Ch. 29.6 Feedback

1. Fundamentals
of Animal Function:
Homeostasis and Feedback
29.6

2. Chapter 29 Fundamentals of Animal Function
Key Concepts
29.6 Animal Function Requires Control Mechanisms

3. 29.6
Homeostasis and Feedback

4. Concept 29.3 Metabolic Rates Are Affected by Homeostasis and
by Regulation and Conformity
Homeostasis refers to stability of the internal
environment and the mechanisms that maintain it.

5. Concept 29.6 Animal Function Requires Control Mechanisms
Four essential elements of a control system:
1. Controlled variable—the characteristic that is being
controlled, such as body temperature
2. Sensors detect current level or state
3. Effectors—tissues or organs that can change the level of
the controlled variable; for example, shivering muscles
4. Control mechanism that uses information from sensors
to determine which effectors to activate to modify the
controlled variable
For body temperature, the control is a group of nerve cells
near the hypothalamus in the brain.

6. Concept 29.6 Animal Function Requires Control Mechanisms
Negative-feedback system: control mechanism that
activates effectors to reduce or negate differences
that exist between the controlled variable and the
set point
Negative feedback is a stabilizing influence and is
often involved in maintaining homeostasis.
Most feedback systems are negative.

7. Figure 29.16 Negative Feedback: A Systems Diagram of the Temperature Control System of a
Mammal

8. Negative Feedback Loop Example:Negative Feedback Loop Example:
HoldingHolding
breath,breath,
COCO22 levelslevels
riserise
Control systemControl system
forces exhale,forces exhale,
inhaleinhale
OO22 // COCO22 levellevel
returns to normalreturns to normal

9. Figure 30.16: Insulin and Blood Sugar

10. Figure 30.14: Coordination of Digestion

11. Concept 29.6 Animal Function Requires Control Mechanisms
Positive feedback: deviations of a
controlled variable from its existing
level are increased or amplified
Positive feedback destabilizes a
system.
Example: Mammalian birth process.
Uterine contractions are stimulated
by the hormone oxytocin.
Increased uterine contraction
stimulates to hypothalamus to
secrete more oxytocin.

12. Figure 29.17 Positive Feedback: The Development of the Force Required for Birth to Occur in
Mammals

13. Positive Feedback Example:Positive Feedback Example:
Torn blood vessel stimulates release ofTorn blood vessel stimulates release of
clotting factorsclotting factors
–growth hormones stimulate cellgrowth hormones stimulate cell
divisiondivision
platelets
fibrin
white blood cell
red blood cell
blood vessel
clot

14. Concept 29.6 Animal Function Requires Control Mechanisms
Biological clocks:
self-contained,
metabolic
mechanisms of
keeping track of time.
Small mammals
alternate running and
not running on a
wheel on a 24-hr
cycle, even if they are
kept in constant
darkness.

15. Figure 29.18 Control of Activity by a Circadian Biological Clock

16. Figure 29.18 Control of Activity by a Circadian Biological Clock
1. Describe the shift in the free-running time in the mouse
in the dark.
2. Scientists have conducted studies of humans living in
caves who did not receive any external cues about time
of day for several months. Using your knowledge of the
mice study, predict how a human’s circadian biological
clock might be affected.

17. Concept 29.6 Animal Function Requires Control Mechanisms
If animals are deprived of all external cues, the clock
“drifts” or runs fast or slow.
In the natural world, biological clocks are reset each
day, such as by the timing of sunrise and sunset.
This resetting is called entrainment.
Circadian clocks have a cycle of about 24 hours.
There are also circannual clocks and circatidal clocks.

18. Concept 29.6 Animal Function Requires Control Mechanisms
Circadian clocks are thought to be universal in all
animals.
In mammals, the master clock consists of nerve
cells in parts of the brain called the
suprachiasmatic nuclei.
The clocks tell animals when to be active and when
to rest, controls hibernation and reproductive
rhythms.