i.
Central nervous system depressant
ii.
Cardiac sensitisation
Cardiac sensitisation
i.
Central nervous system depressant
Central nervous system depressant
Toxicants
cause damage to the central nervous system and the kind of damage depends on
its chemical makeup. Toxins that are fat soluble or have certain ionic
structures readily penetrate our brains and nerves. Others, especially large
complex molecules, cannot easily pierce the blood-brain barrier. Some
neurotoxic chemicals, once they have entered the nervous system in large
amounts, spread widely and
cause damage to the central nervous system and the kind of damage depends on
its chemical makeup. Toxins that are fat soluble or have certain ionic
structures readily penetrate our brains and nerves. Others, especially large
complex molecules, cannot easily pierce the blood-brain barrier. Some
neurotoxic chemicals, once they have entered the nervous system in large
amounts, spread widely and
produce generalized effects; for example, strychnine
causes epileptic seizures,
and many organic solvents cause coma.
Other neurotoxic agents attack only specific groups of cells or fibers and
produce local effects; the designer drug MPTP destroys the pigmented nerve
cells of the midbrain and causes a form of Parkinson’s disease,
while vincristine and other anticancer drugs primarily affect nerve ends and
cause numbness of the hands and feet (peripheral
neuropathy). Stated simply, there is no single type of
neurotoxic disease.
Many
toxins disrupt the chemical balance and functioning of nerve cells without
actually destroying their architecture. Some of these substances cause problems
primarily in the central nervous system (CNS): people may become confused and
delusional (as with phencyclidine, better known as PCP), turn drowsy or even
comatose (heroin), display cognitive impairment (bromine), or have seizures
(tetanus). Other toxins of this sort act primarily on the peripheral nervous system
and produce paralysis (botulism) or abnormal sensations (ciguatera fish toxin).
toxins disrupt the chemical balance and functioning of nerve cells without
actually destroying their architecture. Some of these substances cause problems
primarily in the central nervous system (CNS): people may become confused and
delusional (as with phencyclidine, better known as PCP), turn drowsy or even
comatose (heroin), display cognitive impairment (bromine), or have seizures
(tetanus). Other toxins of this sort act primarily on the peripheral nervous system
and produce paralysis (botulism) or abnormal sensations (ciguatera fish toxin).
Another class of neurotoxins actually degenerates
the structure of nerve cells. This damage can occur in the CNS (as with
mercury) or peripheral nerves (acrylamide monomer). However, neurotoxins rarely
destroy large focal areas of the nervous system. Most chemicals that trigger
structural damage to the nervous system produce a consistent pattern of disease
that closely matches the dose and duration of exposure.
the structure of nerve cells. This damage can occur in the CNS (as with
mercury) or peripheral nerves (acrylamide monomer). However, neurotoxins rarely
destroy large focal areas of the nervous system. Most chemicals that trigger
structural damage to the nervous system produce a consistent pattern of disease
that closely matches the dose and duration of exposure.
A
person may develop different neurotoxic illnesses from exposure to the same
chemicals at different levels. Short-term inhalation of large amounts of the
solvent n-hexane may end in a fatal coma, while exposure to lower
levels for weeks can cause severe peripheral neuropathy with no CNS symptoms. A
few substances produce multiple illnesses following one exposure; for example,
exposure to some organophosphates may produce a sudden (sometimes fatal)
paralysis by inhibiting the action of acetylcholinesterase and, two weeks
later, peripheral neuropathy.
person may develop different neurotoxic illnesses from exposure to the same
chemicals at different levels. Short-term inhalation of large amounts of the
solvent n-hexane may end in a fatal coma, while exposure to lower
levels for weeks can cause severe peripheral neuropathy with no CNS symptoms. A
few substances produce multiple illnesses following one exposure; for example,
exposure to some organophosphates may produce a sudden (sometimes fatal)
paralysis by inhibiting the action of acetylcholinesterase and, two weeks
later, peripheral neuropathy.
ii.
Cardiac
Sensitization
Cardiac
Sensitization
Exposure
to chemical substances can cause adverse effects on the cardiovascular (heart
and blood vessels) or hematopoietic (blood) systems (Cardiovascular or Blood
Toxicity). Exposure to cardiovascular toxicants can contribute to a variety of
diseases, including elevated blood pressure (hypertension), hardening of the
arteries (arteriosclerosis), abnormal heartbeat (cardiac arrhythmia), and
decreased blood flow to the heart (coronary ischemia). Lead, carbon disulfide,
arsenic, cadmium, ozone, and vinyl chloride have all been implicated in the
etiology of cardiovascular disease. Exposure to hematopoietic toxicants can
reduce the oxygen carrying capacity of red blood cells, disrupt important
immunological processes carried out by white blood cells, and induce cancer.
