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Sebaceous gland

Glands in the skin around the hair follicles which produce oil to remove dust and bacteria and to help waterproof the skin. The gland opens onto the top of the hair follicle

Blood vessels

The tubes through which blood is carried around the body eg arteries, veins and capillaries

Cell division

The process by which a parent cell divides into two daughter cells

Hair follicle

Pits in the epidermis of the skin which grow hairs.

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.

Friction

The action of one surface rubbing against another.

Keratin

A fibrous protein from which, for example, hair is made.

Dermis

A layer of connective tissue containing capillaries, sensory nerve endings, lymphatic vessels, sweat glands and hair follicles.

Tissue

A group of cells in an organism that are specialised to work together to carry out a particular function.

Cancer

A mass of abnormal cells which keep multiplying in an uncontrolled way.

Cell

The basic unit from which all living organisms are built up, consisting of a cell membrane surrounding cytoplasm and a nucleus.

Brain

The main organ of the central nervous system made up mainly of grey matter

Structure of the skin

Layers of the skin

The skin has three layers:

  1. The epidermis on the outside. This is made from layers of cells with a basal layer, which is always forming new cells through cell division. The new cells gradually move towards the surface, which takes 1-2 months. As they move up they gradually die, become flattened and develop keratin and the outermost layer of flat dead cells is being continually worn away by friction. The keratin and oil from the sebaceous glands help to make the skin waterproof.

  2. The dermis is the inner layer. The following tissues and structures can all be found in the dermis:
    • Connective tissue – packs and binds the other structures in the skin.
    • Elastic fibres – make the skin resilient.
    • Capillaries – tiny blood vessels.
    • Muscle fibres – to move the position of the hairs.
    • Sensory cells – to sense touch, pressure, heat, cold and pain.
    • Nerve fibres – to activate muscles and glands and relay messages from the sensory cells to the brain.
    • Pigment cells which produce Melanin – a very dark pigment.
    • Sweat glands which open onto the surface as pores
    • Hair follicles – pits in the epidermis in which hairs grow.
    • Sebaceous glands – produce oil to keep hair follicle free from dust and bacteria, and to help to waterproof the skin.
  3. There is a layer of fat underneath and in the lower regions of the dermis. The thickness of this layer varies depending on the place in the body and from person to person. A store of fat is useful to the body as insulation and it can be used for energy when the intake of nutrients is insufficient.

Self-repair

Body cells can detect how crowded they are – the cell density. When cell density decreases, cell division occurs to make new cells and when cell density increases the rate of cell division slows down. This process is usually strictly controlled in the body, however, occasionally, the control mechanism fails and cell division continues at an abnormally high rate. This is how tumours occur in cancer. Cell division is important in skin repair after a cut or other injury to the skin. On the cut surface cell density is lowered, stimulating cell division. New cells gradually fill the gap and, once normal cell density is reached again, cell division slows down to the normal rate. Usually a cut will first fill up with blood which clots and, with other fibres, forms a scab. Underneath the scab the new tissue is being produced to heal the wound.

Click on the numbers above
to see the steps of repair
when the skin is cut.

Artificial skin

In recent years scientists have found a way to make artificial skin using some human skin cells and synthetic materials. It can be used to cover, for example, a burn or a chronic ulcer, and it gradually integrates with the patient′s own skin.

Question 1


a)
Where, in the skin, are the cells which divide to form new cells?
b)
What eventually happens to the cells of the epidermis?
c)
Name the structures in the dermis which move the hairs?
d)
Name the structures in the dermis which produce oil?
e)
Name three other structures found in the dermis?
f)
Why does the rate of cell division increase near a cut?