3. The Negative Feedback Loop

Success Criteria

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

I can describe what the 5 parts of the thermoregulatory system do, and where they are located.
I can explain how these 5 parts of the thermoregulatory system work together in a negative feedback loop.

Vocabulary

Learn these so you can communicate this concept well.

Action potential: An electrical signal that is rapidly transmitted along the neuron.
Control centre: Receives the signals from thermoreceptors, and determines and coordinates a response.
Core temperature: Actual temperature of the vital organs such as the heart, brain and liver.
Counteract: To oppose / offset / correct to bring about homeostasis.
Effector: Cells, tissues and organs that respond to signals from the control centre and causes a response.
Hormone: A chemical signal released by glands that travel great distances through the bloodstream to target cells.
Hypothalamus: Location of the control centre for thermoregulation.
Negative feedback loop: A counteracting mechanism made up of 5 parts that work together to bring the core temperature to 37°C.
Neurotransmitter: A chemical signal that is released by neurons to communicate to another cell over very short distances.
Response: The effect the body has on core temperature, in response to the stimulus.
Set point: Temperature that the body is trying to maintain via thermoregulation (37°C)
Stimulus: Change in body temperature that triggers the need for thermoregulation.
Thermoreceptor: Specialised cells located in the skin and hypothalamus that can detect changes in body temperature.

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook:

Describe the adaptive significance of thermoregulation.
(Adaptive significance refers to the advantages a particular trait provides to an organism in terms of survival and reproduction).

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook:

What organ is the body's thermostat?

Hei Mahi (Do Now)

Do Now in your OneNote/Notebook:

The order of events in this diagram is incorrect. Write down the correct order of events.

Exit Task

In your Learning Journal:

Re-write this interpreting question so it is asking about the Thermoregulatory Negative Feedback Loop:

What are the parts?

Then, write an answer for it.

Exit Task

In your Learning Journal:

Re-write this interpreting question so it is asking about the Thermoregulatory Negative Feedback Loop:

How do the parts influence the whole?

Then, write an answer for it.

Exit Task

In your Learning Journal:

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

How does this relate to...?

Then, write an answer for it.

What is Negative Feedback?

Homeostasis (stable internal environment) is possible due to a mechanism called a NEGATIVE FEEDBACK LOOP.

In thermoregulation, any changes to the CORE TEMPERATURE away from the SET POINT (37°C) triggers the negative feedback loop to COUNTERACT that change, to return the core temperature back to the set point of 37°C.

The thermoregulatory negative feedback loop serves to return the core temperature back to the set point (37°C) as quickly as possible.

What are the 5 Parts of a Negative Feedback Loop?

The negative feedback loop is made up of 5 key parts, found in various areas of the body:

1) Stimulus

The STIMULUS is a change in body temperature that triggers the need for thermoregulation.

2) Receptors (thermoreceptors)

THERMORECEPTORS are specialized cells located in the skin, hypothalamus, and other parts of the body that can detect the stimulus (changes in body temperature). These receptors respond to changes in temperature by sending signals to the control center.

3) Control centre

The CONTROL CENTRE is responsible for receiving the signals from the receptors and determines and coordinates the appropriate response to the stimulus. This center is located in the HYPOTHALAMUS at the base of the brain.

4) Effectors

EFFECTORS are the cells, tissues, and organs that respond to signals from the control center and causes a response to regulate body temperature.

In the case of temperature regulation, effectors include blood vessels, sweat glands, and muscle fibers throughout the body.

5) Response

The RESPONSE is the effect that the body has on the core temperature, in response to the stimulus.

For example, if the body temperature is too high, the effectors may dilate blood vessels in the skin to increase heat loss, or activate sweat glands to increase evaporative cooling. If the body temperature is too low, the effectors may constrict blood vessels in the skin to reduce heat loss, or activate muscle fibers to generate heat through shivering.

The response is designed to restore the body temperature to its normal set point, which is the desired level of body temperature. The greater the change from the set point, the greater the response will be to correct it.

This negative feedback loop continues to operate until the body's internal temperature has stabilized at the set point. The response of the body to the stimulus can be thought of as "opposing" the change in temperature, hence the term "negative feedback loop."

How do the 5 Parts Work Together in a Negative Feedback Loop?

The combination of these 5 parts work together in a feedback loop, where the response of the effectors leads to a change in the core temperature, which is then detected by the receptors, which sends signals to the control center to coordinate a new response.

This process continues until the core temperature returns to the set point and is maintained within a narrow range.

1. Thermoreceptors detect the stimulus (a change in body temperature).

There are two types of receptors in the body that detect changes in temperature.

Peripheral thermoreceptors in the skin

The skin is the largest organ in the body. It plays a vital role in thermoregulation in two ways:

Contains THERMORECEPTORS that detect changes in environmental temperature.
Contains EFFECTORS that can vary the rate of heat loss from the body.

Thermoreceptors in the hypothalamus

The HYPOTHALAMUS also contains thermoreceptors which are sensitive to the temperature deep in the brain (CORE TEMPERATURE).

Figure above: "Peripheral thermoreceptors detect environmental and visceral temperatures and report these to the hypothalamus. Hypothalamic temperature receptors detect internal temperature. The thermoregulatory center initiates heat-loss or heat-gain responses in peripheral organs."

2. The control centre compares the core temperature to the set point (37°C)

The control centre constantly monitors and compares the core temperature (detected by thermoreceptors) to the set point of 37°C.

3. The control centre sends messages to the effectors.

If the core body temperature is not the same as the set point (37°C), the hypothalamus (control centre) sends messages to EFFECTOR organs via the:

Nervous system (ACTION POTENTIALS and NEUROTRANSMITTERS)
Note: an action potential is an electrical signal that is rapidly transmitted along the neuron, while a neurotransmitter is a chemical signal that is released by neurons to communicate to another cell over very short distances.
Endocrine system (HORMONES)
Note: a hormone is a chemical signal released by glands that travel great distances through the bloodstream to target cells.

4. What do effectors do to bring the temperature back to the set point of 37°C?

To lower body temperature: sweating (sweat glands), vasodilation (smooth muscle of skin arterioles), hormonal response (thyroid gland), behavioural response (skeletal muscle).

To increase body temperature: shivering (skeletal muscle), vasoconstriction (smooth muscle of skin arterioles), piloerection, hormonal response (thyroid gland), behavioural response (skeletal muscle).

See Concepts 4 and 5: Thermoregulatory Responses to Different Scenarios for more information.