Download Homeostasis

Importance of Homeostasis in
Mammals
 metabolic reactions are controlled by
enzymes
 enzymes work best in a narrow range
of temperature & pH only
 ∴important to keep internal
environment as steady as possible
Definition: Keeping the internal
environment in a Steady
state
It is controlled by Negative Feedback
Mechanism
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 salts
concentration
skin :
 regulate body
temperature
liver & pancreas :
 regulate blood glucose
level
skin



tissue
cells
kidney
liver
blood
+
pancreas
Osmoregulation
(Water & Mineral salts)


Regulate water potential in
Tissue Fluid
Organ involved: KIDNEYS
Internal
structures
of Kidney
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)

poikilotherms (cold-blooded animals)
 body temperatures vary with that of the
environment
 e.g. reptiles, fish, amphibians
Thermoregulation
(Regulation of Body Temperature)

Homoiotherms (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
gland
Nerve fibres
Structure of Mammalian Skin
Blood capillaries
Epidermis

dead outer layer
 relatively impermeable
 easily peeled off
 protect the underlying tissues
 to prevent mechanical injury
 to prevent bacterial entry
 to reduce water loss
Epidermis


middle layer
 made up of living cells
 become dead as they approach the
surface
black inner layer
 with pigment (melanin) to absorb ultraviolet ray for sunlight
 have cell division to repair the lost outer
layers
Dermis
Blood capillaries
to nourish the cells of the skin
branch into superficial blood capillaries
Sweat gland
surrounded by a network of capillaries
secrete sweat (consists of water, mineral salts,
urea & some waste materials)
characteristic of mammals
Dermis
Hair follicles & Hairs
each hair has a nerve & a capillary attached to it
nerve: receives stimuli
capillary: supply food & oxygen
hairs reduce heat loss & assist in temperature
regulation
Erector muscle
controls the hair movement for temperature
regulation
Dermis
Sebaceous gland
secretes oily substance
to make the skin waterproof
to prevent bacterial entry
Receptors
detect pain, pressure, temperature & touch
Subcutaneous Fat
 beneath the Dermis
 for fat storage
 acts as insulator of heat
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.

Erector 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 subcutaneous 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 contract
 to let less blood flows near the skin
surface
 to have less heat lost by conduction
& radiation
 Erector muscles contract
 pull hairs erect 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 subcutaneous fat &
thicker fur
 as long term responses
 reduce heat loss
 Increase metabolic rate & muscle
contraction
 gain more heat
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)

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
~END~