How does the body stay healthy?

Lesson 1

How does the body maintain homeostasis and stay healthy? And, what are infectious diseases?

Learning outcomes & key terms

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/germs 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

A major job is to maintain homeostasis

Disease

Any condition that impairs the normal function of the body. It 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. It can be chronic and progress slowly or result in rapid decline and death. It 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, meningitis, strep throat, tetanus, tuberculosis, Zika, Covid-19 etc.

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, sex

Pathogen (germ)

An organism capable of causing disease

Examples of pathogens

Bacteria, viruses, fungi, parasitic worms

Science understanding

Biological sciences

Describing how the requirements for life (for example oxygen, nutrients, water and removal of waste) are provided through the coordinated function of body systems such as the respiratory, circulatory, digestive, nervous and excretory systems

Explaining how body systems work together to maintain a functioning body using models, flow diagrams or simulations

Investigating the response of the body to changes as a result of the presence of micro-organisms

Science as a human endeavour

Scientific understanding, including models and theories, is contestable and is refined over time through a process of review by the scientific community

Advances in scientific understanding often rely on technological advances and are often linked to scientific discoveries

People use scientific knowledge to decide whether they accept claims, explanations or predictions, and advances in science can affect people’s lives

Values and needs of contemporary society can influence the focus of scientific research

Science enquiry skills

Formulate questions or hypotheses that can be investigated scientifically

Analyse patterns and trends in data, including describing relationships between variables and identifying inconsistencies

A special interview with Nobel Laureate, Prof Peter Doherty

My story, Prof Robert Booy

Homeostasis

An introduction

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 (what is that in Celsius?)

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 37°C, 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 neighbour 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” 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 nervous system and 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. Others are acquired by ingesting contaminated food or water or by being exposed to organisms in the environment
Globally, infectious diseases resulted in 9.2 million deaths in 2013 (about 17% of all deaths) – the Covid pandemic, 2020-23, alone killed at least 7 million people worldwide
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.

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/

Source: WHO Coronavirus (COVID-19) Dashboard. Accessed 19 Dec. 2023 from
https://covid19.who.int/

Class activity

Part 1

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?

Heart rate and breathing rate
Body temperature
Blood pressure
Blood sugar
Water balance (degree of hydration)
pH level

1.2 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 you hold icepacks for 2-3 minutes

Class members to take temperature again and enter results to plot on graph

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

Part 2

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 internal and external variations. 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 side of the normal range is 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

3.1 Components of Negative Feedback Loop

3.2 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 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

3.3 Students can work together in pairs to research a particular body system

Create a scenario and then complete a 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

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

4.2 Disease

Disease occurs when the normal functioning of the body is impaired – i.e: 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:

4.2.1 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 anaemia

4.2.2 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), or by ingesting contaminated foods. Infectious agents that may be pathogens include viruses, bacteria, fungi, and parasites

Infectious diseases are one of the leading causes of death worldwide

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

Quiz

1) Homeostasis is
a) The how humans stay stationary
b) How the human body maintains a stable condition
c) The study of alternative medicine
d) An early form of human

2) A reaction of the body to a stimulus that causes an opposite output to maintain an ideal level of something is
a) A positive feedback loop
b) A neutral feedback loop
c) A negative feedback loop
d) A neural feedback loop

3) When homeostasis is disrupted
a) The person is healthy
b) Disease occurs
c) Nothing happens
d) The person begins to move

4) An example of a feedback loop is
a) The body sweating when the temperature becomes too high
b) The pancreas secreting glucagon when blood glucose level become too low
c) Changes in blood pressure affecting heart rate
d) All of the above