Homeostasis

Brain CT-scan

Importance of Homeostasis Importance of Homeostasis in Mammalsin 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

MECHANISMMECHANISMnorm

al value

negative

feedback

negative

feedback

Parts of Body involvedParts of Body involved• kidneys : • regulate water & mineral salts

concentration• skin : • regulate body temperature

• liver & pancreas :• regulate blood glucose level

1. Osmoregulation (Water & 1. Osmoregulation (Water & Mineral salts)Mineral salts)

•Regulate water potential in Tissue Fluid•Organ involved: KIDNEYS

Normal Water Content in

Blood

After Sweating

Concentrated Blood

Larger proportion of water is reabsorbed

ConcentrateConcentrated Urine is d Urine is producedproduced

Normal Water Content in

Blood

After Drinking

Diluted Blood

Smaller proportion of

water is reabsorbed

Diluted Diluted Urine is Urine is producedproduced

• 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)

2. Thermoregulation (Regulation 2. Thermoregulation (Regulation of Body Temperature)of Body Temperature)

• Homoiotherms (warm-blooded animals) • keep body temperature constant even in winter by increasing metabolic rate• e.g. birds, mammals

3. Regulation of Blood 3. Regulation of Blood Glucose LevelGlucose 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

Endocrine Overview• Hormones- chemical

messengers travel through body• Target cell or organ- organ

or cells that a hormone affects

Control of Hormone Release• Negative feedback mechanism- hormone

release is triggered by stimulus, rising levels of hormone inhibit further release• Endocrine stimuli-• Hormonal- hormones stimulate the

release of others• Humoral- blood stimulates release of

hormones• Neural- nerves stimulate hormone

release