Transcript module 3 3.1.1 exchange surfacesx

Module 3
3.1.1 Exchange Surfaces
By Ms Cullen
All living things need to obtain oxygen
and nutrients, and excrete waste
substances into the fluid environment
which surrounds them.
• For single-celled
animals their fluid
surroundings will be the
habitat in which they
live, usually fresh or salt
water.
• In a multicellular
organism, single cells
are surrounded by
tissue fluid or
extracellular fluid, with
which they exchange
materials.
Single-celled Organisms
• A small animal like an
amoeba has a large
surface area to volume
ratio.
• This means all parts of its
body are in close contact
with the external
environment.
• As a result it can exchange
all the substances it needs
through diffusion with its
fluid environment.
Small Multicellular Organisms
• In small multicellular organisms
the shape of the organism or parts
of the organism also aids diffusion.
• A good example of this is jellyfish.
Inside their body they have a large
cavity filled with water, which in
effect doubles their surface area
contact with the water.
• Flat worms have a flattened shape
to increase surface area.
• Flowering plants have flattened
leaves with large internal air
spaces.
Large Multicellular Organisms
• Large multicellular organisms have a low surface
area relative to their body volume.
• Most large organisms also have waterproof and
gas proof skin.
• To aid diffusion they require specialised exchange
surface areas. For example alveoli, villi.
• The exchange of substances will be by either
passive diffusion or active transport.
Rate of Diffusion
• Rate of diffusion depends on the concentration
gradient of the internal and external environment, the
exchange surface and the distance travelled.
• It can be calculated by using Fick’s Law:
Rate of diffusion = surface area x difference in concentration
thickness of the exchange surface
• The general rules are; the greater the surface area, the
greater the concentration gradient, the thinner the
separating layers, the faster the rate of diffusion.
Complete Practical Activity 10 ‘The effect of
SA:Vol ratio on rate of diffusion’
Villi in small intestine –
large surface area aids absorption
Alveoli in lungs
Large surface area aids gaseous exchange
The structure and
function of a
mammalian gaseous
exchange system
The pulmonary system
(ventilation/breathing*)
• Air is drawn into the lungs via the nasal and
buccal cavities, which are separated by the
palate to allow feeding and breathing at the
same time.
• Inspired air is warmed, particularly when
inhaled via the nasal cavity.
• Q - Why is this useful?
The pulmonary system; upper
• Nasal hairs trap dust particles and some
microbes.
• The epiglottis covers the TRACHEA when
swallowing to prevent food from entering.
• Q - What is the importance of these
mechanisms?
• The larynx contains vocal cords, which are
adjusted as air passes over them to produce
sounds.
The upper pulmonary system
The pulmonary system; thorax
• The THORAX with its THORACIC CAVITY in
humans is the area between the bottom of
the neck and the DIAPHRAGM.
• It contains the LUNGS and the heart (with
associated structures), and some important
membranes, all of which are protected by the
RIB CAGE.
• Q – Why is it important that the lungs are
contained in an enclosed cavity?
The thoracic cavity
• Q – What major
organs are
contained in the
thoracic cavity?
• Q – Why is the
heart situated in
the thoracic
cavity in close
proximity to the
lungs?
The pulmonary system; full
The pulmonary system; trachea
• The TRACHEA is supported by C-shaped
cartilage rings. This is important for
keeping the airway open when thoracic
pressure falls.
• It is lined with CILIATED EPITHELIAL CELLS
and MUCUS secreting GOBLET CELLS.
• Q – What is the importance of mucus &
cilia?
A cross section through the
trachea. The luman is lined
with ciliated columnar
epithelium with Goblet
cells.
Cartilage in the Trachea
1.Hyoid bone
2. Thyroid cartilage
3. Cricoid cartilage
4. Tracheal cartilages
Cartilage is C-shaped
The pulmonary system; ribs, intercostal muscles
and diaphragm
• The ribs protect the lungs and heart and have EXTERNAL
and INTERNAL INTERCOSTAL muscles between them.
• The external muscles contract to lift the RIB CAGE
upwards and outwards during INSPIRATION (relaxing for
EXPIRATION).
• INTERNAL INTERCOSTAL MUSCLES aid expiration.
• At the bottom of the thoracic cavity is a strong domeshaped MUSCULAR DIAPHRAGM, which can increase the
volume of the thorax when contracted (pulled
down/flat).
Ventilation
The pulmonary system; pleural membranes
& cavity
• The lungs are surrounded by PLEURAL
MEMBRANES (pleurae).
• Between the 2 membranes is a PLEURAL
CAVITY, which contains pleural fluid and is
kept at negative pressure so the lungs follow
the movement of the rib cage.
