Units 7+8 Review Book Flashcards
(26 cards)
Range of tolerance
One way to think about health is that each organism has a range of tolerance for almost any substance.
For each substance it might come into contact with, an organism has an optimum range, inside of which it can maintain homeostasis.
Outside of this range, the organism may experience physiological stress, limited growth, reduced reproduction, and in extreme cases, death.
A toxin
Any substance that, when inhaled, ingested, or absorbed at sufficient dosages, damages a living organism, and the toxicity of a toxin is the degree to which it is biologically harmful.
Almost any substance that is inhaled, ingested, or absorbed by a living organism can be harmful when it is present in large enough quantities—even water!
Dose-response analysis
LD50
Substances are usually tested for toxicity using a dose-response analysis.
In a dose-response analysis, organisms are exposed to a toxin at different concentrations, and the dosage that causes the death of the organism is recorded.
The information from a set of organisms is graphed, and the resulting curve is referred to as a dose-response curve.
The dosage of toxin it takes to kill 50 percent of the test animals is termed LD50, and this value can be determined from the graph. A high LD50 indicates that a substance has a low toxicity; a low one indicates high toxicity.
Poison definition
any substance that has an LD50 of 50 mg or less per kg of body weight.
FDA and the Delaney Clause
The government regulates certain types of toxins in air, water, and food.
The Food and Drug Administration (FDA) is the body that regulates food and related products; it was empowered to do so by the Federal Food, Drug, and Cosmetic Act of 1938.
Delaney Clause
One important part of this act is the Delaney Clause (part of the Food Additives Amendment of 1958), which specifically bans any food additives found to cause cancer in humans or in animal testing.
When the Delaney Clause was included, no one thought it would have a very broad application, but as scientists have identified more and more cancer- causing substances, its relevance has grown.
Non-fatal impacts of toxin levels
If just the negative health effects are plotted on the dose-response curve instead of the level of the toxin at which death occurs, the resulting graph indicates the dosage that causes a change in the state of health.
This type of graph can be used to find the ED50—the point at which 50 percent of the test organisms show a negative effect from the toxin.
The dosage at which a negative effect occurs is referred to as the threshold dose.
Acute vs. chronic effect
An acute effect is an effect caused by a short exposure to a high level of toxin; a snakebite, for example, causes an acute effect.
A chronic effect is what results from long-term exposure to low levels of toxin; an example of this would be long-term exposure to lead paint in a house.
When determining how harmful a substance is, all of the following must be considered:
dosage amount over a period of time
number of times of exposure
size and/or age of the organism that is exposed
ability of the organism to detoxify that substance
organism’s sensitivity to that substance (due, for example, to genetic predisposition or previous exposure)
synergistic effect (when more than one substance combines to cause a toxic effect that’s greater than any one component)
Infections
An infection is the result of a pathogen invading the body, and disease occurs when the infection causes a change in the state of health. For example, HIV, the virus that causes the disease AIDS, infects the body and typically has a long residence time. When it causes a change in a person’s state of health, it has morphed into a disease called AIDS.
Pathogens
bacteria, viruses, or other microorganisms that can cause disease.
five main categories of pathogens.
Pathogens can attack directly or via a carrier organism (called a vector).
Ex. of a pathogen that relies on a vector is the bacteria that causes Rocky Mountain spotted fever. It lives in the bodies of ticks, and when ticks bite humans, the ticks inject the bacteria, which causes the disease.
Pathogens, being single-celled organisms, are usually able to adapt quickly to take advantage of new opportunities to infect and spread through human populations.
Poverty-stricken, low-income areas often lack sanitary waste disposal and have contaminated drinking water supplies, leading to havens and opportunities for the spread of infectious diseases.
However, specific pathogens can occur in many environments, regardless of how sanitary conditions may appear to be.
five main categories of pathogens.
Viruses (and other subcellular infectious particles, such as prions)
Bacteria
Fungi
Protozoa
Parasitic worms
Plague
A disease carried by organisms infected with the plague bacteria.
It is transferred to humans via the bite of an infected organism (vector) or through contact with contaminated fluids or tissues.
