2. Homeostasis: dynamic constancy
Homeostasis term was coined by Walter Cannon in 1932 & defined as
Maintenance of a constant or unchanging internal environment
Steady state term _used by exercise physiologist ( to denote a steady
OR unchanging physiological variable )
Homeostasis & Steady state terms_ used interchangeably
Steady state does not mean that internal environment is completely
normal, but simply it is unchanging.
Homeostasis _ relatively constant internal environment during
unstressed conditions
Internal environment doesn’t remain absolutely constant
Most physiological variables vary around some ‘set’ value & thus
homeostasis represents a rather dynamic constancy
Example_ arterial blood pressure ( change in mean arterial B.P
during 8 min of rest)
3.
4. Homeostasis
When the body’s biological control systems maintain
physiological variables at manageable constant values at
rest, (when the body is not under any stress) it is
called homeostasis.
Blood pressure–Body temperature–Blood glucose levels
5. Steady State
It is a Balance between the demands placed on a body and the
physiological response to those demands
Maintenance of an internal environment by a biological control
system, where a physiological variable (e.g. body temperature)
remains relatively constant yet deviates from its normal value,
which occurs when the body is experiencing stress (e.g. exercise).
6. Body Core Temperature During
Exercise
Changes in body core temperature during
submaximal exercise
Body temperature reaches
a plateau (steady state)
7. To distinguishing between these two terms is the case of body temperature
during exercise.
Graph illustrates the changes in body core temperature during sixty minutes
of constant-load submaximal exercise in a thermoneutral environment
Core temperature reaches a new and steady level within forty minutes after
commencement of exercise.
This plateau of core temperature represents a steady state, since temperature is
constant; however, this constant temperature is above the normal resting body
temperature and thus does not represent a true homeostatic condition.
Therefore, the term homeostasis is generally reserved for describing normal
resting conditions, and the term steady state is often applied to exercise
8. In Summary
Homeostasis is defined as the maintenance of a constant
or unchanging “normal” internal environment during
unstressed conditions.
The term steady state is also defined as a constant
internal environment, but this does not necessarily
mean that the internal environment is at rest and
normal.
When the body is in a steady state, a balance has been
achieved between the demands placed on the body and
the body’s response to those demands.
9. Control Systems of the Body
The body has literally hundreds of different control
systems
Goal is to regulate some physiological variable at or near
constant value
Most intricate of these control systems reside inside the
cell itself
Intracellular control systems
Protein breakdown and synthesis
Energy production
Maintenance of stored nutrients
10. Control Systems of the Body
Organ systems work to help maintain homeostasis for
example
Pulmonary and circulatory systems work together to
Replenish oxygen and remove carbon dioxide
Cardiopulmonary system _ able to maintain normal
level of oxygen & carbon dioxide, even during the
period of strenuous exercise_ end result of good
control system.
11. Nature of the control systems
Non-Biological Control System
if room
Temperature
below 200 C
Thermostat set
at 200 C
Heating System
Room
temperature
Returns to 200 C
Room Temperature
Signals thermostat
To turn off heat
12. Non-Biological Control System
A thermostat-controlled
heating/cooling system
An increase in temperature
above the set point signals
the air conditioner to turn on.
A decrease in room
temperature below the set
point results in turning on the
furnace.
13. Biological Control Systems
Defined as a series of interconnected components
that serve to maintain a physical or chemical
parameter at or near constant.
General components of a biological control system are:
signal to begin the operation of a control system is the
stimulus ( detectable change in the environment)
Stimulus excites a receptor
Receptor Capable of detecting changes
Integrating center
Assesses input and initiates response
Effector
Corrects changes to internal environment
15. Negative Feedback
Most control systems of the body operate via negative feedback
Response reverses the initial disturbance in homeostasis
This feedback is termed negative is that the response of
the control system is negative (opposite) to the
stimulus.
An example of negative feedback can be seen in the respiratory
system's regulation of the CO2 concentration in extracellular fluid.
Example:
Increase in extracellular CO2 triggers a receptor
Sends information to respiratory control center (integrating
center)
Respiratory muscles (effectors) are activated to increase
breathing
CO2 concentration returns to normal, thus establishing
homeostasis
16. Positive Feedback
Response increases the original stimulus
Feedback is termed positive because the response is in
the same direction as the stimulus.
