2. Organisms detect and respond to changes called
stimuli in the internal and external environment.
The environment includes living or biotic as well
as non- living or abiotic factors.
They include factors such as pressure, pain,
light, sound, temperature and chemicals
These changes are detected by specialised
sensory receptors.
Sensory receptors respond to the intensity,
location and duration of a stimulus
3. Receptors can be classified into the
following categories
Mechanoreceptors: that detect pressure and
touch
Chemoreceptors: that detect chemicals
Photoreceptors: that detect light
Thermo receptors: that detect heat and cold
Pain receptors: that detect pain
4. Temperature
The human core body temperature operates at an
optimum 37 (0C)
The environmental or ambient temperature at
which a human can live comfortably is a range of
10 – 40 (0C).
Any lower or higher requires humans to wear
special clothing or change their environment.
Hypothermia (extreme cold) cause heat loss leading
to the slowing down of the bodies metabolism
leading to frostbite and possibly death.
5. Hyperthermia (extreme heat / humidity) can
lead to metabolic breakdown as enzymes
denature above 42 (0C) leading to structural
protein breakdown.
Thermo receptors detect these changes and
send messages to the CNS to either maintain
heat in the body through “shivering” or to lose
heat via “sweating”
8. Light
Light passes through the lens and is focused on
a special layer of photoreceptors in the retina.
These messages are carried through the optic
nerve to the brain where shape and colour is
formed.
Two types of receptors
Rods: detect shape and movement
Cones: detect colour
10. Sound
Sound is captured by the pinna, the external flap
of cartilage. These sound waves are transmitted
towards the eardrum or tympanic membrane.
The waves are then vibrated by the small ear
bones (hammer, anvil, stirrup) or ossicles
through to the cochlea and then via the sensory
or auditory nerve to the brain.
The volume is measured in decibels
The sense of balance is maintained by the
“semi-circular canals” within the inner ear.
12. Chemicals
The presence of chemicals are detected by
chemoreceptors.
Olfactory receptors detect smell
Taste is detected by taste buds on the tongue
which can differentiate between
salty
sweet
sour
bitter
13. In each case stimuli from the environment
which is detected by the sensory nerves and
relayed by the CNS enables one of two
responses
Involuntary or automatic response
Voluntary or conscious response
14. Nervous System
The nervous system is composed of a system of
nerve cells which allow the transmission of
electro-chemical messages. Each nerve cell
consists of a cell body which contains the
nucleus, a number of extensions called
dendrites which receive information which then
passes the information along the axon which is
covered in a myelin sheath.
These impulses can travel up to 100 metres per
second.
16. The nervous system is composed of two parts.
The CNS or central nervous system which is
composed of the brain and spinal cord
The PNS or peripheral nervous system which is
made up of the sensory and motor neurons.
Information or stimuli from the environment are
detected by the sense organs and travel via
sensory nerves to the CNS where a voluntary or
involuntary signal is sent via the motor neuron
to an effector where a response will occur
18. Reflex - arc
A reflex-arc is a rapid automatic or involuntary
response which bypasses the brain. Examples
include
- Knee jerk response
- Blinking of the eye
- Swallowing
In many cases the reflex – arc protects the body
from harm. It can be harmed by drugs such as
alcohol.
20. Stimulus – response model
Homeostasis (steady state)is the maintenance of
an optimum internal environment despite external
changes.
This is achieved by the stimulus - response model
and negative feedback mechanisms.
Stimulus Receptor Transmission Effector
Response Negative Feedback
Negative feedback reverses or inhibits the stimulus
21. Hormone System
Hormones are chemical messengers produced by
endocrine glands in small amounts which regulate
growth and reproduction.
Hormones are either
Steroids derived from cholesterol which are lipid
soluble and can directly effect receptor
molecules within a cell
Proteins derived from amino acids which cannot
pass through cell membrane but instead attach to
“hormone receptor cells” outside a cell
26. Mechanisms which conserve heat
Erection of hairs (goose bumps) which trap layer
of air close to the body
Vasoconstriction – restriction of blood flow from
the skin to the core
Increased production of hormones adrenalin and
thyroxine which increases rate of metabolism
Involuntary shivering producing heat
Voluntary actions such as rubbing hands together
or jumping around
28. Mechanisms which remove heat
Animals have flattened hair or feathers which
prevent trapping of air
Vasodilation – blood is redirected from the
core to the skin
Sweat glands release sweat which evaporates
cooling the body down. In some animals this
done via the tongue (panting)
Metabolic rate is reduced (seasonal)
29. Exchange of materials
It is vital that materials are exchanged between the
internal and external environment.
