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

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