4. Responses to a Cold Environment

Success Criteria

Your learning has been successful if you can do the following:


Learn these so you can communicate this concept well.

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook:

State which one is the odd one out: increased metabolism, sweating, vasoconstriction, shivering. Explain why in your books. 

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook:

1) Define what is considered to be normal body temperature in humans. 

2) Explain why cells need a warm temperature to function.

Exit Task

In your Learning Journal:

Re-write this interpreting question so it is asking about Thyroid hormones:

What is the order?

Then, write an answer for it.

Exit Task

In your Learning Journal:

Re-write this interpreting question so it is asking about Death:

How did it happen?

Then, write an answer for it.

Reminder: In your internal report, you MUST link your report to specific scenarios provided to you. 

How the Negative Feedback Loop NORMALLY Responds to a Cold Environment

The first normal response is always voluntary and behavioural - we may decide to put more clothes on, take shelter from the wind and rain, jump up and down or rub our hands together, or curl into a ball. 

It is only when these voluntary responses are not enough, that the control centre stimulates involuntary responses. 

1) Responses to increase the amount of heat produced 

These three responses generate heat through thermogenesis.

2) Responses to decrease heat loss (to get less cold).

You MUST read the "Biophysical & Biochemical Processes of Sweating and Evaporative Cooling."

Biochemical process of producing thyroxine hormone. 

You MUST read the reading called "Biochemical Processes for a Cold Environment"

Sky level - Fantastic and short explanation of how thyroid hormone is produced. No information on function. 

Sun level - More than what you need to know, but it comprehensively outlines the production and function of thyroid hormone.

When the Negative Feedback Loop STOPS Working in a Cold Environment (Hypothermia)


HYPOTHERMIA is a medical condition in which the core temperature of the body drops below 35°C. When the negative feedback loop is working, the body tries to generate more heat (THERMOGENESIS) through shivering and increasing the basal metabolic rate (through the action of thyroid hormone).

However, the negative feedback loop stops working when the body cannot generate enough heat to compensate for the rate at which heat is being lost. This can lead to range of neurological symptoms, and in severe cases, unconsciousness and death. 

Three Phases & Symptoms

You must read the "Hypothermia Reading" for more information on each symptom. 

Switch to the Positive Feedback Loop = Uncontrollable Fall in Temperature

To try to bring the core temperature back ot the set point, thermogenesis (by voluntary movements, involuntary shivering and increasing metabolism) increases to the point that accessible supplies of glucose run out. This has flow-on effects:

This results in the body no longer being able to generate more heat, and CORE TEMPERATURE drops uncontrollably. 

Prolonged hypothermia can be fatal, due to the effects of extreme hot temperatures on enzymes and membrane permeability. 

ENZYME activity slows down. This means that ATP synthase enzyme no longer produces enough energy for:

MEMBRANE PERMEABILITY and fluidity decreases. This disrupts the distribution of ions:

(Links to Excellence) Enzymes when the core temperature is COLDER than the set point.

At low temperatures, the movement of the enzyme molecules becomes sluggish, and their ability to bind to substrates and catalyze reactions decreases. This results in a decrease in the rate of chemical reactions, which can have a significant impact on the functioning of the body. For example, enzymes involved in energy production and metabolism become less efficient, leading to decreased energy production and an increase in fatigue.

Hypothermia occurs when the core body temperature drops below the normal range of 36-37°C. As the body temperature decreases, the activity of enzymes decreases as well. This can result in a slowing or cessation of many physiological processes, including cellular respiration, metabolism, and cellular function.

(Links to EXCELLENCE) Membrane permeability when the core temperature is COLDER than the set point.

An increase in temperature can cause the phospholipids to become more fluid, which can increase the fluidity of the cell membrane - more than normal. This can increase the permeability of the membrane, allowing ions and other small molecules to move more freely across the membrane - more than what's required to maintain a constant internal environment. 

This increased permeability can lead to the loss of ions and small molecules, leading to cellular dehydration and altering the normal ion gradients across the membrane. This can disrupt normal cellular processes and contribute to the development of cellular damage.

(So, the cell could be spending energy on active transport of ions, but membrane that's too permeable could undo the work done by active transport). 

This increased fluidity can also affect the function of membrane proteins, which are embedded in the lipid bilayer. In extreme cases, high temperatures can cause the lipid bilayer to become so fluid that it can break apart, leading to a loss of membrane integrity and cell death.

Tasks & Homework

Task: Listen to Polly's Experience in Antarctica and Complete the Worksheet

Equipped for a Challenge - Antartica.pdf
1. Polly's Introduction
2. Challenges of Antarctic
3. Equipment
4. Food, drinks, keeping warm long-term

Reading: Biophysical and Biochemical Processes of Thermogenesis

B3.4 (4) Biochemical and Biophysical Responses of Thermogenesis (1).pdf
B3.4 Suggested Report Structure.docx.pdf

Reading: Hypothermia - When the Negative Feedback Loop Stops Working

B3.4 (4) Hypothermia Reading.pdf