1. LEVELS OF BIOLOGICAL ORGANISATION AN INTRODUCTION TO HOMEOSTASIS.

1. LEVELS

OF

BIOLO

GICAL

ORGANISAT

ION

AN

IN

TR

OD

UC

TI O

N T

O H

OM

EO

ST A

SI S

2. HOW

HOMEOSTA

SIS

WORKS

TH

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OL E

OF F

EE

DB

AC

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HOMEOSTASIS:

A definition:

the maintenance of a stable internal environment despite fluctuations in the external environment

COMPONENTS OF HOMEOSTASIS

A system requires three components for homeostasis:

- A receptor;

- A control centre;

- An effector.

These components do specific jobs that allow regulation of the internal environment.

FEEDBACK SYSTEMS

May be negative or positive

Discuss how these devices work:

A toilet cistern when you flush

A hot water cylinder when you run the shower

WHAT UPSETS THE BALANCE?

Various factors apply stress on the internal environment:

Internal factors - within the body, eg pain, high or low blood pressure

External factors - outside the body, eg extremes of temperature

NEGATIVE FEEDBACK...

causes the system to respond to reverse the direction of change. ..

which tends to keep things constant…

so it allows the maintenance of homeostasis.

eg, if there is a fall in calcium in the blood, the parathyroid glands sense the decrease and secrete more parathyroid hormone, thereby increasing calcium release from the bones;

NEGATIVE FEEDBACKIN INCUBATOR

temperature

Temp too high

Temp too low

Temperature

sensor

Thermostat

system with

switch

Heater (switched off)

Temperature

sensor

Heater (switched on)

Thermostat

system with

switch

Incubator temperature at 32 C

Rise inTemp fallsi

Temp risesi

NEGATIVE FEEDBACKA FRIDGE

Fall in

Temperature

sensor

Thermostat

system with

switch

cooling (switched off)

Temperature

sensor

cooling (switched on)

Thermostat

system with

switch

Fridge temperature varies to setting C

Drop in temperature

Rise in temperature

Rise in temperature

Drop in temperature

POSITIVE FEEDBACK…

increases the variable in the same direction…

a destabilising effect that does not result in homeostasis.

Positive feedback is used when rapid change is needed.

eg in childbirth the hormone oxytocin is produced to stimulate and enhance labour contractions

eg clotting mechanism when skin is cut