Negative feedback loops

Negative feedback loop: Homeostasis

1. Physiological homeostasis:
Negative FEEDBack
DR SUTAPADATTA, WBES
ASSISTANT PROFESSOR OF ZOOLOGY
BETHUNE COLLEGE
KOLKATA, WEST BENGAL
INDIA
1
Part 2

2. Homeostasis
The dynamic physiological processes that
maintain a balance (set point)in the internal
variables upon stimulationfrom any sources
for proper functioning of the body by
hormonal or neuronal or both coordination.
This is known as homeostasis.
2

3. Feedback loop
Feedback loopis a system consisting of
a receptor (sensor)
control center (integrator or comparator)
Effector/s
methods of communication.
used to control the level of a variable
in the loop output influences input
feedback loops maintain body homeostasis
3
Input/
Stimulus
Receptor/
Sensor
Effector
Control center
(Hypothalamus )
compares against
set point
Variable
Function
Other
information
Information
flow
Information
flow
Feedback
loop
Afferent
pathway
Efferent
pathway
Feedback
(make
adjustments to
the variable)
(sense
changes in
variable)

4. Feedback loops:
Variables(e.g. temperature) are
parameters that are controlled or affected
by the feedback system.
Receptors (sensors) detect changes in the
variable.
Control centers (integrators) compare the
variable w.r.ta set point and signal the
effectors to elicit a response.
Effectorsexecute the necessary changes
to adjust the variable. There may be more
than one effector.
Methods of communication occurs through
nerves or hormones, but in some cases
receptors and control centers are the
same structures, so that there is no need for
these signaling modes in that part of the
loop.
4
Stimulus
Receptor
Control
center
Effector

5. •Negative feedback loops, a change in a given
direction causes change in the opposite direction.
•Effectors OPPOSE the change
•Variable is pushed BACKtoward the set-point value
•GOAL:stabilize the system, counteract the stimulus
•Ex: thermoregulation, blood sugar
Variable
Counter
response
Homeostasis
Back to
Homeostasis
Unstable
negative Feedback :
5

6. 6
summary:
•FEEDBACK: what happens affects what happens
next
•NEGATIVE FEEDBACK:
The more you have the less you get
Stabilizes a system
Set point
NEGATIVE
FEEDBACK
TIME

7. 7
Input/
Stimulus
Receptor/
Sensor
Effector
Control center
(Hypothalamus )
compares
against set point
Variable
Function Other
information
Information
flow
Information
flow
Feedback
loop
Afferent
pathway
Efferent
pathway
Negative
Feedback
(make adjustments
in opposite direction
s to the stimulus)
(sense changes
in variable)
negative Feedback :

8. 1.Stimulus: external temperature decreases
2.Variable:body temperature.
3.Receptors:Thermoreceptorsdetect a lowered body temperature
and produce nerve impulses that travel to the control center, the
hypothalamus.
4.Control Center:The hypothalamus controls a variety of effectors
that respond to a decrease in body temperature.
5.Effectors: There are several effectors.
•Blood vessels near the skin constrict, reducing blood flow and conserving
heat w.r.tthe environment.
•Skeletal muscles contract rapidly in response to a decrease in body
temperature.
•Thisshiveringhelpsgenerateheat,whichincreasesbodytemperature.
8
EX: CONTROL OF Bodytemperature
Stimulus for
decreasein body
temperature
Thermo receptors
sense temperature
change
Muscle shivers
vasoconstriction
Hypothalamus
compares against
set point (98.6
0
F)
Body temperature
Feedback
Increasein
body
temperature

9. 9
Conditions cause body
temperature to
increase
Thermo receptors
sense temperature
change
Sweat glands secrete
sweat
Vasodilation
Hypothalamus
compares against
set point (98.6
0
F)
Body temperature
Decreasein
body
temperature
EX: CONTROL OF Bodytemperature
1.Stimulus: external temperature increases
2.Variable:body temperature.
3.Receptors:Thermo receptors detect a increased body temperature
and produce nerve impulses that travel to the control center, the
hypothalamus.
4.Control Center:The hypothalamus controls a variety of effectors that
respond to a increase in body temperature.
5.Effectors:There are several effectors.
•Bloodvesselsneartheskindilate,increasingbloodflow(andtheresultant
heatloss)totheenvironment.Redflushinskin.
•Sweatglandsreleasesweatandevaporationcoolstheskininresponse
toaincreaseinbodytemperature.
•Thishelpsgenerateheatloss,whichdecreasesbodytemperature.
Feedback

10. 10
Body temperature falls
Body temperature
rises
•Vasoconstriction, heat is
conserved in body.
•Sweat glands do not
secrete sweat.
•Shivering of involuntary
muscles generate heat.
•Body temperature rises.
•Vasodilation, heat is lost
to environment.
•Sweat glands secrete
sweat.
•Evaporation of sweat
cause heat loss.
•Body temperature falls.
Heat is retained Heat is lost
Normal body
temperature
Negative feedback Negative feedback
THERMOREGULATION

