Lesson 1 

How does the body maintain homeostasis and stay healthy?

And, what are infectious diseases?

Learning outcomes & key terms

Innovation and equal access, inspiration for all.

  • Students can define homeostasis, negative feedback loop, infectious disease
  • Students can use critical and creative reasoning to explain how the body maintains homeostasis through a creative or real life example.
  • Students can explain the difference between health and disease using the terms homeostasis and feedback.
  • Students can recognise the organisms/pathogens that cause infectious disease.

Homeostasis
A key concept in biology. The concept of homeostasis is the description for when the internal conditions of living organisms remain stable (within a normal range), regardless of what is going on in the external environment. These internal conditions include your body temperature, pH level, and glucose level. It is the optimal internal state at which your body operates best.

Maintaining homeostasis
The regulation of your internal environment is done primarily through negative feedback.

Negative feedback 
Negative feedback is a response to a stimulus that keeps a variable close to a set value. Essentially, it either “shuts off” or “turns on” a system when it varies too far from a set value.

Positive Feedback
Some processes in the body are regulated by positive feedback. Positive feedback is when a response to an event increases the likelihood of the event to continue.
An example of positive feedback is milk production in nursing mothers. As the baby drinks her mother’s milk, the hormone prolactin, a chemical signal, is released.
The more the baby suckles, the more prolactin is released, which causes more milk to be produced. Other examples of positive feedback include contractions during childbirth.
When constrictions in the uterus push a baby into the birth canal, additional contractions occur.

Negative feedback loop
This is the underlying mechanism by which homeostasis maintains a balance to ensure optimal metabolic efficiency. Serves to keep a certain variable in check (temperature for eg).
Stimulus: a change occurs (temperature increases)
Sensor: change is detected (by nerve cells in skin and brain)
Control: response to the change (temperature control centre in brain [hypothalamus] sends a command)
Effector: the effect of the response (sweat glands kick in to action – skin makes sweat, blood vessels dilate in order to cool body/decrease temperature and maintain homeostasis)

External variables
Is the climate, diet, stress. Despite these, internal variable stay the same. 

Internal variables
Are items such as body temperature, blood pressure, blood sugar, water balance. Normal range = body temp (36.5-37.2 degrees Celsius), blood pressure (110/75-130/85), hemoglobin (males 130-170g/L, females 120-150g/L  

Hypothalamus
The main job is to maintain homeostasis

Disease
Any condition that impairs the normal functioning of the body. Occurs when homeostasis can’t be achieved. It is a disruption of normal body functions and homeostasis.

Non-infectious/non-communicable disease: a medical condition or disease that is non-infectious. They can be chronic and progress slowly or result in rapid decline and death. includes most cancers, diabetes, hypertension, rheumatoid arthritis, and sickle cell anaemia.

Infectious/communicable disease:  an illness resulting from an infection. It is a disease caused by a pathogen (also known as a germ). Examples include HIV, Ebola, chicken pox, the common cold, hepatitis, influenza, Lyme disease, meningitis, strep throat, tetanus, tuberculosis, Zika virus, and many others.   

Infect
To transmit an infectious disease 

Infection
The invasion of an organism’s body tissues by disease-causing agents, their multiplication, and the reaction of the host tissues to these organisms and the toxins they produce. 

Common ways to become infected
Through person-to-person physical contact, inhaling a pathogen, eating/drinking contaminated foods, contact with an animal carrying the pathogen, insect bites. 

Pathogen (germ)
An organism capable of causing disease. 

Examples of pathogens
Bacteria, viruses, fungi, parasitic worms.

This page is to be used as a reference point. A structured online course and quiz can be accessed by clicking the button below.

Omega TV: Lesson Videos

Homeostasis

An introduction.  Innovation and equal access, inspiration for all.

Suppose that it’s really cold outside — snowing even — and you run out to your mailbox in a short-sleeve shirt. While you’re out there, a neighbour stops by to chat.

Your body wants to maintain its body temperature around 98.6°F.

Your skin senses the cold conditions outside, and nerve impulses are sent from receptors in your skin to your brain that say,

“Hey! It’s cold out here!!”

In an attempt to stay around 98.6°F, your body makes adjustments automatically. Goose pimples form, which actually are the hair follicles on your body tightening to make your body hair stand up higher to help insulate your body.

If that doesn’t help to maintain the normal temperature, you start to shiver. Shivering is an attempt by your body to create heat through movement.

If your chatty neighbor is still rambling on, and shivering doesn’t help keep you warm, your body’s “thermostat” will begin to drop (if it goes too far, hypothermia begins), and your internal furnace[LB2] ” will kick on to create heat internally so that homeostasis — maintaining relatively normal values — occurs.

