Homeostasis in Mammals

Prepared by WS Kwan

Definition: Keeping the internal environment in a Steady state

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

How? 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

Fall

Rise

• kidneys : – regulate water & min

eral salts concentration

• skin : – regulate body temper

ature• liver & pancreas :

– regulate blood glucose level

Parts of Body involvedParts of Body involved

kidney

liver

pancreas

+

skin

tissue cells

blood

Osmoregulation Osmoregulation • Regulate water potential in Tis

sue Fluid• Why important?• Cells will be damaged by absor

bing or losing too much water• Omoregulation is achieved by

Organ : KIDNEYS

NephronNephron (kidney tubule) (kidney tubule)

renal artery

renal vein

capillaries around nephron

Loop of Henle

afferent arteriole

glomerulusefferent arteriole

collecting duct

Normal Water Content in

Blood

Normal Water Content in

Blood

After Sweating

After Sweating

Concentrated Blood

Concentrated Blood

Larger proportion of water is

reabsorbed in kidney tubule

Larger proportion of water is

reabsorbed in kidney tubule

Small volumeSmall volume of of

ConcentratedConcentrated Urine is Urine is

producedproduced

Small volumeSmall volume of of

ConcentratedConcentrated Urine is Urine is

producedproduced

How kidneys maintain a constant water level in the body?

Normal Water Content in

Blood

Normal Water Content in

Blood

After DrinkingAfter Drinking

Diluted Blood

Diluted Blood

Smaller proportion of

water is reabsorbed in kidney tubule

Smaller proportion of

water is reabsorbed in kidney tubule

Large Large volumevolume of of

DilutedDiluted Urine is Urine is producedproduced

Large Large volumevolume of of

DilutedDiluted Urine is Urine is producedproduced

How kidneys maintain a constant water level in the body?

OsmoregulationOsmoregulation (Water & (Water & Mineral saltsMineral salts))

• After having a salty mealSalt concentration in blood increaseExcess salts removed by kidney Salts excreted in solution form, hence extra

water is needed (How to compensate)High blood salt concentration gives body

the sensation of thirsty. (Drink more water)As a result, large volume of concentrated

urine is produced.

How kidneys maintain a constant salt level in the body?

Summary: OsmoregulationOsmoregulation • It is a process to maintain the water

potential of the tissue fluid constant.

• It is done by regulating the amount of water in relation to that of salt in body.

• It is achieved by the kidneys.

• Kidneys regulate both water level & salt level.

ThermoregulationThermoregulation(Regulation of Body Temperature)(Regulation of Body Temperature)Why important ?

• Most metabolic reactions are enzymatic reactions

• Enzymes work best at limited range of temperature

• Enzymes are inactivated at low temperatures• Enzymes are denatured at high temperatures

Poikilotherms (cold-blooded animals)

– body temperatures vary with that of the environment

– e.g. reptiles, fish, amphibians

– keep body temperature constant even in winter by increasing metabolic rate

– e.g. birds, mammals

Homoiotherms (warm-blooded animals)

Maintenance of Body Maintenance of Body TemperatureTemperature

Epidermis

Dermis

Outermost layerMiddle layerInnermost layer

Sweat gland

Blood capillaries

Subcutaneous gland

Receptors

Erector muscle

Nerve fibres

Sebaceous gland

Hair follicle

Structure of Mammalian Structure of Mammalian SkinSkin

Functions of Our Functions of Our SkinSkin

protect the body (epidermis)To provide mechanical protectionTo prevent bacterial entryTo kill germs (antiseptic secretion)To protect from harmful UV

to reduce water loss (epidermis)

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) temperature regulation

Control Body Control Body Temperature Temperature

in Hot in Hot ConditionsConditions

Avoid overheating by

More sweat is produced by sweat glands– evaporation of sweat takes away heat produces a cooling effect

Vasodilation of skin arterioles– arterioles near the surface of the skin d

ilates– to let more blood flows near the skin s

urface– to have more heat lost by conduction &

radiation.

When body is Hot:

Erector muscles relax– hairs lie flat on the skin– reduce thickness of air trapped

among the hairs

Decrease metabolic rate & muscle contraction– gain less heat

Long-term response: Develop thinner subcutaneous fat

& shed their fur to– increase heat loss

Control Body Control Body Temperature Temperature

in Cold in Cold ConditionsConditions

Body reduce heat loss by 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

When body is Cold:

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

Increase metabolic rate & muscle contraction (e.g. Shivering)– gain more heat

Long-term response Develop thicker subcutaneous fat

& thicker fur to reduce heat loss

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

Liver converts

glycogen to glucose

Body cells take up less

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 less insulininsulin

Liver coverts glucose to glycogen

Body cells take up more

glucose

Diabetes Malfunction of pancreas (does not secrete

enough insulin) Cannot control Blood glucose level Symptoms:

Urine with glucose, excessive thirsty (When glucose level is too high)

Treatment: injection of insulin

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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