Example:
Initiation of childbirth stimulates receptors in cervix
Sends message to brain
Release of oxytocin from pituitary gland
Oxytocin promotes increased uterine contractions
17. Gain of a control system
The precision with which a control system maintains
homeostasis is called the gain of the system
OR
Degree to which a control system maintains homeostasis
Gain can be thought of as the “capability” of the control
system
System with large gain is more capable of maintaining
homeostasis than system with low gain
The gain of negative feedback control system is defined as
the ratio of the amount of correction needed to
maintain homeostasis to the amount of the
abnormality that exists after correction by the system
18. Gain = amount of correction needed/amount of
abnormality that exist after correction
Person leaves a comfortable room( 22 c) & enters in
cold room( 0c) for 20 mins
Upon entering room, persons body temp is 37 c, but
after 20 min it has decreased to 36 c
Control system automatically decrease skin blood flow
to minimize heat loss & initiate shivering to increase
heat production
These changes prevent body temp from decreasing
drastically.
Feedback gain of this system can be calculated as:
Feedback gain=22c-0c/37c-36= 22/1=22
19. High gain of 22 means that for each degree change in
body temp that occurred in cold room, there would
have been a 22 times greater change in temperature
most important control systems of the body have large
gains.
For example, control systems that regulate body
temperature, breathing (i.e., pulmonary system), and
delivery of blood (i.e., cardiovascular system) all have
large gains
these control systems all deal with life-and-death
issues.
20. In Summary
A biological control system is composed of a sensor, a
control center, and an effectors.
Most control systems act by way of negative feedback.
The degree to which a control system maintains
homeostasis is termed the gain of the system.
A control system with a large gain is more capable of
maintaining homeostasis than a system with a low
gain.
21. Examples of Homeostatic Control
Regulation of arterial blood pressure:
Baroreceptor system is responsible for the
regulation of blood pressure
Baroreceptors ( pressure sensitive receptors) located in
carotid arteries & the arch of aorta.
Arterial b.p increases- stimulated-nerve impulses(
cardiovascular control center in medulla)
Decreases the impulses transmitted to the heart,
lowers the amount of blood pumped by the heart
Pressure returns to normal
22. Examples of Homeostatic Control
Regulation of blood glucose
Requires the hormone insulin
Diabetes
Failure of blood glucose control system
23. Example: Regulation of Blood
Glucose
The pancreas acts as
both the sensor and
effector organ
24. Stress Proteins Assist in the Regulation of Cellular
Homeostasis:
The cellular stress response is a biological control
system in cells that battles homeostatic
disturbances by manufacturing proteins
designed to defend against stress
proteins play critical roles in normal cell function by
serving as intracellular transporters or as enzymes that
catalyze chemical reactions.
Damage to cellular proteins by stress (e.g., high
temperature) can result in a disturbance in
homeostasis. To combat this type of disruption in
homeostasis, cells respond by rapidly manufacturing
protective proteins called stress proteins
25.
26. Failure of a Biological Control
System Results in Disease
Failure of any component of a control system results
in a disturbance of homeostasis
Example:
Type 1 diabetes
Damage to beta cells in pancreas
Insulin is no longer released into blood
Hyperglycemia results
This represents failure of “effector”
27. Exercise: a test of homeostatic
control
Exercise disrupts homeostatic variables i.e. during heavy exercise sk.
Muscle produces large amount of lactic acid (increases acidity),
increase muscle oxygen requirements, large amount of CO2 produced ,
large amount of heating that must be removed to prevent over heating
Control systems are capable of maintaining steady state during
submaximal exercise in a cool environment
Intense exercise or prolonged exercise in a hot/humid environment
may exceed the ability to maintain steady state.
Severe disturbances In homeostasis results in fatigue and cessation
of exercise
28. In Summary
Exercise represents a challenge to the body’s control
systems to maintain homeostasis.
In general, the body’s control systems are capable of
maintaining a steady state during most types of
exercise in a cool environment.
However, intense exercise or prolonged work in a
environment (i.e., high temperature/ humidity) may
exceed the ability of a control system to maintain
steady state, and severe disturbances of homeostasis
may occur.