 

Homeostasis and body temperature

The control of body temperature in humans is a good example of homeostasis in a biological system. In humans, normal body temperature fluctuates around the value of 37 °C (98.6 °F), but various factors can affect this value, including exposure, hormones, metabolic rate, and disease, leading to abnormally high or low temperatures.

The body’s temperature regulation is controlled by a region in the brain called the hypothalamus.

Feedback about body temperature is carried through the bloodstream[LB3] to the brain and results in compensatory adjustments in the breathing rate, the level of blood sugar, and the metabolic rate. Heat loss in humans is aided by reduction of activity, by perspiration, and by heat-exchange mechanisms that permit larger amounts of blood to circulate near the skin surface.

Heat loss is reduced by insulation, decreased circulation to the skin, and cultural modification such as the use of clothing, shelter, and external heat sources. The range between high and low body temperature levels constitutes the homeostatic plateau—the “normal” range that sustains life. As either of the two extremes is approached, corrective action (through negative feedback) returns the system to the normal range.

Failure of Homeostasis

Many homeostatic mechanisms such as these work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail.

When they do, cells may not get everything they need, or toxic wastes may accumulate in the body. If homeostasis is not restored, the imbalance may lead to disease or even death.

  • Many organisms live in and on our bodies. They’re normally harmless or even helpful, but under certain conditions, some organisms may cause disease.
  • Some infectious diseases can be passed from person to person. Some are transmitted by bites from insects or animals. And others are acquired by ingesting contaminated food or water or being exposed to organisms in the environment.
  • Globally, infectious diseases resulted in 9.2 million deaths in 2013 (about 17% of all deaths.
    While disease is often a result of infection or injury, most diseases involve the disruption of normal homeostasis. Positive and negative feedback are important for normal physiological function, and anything that prevents feedback from working could lead to disease if the mechanisms of disruption become strong enough.
  • Homeostasis underpins at a systems level the regulatory control of immunity and metabolism.
    • Disease is any failure of normal physiological function that leads to various negative symptoms in the body. While disease is often a result of infection or injury, most diseases involve the disruption of normal homeostasis. Positive and negative feedback are important for normal physiological function, and anything that prevents feedback from working could lead to disease if the mechanisms of disruption become strong enough.

 

Source: Boundless. “Disease as Homeostatic Imbalance.” Boundless Anatomy and Physiology. Boundless, 26 May. 2016. Retrieved 25 Aug. 2016 from https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/introduction-to-anatomy-and-physiology-1/homeostasis-32/disease-as-homeostatic-imbalance-285-9170/ 

Class activity

Part 1  

1. What is normal/healthy in regards to the human body?

Discuss this as a class group.

How can we tell what is normal?

What are the markers that give us hints? Hint: think about when you go to the doctor, what body systems do they check?

  • Body temperature
  • blood pressure
  • blood sugar
  • Water balance (degree of hydration)
  • pH level

 

2. Lab: Body temperature as a marker of health

Everyone in class take own temperature and plot on a graph. (Use a collaborative, interactive graph that students can individually enter data and shows up in graph with all results from class, see, https://www.geogebra.org/graphing

  • What do you notice? (everyone falls within a very similar range).
  • Web search: what is the ‘normal’ body temperature?
  • Did you find an absolute number or a range? (the idea of a range is important to point out for the concept of homeostasis; 36.5-37.2 degrees Celsius).

Make hypothesis about what you would expect to happen to body temperature if hold icepacks for 2-3 minutes. Class members to take temperature again and enter results to plot on graph.

 

  • What did you notice?
  • Why do you think this is? (temperature remained relatively stable despite cold)

Part 2

1. Introduction to homeostasis.

‘Normal’ or healthy in the human body is a result of something called homeostasis.

Homeostasis: the optimal internal state at which your body operates best. This requires constant adjustments to stay stable despite consistent internal and external variables. It is a little bit like a seesaw.

The maintenance or regulation of this state is determined by negative feedback. When the ‘normal’ range of healthy is challenged and either sides of the normal range are exceeded, corrective action is taken to restore or return to the normal range.

Watch the videos on Homeostasis to learn what it is and how it operates within the human body. 

Part 3

1. Real life examples of Homeostasis

Read narrative scenario example below and/or use lab experience and video option above.

Suppose that it’s really cold outside — snowing even — and you run out to your mailbox in a short-sleeve shirt. While you’re out there, a neighbour stops by to chat. Your body wants to maintain its body temperature around 98.6°F. Your skin senses the cold conditions outside, and nerve impulses are sent from receptors in your skin to your brain that say, “Hey! It’s cold out here!!”

In an attempt to stay around 98.6°F, your body makes adjustments automatically. Goose pimples form, which actually are the hair follicles on your body tightening to make your body hair stand up higher to help insulate your body. If that doesn’t help to maintain the normal temperature, you start to shiver. Shivering is an attempt by your body to create heat through movement.