It has distinct forms (bubonic, septicemic, and pneumonic), but all are characterized by fever, chills, headaches, and nausea.
Tuberculosis
a bacterial infection that typically attacks the lungs. It is spread by breathing in the bacteria from the bodily fluids of an infected person.
Its symptoms include chronic cough with bloody mucus, fever, night sweats, and weight loss.
Cholera
a bacterial disease that is contracted from infected water.
Its main symptom is large amounts of watery diarrhea, which can lead to severe dehydration.
Poverty, poor sanitation, and lack of clean drinking water are risk factors for the disease.
Dysentery
type of gastroenteritis (inflammation of the stomach and small intestine) that results in diarrhea with blood, plus often fever and abdominal pain.
It has multiple possible causes, including bacteria, amoebas, chemicals, and parasitic worms.
The main risk factor for dysentery is contamination of food and water, usually from untreated sewage in streams and rivers.
Malaria
a parasitic disease caused by bites from infected mosquitoes.
It is widespread in the tropical and subtropical regions of the globe, especially in sub-Saharan Africa.
It causes fever, tiredness, vomiting, headaches, and, in severe cases, yellowed skin, seizures, coma, and even death.
There have been strident efforts worldwide to eradicate this disease, but results have been much more successful in some places than in others.
West Nile virus
transmitted to humans via bites from infected mosquitoes.
It is closely related to the viruses that cause zika, dengue, and yellow fever.
West Nile virus causes West Nile fever, a disease characterized by fever, headache, vomiting, rash, and in severe cases encephalitis or meningitis.
Zika
a virus caused by bites from infected mosquitoes.
It can be transmitted through sexual contact and from a pregnant mother to a fetus.
It tends to cause fever, red eyes, joint pain, headache, and rash; it can cause microencephaly and other brain malformations when transferred to a fetus, and in adults it has been linked to Guillain–Barré syndrome, a rapid-onset muscle weakness.
Severe acute respiratory syndrome (SARS)
a viral respiratory disease caused by severe acute respiratory syndrome coronavirus (SARS-CoV-1).
There was an outbreak of this disease in 2002–2004.
The respiratory symptoms were a form of pneumonia.
Another coronavirus, MERS- coronavirus (MERS-CoV) caused an outbreak of Middle East respiratory syndrome (MERS), another viral respiratory illness, in 2012–2013. In 2019–2022, a much more severe outbreak of the related virus strain severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) caused the COVID-19 pandemic.
These viruses tend to move from animals to humans and are transferred by inhaling or touching infected fluids.
Things making people sick other than pathogens
As you’re probably well aware, other things besides pathogens can make people ill, including environmental factors such as tobacco smoke, UV radiation, or asbestos.
Also, although you may be exposed to a toxin or an infectious agent and not experience a change in the state of your health, someone else who’s exposed to the toxic agent or pathogen could become very ill.
It takes careful study to predict the range of likely effects a given toxin or pathogen will have.
In fact, it can often be difficult to establish cause and effect between pollutants and other toxins and human health issues, because humans experience exposure to a variety of chemicals and pollutants.
Risk , risk assessment and management
The degree of likelihood that a person will become ill after exposure to a toxin or pathogen is called risk.
Many environmental, medical, and public health decisions are based on potential risk.
Calculating risk is referred to as risk assessment, and risk management means using strategies to reduce the amount of risk.
The U.S. Department of Public Health and Public Services is an organization that makes use of risk assessment and management.
pollutant
A pollutant is any substance (or energy) that, when introduced into its environment, renders the air, soil, water, or some other natural resource harmful, or adversely affects its usefulness. We’ll start by examining pollutants that affect the air.
Human-caused pollution
Although you may think that human-caused pollution is a relatively new phenomenon, people have added pollutants to the air throughout the history of humankind.
Early humans’ fire created pollutants, and the Romans’ lead smelting resulted in air pollution that drifted thousands of miles from the source—and has even been discovered trapped in the ice of Greenland!
It is true, however, that the large-scale production of pollutants began with the Industrial Revolution, and this is especially true of air pollution. The beginning of the Industrial Revolution marked the entrance of pollutants from fossil fuel into the atmosphere, for example, which has been environmentally disastrous.
