follicle at a rate of about 1.25 centimetres a month. After a phase of growth lasting several months or years, a hair rests, then loosens and falls out. About a hundred hairs fall out each day.
The nails are convex translucent plates of dead cells containing the tough protein, keratin. A nail grows from its nail bed, which is partly visible as the half moon. Nails protect the sensitive fingertips and grow about 1 millimetre every ten days.
When things go wrong
A rash is an important sign that something is wrong with the skin or with the body generally. It can be composed of flat discoloured spots or patches; red, round, raised pimples with or without a head; blisters of varying sizes; or combinations of these three. Small purple spots, weals, ulcers or small solid lumps are other variations. A rash may be characteristic of a particular disorder or may be common to many. The history of the accompanying illness, if any, together with an accurate description of the rash can often lead to the correct diagnosis, but sometimes it’s impossible to be sure without special tests. Causes of a rash include heat, bacterial or viral infection, allergy and insect bites.
Some common rashes in children are those associated with infectious diseases such as measles and chickenpox. The rash in each of these conditions has a characteristic pattern of onset, duration, appearance, area first affected and final distribution about the body.
Related posts: