Homeostasis refers to the body's ability to maintain stable internal conditions such as temperature and blood sugar levels. It is regulated through feedback mechanisms - primarily negative feedback loops that work to reduce the effect of a stimulus and return the body to its set point. Key components of homeostasis include receptors that detect changes, a control center that receives this information and communicates messages, and effectors that respond to bring the condition back into the normal range. Examples provided include regulation of blood pressure and temperature through negative feedback as well as the positive feedback loop involved in blood clotting.

1. Anatomy & Physiology
Homeostasis
Ikramullah

2. Objectives
At the end of the lecture, students will able to
• Define the term “Homeostasis”.
• Discuss factors which effect Homeostasis.
• Define feedback mechanisms and its components.
• Discuss the role of feedback mechanisms in the maintenance of
homeostasis with example.

4. Homeostasis is the regulation and
maintenance of the internal
environment of the body

5. Homeostasis
• Homeostasis Conditions within the body must remain within a narrow
range – like your body temperature
• Homeostasis involves keeping the internal environment within set
ranges

6. Homeostasis
• A property of cells, tissues, and organisms that allows the maintenance and
regulation of the stability and constancy needed to function properly.
• Homeostasis refers to the body's need to reach and maintain a certain state of
equilibrium.
• The term was first coined by a physiologist named Walter Cannon in 1926.
• More specifically, homeostasis is the body's tendency to monitor and maintain
internal states, such as temperature and blood sugar, at fairly constant and stable
levels.

7. Homeostasis
• Homeostasis is a healthy state that is maintained by the constant adjustment
of biochemical and physiological pathways.
• An example of homeostasis is the maintenance of a constant blood pressure
in the human body through a series of fine adjustments in the normal range of
function of the hormonal, neuromuscular, and cardiovascular systems.
• These adjustments allow the maintenance of blood pressure needed for body
function despite environmental changes and changes in a person's activity
level and position.
• Other homeostatic mechanisms, for example, permit the maintenance of body
temperature within a narrow range.

8. How Is It Maintained?
• Your body has set points for a variety of states including temperature, weight,
sleep, thirst, and hunger. When the level is off (in either direction, too much or too
little), homeostasis will work to correct it. For example, to regulate temperature,
you will sweat when you get too hot or shiver when you get too cold.
• Another way to think of it is like the thermostat in your house. Once set at a certain
point, it works to keep the internal state at that level. When the temperature drops
in your house, your furnace will turn on and warm things up to the preset
temperature.

9. Conti………….
In the same way, if something is out of balance in your body, a physiological
reaction will kick in until the set point is once again reached. Here's how the
primary components of homeostasis work:
Stimulus: A stimulus from a change in the environment kicks something out of
balance in the body.
Receptor: The receptor reacts to the change by informing the control unit.
Control unit: The control unit then communicates the change needed to bring
the body back into balance.
Effector: The effector receives this information and acts on the change that is
needed.

10. Control systems help maintain
homeostasis.
 Sensors gather data
 Control center receives data,
sends messages
 Communication system
delivers messages to target
organs, tissues
 Targets respond to change
pore
sweat
glands
hair
follicle
muscle
goose
bump

11. Feedback mechanism
A feedback loop will work to decrease or increase the effect of the stimulus.
There are two type of feedback, positive and negative.
Positive feedback increase the effect of the stimulus while negative feedback
decrease the effect of the stimulus.
In homeostasis, negative feedback loops are most common, as the body is
typically attempting to decrease the effect of the stimulus to get the body back
to equilibrium.

12. Positive Feedback
• Positive feedback is a mechanism in which an output is enhanced in order to
maintain homeostasis.
• Positive feedback mechanisms are designed to accelerate or enhance the
output created by a stimulus that has already been activated.
• Positive feedback mechanisms are designed to push levels out of normal
ranges.

13. Positive Feedback
• This process can be beneficial but is rarely used because it may
become uncontrollable.
• A positive feedback example is blood platelet accumulation and
aggregation, which in turn causes blood clotting in response to an
injury of the blood vessels.

14. Negative Feedback
• Negative feedback mechanisms reduce output or activity to return an organ
or system to its normal range of functioning. Regulation of blood pressure is
an example of negative feedback.
• Blood vessels have sensors called baroreceptors that detect if blood pressure
is too high or too low and send a signal to the hypothalamus.
• The hypothalamus then sends a message to the heart, blood vessels, and
kidneys, which act as effectors in blood pressure regulation.

15. Negative Feedback
• If blood pressure is too high, the heart rate decreases as the blood vessels
increase in diameter ( vasodilation ), while the kidneys retain less water.
• These changes would cause the blood pressure to return to its normal range.
• The process reverses when blood pressure decreases, causing blood vessels
to constrict and the kidney to increase water retention.

16. Negative Feedback
• Temperature control is another negative feedback mechanism. Nerve cells relay
information about body temperature to the hypothalamus.
• The hypothalamus send signals several effectors to return the body temperature
to 37 degrees Celsius (the set point).
• The effectors may signal the sweat glands to cool the skin and stimulate
vasodilation so the body can give off more heat.

17. Negative Feedback
• If body temperature is below the set point, muscles shiver to generate heat
and the constriction of the blood vessels helps the body retain heat.
• This example is very complex because the hypothalamus can change the
body’s temperature set point, such as raising it during a fever to help fight
an infection.
• Both internal and external events can induce negative feedback
mechanisms.

18. Negative Feedback Loop Example:
Holding
breath,
CO2 levels
rise
Control system
forces exhale,
inhale
O2 / CO2 level
returns to normal

21. More Example of Positive and Negative
Feedback Mechanism
Maintenance of Life
• Negative feedback summary:
• Prevents sudden, severe changes in the body
• Corrects the set point
• Causes opposite of bodily disruption to occur, i.e. the ‘negative’
• Limits chaos in the body by creating stability
• Most common type of feedback loop
• Examples: body temperature, blood pressure & glucose regulation

22. Maintenance of Life
Receptors
Control center
(set point)
Effectors
(muscles or glands)
Response
(Change is corrected.)
Stimulus
(Change occurs
in internal
environment.)
(Change is compared
to the set point.)

24. Maintenance of Life
Positive feedback summary:
• Increases (accelerates) the actions of the body
• Produces more instability in the body
• Produces more chaos in the body
• There are only a few types necessary for our survival
• Positive feedback mechanisms are short-lived
• Controls only infrequent events that do not require continuous adjustments
• Considered to be the uncommon loop
• Examples: blood clotting and child birth

25. Positive feedback in child birth