Science (Communication) and Wikipedia - Potentials and Pitfalls
Maintaining Internal Stability: Homeostasis
1. HomeostasisHomeostasis
A condition in which the internal
environment of the body remains
relatively constant despite changes in
the external environment. Examples
would be the maintenance of body
temperature and levels of glucose in
the blood
2. IMPORTANTIMPORTANT
Information in your ebookInformation in your ebook
• Go to the eBook
• Once in the book, there is a search field in the top
left
• Put “homeostasis” in the search box
• Hit enter
• On the left you will find homeostasis in every
chapter. Chapter 1 explains it but all the other
chapters discuss homeostasis in relationship to the
material in that chapter
3. Homeostatic mechanisms are designed to reestablish
homeostasis when there is an imbalance.
The Home Heating System
1. When the temperature of a room decreases below a set point, the
thermostat electrically starts the furnace.
2. As the temperature of the room rises to the set point, the thermostat
shuts down the furnace.
3. As the room cools, step one is repeated.
There are three components to this system:
1. The Sensor which detects the stress.
2. The Control Center which receives information from the sensor and
sends a message to the Effector.
3. The Effector which receives the message from the control center
and produces the response which reestablishes homeostasis.
4. There are three components to a homeostatic system:
1. The Sensor which detects the stress.
2. The Control Center which receives information from the sensor
and sends a message to adjust the stress.
3. The Effector which receives the message from the control
center and produces the response which reestablishes
homeostasis
It should be noticed that
1. the heat produced by the furnace shuts the furnace down
through the thermostat.
2. the original stress is reduced, i.e., the room warms up.
Homeostatic mechanisms that show these two
characteristics are operating by negative feedback
5. Interpret the arrows in
textbook’s flow charts as
“leads to” or “causes.”
e.g., decreased room temperature
causes increased heat loss from the
body, which leads to a decrease in
body temperature, etc.
The homeostatic control system: example
7. Sodium homeostasis:
Consuming greater amounts of dietary sodium initiates a set of
dynamic responses that include greater excretion of sodium in the
urine.
The amount excreted would likely exceed the amount ingested until
the “set point” is restored.
Example
8. Hyperthermia Heat receptors
in the skin
Hypothalamus
Stress
Sensors Control Center
Increased
activity of
sweat glands
Increased blood
flow to the skin
Effectors
Perspiration
evaporates
cooling the skin
Effect
Stress is reduced
shutting down
mechanism
Homeostatic Regulation of Body Temperature through
Negative Feedback
9. example: concentration of glucose in the blood
example: 70 to 110 mg glucose/dL of blood
example: diet and energy metabolism
A strategy for exploring homeostasis
• Identify the internal environmental variable.
•Establish the “set point” value for that variable.
• Identify the inputs and outputs affecting the variable.
10. example: resting versus exercising
example: certain endocrine cells in the pancreas
“sense” changes in glucose levels
example: a hormone that increases glucose
synthesis by the liver
Many homeostatic mechanisms utilize neural communication.
• Examine the balance between the inputs and outputs.
• Determine how the body monitors/senses the variable.
• Identify effectors that restore the variable to its set point.
A strategy for exploring homeostasis
14. Negative Feedback Via a Hormonal Pathway
Regulation of Blood Sugar
Hormones play an important role in many homeostatic pathways.
Hormones are produced by endocrine glands. They enter the
blood after being produced and travel throughout the body.
However, hormones have their effect on specific target tissues.
15. Positive Feedback Mechanisms
Homeostatic systems utilizing positive feedback exhibit two primary
characteristics:
1. Time limitation – Processes in the body that must be completed within a
constrained time frame are usually modified by positive feedback.
2. Intensification of stress – During a positive feedback process, the initial
imbalance or stress is intensified rather than reduced as it is in negative
feedback.
Typical Positive Feedback Process
Stress Sensor Control Center
EffectorIntensifies
16. Positive feedback “mini-loops” are built into pathway to speed up
production of chemicals needed to form the clot. Entire sequence of
clotting is a negative feedback pathway:
Feedback in Coagulation
17. Harmful Effects of Positive Feedback
Positive feedback can be harmful. Two specific
examples of these harmful outcomes would be:
1. Fever can cause a positive feedback within
homeostasis that pushes the body temperature
continually higher. If the temperature reaches 45
degrees centigrade (113 degrees Fahrenheit)
cellular proteins denature bringing metabolism to a
stop and death.
2. Chronic hypertension can favor the process of
atherosclerosis which causes the openings of blood
vessels to narrow. This, in turn, will intensify the
hypertension bring on more damage to the walls of
blood vessels.
