The document discusses homeostasis and how the body maintains internal balance. It defines homeostasis as the stable internal environment of the body. It describes how homeostasis is achieved through negative feedback loops. Negative feedback loops work to reduce any deviations from the normal set point. For example, if body temperature rises, the body engages mechanisms like sweating to cool down and return to the normal temperature. The document also mentions positive feedback loops help amplify necessary responses, like increased milk production when a baby suckles. Overall, the body uses feedback mechanisms and interactions between organ systems to constantly monitor and adjust internal conditions to maintain homeostasis.

1. Homeostasis

2. All metabolic processes have one
main goal: achieving balance and
comfort in your body.
Homeostasis = the state of a
stable, balanced, internal
environment.
Root words! Homeo? Stasis?
Metabolism

3. Homeostasis
Dynamic process of self-regulating controls
which create a stable internal environment
External conditions are always changing
To survive, internal conditions must remain
relatively stable…How???

4. Homeostasis
Maintaining a stable
internal environment
Organ systems
function to maintain
homeostasis
Examples?

5. Homeostasis
1. Body has a set point (normal, balanced)
2. Receptors in the body detect deviations
away from set point
3. Brain interprets information
4. Triggers a set of events (using effectors) to
bring the situation back to normal

6. Homeostasis
• Maintenance of a stable internal
environment = a dynamic state of
equilibrium
• Homeostasis must be maintained for
normal body functioning and to sustain
life
• Homeostatic imbalance – a disturbance
in homeostasis resulting in disease

7. The body constantly checks
itself to make sure it stays in
homeostasis.
If a system is off-balance or
unstable, the body begins the
necessary metabolic
processes to fix it and restore
homeostatic balance.
How does the body maintain
homeostasis?

8. Maintaining Homeostasis
• The body communicates through neural
and hormonal control systems
• Receptor
• Responds to changes in the environment
(stimuli)
• Sends information to control center

9. Maintaining Homeostasis
• Control center
• Determines set point
• Analyzes information
• Determines appropriate response
• Effector
• Provides a means for response to the
stimulus

11. One way the body checks itself is using
feedback loops:
Positive feedback loops
&
Negative feedback loops
How does the body maintain
homeostasis?

12. Negative Feedback Loops
Negative feedback loops reduce or decrease the
occurrence of events that the body needs less of.
Rely on:
Sensors = detect changes in the body that
deviated from homeostasis and notify the brain
Effectors = respond to the changes to regain
homeostasis

13. Negative Feedback Loops
Example:
• Body gets too hot…exceeds 37°C
(98.6°F)
• Sensors (like nerve endings in
skin) send signal to brain
• Brain stimulates sweat glands
• Body cools to normal, comfortable
temperature
Negative feedback loops reduce or decrease the
occurrence of events that the body needs less of.
The loop stops once homeostasis is reached.

14. Feedback Mechanisms
• Negative feedback
• Includes most homeostatic control
mechanisms
• Shuts off the original stimulus, or reduces
its intensity
• Works like a household
thermostat

16. Homeostasis – Negative Feedback
NEGATIVE FEEDBACK – Correction occurs
opposite direction of stimulus
Examples:
Body temp rises; cooling mechanisms activated
Body temp drops; heating mechanisms activated
Other examples?
Blood sugar levels, blood oxygen levels

17. Blood Sugar Regulation

18. Feedback Mechanisms
• Positive feedback
• Increases the original stimulus to push the
variable farther
• In the body this only occurs in blood clotting
and birth of a baby

20. Positive Feedback Loops
Example:
• A baby suckles on its mother’s nipple
• This action stimulates a nerve response
into mom’s spinal cord and up to her
brain
• Brain tells her body to produce more milk
Positive feedback loops amplify or increase the
occurrence of events that the body needs more of.
The loop continues until one of the steps is removed or stopped.

21. Homeostasis – Positive Feedback
POSITIVE FEEDBACK - Stimulus amplifies
response in the same direction
Why?

22. Homeostasis – Positive Feedback
Examples:
Chemicals present in a blood clot lead to more
clotting
A baby drinking mother’s milk causes more milk
production
Pressure in the uterus during childbirth leads to
stronger contractions
Positive Feedback responses are typically
short-term… why?

23. Homeostasis
VITAL SIGNS
A measure of homeostasis
Indicate that someone is alive
What is measured in a test of vital signs?

24. Vital Signs
Monitored to determine level of health:
Vital Sign What is it? Normal
Body Temp 97o-100oF
Blood Pressure 100/60 - 140/90
Heart Rate 60-100 beats/min
Resp Rate 12-20 breaths/min
Pupils Dilate and contract
Blood O2 level >90%
Reflexes Responsive

25. 1-6 Homeostasis – Keeping our
organ systems in balance
• Homeostasis: the ability of an organism to harness
mechanisms for the preservation (maintenance) of an
almost constant internal state in the face of perturbations
• Homeostasis first put forth by Claude Bernard and later
championed by Walter Cannon
• Systems respond to external and internal changes to
function within a
normal range (body temperature, fluid balance, etc.)
• Both passive and active mechanisms involved
© 2012 Pearson Education, Inc.

