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Importance of Importance of Homeostasis in MammalsHomeostasis 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 abovenormal value
Fall below normal value
normal value
Corrective Mechanis
m
Corrective Mechanis
m
NEGATIVE NEGATIVE FEEDBACK FEEDBACK
MECHANISMMECHANISM
normal
value
negative
feedback
negative
feedback
• kidneys : – regulate water & mine
ral salts concentration• skin :
– regulate body temperature
• liver & pancreas :– regulate blood glucose
level
Parts of Body involvedParts of Body involved
kidney
liver
pancreas
+
skin
tissue cells
blood
Osmoregulation Osmoregulation (Water & Mineral salts)(Water & Mineral salts)
•Regulate water potential in Tissue Fluid
•Organ involved: KIDNEYS
Normal Water Content in
Blood
Normal Water Content in
Blood
After Sweating
After Sweating
Concentrated Blood
Concentrated Blood
Larger proportion of water is reabsorbed
Larger proportion of water is reabsorbed
ConcentrateConcentrated Urine is d Urine is producedproduced
ConcentrateConcentrated Urine is d Urine is producedproduced
Normal Water Content in
Blood
Normal Water Content in
Blood
After DrinkingAfter Drinking
Diluted Blood
Diluted Blood
Smaller proportion of
water is reabsorbed
Smaller proportion of
water is reabsorbed
Diluted Diluted Urine is Urine is producedproduced
Diluted Diluted Urine is Urine is producedproduced
Osmoregulation Osmoregulation (Water & Mineral salts)(Water & Mineral salts)
• After having a very salty mealproduce concentrated urine to remove
excess salts in solution formextra water is needed to be excreted
along with the excess saltssensation of thirst (drink more water to
compensate for the water loss)
ThermoregulationThermoregulation(Regulation of Body (Regulation of Body
Temperature)Temperature)• poikilotherms (cold-blooded animals)
– body temperatures vary with that of the environment
– e.g. reptiles, fish, amphibians
• Homoiotherms (warm-blooded animals) – keep body temperature constant even
in winter by increasing metabolic rate– e.g. birds, mammals
ThermoregulationThermoregulation(Regulation of Body (Regulation of Body
Temperature)Temperature)
Maintenance of Body Maintenance of Body TemperatureTemperature
Epidermis
Dermis
Outermost layerMiddle layerInnermost layer
Sweat gland
Blood capillaries
Subcutaneous fat
Receptors
Erector muscle
Nerve fibres
Sebaceous gland
Hair follicle
Structure of Mammalian Structure of Mammalian SkinSkin
EpidermisEpidermis• dead outer layer
– relatively impermeable– easily peeled off– protect the underlying
tissues•to prevent mechanical injury
•to prevent bacterial entry•to reduce water loss
• middle layer– made up of living cells– become dead as they approach
the surface• black inner layer
– with pigment (melanin) to absorb ultra-violet ray for sunlight
– have cell division to repair the lost outer layers
EpidermisEpidermis
DermisDermisBlood 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
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 regulationErector muscle
– controls the hair movement for temperature regulation
DermisDermis
Sebaceous gland– secretes oily substance
•to make the skin waterproof•to prevent bacterial entry
Receptors – detect pain, pressure, temperature &
touch
DermisDermis
beneath the Dermis for fat storage acts as insulator of heat
Subcutaneous Subcutaneous FatFat
Functions of Our Functions of Our SkinSkin
protect the body (epidermis)to provide mechanical
protectionto prevent bacterial entryto reduce water loss
temperature regulation (hair)
Functions of Our Functions of Our SkinSkin
excretion of sweat (sweat gland)store fats (subcutaneous fat)sensation (numerous receptors )production of vitamin D under
ultra-violet light (inner epidermis)
Control Body Control Body Temperature Temperature
in Hot in Hot ConditionsConditions
More sweat is produced by sweat glands– evaporation of sweat takes away heat
which produces a cooling effectVasodilation 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 Control Body Temperature Temperature
in Cold in Cold ConditionsConditions
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
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 Regulation of Blood Glucose LevelBlood 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)
Liver converts glycogen
to glucose
normal normal blood blood
glucose glucose levellevel
Blood glucose Blood glucose level fallslevel fallsSoon Soon
after after a a
mealmeal
Long Long after after
a a mealmeal
Blood Blood glucose glucose
level riseslevel rises
normal normal blood blood
glucose glucose levellevel
Too Too HigHighh
Too Too LowLow
PancreaPancreas s
secretes secretes insulininsulin
Pancreas Pancreas secretes secretes
less insulinless insulin
Liver coverts glucose
to glycogen
~~ ENDEND
~~