Download Homeostasis- negative feedback

What has happened to
these people?
How did people understand
unusual diseases in the old
days ?
 Witch craft
 Punishment from God
How do scientists understand
diseases?
Definition: Keeping the internal
environment in a Steady
state
It is controlled by Negative Feedback
Mechanism
Homeostatic control system
 The body can regulate its internal
environment through a multitude of feedback
systems
 A feedback system is a cycle of events in
which the status of body condition is
continually monitored, evaluated, changed,
re-monitored, re-evaluated and so on.
 Any disruption that changes a controlled
condition is called a stimulus
Three basic components
RECEPTOR
CONTROL SYSTEM

EFFECTOR
 RECEPTOR
a body structure that monitors changes in a
controlled condition and sends input in the
form of nerve impulses or chemical signals to a
control center.
 CONTROL SYSTEM
evaluates the input it receives from
receptors and generates output commands
when they are needed.
output from the control center can occur in
several forms: nerve impulses, hormones ,
or other chemical signal
 EFFECTOR
is a body structure that receives output from
the control centre and produces a response
or effect that changes the controlled
condition.
either depressing it (negative feedback) or
enhancing it (positive feedback)
Feedback System
Negative feedback
 Homeostatic mechanism
that reduces the
intensity of the
original stimulus
 Consequently causes a
change in a variable that
is opposite in direction
to the initial change
Positive feedback
 A feedback mechanism
in which the response
enhances the original
stimulus
Rise above
normal value
normal
value
Corrective
Mechanism
NEGATIVE
FEEDBACK
MECHANISM
Fall below
normal value
Corrective
Mechanism
negative
feedback
normal
value
negative
feedback
Parts of Body involved
 kidneys :
 regulate water & mineral
skin
salts concentration
tissue
cells
 skin :
 regulate body temperature
 liver & pancreas :
kidney
 regulate blood glucose
level
liver
blood
+
Excretory system
pancreas
Osmoregulation
(Water & Mineral salts)
Regulate water potential in
Tissue Fluid
Organ involved: KIDNEYs
System involved : Urinary
system
After Sweating
Normal Water
Content in Blood
Concentrated
Blood
Larger
proportion of
water is
reabsorbed
Concentrated
Urine is
produced
After Drinking
Diluted Blood
Normal Water
Content in Blood
Smaller
proportion of
water is
reabsorbed
Diluted Urine
is produced
Osmoregulation
(Water & Mineral salts)
 After having a very salty meal
 produce concentrated urine to remove
excess salts in solution form
 extra water is needed to be excreted along
with the excess salts
 sensation of thirst (drink more water to
compensate for the water loss)
Thermoregulation
(Regulation of Body Temperature)
 Cold-blooded animals
 body temperatures vary with that of the
environment
 e.g. reptiles, fish, amphibians
Thermoregulation
(Regulation of Body Temperature)
 Warm-blooded animals
 keep body temperature constant even in
winter by increasing metabolic rate
 e.g. birds, mammals
Maintenance of Body Temperature
Hair Sebaceous
follicle gland
Erector Receptors
muscle
Epidermis
Dermis
Outermost
layer
Middle
layer
Innermost
layer
Sweat gland
Subcutaneous fat
Nerve fibres
Blood capillaries
Structure of Mammalian Skin
Functions of Our Skin

protect the body (epidermis)
 to provide mechanical protection
 to prevent bacterial entry
 to reduce water loss

temperature regulation (hair)
Functions of Our Skin




excretion of sweat (sweat gland)
store fats (subcutaneous fat)
sensation (numerous receptors )
production of vitamin D under ultra-violet light
(inner epidermis)
Control Body
Temperature in
Hot Conditions
More sweat is produced by sweat glands
 evaporation of sweat takes away heat which
produces a cooling effect
Vasodilation of skin arterioles
 arterioles near the surface of the skin dilates
 to let more blood flows near the skin surface
 to have more heat lost by conduction &
radiation.
Muscles relax
 hairs lie flat on the skin
 reduce thickness of air trapped among
the hairs (not effective in human
because human’s hairs are short)
 Develop thinner fat & shed their fur
 as long term responses
 increase heat loss
 Decrease metabolic rate & muscle
contraction
 gain less heat
Control Body
Temperature in
Cold Conditions
 Vasoconstriction of skin arterioles
 arterioles near the surface of the
skin constrict
 to let less blood flows near the skin
surface
 to have less heat lost by conduction
& radiation
 Muscles contract
 pull hairs for trapping more air
 thicker layer of air acts as a good
insulator of heat
 Less sweat is produced by sweat glands
 reduce heat loss by evaporation
 Develop thicker fat & thicker fur
 as long term responses
 reduce heat loss
 Increase metabolic rate & muscle
contraction
 gain more heat
Nervous system
Regulation of
Blood Glucose Level
controlled by Negative feedback
mechanism
 controlled by insulin secreted from the
islets of Langerhans in pancreas
 Diabetes - malfunction of pancreas
(does not secrete enough insulin)
 Digestive system

Soon
after a
meal
Too
High
Pancreas
secretes
insulin
Liver
coverts
glucose to
glycogen
normal blood
glucose level
Long
after a
meal
Too
Low
Blood glucose
level falls
normal blood
glucose level
Pancreas
secretes less
insulin
Liver
converts
glycogen to
glucose
Blood glucose
level rises