The Skin: A closer look
The skin is the largest organ in the body and one of the most accessible - you can see it and feel it - which can hardly be said of the liver, for example. It is also one of the most interesting organs. It grows from within outwards and is constantly replacing itself.
How deep is skin deep?
The skin is composed of four layers. They are:
The outer, horny layer of dead cells
The living, growing epidermis
The layer of subcutaneous fat, which varies in thickness in different parts of the body
Distinct from the skin itself but closely related to it in position and function are the sweat glands, hair follicles, sebaceous glands and nails.
What is the connection between the skin and blood circulation?
The skin's extremely rich blood supply is channeled mainly through tiny blood vessels called capillaries. If all the capillaries in the skins were to expand at the same time, they could absorb more than a third of all the blood circulating in the body. That is why we sometimes feel giddy after a hot bath. So much blood has been drawn into the capillaries as part of the process of temperature control that not enough is reaching the brain.
If the skin is injured, the edges of the wound will heal with a bridge of scar tissue. This is a primitive structure-thinner, more stretchy and less even than normal skin. As all healing is accompanied by an increase in blood supply to the site of injury, a new scar appears pinkish. This colour fades when healing is complete. Some people get such large, protruding scars that special treatment may be needed to remove the scar, while for others, the cuts may heal leaving scarcely a mark behind.
Why are some parts of the skin more sensitive?
The number of nerves and nerve endings in an area of the skin depends on the location. The most sensitive parts of the body including the fingertips, face, breasts and genital area, have so many sensitive nerve endings that it is impossible to prick anywhere into them without it being felt. On the back, by contrast, the nerve endings are fairly sparse and there may be as much as 4 cm between painful pin pricks.
Why are some people darker than others?
Melanin, produced by melanocytes in the body is responsible for the colour of the skin. Everyone, no matter what their skin colour, is born with the same number of melanocytes. What varies in every person is the melanocytes' ability to produce melanin. Pale-skinned people produce very little melanin, dark-skinned people produce more, and black-skinned people produce a great deal.
The function of the melanin is to act as a natural sunscreen. It filters off the harmful wavelengths of sunlight so that they cannot penetrate into and damage the deeper layers of the skin.
When the skin is exposed to sunlight, the melanocytes are stimulated to produce more melanin to screen off the ultraviolet radiation efficiently. As a result, the skin changes colour. Tanning is, therefore, the outcome of deliberately injuring the skin.
What are the functions of the skin?
The functions of the skin are:
To control the temperature of the body
To eliminate the waste
To form a barrier and an outer covering for the body
To produce vitamin D