26. 1-Homeostasis
• Mechanisms of Regulation
• Autoregulation (intrinsic)
• Automatic response in a cell, tissue, or organ to some
environmental change (e.g., cells release chemicals in response
to decline in O2 during exercise that increase blood vessel
dilation and thus blood flow to active tissues)
• Extrinsic regulation
• Simultaneous control of several systems by nervous or
endocrine input (e.g., nervous system control of heart rate and
central and peripheral blood flow to active tissues in low O2)
© 2012 Pearson Education, Inc.

27. Figure 1-2 The Control of
Room Temperature
Normal
condition
disturbed
Information
affects
RECEPTOR
Thermometer
STIMULUS:
Room temperature
rises
HOMEOSTASIS
Normal room
temperature
RESPONSE:
Room temperature
drops
CONTROL CENTER
(Thermostat)
Normal
condition
restored
EFFECTOR
Air conditioner
turns on
Sends
commands
to
20° 30° 40°
In response to input from a receptor (a thermometer), a thermostat
(the control center) triggers an effector response (either an air condi-
tioner or a heater) that restores normal temperature. In this case,
when room temperature rises above the set point, the thermostat
turns on the air conditioner, and the temperature returns to normal.
Air Air
conditioner conditioner
turns on turns off
Time
With this regulatory system, room
temperature fluctuates around the
set point.
Room
temperature
(°C)
22
Normal
range
• Required Parts for Control:
• Receptor – Receives stimulus
• Control center - processes
signal & sends instructions
• Effector – Carries out instructions
© 2012 Pearson Education, Inc.

28. Figure 1-3 Negative Feedback in the Control of Body Temperature
Normal
temperature
disturbed
Information
affects
RECEPTORS
Temperature
sensors in skin
and
hypothalamus
STIMULUS:
Body temperature
rises
HOMEOSTASIS
Normal body
temperature
RESPONSE:
Increased heat loss,
body temperature
drops
CONTROL
CENTER
Normal
temperature
restored
EFFECTORS
• Sweat glands
in skin increase
secretion
• Blood vessels
in skin dilate
Sends
commands
to
Events in the regulation of body temperature, which are
comparable to those shown in Figure 1-2. A control center
in the brain (the hypothalamus) functions as a thermostat
with a set point of 37°C. If body temperature exceeds
37.2°C, heat loss is increased through enhanced blood flow
to the skin and increased sweating.
Vessels
dilate,
sweating
increases
Vessels
constrict,
sweating
decreases
Time
The thermoregulatory center keeps
body temperature fluctuating
within an acceptable range, usually
between 36.7 and 37.2°C.
Body
temperature
(°C)
Normal
range
37.2
37
36.7
Thermoregulatory
center in brain
© 2012 Pearson Education, Inc.

29. 1-7 Negative and Positive
Feedback
• The Role of Negative Feedback
• The response of the effector negates the stimulus or disturbance
(i.e., inverts the signal)
• Body is brought back into homeostasis
• Normal range is achieved
• The Role of Positive Feedback
• The response of the effector increases and amplifies the stimulus
or disturbance (i.e., in the same direction as the original signal)
• Body is moved away from current “set point”
• Normal range is lost
• Used to speed up certain processes (e.g., blood clotting, child birth)
© 2012 Pearson Education, Inc.

30. Figure 1-4 Positive Feedback: Blood Clotting
Clotting
accelerates
Positive
feedback
loop
Blood clot
Chemicals
This escalating process
is a positive feedback
loop that ends with the
formation of a blood clot,
which patches the vessel
wall and stops the bleeding.
As clotting continues,
each step releases
chemicals that further
accelerate the process.
The chemicals start chain
reactions in which cells,
cell fragments, and
soluble proteins in the
blood begin to form a clot.
Damage to cells in the
blood vessel wall releases
chemicals that begin the
process of blood clotting.
Chemicals
© 2012 Pearson Education, Inc.

31. 1-7 Negative and Positive
Feedback
• Systems Integration
• Systems work together to maintain homeostasis
• Homeostasis is a state of equilibrium
• Opposing forces are in balance
• Dynamic equilibrium — continual adaptation
• Physiological systems work to restore balance
• Failure results in disease or death
© 2012 Pearson Education, Inc.

32. Table 1-1 The Roles of Organ Systems in Homeostatic Regulation
© 2012 Pearson Education, Inc.