What has happened to these people?

How did people understand unusual diseases in the old days ?Witch craftPunishment from

God

How do scientists understand diseases?

Definition: Keeping the internal environment in a Steady state

It is controlled by Negative Feedback Mechanism

Homeostatic control system

The body can regulate its internal environment through a multitude of feedback systems

A feedback system is a cycle of events in which the status of body condition is continually monitored, evaluated, changed, re-monitored, re-evaluated and so on.

Any disruption that changes a controlled condition is called a stimulus

Three basic components RECEPTOR

CONTROL SYSTEM

EFFECTOR

RECEPTOR

a body structure that monitors changes in a controlled condition and sends input in the form of nerve impulses or chemical signals to a control center.

CONTROL SYSTEM

evaluates the input it receives from receptors and generates output commands when they are needed.

output from the control center can occur in several forms: nerve impulses, hormones , or other chemical signal

EFFECTOR is a body structure that receives output

from the control centre and produces a response or effect that changes the controlled condition.

either depressing it (negative feedback) or enhancing it (positive feedback)

Feedback SystemNegative feedbackHomeostatic

mechanism that reduces the intensity of the original stimulus

Consequently causes a change in a variable that is opposite in direction to the initial change

Positive feedbackA feedback

mechanism in which the response enhances the original stimulus

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

Parts of Body involvedParts of Body involvedkidneys :

regulate water & mineral salts concentration

skin : regulate body

temperatureliver & pancreas :

regulate blood glucose level

Excretory system

kidney

liver

pancreas

+

skin

tissue cells

blood

Osmoregulation Osmoregulation (Water & Mineral salts)(Water & Mineral salts)

Regulate water potential in Tissue Fluid

Organ involved: KIDNEYsSystem involved : Urinary system

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 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)

ThermoregulationThermoregulation(Regulation of Body (Regulation of Body Temperature)Temperature)Cold-blooded animals

body temperatures vary with that of the environment

e.g. reptiles, fish, amphibians

ThermoregulationThermoregulation(Regulation of Body (Regulation of Body Temperature)Temperature)Warm-blooded animals

keep body temperature constant even in winter by increasing metabolic rate

e.g. birds, mammals

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

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 SkinFunctions 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 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 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.

Muscles relaxhairs lie flat on the skinreduce thickness of air trapped among the hairs (not effective in human because human’s hairs are short)

Develop thinner fat & shed their furas long term responses increase heat loss

Decrease metabolic rate & muscle contractiongain less heat

Control Body Control Body Temperature Temperature

in Cold in Cold ConditionsConditions

Vasoconstriction of skin arteriolesarterioles near the surface of the skin constrict

to let less blood flows near the skin surface

to have less heat lost by conduction & radiation

Muscles contractpull hairs for trapping more air

thicker layer of air acts as a good insulator of heat

Less sweat is produced by sweat glandsreduce heat loss by evaporation

Develop thicker fat & thicker furas long term responses reduce heat loss

Increase metabolic rate & muscle contractiongain 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)

Digestive system

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