about the internal environment and external environment

1. Homeostasis
DR.P.HAMAMBULU

2. Homeostasis
• A condition in which the internal
environment of the body remains
relatively constant despite changes in
the external environment. Examples
would be the maintenance of body
temperature and levels of glucose in
the blood

3. Homeostatic mechanisms
• Homeostasis is achieved through negative
or positive feedback mechanism.
• Negative feedback: Includes most
homeostatic control mechanisms. Shuts
off the original stimulus, or reduces its
intensity. Works like a household
thermostat. Examples iclude control of
blood pressure and temperature
regulation.

4. Homeostatic mechanisms
• Positive feedback: Increases the original
stimulus to push the variable farther e.g. in
blood clotting and during the birth of a
baby
• Homeostatic mechanisms are designed to
reestablish homeostasis when there is an
imbalance.

5. The Home Heating System
1. When the temperature of a room decreases below a set point, the
thermostat electrically starts the furnace.
2. As the temperature of the room rises to the set point, the thermostat
shuts down the furnace.
3. As the room cools, step one is repeated.
There are three components to this system:
1. The Sensor which detects the stress.
2. The Control Center which receives information from the sensor and
sends a message to the Effector.
3. The Effector which receives the message from the control center
and produces the response which reestablishes homeostasis.

6. There are three components to a homeostatic system:
1. The Sensor which detects the stress.
2. The Control Center which receives information from the sensor
and sends a message to adjust the stress.
3. The Effector which receives the message from the control
center and produces the response which reestablishes
homeostasis
It should be noticed that
1. the heat produced by the furnace shuts the furnace down
through the thermostat.
2. the original stress is reduced, i.e., the room warms up.
Homeostatic mechanisms that show these two
characteristics are operating by negative feedback

7. Hyperthermia Heat receptors
in the skin
Hypothalamus
Stress
Sensors Control Center
Increased
activity of
sweat glands
Increased blood
flow to the skin
Effectors
Perspiration(swea
t) evaporates
cooling the skin
Effect
Stress is reduced
shutting down
mechanism
Homeostatic Regulation of Body Temperature through
Negative Feedback

8. Homeostasis Using a Neural
Pathway
Control center
Many homeostatic
mechanisms use a
nerve pathway in which
to produce their effects.
These pathways
involve an afferent path
which brings sensory
messages into the
brain and an efferent
path which carries
outgoing nerve
messages to effectors.

9. Hyperglycemia Pancreas-beta cells
Sensor and Control center
Insulin is released
into blood
Liver and Muscle cells
take up glucose from
the blood
Effectors
Blood glucose
is reduced
Stress is reduced
shutting down
mechanism
Stress
Homeostatic Regulation of Blood Sugar through
Negative Feedback

10. Negative Feedback Via a Hormonal Pathway
Regulation of Blood Sugar
Hormones play an important role in many homeostatic pathways.
Hormones are produced by endocrine glands. They enter the
blood after being produced and travel throughout the body.
However, hormones have their effect on specific target tissues.

11. Positive Feedback Mechanisms
Homeostatic systems utilizing positive feedback exhibit two primary
characteristics:
1. Time limitation – Processes in the body that must be completed within a
constrained time frame are usually modified by positive feedback.
2. Intensification of stress – During a positive feedback process, the initial
imbalance or stress is intensified rather than reduced as it is in negative
feedback.
Typical Positive Feedback Process
Stress Sensor Control Center
EffectorIntensifies

12. Homeostatic Regulation of Child Birth through
Positive Feedback
Pressure of Fetus on
the Uterine Wall
Nerve endings in the uterine
wall carry afferent messages
to the Hypothalamus
Production and Release
of Oxytocin into the
Blood
Increasing strength of
uterine contractions
Intensifies
The birth of the child will bring this process to a close.

13. Positive feedback “mini-loops” are built into pathway to speed up
production of chemicals needed to form the clot. Entire sequence of
clotting is a negative feedback pathway:
Feedback in Coagulation

14. Harmful Effects of Positive Feedback
Positive feedback can be harmful. Two specific
examples of these harmful outcomes would be:
1. Fever can cause a positive feedback within
homeostasis that pushes the body temperature
continually higher. If the temperature reaches 45
degrees centigrade cellular proteins denature
bringing metabolism to a stop and death.
2. Chronic hypertension can favor the process of
atherosclerosis which causes the openings of blood
vessels to narrow. This, in turn, will intensify the
hypertension bring on more damage to the walls of
blood vessels.

15. END!