Physiology is the science of life

1. Physiology of Homeostasis
Dr. Ramadan Saad
PHSL222 Principles of

2. Homeostas
is
Homeostasis homeo-,
the same) is the
existence and
maintenance of a
relatively constant
environment within the
body despite
fluctuations in either the
external environment or
the internal environment.

3. Homeostatic
Regulation
This process of adjustment (called
homeostatic regulation) involves:
1.a receptor (which receives information about a
change in the environment),
2.a control center (which receives and
processes information from the receptor),
and
3.an effector (which responds to signals from the
control center by either opposing or enhancing the
stimulus).
1. Receptor
2.Afferent Pathway
3.Integratingor control center

4. FEEDBACK MECHANISMS

5. Feedback
The signal sent by the effector is called feedback;
feedback can be either negative orpositive.
•Negative feedback:when the effector opposes the
stimulus (such as a dropping temperature) andreverses
the direction of change (causing the temperature to
rise). Example: Decrease in Blood Glucose and Bloodpressure.
•Positivefeedback:when the effector reinforces the
stimulus (such as uterine contractions duringchildbirth,
which trigger the release of the hormone oxytocin) and
amplifies the direction of change (causing even greater
contractions and further release of oxytocin). Example:
Blood clotting, protein digestion, a temperature of100.2F causes
further increase

6. Negative Feedback – Temp
Regulation
Responseto Heat Stress
1.Thermoreceptors in skin detect a rise in
body temperature
2.Nervous system in brain sends
messageto hypothalamus
3.Hypothalamus response:
Sweating:Sweat glands to initiate
sweating – evaporation of sweat cools
body
Vasodilation: Blood vessels to dilate – more
blood glows to skin, which has been cooled by
evaporation

7. Negative Feedback – Temp
Regulation
Effector
Effector
Regulator center

8. Negative Feedback – Temp
Regulation
1.Thermoreceptors in the skin senda
message to the hypothalamus
2.Hypothalamus response:
– Vasoconstriction:Constricts smooth muscle of
arterioles – blood flow is limited, heat loss from
skin is reduced
– Piloerection: Constricts smooth muscle around
hair follicles, causing hair to stand on end –
erect hair traps warm air next toskin
– shivering: Skeletal muscles to initiate
rhythmic contractions (10 – 20x per minute)

9. Negative Feedback – Temp
Regulation
Regulator center
Effector
Effector

10. Positive Feedback during
childbirth

11. Controlling Glucose
levels
Your cells also need an exact level of glucose in the blood.
Excess glucose gets turned into glycogen in the liver
This is regulated by 2 hormones (chemicals) from the
pancreas called:
Insulin
Glucagon

12. Negative Feedback Example:
Insulin in Blood Glucose Regulation

13. If there is too
much glucose in
the blood,
Insulin converts
some of it to
glycogen
Glycogen
Glucose in the blood

14. If there is not
enough glucose
in the blood,
Glucagon
converts some
glycogen into
glucose.
Glycogen
Glucose in the blood

15. The glucose in the
blood increases.
Glycogen
Glucose in the blood
But there is no
insulin to convert
it into glycogen.
Glucose
concentration rises
to dangerous
levels.
Diabetes

16. Which is an example of negative feedback?
1. Lowering of blood glucose after meal.
2. Blood clotting after injury
3. Lactation during nursing
4. Uterine contraction during nursing
The body’s thermostat is located in the ___.
1. Cerebral cortex
2. Hypothalamus
3. Spinal cord
4. Cerebellum

17. Carry Home
Message
1.Negative Feedback:
Example 1.Decrease in
blood glucose 2.Decrease in
blood pressure
2.Positive Feedback: Example
1.Clotting
2.Protein
digestion
3.A temperature of 100.2 0Fcauses further
increase