The document discusses homeostasis and biological control systems. It defines homeostasis as the maintenance of relatively constant internal conditions, such as blood pressure and temperature, during unstressed conditions. Steady state refers to maintaining internal balance when the body is under stress, such as during exercise, where a variable may change but remain constant. Biological control systems use negative feedback to detect changes and activate responses to correct deviations and restore homeostasis. They have components like sensors, control centers, and effectors. Control systems with high feedback gain precisely maintain homeostasis. Examples describe systems regulating blood pressure and glucose. Failure of a component can cause disease. Exercise challenges homeostasis, but control systems can maintain steady state during most routine exercise.

1. ALINA JAMIL
LECTURER
HAYAT INSTITUTE OF REHABILITATION

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)

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

14. Components of a Biological Control System

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

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.

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