Topic 12: The Human Body,
Homeostasis, & Feedback
Mechanisms
The Human Body
Human require many systems for
digestion, respiration, reproduction,
circulation, excretion, movement,
coordination, & immunity
The components of the human body,
from organ systems to cell organelles,
interact to maintain homeostasis.
What is Homeostasis?
The maintenance of a constant
environment in the body.
Achieved by many different internal
controls mechanisms that detect
deviations and make corrective actions.
If there is a disruption in any human body
system there may be a corresponding
disruption in homeostasis
What is Homeostasis?
Body cells work best if they have the correct
– Temperature
– Water levels
– Glucose concentration
Your body has mechanisms to keep the cells
in a constant environment OR Dynamic
Equilibrium
Homeostasis
In order to maintain homeostasis the body
uses feedback loops. There are 2 types
of feedback loops:
– Negative
– Positive
Negative Feedback
It is a process by which a receptor, an
integrator and an effector detects processes
and responds to a change in a body constant
so that a reverse affect takes place.
Negative feedback is when the response is
opposite to the stimulus.
This allows the body to stay constant
(maintain homeostasis)
Negative Feedback
A good example of negative feedback is the
cruise control in my car.
A good thing to use
if you have a “heavy
foot!!”
The cruise control has a sensor that senses the
speed of the car as well as a control mechanism
that processes the information from the sensor. It
then adjusts the speed of the car by manipulating
the accelerator.
Okay but where is the negative part?
Negative Feedback Continued
If I go downhill the car naturally
speeds up a bit. The sensor senses this
and the controller decreases the speed
by easing up on the accelerator.
Can you see that the response (slowing
down) is opposite to the stimulus
(speeding up)?
Negative Feedback Continued
Likewise as the car goes uphill and slows
down a bit. The cruise control works the
accelerator to increase the speed.
Again the response (speeding up) is
opposite of the stimulus (slowing down).
This is negative feedback in action.
Examples of Homeostasis & Negative
Feedback Mechanisms
1.
Temperature Regulation
2.
Regulation of Blood Sugar Levels
3.
pH Balance
4.
……and remember the stomates and
guard cells in plants
Negative Feed Back: Human Body Temperature Regulation
Humans maintain a relatively constant body
temperature of about 37° C.
•when we "heat up" we sweat if possible
•the evaporation of this perspiration returns
the body to its original temperature
Receptor Proteins
•Receptor Proteins are the 1st part of a feedback loop,
and are found in every cell, in every organ & tissue.
•Send nerve impulses to brain as a result of
environmental stimulants.
•For example: receptor proteins on skin cells detect
changes in temperature and send that information to the
brain.
•If nerve or hormone signal are blocked, cellular
communication is disrupted and homeostasis is affected.
Outside Cell
Receptor
Protein
Inside Cell
Cell
Membrane
Integrator (The Brain)
•2nd part of negative
feedback loop
•Sends messages to glands,
muscles and/or organs
•The brain receives
information from the
receptor proteins and
sends a message to either
the sweat glands or the
muscle cells.
Effector (part of the body)
•3rd part of negative
feedback loop.
•Receptor proteins
receive info from brain
causing a change in
internal conditions.
•Sweat glands enable the
body to cool off when
they produce sweat and
muscle cells enable the
body to warm up when
they contract (shivering).
Hair follicle
1 - Sweat gland
2 - Sebaceous gland
3- Muscle
3
RECEPTOR PROTEINS
( ON CELLS)
EFFECTORS
(PARTS OF BODY)
RESPONSE=SWEAT
Heat
Gained
Heat
Lost
INTEGRATOR
(BRAIN)
EFFECTORS
(PARTS OF BODY)
RESPONSE =
SHIVERING
Negative Feedback Loop:
Home heating system
Thermostat is set at a desired temp.
Furnace turns on and heats the house to
desired temp
When desired temp is reached the furnace
turns off.
The house cools & temp drops below the
desired temp. the furnace turns on & the
house warms back up to desired temp.
