Physiological adaptations for survival
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External environment refers to the surrounds
of an organism- temperature, humidity, wind
etc. It can vary widely (even in one day- think
about Melbourne weather!)
Internal environment inside organisms need
to be maintained within a tolerance range.
Eg. Humans internal body temp (36.1-37.8)
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Homeostasis refers to the maintenance of a
relatively stable internal environment.
When challenges cause a deviation from the
normal conditions, the organism has
mechanisms that act to restore the normal
state. (Eg Shivering, sweating)
Refer to pg 300 table 10.1
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The two major systems contributing to
homeostasis are:
 The nervous system (nerves)
 The endocrine system (hormones)
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Other cells and systems also contribute to
homeostasis.
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The nervous system consists of:
 Brain (CNS)
 Spinal cord (CNS)
 All nerve cells (PNS)
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CNS refers to the Central Nervous system
PNS refers to the Peripheral Nervous system
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Nerve cells (AKA neurons) have a large cell
body (with the nucleus) and an extension
stemming off this called axon- they carry
messages to other cells
Also stemming off the cell body are
dendrites – they receive messages
See picture pg 302
There are three kinds of neuron:
 Affector (sensory) neurons
 ‘information detectors’ send messages back to
the CNS
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Effector (motor) neurons
 ‘responders’ send messages from the CNS, cause
cells to respond
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Connecting neurons- link neurons together
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Start from here after temperature regulation
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Sense organs monitor our external
environment and send messages back to the
CNS in the form of electrical impulses.
When the message reaches the CNS, the
brain stimulates effectors to complete a
response (to the external stimulus)
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Light enters the human eye through the cornea
It passes through the lens where it is focussed onto the
retina
It contains two kinds of photoreceptors known as rods and
cones
Rods and cones contain light sensitive pigments
Fibres lead to the optic nerve at the back of the eye
carrying information to the brain
Concentrated in the central region of the retina, cones
cells function in high light intensities, detecting colour and
detail.
Cones provide us with our central vision
Rod cells detect light with low intensity and can detect
movement
Taste receptors are located in the taste buds on
the tongue.
 Each tastebuds contains 50 receptors cells.
 Receptors transmit encoded information about
taste of food in the mouth. The brain then
decodes and interprets the information.
 These receptors can detect chemical substances
in the saliva of the mouth.
 Five basic taste: sour, salt, bitter, sweet and
umami (a taste sensation produced by
monosodium glutamate [MSG] and other
glutamates found in fermented foods.
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Olfactory receptors are located on bony outgrowths inside the
nasal cavity.
In humans they are nerve cells. The fibres from these form the
olfactory nerve leading to the brain.
Olfactory receptors in the nose can detect substances at a
concentration 10,000 times less than that required for detection
by taste receptors.
Some people cannot smell scent: e.g. scent of flowers
The taste of many foods come form the combination of several
sensory inputs.
There are 3 types of stimuli:
 Olfactory stimuli- arising from the odour of food before and while it is
in the mouth
 Tactile stimuli- arising from the texture of food
 Gustatory stimuli- arising from the taste of dissolved food
 Temperature stimuli- such as the heat or coldness of food
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Receptors to detect stimuli that produce
sensations of touch pressure, temperature and
pain are distributed over the entire skin surface.
In order to stimulate the receptors an object
must make physical contact with the outer body
surface
Mammals use their whiskers as extensions of
their body, to increase their ability to collect
information from their surroundings
Pain is a valuable sensations that tells us that the
stimulus is causing tissue damage
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In mammals, birds, reptiles and amphibians, sound
receptors are concentrated in the ear.
There are three regions in the human ear.
The outer ear is made of cartilage, this leads to the ear
canal.
To the middle ear is an air filled cavity. Sound waves
cause the eardrum to vibrate and this vibration is then
conducted across the middle ear to the inner ear.
The inner ear magnifies the sounds.
The inner ear consists of small coiled structure called
the cochlea which is filled in the inner ear. Information
about the sound is then encoded into nerve impulses
and sent to the brain.
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Go to chapter review pg 337
Answer Q 3, 4, 5, 6, 7, 9, 10, 12, 13
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Core temperature is maintained at about 37
degrees
Changes to external temperature are
detected by receptors in the skin: cold and
hot receptors
These send a message to the hypothalamus
in the brain
The hypothalamus serves as the temperature
control centre of the brain
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Homeostasis requires a stable internal body
temp. Ways of gaining heat
Ways of losing heat
Basic metabolic processes
Evaporation of sweat
Shivering
Panting
Exercise /muscular activity
Convection
Radiation & conducting TO
the body
Radiation and conduction
FROM the body
Conduction= transfer of heat to other
‘objects’
Convection= air currents taking heat away
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Shivering: contraction & relaxation of small
muscle groups
Metabolic processes produce heat. The
hypothalamus produces TRH which instructs the
pituitary to secrete TSH which stimulates the
thyroid. The thyroid releases thyroxine which
increases metabolic activity
Hypothalamus can instruct blood vessels to
constrict (in the skin) to reduce the amount of
heat lost via the skins surface
TSH = Thyroid stimulating hormone
TRH= Thyrotropin- releasing hormone
Hypothalamus
releases TRH
Pituitary
(stimulated by
TRH) releases
TSH
Thyroid
(stimulated by
TSH) releases
thyroxine
Thyroxine
increases
metabolic rate
Body becomes
warmer
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When the core body temperature is set to
exceed 37 degrees, the hypothalamus acts to
increase heat loss by:
 Dilation of blood vessels at the skins surface
 Metabolic activity is reduced (secretion of TRH is
reduced therefore....TSH is reduced, therefore...)
 Sweat glands are activated (evaporation of sweat
requires heat energy)
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Ectothermic: relies on external heat source eg
snake
Poikilothermic: have fluctuating
temperatures
Endothermic: have an internal heat source
(able to generate their own heat) eg people
Homeothermic: have a constant body
temperature
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Kidneys- are responsible for water balance.
They eliminate nitrogenous wastes and cause
water to be reabsorbed
ADH (antidiuretic hormone) and renin act on
the kidneys to absorb more water to be
returned to the body (to prevent
dehydration)
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Complete biochallenge pg 336