Homeostasis and feedback systems

Question 1

Define homeostasis

Answer 1

Homeostasis is the maintenance of a stable internal environment

Question 2

Stimulus - response model

Answer 2

Stimulus -> receptor -> control centre -> effector -> response -> feedback

silly respiration controls and effects rest and feelings

Question 3

Stimulus

Answer 3

any kind of detectable external or internal change in the environment

eg. Change in light, sound, heat,
* Core body temperature change
* Blood glucose level change

A Stimulus that causes a disruption to homeostasis is said to cause a deviation from the set
point

Question 4

Receptor

Answer 4

Specialised parts of the nervous system with the ability to sense changes in the environment

Constantly monitor conditions

Examples
* Photoreceptors
* Thermoreceptors
* Chemoreceptors

Question 5

Control centre

Answer 5

Compares current conditions to the set point, then facilitates the response via the effector

Examples
* Hypothalamus - controls the release of hormones from the pituitary gland
* Hormones then communicate to effectors to carry out a response

Question 6

Effector

Answer 6

Causes changes to compensate for the deviation (does the work)
* Examples
* Muscles
* Sweat glands
* Thyroid gland – produces thyroxin hormone

Question 7

Response

Answer 7

A response is what the effector actually does in response to the signal from the control centre

Causes a return to set point

Examples
* Shivering to increase body temperature

Question 8

Feedback

Answer 8

The response reverses or counteracts the stimulus; it is called a negative
feedback mechanism

Question 9

Apply stimulus model to Glucose regulation

Answer 9

Stimulus ->

Change in blood glucose levels - either increase after eating or decrease during fasting

receptor ->

specialised cells in pancreas called beta cells (high blood glucose) and alpha cells (low blood glucose)

control centre ->

Pancreas processes info from receptors and releases hormones to fix the imbalance

effector ->

cells in the liver and muscles respond to the signals from the pancreas

response ->

High blood glucose -> beta cells release insulin, signaling the liver and muscle cells to absorb glucose from the blood storing as glycogen, lowering blood glucose

Low blood glucose -> Alpha cells release glucagon triggering the liver to convert stored glycogen back into glucose and release it in the blood stream raising blood glucose levels

feedback ->

As blood glucose levels return to normal, the release of insulin or glucagon decreases. As the receptors can detect that the stimulus has been counteracted. This feedback loop prevents extreme fluctuations, maintaining homeostasis