Homeostasis and Negative Feedback

Define: Homeostasis

• why?

maintaining a relatively stable internal environment

• essential for the functioning of the body

Define: Set point

• can it be adjusted?

the target value the body aims to maintain

• yes, the hypothalamus can readjust the set point depending on the situation

What organ is the main homeostatic control center?

the hypothalamus

Define: Negative Feedback

a mechanism that opposes a stimulus to return homeostatic variable towards it set point

Define: Dynamic equilibrium (steady state)

• what does this require?

that state in which homeostatic variables fluctuate within a narrow range around the set point

• requires constant energy

Define: Antagonistic control

• how is it done?

• what is this a requirement for?

bi-directional control that can both raise and lower a variable to oppose change

• done with negative feedback

• required for true homeostatic regulation

What are the three essential components for homeostasis and negative feedback?

Response loop:

Sensor/Receptor: detects the stimulus and sends information to the integrator

Integrating Center: receives input, compares it to the set point, and signals the effectors

Effector: the component (muscle,gland,etc) that carries out the response to move the variable back toward the set point

What is an important thing to note about homeostasis and NF?

all homeostatic mechanisms utilize negative feedback not all cases of negative feedback are homeostatic

Set point variability

• example of situation

the hypothalamus can readjust the set point depending on the situation, bringing with the homeostatic variables

• raising the temperature set point when sick to fight the bacteria

• when the temperature breaks, lowering the set point, you begin to sweat

In Part One of the Water Bath Lab, only the heating element can be used to regulate the temperature of water. Is this a good or back example of NF and homeostasis? Why or why not?

• identify the essential components

• identify the missing parts

sensor: thermometer

integrating center: us

effector: hot plate

Part 1 is a good example of NF but not homeostasis. NF does not require antagonistic control, simply opposing the stimulus to return it to its original set point and turning it off. Whether it can do it only one way or both is a great example of NF.

It is not a great example of homeostasis because it lacks the antagonistic control required to keep the dynamic equilibrium of the homeostatic variables around the set point. In part 1 we can only heat up the water and have no way to cool it down if it surpasses the set point, therefore it does not accurately represent homeostasis.

Use the fish tank analogy to compare with lab part 1

sensor: thermometer

integrating center: control box

effector: heater

The fish tank is a great example of NF. The thermometer will detect a drop in temperature and communicate with the control box. The control box will compare the received value to the set point and chose to turn on the heater. The heater will continue until it reaches the set point, turning off.

Similarly to the problems in lab 1, there is no antagonistic control, because we can only heat the water and not cool it down.

What are the essential factors required to maintain homeostasis?

1) set point, 2) dynamic equilibrium, 3) antagonistic control

1) sensor/receptor, 2) integrator/control center, 3) effector

In Part Two of the Water Bath Lab, the heating and cooling element can be used to regulate the temperature of water. Is this a good or back example of NF and homeostasis? Why or why not?

• identify the essential components

• identify the added parts

sensor: thermometer

integrating center: us

effector: hot plate and ice

Part 1 and Part 2 are good examples of negative feedback; now there’s an added antagonistic control element where NF can oppose the stimulus and stop bidirectionally for a rise in temperature and a drop.

With the addition of ice in part 2, along with the hot plate, we have antagonistic control, able to both cool and heat up the water and can therefore move in both directions to maintain a dynamic equilibrium around the set point.

Examples of homeostatic control mechanism: Temperature regulation

• does antagonistic control exist?

Response to temperature drop

Sensors: receptors collect body temperature for the whole body and communicate to the hypothalamus

Integrating Center: the hypothalamus receives the value and compares it to the set point, determining what to do

Effectors:

• skeletal muscles shiver, increasing ATP production and heat

• subcutaneous blood vessels constrict: decreasing the surface area to keep heat (blood) at the core

Antagonistic control: Response to temperature rise

Sensors: receptors collect body temperature for the whole body and communicate to the hypothalamus

Integrating Center: the hypothalamus receives the value and compares it to the set point, determining what to do

Effectors:

• sweat glands will release sweat for evaporative cooling

• subcutaneous blood vessels will dilate, allowing heat from blood to escape through the skin

HO: Define Positive feedback.

• whats the difference between NF?

• What are two examples?

response of the integrating center reinforces the stimulus rather than stopping it, destabilizing the system until an intervention outside the loop ends it.

• in NF the response opposes or removes the stimulus, stopping the response loop

• Child birth

  • uterine contractions push babys head against the cervix → sensory signals from the cervix are sent to the brain → brain stimulates the posterior pituitary gland to release oxytocin → oxytocin travels to the uterus via circulation → oxytocin exemplifies uterine contraction →

  • response loop continues until the baby is delivered

• Blood clot

  • When a blood vessel gets injured platelets stick to the damage site and release chemicals to attract even more platelets (positive feedback ) to eventually form a platelet plug and seal off the blood vessel (negative feedback)