Environmental Factors, Medical Technologies and Careers

Your body and the world around it

All unit long, you have seen homeostasis respond to everyday challenges: a cold morning, a salty snack, a sprint. But many of today's challenges to homeostasis come from human activity: a hotter climate, smoke from larger wildfires, chemicals released into the air and water. At the same time, human ingenuity has produced technologies that restore homeostasis when the body can't: dialysis, insulin pumps, hormone replacement, chemotherapy.

In this lesson you will evaluate both sides, as the curriculum asks: the impact of environmental factors and chemicals on the body (overall expectation E1), and the effects of medical treatments on homeostasis (E3.3). You will finish by looking at careers in this field.

Heat, cold and a changing climate

You saw in the thermoregulation lesson that extreme heat can overwhelm the body's cooling system. As the climate warms, many parts of Canada are experiencing more frequent and more intense heat waves. Heat-related illness is most dangerous for older adults, babies, outdoor workers, people with heart, lung or kidney conditions and people without access to cooling. Many Canadian cities now open cooling centres during heat warnings and check on vulnerable residents. Cold remains a risk too, especially for people experiencing homelessness during deep-freeze warnings.

Air pollution and wildfire smoke

Canada's 2023 wildfire season was the most destructive on record, and smoke spread across much of the country, including Ontario. Smoke contains fine particulate matter (PM2.5), particles small enough to reach the alveoli. They can trigger inflammation, worsen asthma and other lung conditions, and strain the heart. Environment and Climate Change Canada publishes the Air Quality Health Index (AQHI), a scale that helps people decide when to reduce outdoor activity.

Chemicals that act like hormones: endocrine disruptors

Some chemicals released by human activity can mimic or block hormones, because their shape lets them bind to hormone receptors (remember: target cells respond to anything that fits their receptors). These are called endocrine disruptors. Examples studied by scientists include bisphenol A (BPA), once common in hard plastics and can linings; some phthalates (used to soften plastics); and some older pesticides such as DDT (now banned in Canada).

BPA can weakly activate estrogen receptors. In 2010, Canada became one of the first countries to declare BPA toxic and banned it in polycarbonate baby bottles, as a precaution for infants, whose hormone systems are developing. Scientists continue to study how low, long-term exposures to such chemicals affect people.

Hormones in food: what's actually allowed in Canada

People often worry about "hormones in food". In Canada, Health Canada approves some growth-promoting hormone implants for beef cattle, with strict limits on residues in meat. Hormones are not approved for use in poultry, and the growth hormone rbST (used in some other countries to increase milk production) is not approved for dairy cows in Canada. So a "no added hormones" label on Canadian chicken is true of all Canadian chicken. Being able to check a claim like this is part of evaluating evidence.

Heavy metals and the nervous system

Lead interferes with the development of the nervous system, especially in young children; health agencies consider no level of lead exposure to be safe. Old lead pipes and old paint are the main sources in Canada today, which is why Ontario requires schools and child care centres to test their drinking water for lead.

Mercury released by industry can be converted by bacteria in lakes and rivers into methylmercury, which is absorbed easily and excreted slowly. It bioaccumulates in organisms and biomagnifies up food chains, reaching its highest levels in large predatory fish. Methylmercury damages the nervous system, causing numbness, tremors, problems with coordination, vision and hearing, and harm to developing babies.

From 1962 to 1970, a chemical plant connected to a pulp and paper mill in Dryden, Ontario, released mercury into the English–Wabigoon River system. Grassy Narrows First Nation (Asubpeeschoseewagong Netum Anishinabek), whose way of life and economy were closely tied to fishing these waters, continues to live with the health, social and economic effects decades later, as does Wabaseemoong Independent Nations (Whitedog) farther downstream. Community members have led a long campaign for recognition, cleanup and care, and governments have committed funding for river cleanup and a specialized care facility. This history shows how an environmental decision can affect the homeostasis of a whole community for generations, and why the voices of affected communities matter in environmental decisions.

Medical treatments and homeostasis

Medical treatments are themselves powerful changes to homeostasis. Understanding feedback helps explain their benefits and side effects.

Chemotherapy uses drugs that kill or stop the division of rapidly dividing cells. Cancer cells divide rapidly, but so do cells in the bone marrow (which make blood cells), the lining of the digestive tract and hair follicles. That is why chemotherapy can cause infections (fewer white blood cells), fatigue (fewer red blood cells), nausea and mouth sores, and temporary hair loss. Supportive treatments, such as anti-nausea medicines and growth factors that stimulate blood cell production, help the body restore balance. Most normal tissues recover after treatment ends.

Hormone therapies use what you learned about receptors and feedback:

• Replacement: insulin for type 1 diabetes, levothyroxine for hypothyroidism, desmopressin for diabetes insipidus.
• Blocking: some breast cancers grow in response to estrogen. Drugs such as tamoxifen block estrogen receptors on the cancer cells. Some prostate cancer treatments lower testosterone or block its receptors.
• Suppressing: long-term corticosteroids suppress the HPA axis (which is why they are tapered).

Other technologies that restore homeostasis include dialysis and transplants (kidney lesson), insulin pumps and CGMs (diabetes lesson) and deep brain stimulation, in which electrodes deliver small electrical pulses to specific brain areas to reduce the tremors of Parkinson's disease.