Homeostasis and feedback
The Human Body
An IRSC Live Virtual Lesson
By: Diana Lenartiene, Ed. S.
The biological definition of homeostasis is “the
tendency of an organism or cell to regulate its internal
environment and maintain equilibrium, usually by a
system of feedback controls, so as to stabilize health
and functioning”. Generally, the body is in homeostasis
when it’s needs are met and it’s functioning properly.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Every organ in the body contributes to homeostasis.
A complex set of chemical, thermal, and neural
factors interact in complex ways, both helping and
hindering the body while it works to maintain
homeostasis.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Homeostatic control
To maintain homeostasis, communication within the body is
essential. The image below is an example of how a homeostatic
control system works. Here is a brief explanation:
Stimulus- produces a change to a variable (the factor being
regulated).
Receptor- detects the change. The receptor monitors the
environment and responds to change (stimuli).
Input- information travels along the (afferent) pathway to the
control center. The control center determines the appropriate
response and course of action.
Output- information sent from the control center travels down the
(efferent) pathway to the effector.
Response- a response from the effector balances out the original
stimulus to maintain homeostasis.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Think of it as an extremely complex balancing act. Here’s a diagram
of the process.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Afferent pathways- carry nerve impulses into the central
nervous system. For instance, if you felt scorching heat
on your hand, the message would travel through
afferent pathways to your central nervous system.
Efferent pathways- carry nerve impulses away from the
central nervous system to effectors (muscles, glands).
The feeling of heat would travel through an afferent
pathway to the central nervous system. It would then
interact with the effector and travel down the efferent
pathway, eventually making the person remove their
hand from the scorching heat.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Negative feedback mechanisms
Almost all homeostatic control mechanisms are negative
feedback mechanisms. These mechanisms change the variable
back to its original state or “ideal value”.
A good example of a negative feedback mechanism is a home
thermostat (heating system). The thermostat contains the
receptor (thermometer) and control center. If the heating
system is set at 70 degrees Fahrenheit, the heat (effector) is
turned on if the temperature drops below 70 degrees
Fahrenheit. After the heater heats the house to 70 degrees
Fahrenheit, it shuts off effectively maintaining the ideal
temperature.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
http://www.opencurriculum.org/5385/homeostasis-and-regulation-inthe-human-body/
The control of blood sugar (glucose) by insulin is another good
example of a negative feedback mechanism. When blood
sugar rises, receptors in the body sense a change . In turn, the
control center (pancreas) secretes insulin into the blood
effectively lowering blood sugar levels. Once blood sugar
levels reach homeostasis, the pancreas stops releasing insulin.
These are just two examples of negative feedback
mechanisms within our body, there are 100’s, can you think of
a few more?
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Positive feedback mechanisms
A positive feedback mechanism is the exact opposite of a
negative feedback mechanism. With negative feedback, the
output reduces the original effect of the stimulus. In a positive
feedback system, the output enhances the original stimulus. A
good example of a positive feedback system is child birth.
During labor, a hormone called oxytocin is released that
intensifies and speeds up contractions. The increase in
contractions causes more oxytocin to be released and the cycle
goes on until the baby is born. The birth ends the release of
oxytocin and ends the positive feedback mechanism.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Another good example of a positive feedback mechanism is
blood clotting. Once a vessel is damaged, platelets start to cling
to the injured site and release chemicals that attract more
platelets. The platelets continue to pile up and release
chemicals until a clot is formed.
Just remember that positive feedback mechanisms enhance the
original stimulus and negative feedback mechanisms inhibit it.
http://anatomyandphysiologyi.com/homeostasis-positivenegative-feedbackmechanisms/
Negative Feedback
Positive Feedback
1.Resist change in the body
1. Reinforce change
and bring back the original state.For example when in the body that results in a positive out come. For
you are exposed to cold your body temperature
example when a pregnant mother is ready to
drops and your body make changes to bring it back deliver the bab, the hormone oxytocin levels shoots
to the body temperature. 2. In this feedback loop,
up causing stronger uterine contractions. 2. Values
the values remain with in a range. For example blood goes out of range
sugar is maintained at 100mg/ml. If blood sugar level 3. Very uncommon
goes up te control center pancreas steps in and
4. Positive feedback loop is also triggered by a
produce insulin hormone, which helps to pump sugar stimulus and
into cells.Once the sugar levels reach normal
pancreas stops secreting insulin.
3. Common in the body
4. This feedback loop is initiated by a stimulus that
disturbs the homeostasis of a body system.For e.g.
Eating sugar disrupts the glucose balance in the
blood and triggers the Negative feedback loop of
insulin.
http://biochemhelp.com/define-homeostasis-what-is-the-difference-between-negativeand-positive-feedback-systems.html
Table 1: Types of Homeostatic Regulation in the Body
Tissues, Organs and Organ
Systems Involved
Kidneys, urinary bladder,
Antidiuretic hormone (ADH), ureters, urethra (urinary
Osmoregulation (also known Excess water, salts, and urea
aldosterone, angiotensin II, system), pituitary gland
as excretions)
expelled from body
carbon dioxide
(endocrine system), lungs
(respiratory system)
Skeletal muscle (muscular
Sweating, shivering,
system), nerves (nervous
dilation/constriction of blood
system), blood vessels
vessels at skin surface,
(cardiovascular system), skin
Thermoregulation
Nerve Impulses
insulation by adipose tissue,
and adipose tissue
breakdown of adipose tissue
(integumentary system),
to produce heat
hypothalamus (endocrine
system)
Release of insulin and
glucagon into the blood in
response to rising and falling
blood glucose levels,
Pancreas (endocrine system),
respectively; increase in
liver (digestive system);
Insulin, glucagon, cortisol,
breathing rate in response to
adrenal glands (endocrine
Chemical Regulation
carbon dioxide, nerve
increases carbon dioxide
system) lungs (respiratory
(including glucoregulation)
impulses, erythropoietin
levels in the blood, and
system), brain (nervous
(EPO)
release of carbon dioxide
system), kidneys (urinary
into exhaled air from lungs,
system)
secretion of erythropoietin
by kidneys to stimulate
formation of red blood cells
Homeostatic Processes
Hormones and Other
Messengers
http://www.opencurriculum.org/5385/homeostasis-and-regulation-in-the-human-body/
• Homeostasis is from the Greek and means staying the same.
• Homeostasis has internal and external stimuli which effect it
and cause the body to give negative or positive feedback.
• Negative feedback is more common than positive feedback
• A feedback loop is the set of stimulus and response activities
related to a specific situation. We studied several examples.
• Prolonged exposure to negative feedback can cause disease
or death. This is why Homeostasis is so important to the
human body.
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Thank you for viewing this presentation.
Diana Lenartiene, IRSC ABE Instructor