Negative Feedback
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
Increase in Blood Glucose
Level
After eating blood glucose
level increases
Brain sends message to
pancreas to release insulin
into blood
Insulin allows body cells to
absorb glucose
Insulin also stimulates the
liver to convert some
glucose into glycogen ( a
form of stored energy)
The result…..blood glucose
level decreases &
homeostasis occurs.
QuickTime™ and a
decompressor
are needed to see this picture.
Glycogen
If there is too
much glucose in
the blood,
Insulin converts
some of it to
glycogen
Glucose in the blood
Diabetes
Some people do not produce enough insulin.
When they eat food, the glucose levels in
their blood cannot be reduced.
This condition is known as Type 1
DIABETES.
Diabetics have to inject insulin into their
blood, continually monitor their blood glucose
levels, and be careful of their diet.
Diabetes can lead to other health conditions
including glaucoma & poor circulation.
Glucose
Concentration
Glucose levels rise
after a meal.
Insulin is produced
and glucose levels
fall to normal
again.
Normal
Meal eaten
Time
Glucose
Concentration
Glucose levels rise
after a meal.
Diabetic
Insulin is not
produced so
glucose levels stay
high
Meal eaten
Time
Negative Feedback:
Decrease in Blood Glucose Level
•After not eating for a while blood glucose level
decreases.
•Brain sends a message to the pancreas to release
glucagon ( a type of protein) into the blood
•Glucagon stimulates the liver to convert glycogen
(stored energy) into glucose
•Glucose levels in the blood increases & the body
returns to homeostasis
Glycogen
If there is not
enough glucose
in the blood,
Glucagon
converts some
glycogen into
glucose.
Glucose in the blood
Body Systems Involved in
Blood Glucose Regulation
• Endocrine system: produces
insulin and glucagon
(hormones/proteins)
•Circulatory System: transports
hormones (insulin & glucagon),
glucose & glycogen to cells in the
body.
•Nervous System: stimulates a
response by sending and receiving
messages to & from cells….as a
result glucose levels increase or
decrease.
QuickTime™ and a
decompressor
are needed to see this picture.
Acids/
Bases/pH
Scale
pH Scale:
Indicates the
concentration
of H+ ions in
solution
pH levels
must be
maintained
Especially
for digestion
to work
properly
Acids
pH of less than 7 (Example: HCl)
Bases

pH of greater than 7 (Example: Bleach,
Ammonia
Buffers
Weak acids or bases that can react with strong acids or
bases to prevent sharp changes in pH.
These are important for maintaining a constant internal
environment…..homeostasis (between 6.5 and 7.5 for
most cells)
Think of treatments used for stomach aches
For digestive enzymes to work properly, pH balance
must be maintained
To test for acid & bases: Litmus paper
base = blue
acid = red
Remember…Homeostasis in Plants
Negative Feedback Mechanism
Maintenance of Water
•plants need to regulate water loss and
carbon dioxide intake for
photosynthesis and other life activities
•when plants do not keep enough water
in their cells, they wilt and die
stomate: a microscopic hole in a plant leaf which allows gases
to enter and leave and water vapor to leave as well. Stomata is
the plural of stomate.
guard cells: open and close the stomate.
•the ability of the guard cell to close during periods of limited
water availability for the plant allows the plant to maintain
water homeostasis
Positive Feedback Mechanisms
Positive feedback is where the response
is the same as the stimulus.
In positive feedback the response can be
magnified.
Positive Feedback Mechanisms
A good example of positive feedback is the
feedback you hear from sound systems in
concerts.
In this example the stimulus (sound going into
microphone) is processed to produce a
magnified response (sound coming out of the
speakers).
Sometimes the microphone picks up sound from
the speakers and continues to magnify it until it is
out of control (the feedback that hurts your
ears).
Example in Humans:
Oxytocin & Child Labor
Positive Feedback in the Human Body
The release of oxytocin to intensify the
contractions that take place during childbirth
.[
In positive
feedback the
response can
be magnified.
Name 2 systems that work
together.
Circulatory – respiratory
Skeletal – muscular
Digestive – circulatory
Nervous – muscular
Integumentary – circulatory
Endocrine – circulatory
Excretory - circulatory
How do they work together? ……. You will
investigate through your project &
presentation!!