1.3 Main effects and routes of attack of chemicals Flashcards Preview

B01. Principles of toxicology and epidemiology > 1.3 Main effects and routes of attack of chemicals > Flashcards

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1

There are a number of factors that determine the type of toxic effect a chemical can
have on you. These factors include the:

 Route(s) of entry by which the chemical gets into the body (chemicals have
different routes of entry. Some chemicals can enter the body in more than one
way. Different health effects can occur depending on the route of entry).
 Physical form of the chemical (solids, dust, fibre, liquid, vapour, gas, mist).

2

Some substances damage skin, while others pass through it and damage other
parts of the body. Skin gets contaminated by:

 direct contact with the substance, for example: if you touch or dip hands in it
 splashing
 substances landing on the skin, for example: airborne dust
 contact with contaminated surfaces (including contact with contamination inside
protective gloves). 


3

Physical form 5

Dust
Solid
Gas
Vapour
Liquid

4

Dust is divided into two categories depending on size:

 ‘Inhalable dust’ (sometimes referred to as total inhalable dust) is the total
dust that will enter the nose and mouth and lungs during breathing.
 ‘Respirable dust’ is dust of such a size that it is able to enter the lower levels of
the lung during normal breathing (approx. 0.5 to 7.0 micron). Respirable dust is
often in the form of long particles with sharp edges which cause scarring of the
lung lining (fibrosis). This limits the capacity of the lungs and, therefore, the
amount of air in the lungs.

5

Fibres of 0.5 μm or less can enter the lungs and become trapped in the alveoli.
These can cause lung damage, for example:

scarring (fibrosis), with a resulting
loss of lung function. Larger fibres may be ingested by macrophages.

6

Fume is formed by

the vaporisation or oxidation of molten metal, for example: lead
fume/welding fume. The particles are usually less than 1μm and therefore are
respirable.

7

There are two types of defensive responses:

 Basic – preventing the chemical or biological agent entering the body:
- the skin
- the eye
- the respiratory system
- the digestive system
 Auto-immune – attacking the agent directly:
- innate (non-specific)
- adaptive (specific)

8

The air reaches the tiny air sacs (alveoli) in the inner part of the lungs with any dust
particles smaller than

5-7 μm

9

Besides macrophages, the lungs have another system for the removal of dust.

The lungs can react to the presence of germ-bearing particles by producing certain proteins. These proteins attach to particles to neutralise them.

10

Several factors influence the effects of inhaled particles:

 Size and heaviness of the particles are important because large and heavy
particles settle more rapidly.
 Chemical composition is important because some substances, when in
particle form, can destroy the cilia that the lungs use for the removal of particles.
 Cigarette smoking may alter the ability of the lungs to clear themselves.
 Breathing rates: the amount of dust settling in the lungs increases with the
length of time the breath is held and how deeply the breath is taken which
means manual labourers exerting themselves are at greater risk than sedentary
workers.
 Breathing is through the nose or mouth is also important. If breathing
through the mouth the first defence mechanism of the nose is by passed.

11

Dermatitis is inflammation of the skin caused by contact with a range of materials.
These include detergents, toiletries, chemicals and even natural products like foods
and water (if contact is prolonged or frequent). It can affect all parts of the body, but
it is most common to see the hands affected. There are different types of contact
dermatitis:

 Irritant dermatitis (sometimes known as ‘primary’ dermatitis).
 Allergic dermatitis.

12

Irritant dermatitis is usually caused by

chemicals etc. that dry out and damage the
skin. It can occur quickly after contact with a strong irritant, or over a longer period
from repeated contact with weaker irritants. Irritants can be chemical, biological,
mechanical or physical. Repeated and prolonged contact with water (for example:
more than 20 hand washes or having wet hands for more than 2 hours per shift)
can also cause irritant dermatitis.

13

Allergic dermatitis can occur when

the sufferer develops an allergy to a
substance. Once someone is ‘sensitised’, it is likely to be permanent and any skin
contact with that substance will cause allergic contact dermatitis. Often skin
sensitisers are also irritants. The allergic reaction can show up hours or days after
contact.

14

2 types of immune system

The innate (non-specific) immune system is the first line of defence against
invading micro-organisms. The innate immune system exists at birth, and does not
change very much through life. It responds rapidly to infection, but has neither
memory nor any specificity.

The main cells used in the innate system are phagocytes which are attracted to an
organism, bind to it, engulf it by endocytosis and release cytotoxic materials to kill
it. Digestive enzymes are then released onto the organism. The process is known
as phagocytosis.

The adaptive (specific) immune system produces a slower response than that of
the innate immune system, but the response is highly specific. Each lymphocyte is
antigen specific (an antigen is the foreign substance on the surface of an invading
organism).

The adaptive system has a memory and therefore mounts a fast immune response
to previously encountered microbes.

15

The cells of the adaptive immune system are:

 B-lymphocytes which mature in the Bone and produce antibodies to eliminate a
specific antigen.
 T-lymphocytes which mature in the Thymus and are of two types:
- T helper cells
- T killer (cytotoxic) cells.

16

Other defences include:

 the eye blinking to protect against excessive light
 the eye watering to remove, for example, dust
 the adrenaline ‘fight or flight response’ (note: this can also cause an over
immune response, for example: to sensitising asthmagens)
 pain from the skin, muscles etc.