The document discusses feedback mechanisms in biology. It provides examples of negative feedback loops that help regulate important systems in the body like temperature, glucose levels, water regulation, and stress hormones. Negative feedback acts to oppose changes and maintain homeostasis. It also discusses positive feedback loops that enhance changes, like childbirth contractions or blood clotting, which help complete a process before being suppressed.

1. It does not have to do with food…
But, you have some in your body
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2. What is Feedback?
Feedback is the process
in which part of the
output of a system is
returned to its input in
order to regulate its
further output.

3. Negative Feedback
 Negative feedback occurs when the
output of a system acts to oppose
changes to the input of the system.
 A thermostat is an example of a negative
feedback system.

4. A thermostat is a device for regulating the temperature of a system so that
the system's temperature is maintained near a desired setpoint temperature.
Room temp is
below the
setpoint
Room temp is
above the
setpoint
Room temp
increases
Room temp
decreases
Set point
is reached
Set point
is reached

5. Negative Feedback in Biology
 Negative feedback also
regulates many systems in
organisms.
 The endocrine system is one
example.
 This diagram shows a
negative feedback loop for
stress hormones.
 Areas of negative feedback
are indicated with a minus
sign, (-).

6. Endocrine System
 The endocrine system is
composed of glands that
produces chemical
messengers called hormones.
 Hormones are produced in
one part of the body and
travel to target organs
through the bloodstream.

7. Endocrine system
 Glands of the endocrine
system include:
 Pituitary gland
 Thyroid Gland
 Parathyroid glands
 Thymus
 Adrenal glands
 Pancreas
 Ovary and Testis

8. Endocrine System
 The brain continuously sends signals
to the endocrine glands to secrete
and release hormones and the
glands, in turn, send feedback to the
nervous system.
 The hypothalamus in the brain
is the master switch that
sends signals to the pituitary
gland which can release up to eight
hormones into the bloodstream.
 The hormone travels to its target
organ and usually results in the
release of another hormone into the
bloodstream.

9. Endocrine System
 The hypothalamus then detects the rising hormone
levels from the target organ and decreases the
release of hormones from the pituitary which results
in a decrease in hormone release from the target
organ.
 The process of maintaining normal body function
through negative feedback mechanisms is called
homeostasis.

10. Glucose and Insulin
 Glucose intake occurs during
digestion of food that is needed
for energy expenditure to perform
routine physical activities.
 The pancreas is the key organ that
regulates the glucose levels in
body by secreting two hormones,
insulin and glucagon.
 The liver also helps to store the
excess glucose in form of glycogen
to be utilized later.
Pancreas
Liver

11. Glucose and Insulin Negative Feedback
Loop
Increases
Glucose
Levels
Boy eating cake
Stimulates β cells of
pancreas to secrete insulin
Insulin stimulates the
cells to take up glucose
from the blood.
Lowers Blood
Glucose levels
CYCLE 1
(-)

12. Low Blood Glucose
Levels
Stimulated Alpha Cells in
Pancreas
Glucagon is released
Glucagon stimulates liver cells to
release glucose into the blood
High blood glucose levels
and Cycle 1 continues
CYCLE 2
(-)

13. Glucose and Insulin Negative Feedback
Loop
 Two primary Hormones
The opposite actions of these two hormones, insulin and
glucagon, helps to maintain normal blood sugar levels in
the body hence maintain homeostasis of the body.
Insulin Glucagon
Lowers Blood Glucose
Levels
Raises Blood Glucose
Levels

14. Take a Break and Chat With Your
Neighbor!
 Turn to the person behind or in front of you and
discuss the following topics:
 What is a feedback and an example of a negative
AND positive system?
 What is the endocrine system and why is it
important?
 Define homeostasis and how normal body
function is maintained with feedback
mechanisms.

15. Kidneys and Water Regulation
 The kidneys play a key role in maintaining
water regulation.
Renal Cortex
Renal Medulla

16. Kidney and Water Regulation
 The nephron is the
most important
functional part of the
kidney.
 It filters nutrients like
salts and amino acids
in the Bowman’s
capsule into
ascending loop and
filters the urine.

17. Kidney and Water Regulation
Anti-Diuretic Hormone, ADH (also called vasopressin), is
secreted by the pituitary gland and acts on the nephron
to conserve water and regulate the tonicity of body fluids.
Anti-
Diuretic
Hormone
ADH acts on Nephron to
reabsorb water and decrease
blood osmolality (saltiness)

18. ADH regulated water conservation in
kidneys Excess water
in the blood
Stimulates osmoreceptors in
hypothalamus to send signals to
the pituitary gland
Pituitary glands secretes
low levels of ADH
Less ADH makes the tubules less
permeable and less water is reabsorbed
back into the bloodstream (urine is
dilute).
Less water in the
blood
ADH makes the tubules more permeable
and more water is reabsorbed back into the
bloodstream (urine is concentrated).
Stimulates osmoreceptors in
hypothalamus to send signals to
the pituitary gland
Pituitary glands secretes
high levels of ADH

19. ADH regulated water conservation in
kidneys
 Osmoregulators send negative feedback to the
hypothalamus about the concentration of water in the
bloodstream.
 The hypothalamus then stimulates the pituitary glands
to secrete high or low concentrations of anti-diuretic
hormone.
 ADH then makes the tubules more or less permeable
and hence, maintains water and electrolyte
homeostasis.

20. Temperature regulation of Body
 Animals that are capable of maintaining their bogy
temperature within a given range are called
homeotherms.
 Temperature is regulated by negative feedback
control.
 Thermoreceptors located in hypothalamus detect
temperature fluctuations in the body.

21. Temperature Regulation of the Body
 Increased temperature causes
vasodilatation (blood vessels near
the surface of the skin dilate).
 The large surface area allows heat
to be lost from the blood and
lowers the body temperature.
 Sweating also helps lower the temperature.
 Decreased temperature causes vasoconstriction (blood vessels
constrict) and minimal heat loss occurs which helps maintain
body temperature.
 Hair on the body provides insulation and helps maintain body
temperature.

22. Positive Feedback
 A positive feedback loop occurs when the output of a
system acts to enhance the changes to the input of the
system.
 One example of a biological positive feedback loop is
the onset of contractions in childbirth.
 When a contraction occurs, the hormone oxytocin
is released into the body, which stimulates further
contractions.
 This results in contractions increasing in amplitude
and frequency.

23. Positive Feedback
 Another example is blood clotting.
 The loop is initiated when injured tissue releases
signal chemicals that activate platelets in the
blood.
 An activated platelet releases chemicals to activate
more platelets, causing a rapid cascade and the
formation of a blood clot.
 Lactation involves positive feedback so that the more
the baby suckles, the more milk is produced.

24. Positive Feedback
 In most cases, once the purpose of the feedback loop is
completed, counter-signals are released that suppress or
break the loop.
 Childbirth contractions stop when the baby is out of
the mother's body.
 Chemicals break down the blood clot.
 Lactation stops when the baby no longer nurses.

25. Take a Break and Chat With Your
Neighbor!
 Turn to the person behind or in front of you and
discuss the following topics:
 What are the roles of the kidneys in the body?
 How do the kidneys compare or contrast to the
feedback systems in the endocrine system?
 How does the body regulate temperature?
 Define and give examples of a positive feedback
system in the body.