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Skin structure and function

Age range 14-16

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What does the skin do?

Skin has many functions and useful properties:

  • Control of body temperature
  • Keeping out infection
  • It´s a waterproof barrier
  • Protects delicate tissues underneath
  • Mends itself when damaged

Temperature control

Body temperature is normally 37ºC no matter what the temperature of the surroundings. It is controlled by a feedback system, that is, information about the temperature of the body, for example from the temperature sensitive receptors in the skin, is fed back to the hypothalamus, the temperature-regulating centre of the brain. The brain then sends messages to parts of the body, including the skin, to keep heat in or to lose excess heat.

Other feedback systems are used in controlling the amount of glucose and water in the blood.

Keeping temperature, glucose and water at the right levels is known as homeostasis and is important for the chemical processes of the body to work properly.

If the body is too cold...

...the hairs are raised by small muscles to trap a layer of air near the skin giving the appearance of goose bumps. Air is an insulator so this helps to keep heat in. Shivering, a trembling of the muscles, produces more heat and, during shivering, there is usually an increase in the rate of respiration, which also warms the surrounding tissues.

The rate of heat loss depends on the amount of blood flowing through the skin. When cold, blood is kept away from the surface by vasoconstriction, that is, narrowing of the blood vessels leading to the skin capillaries. Very little blood then flows through these capillaries and this minimises the loss of heat from the skin.

If the body is too hot...

An Athlete works up a sweat on a treadmill
Exercise makes you hot - and so you sweat

...the blood vessels leading to the skin capillaries dilate, known as vasodilation. This allows lots of blood to flow near the surface and heat is lost through the skin by convection and radiation.

To further reduce the body temperature, sweating occurs. Sweat is mostly water with some salt (sodium chloride). It is produced by the sweat glands and pours out onto the surface of the skin. Here the water evaporates, which removes heat from the skin therefore cooling the skin down. Salt is left on the skin so the skin can taste a bit salty after sweating. If sweating is excessive, too much salt can be lost from the body upsetting the ion balance in the blood which can lead to cramps.

In very hot environments, excessive sweating (up to two pints in an hour) can also lead to dehydration. Dehydration causes a reduction in the amount of sweating and the body temperature stays too high. If this happens, the normal mechanisms for temperature control break down –

Two athletes run around a red running track
a very dangerous, potentially fatal, situation for the body. It is important, then, to drink enough water so that this situation does not develop.

It is possible to acclimatise the body over a period of several weeks to hotter conditions. Acclimatisation results in the progressive decrease in salt concentration of sweat, while the volume of sweat increases. This has the advantage of not losing too much salt from the body, and, as long as water intake is adequate, dehydration does not occur. Sportspeople, who normally live in temperate climates, can prepare themselves for sporting events by living and training in the hot conditions for several weeks before the events and in this way can maintain their usual standards while performing in the hot climate.

A waterproof coat

Water droplets rest on top of the skin on someone's arm
Water droplets on skin

Keratin in the epidermis and oil produced by the sebaceous glands help to make our skin waterproof. This means we don´t go soggy in the bath or dry up in the sun!


Keeping bugs out

Millions of microorganisms live harmlessly on the skin and in the air around us. The skin forms a very effective barrier to stop them entering the body unless damaged, when infections can then occur.

Skin colour

Melanin is a pigment that gives skin a colour from pink through brown to black. People are different colours because their skin contains different amounts of melanin.

Melanin protects skin from ultra-violet (UV) radiation. When skin is exposed to the sun, more melanin is produced and the skin darkens. An albino person has skin which contains no melanin. Therefore they have no natural protection from UV rays. Their skin must be covered up in sunlight.

A black boy and a white girl smiling
People with different amounts of melanin in their skin
An albino gerbil with completely white fur and red eyes
Albino gerbil

Question 2

Study the sentences below, and drag and drop in the missing words.
melanin
muscles
dehydration
37°C
brain
more
keratin
entering
1. Body processes work best at
 
.
2. The
 
 sends messages to the skin to make or lose heat.
3. When shivering, the hairs are moved by small
 
.
4. Vasodilation allows
 
 blood to flow to the skin.
5. Too much sweating can lead to
 
.
6. Skin stops micro-organisms from
 
 the body.
7.
 
 and oil make the skin waterproof.
8. Albino people have no
 
 in their skin.

 

Hypothalamus
An area of the brain which regulates hormone release, temperature control, hunger, thirst and sleep.
Glucose
A type of sugar: a monosaccharide with six carbon atoms (a hexose sugar).
Vasoconstriction
The narrowing of blood vessels which restricts the flow of blood.
Capillaries
Very small blood vessel with walls made of a single layer of epithelial cells. Exchange of materials, such as nutrients, oxygen and carbon dioxide, takes place between the blood and the cells of the body across the capillary walls.
Vasodilation
The widening (dilation) of blood vessels which allows more blood to flow.
Convection
The transfer of heat by the upward movement of a heated, and therefore less dense, liquid or gas.
Radiation
The emission of heat, light or other electromagnetic waves.
Sweat
A watery liquid secreted by sweat glands, which contains dissolved urea, lactic acid and sodium, potassium and chloride ions.
Dehydration
The state of the body when it does not have enough water.
Keratin
A fibrous protein from which, for example, hair is made.
Epidermis
The outer layer of the skin. Cells in the lower epidermis divide constantly. As they move up towards the surface, the cells flatten and develop tough keratin fibres. Then they die and flake off.
Sebaceous gland
Produces an oily substance which keeps the epidermis waterproof and prevents it from drying out. The gland opens onto the top of the hair follicle.
Melanin
Dark brown or black pigment found in the skin, hair and irises of the eyes. The skin produces more melanin when exposed to the sun.
UV radiation
Invisible rays that are part of the electromagnetic spectrum. They have a wavelength just shorter than the violet end of the visible spectrum.
Albino
A person with little or no pigment in the eyes, skin and hair. They have inherited an altered copy of a gene that does not work properly and so the body does not make the usual amounts of .