• The inner (visceral) pleura is attached to the
lungs and the outer (parietal) pleura is
attached to the wall of the chest
The pulmonary system; pleural membranes
& cavity
• The pleural fluid lubricates the membranes so they
can slide against each other with ease during
ventilation allowing the lungs to move ‘friction-free’
against the wall of the thorax.
• The pleural membranes also separate the lungs; so if
one is punctured the other can still function.
• Pleurisy (pleuritis) is a an inflammation, often from
infection, of the pleural membranes.
• It leads to painful breathing and disruption to the
negative pressure system.
Pleural membranes
The pulmonary system; bronchi,
bronchioles & alveoli
• The trachea divides into 2 BRONCHI (singular =
BRONCHUS), which are also held open, under
low thoracic pressure, by rings of cartilage.
• The bronchi divide into many BRONCHIOLES,
which are less than 1mm thick and generally
contain no cartilage.
• Bronchioles terminate in air sacs called
ALVEOLI, which are the site of GAS EXCHANGE.
Bronchi and bronchioles are surrounded by a
layer of smooth muscle, which is located between
the cartilage and epithelium. This can contract
limiting the amount of air to & from the alveoli.
Alveoli
Elastic fibres form the bulk of
the connective tissue present
in the walls of the alveoli.
These dilate (widen) the
airways.
Alveoli (singular = alveolus)
• Alveoli are highly specialised for gas exchange
with adaptations that speed up the rate of
DIFFUSION.
• They have a LARGE SURFACE AREA.
• They have an EXTREMELY THIN EXCHANGE
SURFACE.
• The epithelial layer is ONE CELL THICK.
• There is a STEEP CONCENTRATION GRADIENT
between their contents and their surrounding
capillaries.
Gas exchange at alveoli
• Alveolar septal cells secrete a phospholipid
SURFACTANT; lowering the surface tension of
the water lining them.
• This prevents alveolar collapse.
• Oxygen diffuses across the alveolar epithelium
then across the capillary endothelium and
combines with the HAEMOGLOBIN of RED
BLOOD CELLS.
• Haemoglobin has a high affinity for oxygen
thus making this process more efficient.
Gas exchange at alveoli
• The oxygen diffuses into the capillary
down it’s concentration gradient.
• Carbon dioxide diffuses from the
blood plasma the opposite way
down it’s concentration gradient and
is breathed out.
Gas exchange at alveoli
• The alveoli have an extensive blood supply.
• De-oxygenated blood is supplied to the lungs
by branches of the PULMONARY ARTERY,
which branch again into capillaries.
• Oxygenated blood is carried via capillaries to
branches of the PULMONARY VEIN from
where it will be taken to the left atrium of the
heart.
• Can you remember the many ways the alveoli
are adapted for gas exchange?
Gas exchange at alveoli
Comparison of inhaled and exhaled air (%)
Inhaled
Alveolar
Exhaled
O2
20.95
13.80
16.40
CO2
0.04
5.50
4.00
N2
79.01
80.70
79.60
H2O
variable
saturated Saturated
Notes
When inhaling & exhaling…
Inspiration/
Inhalation
External intercostal
muscles
Diaphragm
Thorax volume
Thorax pressure
(pressure on lungs)
Air movement
Expiration/
exhalation
Inhalation
Expiration
Hmmm…Interesting
• A drop in O2 concentration in the blood has almost
no effect on the rate of ventilation. It is usually
changes in carbon dioxide concentration that affect
ventilation rate.
• If you are healthy it is not possible to stop breathing.
You could hold your breath and become
unconscious, but the body will resume breathing by
itself.
• Lungs also act as a shock absorber for the heart.
• Lungs can filter out small blood clots formed in veins.
Useful Websites:
• http://www.smm.org/heart/lungs/vascular.ht
m
• http://www.footprintsscience.co.uk/alveoli.htm
Measuring Lung Capacity
The Breathing Cycle
(measured by a spirometer)
The Breathing Cycle
(measured by a spirometer)
• Tidal Volume: breathing rate normally at rest. A person
usually takes in and expels ½ a litre of air during each
respiratory cycle.
• Ventilation Rate: the volume of air breathed per minute.
ventilation rate = tidal volume x frequency of inspirations.
During muscular exercise the frequency and depth of
breathing increases resulting in a greater ventilation rate.
• Inspiratory Rate: In a deep breath, you can take approx.
3 litres of air over and above the tidal volume.
The Breathing Cycle
(measured by a spirometer)
• Expiratory Reserve Volume: Extra air expelled (approx 1
litre) after normal expiration.
