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2.5 The Blood
Source: US Federal Government via Wikimedia commons
Figure 2.5 - Electron Micrograph of blood cells showing white blood cells, red blood cells and platelets
Production of haemoglobin, the oxygen-carrying red pigment in red cells, is inhibited by inorganic lead interfering with enzyme systems. The result is
anaemia characterised by pale skin and mucous membranes, fatigue and sometimes breathlessness on exertion. Arsine and stibine cause red cell
break-up haemolysis and the result is again anaemia. X-irradiation nuclear accidents and benzene can cause leukaemia overgrowth of blood cells,
probably by action on DNA synthesis. Oxygen transport can be affected in two ways, both being forms of asphyxia.
In atmospheres where normal air is displaced by inert gases like nitrogen, methane, helium and carbon dioxide, the oxygen content normally 21 is
diluted and hypoxia low oxygen tension in the blood results. This initially will lead to a compensatory increased pulse and respiratory rate. If hypoxia
continues, judgement will be impaired and the person will lapse into
28 unconsciousness and eventually die. Breathing 100 inert gas sticking head
into a gas-filled chamber will cause instant unconsciousness. The other industrial form of asphyxia is chemical asphyxia. Aniline and
nitrobenzene, as liquids absorbed through intact skin, and inhaled carbon monoxide, interfere with the bloods ability to carry oxygen linked with
haemoglobin, as oxyhaemoglobin. Aniline and nitrobenzene link with haemoglobin to form methaemoglobin leading to cyanosis a blue tinge to the
mucous membranes, especially the lips. Carbon monoxide combines with haemoglobin in competition with oxygen to form carboxyhaemoglobin, a bright
crimson pigment, making the sufferer appear cherry red.
2.6 Respiratory system
The major function of the respiratory system is gas exchanged between the external environment and the circulatory system. This involves taking in
oxygen from the air to the blood and releasing carbon dioxide and other gaseous waste products from the blood back into the air.
Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely
thin approx. 0.2 micrometres. These walls are composed of a single layer of epithelial cells in close proximity to the blood capillaries which in turn are
composed of a single layer of endothelial cells. The close proximity of these two cell types allows permeability to gases and, hence, gas exchange.
Oxygen is taken into the blood whilst excess carbon dioxide is released.
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Source: Wikimedia commons
Figure 2.6 - Respiratory Sytem
Like the skin and the eye, the lungs are affected by irritants and allergens. They also respond in the forms of fibrotic pneumoconiosis and malignant
disease to a variety of industrial agents. Particles greater than 10 μm in diameter are filtered by the nose. The
branching structure of the airways encourages deposition of 2- 10 μm particles
which can then be cleared by the mucociliary escalator. In the alveoli remaining particles either pass back up the bronchial tree freely or are
phagocytosed by macrophages and taken to the mucociliary escalator or to the surrounding lymphatic system. Despite their efficiency, large volumes of
particles can overwhelm these defence mechanisms.
Irritation caused by gases and fumes produce inflammation of the respiratory
tract and the symptoms tend to be acute or delayed, depending on the solubility of the toxic agent. There can also be chronic effects. Chronic effects
from prolonged exposure may be chronic bronchitis and permanent lung damage.
Allergic reactions to substances can cause occupational asthma. Symptoms include severe shortness of breath as well as wheezing, coughing and chest
tightness. Certain substances such as isocyanates used in paints, flour dust
30 and various fumes can cause asthma. These substances are called
respiratory sensitisers or asthmagens. They can cause a change in people‟s airways, known as the hypersensitive state.
Not everyone who becomes sensitised goes on to get asthma. But once the lungs become hypersensitive, further exposure to the substance, even at quite
low levels, may trigger an attack.
Pneumoconiosis is the reaction of the lungs to inhaled mineral dust and the
resultant alteration in their structure. The major causes are coal dust, silica and asbestos and they all lead to scarring of the lungs known as collagenous
fibrosis. Pneumoconiosis may not produce any symptoms for years. However, as the lungs become less flexible and porous their function is greatly reduced.
The symptoms include shortness of breath, cough, and general ill feeling. The shortness of breath usually begins only with severe exertion. As the disease
progresses, shortness of breath may be present all of the time. The cough initially is not associated with sputum, but may eventually be associated with
coughing up blood. Due to poor oxygenation of the blood by the damaged lungs, the nails and lips may appear pale or bluish.
Chronic obstructive pulmonary disease COPD refers to chronic bronchitis
and emphysema. These are two lung diseases which often occur together and result in the airways becoming narrowed. This leads to a limitation of the flow
of air to and from the lungs causing shortness of breath. Unlike occupational asthma the narrowing of the airways is not easy to reverse and usually gets
progressively worse over time. COPD can be triggered by a wide range of particles and gases which cause the body to produce an abnormal
inflammation of the tissues.
Malignant tumours of industrial origin can affect the lungs and surrounding
tissues. Lung cancer has been discovered in people working with asbestos miners, insulators and this risk is potentiated by cigarette smoking, arsenic
pesticides, chromium pigment manufacturers, polycyclic aromatic hydrocarbons coal gas manufacture, tar workers and ionising radiations
uranium miners. Wood dust hardwood furniture makers, leather dust and nickel dust have caused nasal sinus cancer.
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2.7 The Gastro Intestinal Tract