The following organs contain special structures to
maximise the exchange,
Kidney: nephron Lungs: alveoli Intestine: villi
Exchange surfaces are
thin: to decrease the distance that materials need to
diffuse across
moist: to keep cells alive and provide a layer for
substances like oxygen to dissolve in prior to diffusion
large surface area: to provide a larger area over which
diffusion can occur
30.
31. Role of blood and lymph capillaries
Arteries carry blood away from the heart and
veins carry blood back to the heart
Capillaries link arteries and veins. They are very
thin allowing for the exchange of material and
removal of wastes.
Lymph capillaries drain excess fluid which has
“leaked” from surrounding tissues into the
lymphatic system and return the excess fluid
back to the circulatory system near the heart.
34. The Kidney
The structural and functional unit of the kidney
is the nephron. The nephron maximises the
surface area for exchange.
One nephron consists of
- Bowmans capsule
- Glomerulus
- Long thin tubule
Nephrons have a rich blood supply, thin and
moist conditions
37. 20 % of the blood is diverted to kidney via the renal
artery
Filtration
Blood enters the glomerulus – a “ball” of capillaries
and under considerable pressure into the Bowmans
capsule via a semi-permeable membrane,
separating molecules according to size. Larger
molecules such as rbc and proteins are not filtered
but continue along capillaries which surround the
nephron.
The remaining 20% of blood plasma becomes
filtrate. This will include glucose, water and urea
38. Reabsorption
As the filtrate passes along the proximal tubule,
Loop of Henle and distal tubule, certain
substances which are useful i.e. water and
glucose are actively reabsorbed.
Rate of reabsorption can be affected by
hormones such as Anti-Diuretic Hormone (ADH)
which controls water reabsorption.
Alcohol decreases rate of ADH therefore
increasing rate of urine production
39. Chemicals such as drugs and poisons are
excreted from the capillaries into the tubule.
About 99% of water is reabsorbed meaning
urine becomes very concentrated
150 litres of blood passes through kidney each
day with 148.5 reabsorbed leaving about 1.5
litres of urine to be excreted.
40. Lungs
The structural and functional unit of the lung is
the alveoli. They provide the gas exchange
surface area in which oxygen and carbon dioxide
are exchanged between blood and the air
Alveoli provide:
- A large surface area
- A thin membrane ( 1 cell thick)
- A moist layer to assist with diffusion
41. Normal composition of air is approximately
Oxygen 20 %
Nitrogen 80 %
Other gases (CO2) < than 1 %
Blood returning to lungs contains between
12 & 15 % dissolved Oxygen
80 % Nitrogen
3-4 % CO2
43. Inspiration
Diaphragm contracts and pulls down
Intercostal muscles contract pulling ribs upwards
and outwards
Increase in volume of chest cavity and decrease
in pressure
Air is then forced into lungs by greater air
pressure outside of the body
44. Expiration
Diaphragm, ribs and intercostal muscles relax
Decrease in volume of chest cavity and increase
in pressure
Air passively leaves lungs due to the change in
air pressure.
During exercise air can be expelled forcibly by
abdominal muscles
45. Gas Exchange
Gas exchange occurs across the alveolar membrane
in the following manner:
O2 from alveolus blood capillaries
CO2 from the blood capillaries alveolus
O2 and CO2 move across the alveolar membrane by
diffusion.
Rate of diffusion is affected by:
concentration gradient of gases
Rate of blood flow
Rate / depth of breathing
46. O2 is attached to haemoglobin inside rbc’s
forming oxyhaemoglobin.
CO2 is transported in the main as bicarbonate
ions dissolved in the plasma and some attached
to haemoglobin
The build up of CO2 is the stimulus for the
“respiratory centre” to breathe more rapidly and
deeply.
47. Lung function impairment
Asthma
Bronchioles constrict reducing volume and rate of
breathing.
Emphysema
Reduced area of alveolar membrane which limits
diffusion.
Pneumonia
Accumulation of fluids reduces effective volume and rate
of diffusion.
Carbon monoxide poisoning
Up to 200 x more attracted to haemoglobin than oxygen
reducing its availability leading to loss of consciousness
48. Small Intestine -Villi
Villi are finger like projections from the wall of
the small intestine that assist in the absorption
of soluble materials from the intestine into the
bloodstream. Villi provide a
Thin
Moist membrane
Large surface area
Rich blood supply
51. Structural features of villi
Lacteal in the core of each villus (part of
lymphatic system)
Epithelial cells surrounding villus are covered in
microvilli increasing surface area
Rich capillary network
52. Nutrients are absorbed from the small intestine by
both active and passive processes
Passive
Glucose, amino acids, nucleotides and ions are
moved via diffusion into the blood capillaries in the
villi
Active
Active transport will move substances against a
concentration gradient
Products of fat digestion are absorbed then moved
by exocytosis out of the cells into the lacteal
