5. Responses to a Hot Environment
Your learning has been successful if you can do the following:
Learn these so you can communicate this concept well.
Do Now in your OneNote/Notebook:
1) List 2 causes of rising body temperature.
2) Think of 4 ways a rising body temperature can be countered.
3) What do you think "vasodilation" means?
Do Now in your OneNote/Notebook:
What's the difference between thyroid hormone and norepinephrine?
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 Hot Environment
The first normal response is always voluntary and behavioural - we may decide to take some clothes off, spread out or fan ourselves, or move to the shade.
It is only when these voluntary responses are not enough, that the control centre stimulates involuntary responses.
1) Responses to increase heat loss (to cool down).
SWEAT GLANDS in the skin (effector) produces SWEAT (response). This sweat EVAPORATES from the skin, taking heat energy away with it.
SMOOTH MUSCLE in ARTERIOLES (effector) relax, causing VASODILATION (response). This allows more blood to flow to the extremities so more heat is RADIATED to the surroundings.
(Vestigial) Arrector pili muscles (effector) relax, lowering the skin hairs (response). This allows air to circulate over the skin so more heat is lost by convection.
2) Responses to decrease the amount of heat produced (to get less hot).
Skeletal muscles (effector) stop shivering (response).
THYROID GLANDS (effector) stop secreting THYROXINE to decrease the BASAL METABOLIC RATE, and therefore reduce THERMOGENESIS (response).
You MUST read the "Biophysical & Biochemical Processes of Sweating and Evaporative Cooling."
Biophysical & Biochemical Process of Sweating.
Biophysical process of evaporative cooling.
When the Negative Feedback Loop STOPS Working in a Hot Environment (Hyperthermia)
HYPERTHERMIA refers to those conditions that take place when core temperature climbs to 39°C or higher. When the body produces more heat than it can get rid of, the body can lose too much water from sweating, that the severe dehydration can cause the negative feedback loop to stop working.
Three Phases & Symptoms
Phase 1: Overexertion - a flushed red face and rapid short breaths.
Phase 2: Heat exhaustion - red skin, rapid breathing, profuse sweating, dry mouth, cramps, nausea, and vomiting
Phase 3: Heat stroke - core temperature reaches 41°C or higher, sweat is no longer produced, leading to a hot and dry skin, disorientation, collapse, and unconsciousness.
You must read the "Hyperthermia Reading" for more information on each symptom.
Switch to the Positive Feedback Loop = Uncontrollable Rise in Temperature
To try to bring back CORE TEMPERATURE to the SET POINT, sweating increases and dehydration occurs. Once the individual loses around 12% of their water, the situation becomes critical.
Severe dehydration causes flow-on effects that ultimately leads to a POSITIVE FEEDBACK LOOP, where the body's response to a stimulus actually amplifies the stimulus instead of reducing it. Positive feedback, therefore, results in the core temperature continues to rise uncontrollably - the body produces more heat and amplifies the stimulus rather than counteracts it.
Prolonged hyperthermia can be fatal, due to the effects of extreme hot temperatures on ENZYMES and MEMBRANE PERMEABILITY.
Dehydration leads to:
A decrease in BLOOD VOLUME and therefore BLOOD PRESSURE. The body tries to increase blood pressure by:
Increasing HEART RATE - however, this ends up increasing AEROBIC RESPIRATION and therefore the amount of heat produced
VASOCONSTRICTION, to direct blood to vital organs - however, this ends up damaging some other tissues (leading to vomiting and more dehydration) and reducing heat loss via radiation.
Sweating stops to conserve water (and blood volume).
Heat is no longer lost by EVAPORATIVE COOLING.
(Links to EXCELLENCE) Enzymes when core temperature is HOTTER than the set point.
(Links to EXCELLENCE) Membrane permeability when core temperature is HOTTER than the set point.
When the body temperature decreases, the phospholipids and therefore the cell membrane becomes less fluid. This can lead to changes in the permeability of the membrane, making it more difficult for ions and other small molecules to cross the membrane causing disruptions in normal cell function.
For example, changes in ion gradients across the membrane can interfere with the normal function of ion channels and transporters, which play critical roles in maintaining cell membrane potential, transmitting nerve impulses, and transporting ions and other small molecules into and out of the cell.
This decreased permeability can also affect the function of membrane proteins and enzymes, which may become more rigid and less able to perform their normal functions. In extreme cases, low temperatures can cause the lipid bilayer to become so rigid that it can no longer maintain its integrity, leading to cell damage or death.
For example, hypothermia can also disrupt normal membrane-associated enzyme activity, which can interfere with a wide range of metabolic processes. For example, enzymes involved in the breakdown of glucose to produce ATP may become less efficient, reducing the cell's ability to produce energy.
Tasks & Homework
Task: Analyse these Results about Sweating
Reading: Biophysical & Biochemical Processes
Task: Complete these activities in pairs.
What happens when you get heat stroke? (TED-Ed)
Why do we sweat? (TED-Ed)