Routes of entry

Harmful substances can enter the body by:

Inhalation through the respiratory system

Ingestion via the mouth into the digestive system

Absorption through the skin often via cuts and grazes or through the mucous membrane of the eye

Injection by needles, nails, gases and liquids under pressure

Of the above routes of entry that of inhalation is considered to be the most hazardous as the lungs rapidly transfer substances to the blood and then around the body.

Inhalation

 The respiratory tract consists of the windpipe which branches into two bronchi, one supplying each lung.

Each of the bronchi then subdivides into smaller branches known as bronchioles which end in air sacs or alveoli which have very thin walls.

The alveoli are surrounded by blood vessels and oxygen is transferred into the blood from the alveoli and carbon dioxide is passed back from the blood into the air sacs and is exhaled. Any other substances inhaled with the oxygen can also pass in to the bloodstream and cause toxic effects.

The lungs are surrounded by a tough membrane, the pleura, which if inflamed give rise to pleurisy.

Pneumoconiosis

Reaction of the lungs to the presence of dust. The harmful effect of the dust is determined largely by the particle size .

Respirable Dust

This is the proportion of the inhalable dust in the air which reaches the gas exchange region of the lungs and which may be retained in the lungs on inhalation. The amount depends on the duration of exposure, particle size, the concentration of the dust and type of breathing.

Dust causes a tissue reaction in the lungs, asbestos affecting the lower lungs and coal/silica the upper lungs.

Pneumoconiosis can be caused by substances such as:

• Metal dusts such as iron, tin and barium

• Beryllium – toxic light weight but brittle metal used as hardening agent in alloys.

• Organic dusts such as hay

• Talc. Hydrated magnesium silicate from metamorphic rock-Talcum.

• Cobalt. Powder lubricant and filler in paper, very soft used in chalk

• Man made fibres, eg mineral wool.

The symptoms include coughing and breathlessness.