11. 11
Highblood
glucose level
after eating
Glucose receptor in
pancreatic beta cells
Increased glucose
uptake into fat and
muscle cells
Glucose storage at liver
and muscle as
glycogen
Beta cells release
insulin and reaches
above set point
Blood glucose level
Decreasein
blood
glucose
level
EX: control of blood glucose level
1.Stimulus: After a meal, the small intestine absorbs glucose from
digested food.
2.Variable: Blood glucose levels rise.
3.Receptor: Increased blood glucose levels stimulate the pancreatic
beta cells to produce insulin.
4.Control center: Insulin triggers liver, muscle, and adipose cells to
absorb glucose for storage. Subsequently blood glucose levels fall.
5.Effector: Once glucose levels drop below SET POINT, there is no
longer a sufficient stimulus for insulin release, and the beta cells stop
releasing insulin.
Feedback

12. 12
Lowblood
glucose level
after fasting
Glucose receptor in
pancreatic alpha cells
Decreased glucose
uptake into fat and
muscle cells
Induce glycogenolysis
in liver and muscle
Alpha cells release
glucagon and reaches
above set point
Blood glucose level
Increasein
blood
glucose
level
EX: control of blood glucose level
1.Stimulus: A fasting or long gap between meals
2.Variable: Blood glucose levels fall.
3.Receptor: Decreased blood glucose levels stimulate the
pancreatic alpha cells to produce glucagon.
4.Control center: Glucagon triggers liver, muscle, and adipose cells
to breakdown storage glycogen to glucose. Subsequently blood
glucose levels rise.
5.Effector: Once glucose levels rise above SET POINT, there is no
longer a sufficient stimulus for glucagon release, and the alpha
cells stop releasing glucagon.
Feedback

13. 13
liver
BODY CELLS
TAKE UP
MORE
GLUCOSE.
Blood
glucose
Level falls.
Blood
glucose
level rises.
STIMULUS:
Blood glucose
level falls.
STIMULUS:
Blood glucose
level rises.
HOMEOSTASIS:
Blood glucose level
(90mg/100mL, set
point)
GLUCAGON
INSULIN
liver
pancreas
pancreas

14. 14
Lack of
Calcium in diet
Calcium receptor in
sensory cells of
parathyroid gland
Kidneys stop calcium
secretion in urine
Bone cells
(Osteoclasts) release
calcium from bone
Parathyroid gland
secretes parathyroid
hormone (PTH)
Blood calcium level
Increasein
blood
calcium
level
EX: control of blood calcium level
1.Stimulus:Lackofcalciumindiet.
2.Variable:Bloodcalciumlevelsfall.
3.Receptor:Decreasedbloodcalciumlevelsstimulatethe
cellsinparathyroidgland.
4.Controlcenter:Thechiefcellsinparathyroidglandto
produceandsecretParathyroidhormone(PTH).
5.Effector:PTHcauseseffectororgans(thekidneysandbones)to
respond.Thekidneyspreventcalciumfrombeingexcretedintheurine.
Osteoclastsinbonesbreakdownbonetissueandreleasecalcium.
•WhenbloodcalciumlevelsareaboveSETPOINT,less
parathyroidhormoneisreleased.
Feedback

15. 15
Highcalcium
level
Calcium receptor in
thyroid gland
Kidneys stop calcium
absorption from urine
Bone cells
(Osteoblasts) deposit
calcium in bone
Parafollicular cells in
Thyroid gland
release Calcitonin
Blood calcium level
Decreasein
blood
calcium
level
EX: control of blood calcium level
1.Stimulus: Diet for calcium rich food.
2.Variable: Blood calcium levels rise.
3.Receptor: Increased blood calcium levels stimulate the
parafollicular cells (C cells) inthyroid gland.
4.Control center: The C cells in thyroid gland produce and secret
Calcitonin.
5.Effector: Calcitonin prevents bone breakdown and causes the
kidneys to reabsorb less calcium from the filtrate, allowing excess
calcium to be removed from the body in urine.
•Once calcium levels drop below SET POINT, there is no longer
a sufficient stimulus for Calcitonin release, and the C cells
stop releasing Calcitonin.
Feedback

16. 16Osteoclasts
degrade bone
matrix releasing
calcium
Blood
calcium
Level rises.
Blood
calcium
level falls.
STIMULUS:
Blood calcium
Level rises.
STIMULUS:
Blood calcium
level falls.
HOMEOSTASIS:
Blood calcium level
(9-11mg/100mL, set
point)
Calcitonin
PTH
Osteoblasts
deposit calcium
in bone
Parathyroid
glands
Thyroid
gland

17. 17
https://www.slideshare.net/SutapaDatta6/physiological-
homeostasis-part-1
Link of part-1 homeostasis