• Vital Capacity: Total amount of expired air after a
maximum inspiration (ie. tidal volume plus inspiration and
expiration reserve volumes). For an average person this is
between 4-5 litres, an athlete over 6 litres.
• Residual Volume: 1.5 litres of air remains in the lungs
even after maximum respiration.
• Of the ½ litre of air inspired only 350cm3 gets into the
parts of the lungs where gaseous exchange takes place.
The rest remains in the trachea and bronchioles, known as
dead space.
• Minute Volume (VE) is the product of tidal
volume and the rate of ventilation.
VE = ventilation rate (breaths per min) x tidal volume (cm3)
• The minute volume is basically the amount of
air breathed in and out per minute. It
increases during exercise – the tidal volume
increases first and then the ventilation rate
increases.
VC – Vital Capacity
IRV – Inspiratory Reserve Volume
TV – Tidal Volume
ERV – Expiratory Reserve Volume
IC – Inspiratory Volume RV – Residual Volume
FRC – Functional Residual Capacity (volume of air that stays
in lungs when breathing at rest)
The Peak Flow
• The Peak Flow is the maximum rate at which
air flows out of the lungs. Usually 400-600dm3
per min.
• Peak Flow varies with age, sex and size.
The structure and
function of a other
gaseous exchange
systems
Gas exchange in bony fish
• Fish have very specialised gaseous exchange
surfaces because water is 1000x denser than air,
100x more viscous and has a much lower oxygen
content.
• The skin of bony fish is covered with impermeable
scales and therefore gas exchange has to occur
through gills.
• Fish maintain a flow of water in one direction over
the gills.
• The gills are contained in a cavity with a covering
operculum (bony flap) which helps maintain water
flow over the gills.
Gas exchange in bony fish
• Each gill is supported by a bony gill arch
and has 2 stacks of thin lamellae which lie
on top of each other like pages in a book.
• The lamellae need to be kept apart by
water to prevent them sticking together.
• The upper and lower surface of each
lamellae have projections called gill plates,
these increase the surface area further.
Gas exchange in bony fish
• Blood flows from an afferent vessel in each gill
and back through an efferent vessel.
• Water passes in the opposite direction to blood
flow. This ensures blood meets water with a
higher concentration of oxygen then it’s own.
• The effect of this is that oxygen diffuses out of
the water where it is in high concentration, into
the blood, where it is in a low concentration.
• This is known as the counter current mechanism.
Gas exchange in bony fish
• Bony fish ventilate their gills.
• How?
• Muscular contractions cause water to move into the
buccal cavity through the mouth, the pharynx, over the
gills and out through the valves of the opercular.
• Most fish use muscles to change the volume of their
buccal cavity, pharynx, gill cavity and opercular cavity.
• As the volume of a cavity becomes less this increases
the pressure and squeezes the water to where there is
less pressure.
Gas exchange in bony fish
How are gills adapted?
• Large surface area
• Good blood supply
• Thin layers
Gas exchange in insects
• Insects have a segmented body and a rigid exoskeleton. The
exoskeleton is covered by a layer of wax which is impermeable
to water and gases.
• Instead gases diffuse through spiracles, these are small holes,
which are located in the thorax and abdomen.
• The spiracles lead to a network of large tubs called tracheae,
which branch into smaller tubes called tracheoles.
• These tracheoles grow between and even into the insect’s
body cells.
• The outer tracheae are covered in chitin which keep the
tracheae open, but as a result they are impermeable to gases.
• The tracheoles are permeable to gases as they are elongated
single cells with no chitin.
• Carbon dioxide diffuses from the cells to the tracheoles and
oxygen diffuses from the tracheoles to the cells.
Gas exchange in insects
Gas exchange in insects
Gas exchange in insects
• Most gaseous exchange occurs by diffusion.
• The diffusion distance must be short. The distance between the
spiracle and the tracheoles must be short or the insect will die, this
explains why insects are relatively small.
• The tiny tracheoles provide a large surface area and gases dissolve
in moisture on the walls of the tracheoles. At the end of the
tracheoles there is tracheal fluid which limits the penetration of
air for diffusion.
• Insects can ventilate their tracheoles; by compressing their bodies
they squeeze air from the tracheal tubes. This is then replaced with
fresh air when the body returns to its normal size.
• When insects are active, lactic acid accumulates in their muscles so
that water moves by osmosis from the lining of the tracheoles into
the muscle cells.
• This movement of water increases the free volume within the
tracheoles which, if the spiracles are open, will cause fresh air to
move deeper into the tracheoles, as there is a larger surface area
for diffusion to occur.