Chronic exposure to benzene (a component of gasoline fuel) leads to the
decreased production of all types of blood cells, and ultimately to leukemia, a
cancerous proliferation of white blood cells.
to chemical substances can cause adverse effects on the cardiovascular (heart
and blood vessels) or hematopoietic (blood) systems (Cardiovascular or Blood
Toxicity). Exposure to cardiovascular toxicants can contribute to a variety of
diseases, including elevated blood pressure (hypertension), hardening of the
arteries (arteriosclerosis), abnormal heartbeat (cardiac arrhythmia), and
decreased blood flow to the heart (coronary ischemia). Lead, carbon disulfide,
arsenic, cadmium, ozone, and vinyl chloride have all been implicated in the
etiology of cardiovascular disease. Exposure to hematopoietic toxicants can
reduce the oxygen carrying capacity of red blood cells, disrupt important
immunological processes carried out by white blood cells, and induce cancer.
Chronic exposure to benzene (a component of gasoline fuel) leads to the
decreased production of all types of blood cells, and ultimately to leukemia, a
cancerous proliferation of white blood cells.
Toxicants
to the cardiovascular system may influence the contractile or
electrophysiologic functions of the heart or they may interfere with normal
vascular function. Recall that specialised terms used to describe cardiac
function include chronotropy (rate of contraction), inotropy (force of
contraction), dromotropy (rate of electrical conduction), and bathmotropy
(degree of excitation).
to the cardiovascular system may influence the contractile or
electrophysiologic functions of the heart or they may interfere with normal
vascular function. Recall that specialised terms used to describe cardiac
function include chronotropy (rate of contraction), inotropy (force of
contraction), dromotropy (rate of electrical conduction), and bathmotropy
(degree of excitation).
1. Describe the storage of toxic chemicals in
biological systems.
biological systems.
Toxicity in biological system is the degree to which a
substance can damage an organism. Toxicity can refer to the effect on a whole
organism, such as an animal, bacterium, or plant,
as well as the effect on a substructure of the organism, such as a cell (cytotoxicity) or an organ such as
the liver (hepatotoxicity). By extension, the
word may be metaphorically used to describe
toxic effects on larger and more complex groups, such as the family
unit or society at large.
substance can damage an organism. Toxicity can refer to the effect on a whole
organism, such as an animal, bacterium, or plant,
as well as the effect on a substructure of the organism, such as a cell (cytotoxicity) or an organ such as
the liver (hepatotoxicity). By extension, the
word may be metaphorically used to describe
toxic effects on larger and more complex groups, such as the family
unit or society at large.
A
central concept of toxicology is that effects are dose-dependent;
even water
can lead to water intoxication
when taken in too high a dose, whereas for even a very toxic substance such as snake venom there is a dose
below which there is no detectable toxic effect. Toxicity is species-specific,
making cross-species analysis problematic. Newer paradigms
and metrics are evolving to bypass animal testing, while maintaining
the concept of toxicity endpoints.
central concept of toxicology is that effects are dose-dependent;
even water
can lead to water intoxication
when taken in too high a dose, whereas for even a very toxic substance such as snake venom there is a dose
below which there is no detectable toxic effect. Toxicity is species-specific,
making cross-species analysis problematic. Newer paradigms
and metrics are evolving to bypass animal testing, while maintaining
the concept of toxicity endpoints.
References
Klaassen,
C., M. (1991). Casarett and Doull’s Toxicology. The Basic Science
of Poisons, 5th Ed. Pergamon Press, NY.
C., M. (1991). Casarett and Doull’s Toxicology. The Basic Science
of Poisons, 5th Ed. Pergamon Press, NY.
Lu,
F.C. (1991) Basic Toxicology. 2nd Edition
F.C. (1991) Basic Toxicology. 2nd Edition
Stacey,
N.H. (2007). Occupational
Toxicology. Taylor & Francis.
N.H. (2007). Occupational
Toxicology. Taylor & Francis.
Tanner,
C.(2004). Occupational and Environmental
Causes of Parkinsonism. Occupational Medicine 7(3): 5-3-513.
C.(2004). Occupational and Environmental
Causes of Parkinsonism. Occupational Medicine 7(3): 5-3-513.
Zakrzewski,
S.F. (1997). Principles of Environmental Toxicology.
American Chemical Society, Washington, DC.
S.F. (1997). Principles of Environmental Toxicology.
American Chemical Society, Washington, DC.