If your chatty neighbor is still rambling on, and shivering doesn’t help keep you warm, your body’s “thermostat” will begin to drop (if it goes too far, hypothermia begins), and your “furnace” will kick on to create heat internally so that homeostasis — maintaining relatively normal values — occurs.

2. Components of Negative Feedback Loop

3. Practical application: Complete Negative Feedback Loop model

The control of body temperature in humans is a good example of homeostasis in a biological system.

In humans, normal body temperature fluctuates around the value of 37 °C (98.6 °F), but various factors can affect this value, including exposure, hormones, metabolic rate, and disease, leading to excessively high or low temperatures. The body’s temperature regulation is controlled by a region in the brain called the hypothalamus.

Feedback about body temperature is carried through the bloodstream to the brain and results in compensatory adjustments in the breathing rate, the level of blood sugar, and the metabolic rate. Heat loss in humans is aided by reduction of activity, by perspiration, and by heat-exchange mechanisms that permit larger amounts of blood to circulate near the skin surface.

Heat loss is reduced by insulation, decreased circulation to the skin, and cultural modification such as the use of clothing, shelter, and external heat sources. The range between high and low body temperature levels constitutes the homeostatic plateau—the “normal” range that sustains life. As either of the two extremes is approached, corrective action (through negative feedback) returns the system to the normal range.

4. Have students work together in pairs to research a particular body system

Create a scenario and then complete negative feedback loop model.

Examples include: high temperature, high/low blood pressure, high/low blood sugar, water balance etc using Interactive Element #4 (interactive diagram of negative feedback loop).

Part 4

1. Question: what happens when homeostasis fails?

  • Many homeostatic mechanisms such as these work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do, cells may not get everything they need, or toxic wastes may accumulate in the body. If homeostasis is not restored, the imbalance may lead to disease or even death.
  • Introduce concept of disease as the opposite of healthy or the result of a homeostatic imbalance.

 

2. Disaese

Disease occurs when the normal functioning of the body is impaired – ie: homeostasis can’t be achieved/homeostatic balance is disrupted. This is usually a result of something preventing the feedback from working effectively.

There are two broad categories of disease:

  • Non-infectious disease:non-infectious/non-communicable disease: a medical condition or disease that is non-infectious. They can be chronic and progress slowly or result in rapid decline and death. includes most cancers, diabetes, hypertension, rheumatoid arthritis, and sickle cell anemia
  • Infectious or communicable disease: an illness resulting from an infection that can spread from one person to another through contact with bodily fluids, by aerosols (coughing and sneezing), via a vector (eg mosquito), by ingesting contaminated foods. Infectious agents or pathogens include viruses, bacteria, fungi, parasites or protozoa.
  • Infectious diseases are one of the leading causes of death worldwide.

 

Further Reading

http://www.yourgenome.org/facts/what-are-infectious-diseases
http://www.mayoclinic.org/diseases-conditions/infectious-diseases/home/ovc-20168649
http://www.who.int/topics/infectious_diseases/en/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4439431/
http://www.dummies.com/education/science/biology/how-homeostasis-keeps-your-system-in-balance/
https://en.wikipedia.org/wiki/Elizabeth_Blackburn

Teacher Resources
http://www.australiancurriculum.edu.au/science/curriculum/f-10?layout=1#level9 

Lesson plan and learning resources for homeostasis topic: http://www.ck12.org/biology/Homeostasis/?referrer=concept_details&conceptLevel=&conceptSource=ck12&by=ck12&difficulty=all#all

Examples of homeostasis in the human body: http://www.brighthub.com/science/medical/articles/112024.aspx

Examples of negative feedback: http://examples.yourdictionary.com/examples-of-negative-feedback.html    

Lesson plan and learning resources for pathogens and infectious disease: http://www.ck12.org/life-science/Pathogens-in-Life-Science/?by=ck12&difficulty=all#all
http://www.pbslearningmedia.org/resource/tdc02.sci.life.reg.lp_humanreg/human-body-regulation/

1. Human body systems and how they contribute to homeostasis.

Can you create an interactive table with definitions, visual, explanation of role in homeostasis.

2. Choose a creative way to communicate how your lifestyle may positively or negatively affect your body’s ability to maintain homeostasis.
 
3. Find 3 examples of the negative feedback loop in every day life.

Lesson 1 Summary

  • Homeostasis is a key concept in health
  • Our body systems are interrelated and contribute to homeostasis.
  • A negative feedback loop helps maintain homeostasis.
  • Disease occurs when homeostasis can’t be achieved
  • Infectious diseases have far reaching implications as they spread easily and are a leading cause of death in the world.

Next Lesson:

Lesson 2 – How are infectious diseases caught?