Transcript Gas Exchange

Exchange Systems
F211
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Explain, in terms of surface-area-to-volume ratio, why multicellular organisms
need specialised exchange surfaces and single-celled organisms do not.
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Exchange surfaces
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What do cells need to keep them alive?
Oxygen for aerobic respiration
Glucose for energy
Proteins
Fats to make membranes
Minerals- to maintain water potential and
help action
Exchange surfaces
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What waste do cells need to get rid of?
Carbon dioxide
Oxygen
Other wastes such as ammonia or urea
which contain excess nitrogen
1cm3 organism
1cm3
Surface area :
volume ratio = 6:1
8cm3 organism
surface area:volume
ratio = 3:1
27 cm3 organism surface are :
volume ratio = 2:1
Larger organisms need a larger area to exchange more
substances
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What makes an exchange surface efficient?
Feature
How it helps
Large surface area
Larger area for molecules to
diffuse
Thin barrier
Shorter distance for
diffusion
Permeable membrane
Allow molecules through
Good supply/removal of
molecules required
Maintain diffusion gradient
Examples
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Small intestine
Liver
Lungs
Root hairs
Hyphae of fungi
Week 7
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Describe the features of an efficient exchange surface with reference to diffusion
of oxygen and carbon dioxide across an alveolus.
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Describe the features of the mammalian lung that adapt it to efficient gas
exchange.
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Outline the mechanism of breathing (inspiration and expiration) in mammals,
with reference to the function of the rib cage, intercostal muscles and
diaphragm.
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Lungs and breathing
Label as many parts as you can.
Lungs and breathing
Larynx
Trachea
Right lung
Left lung
Right bronchus
Left bronchus
Intercostal
Muscles
Bronchioles
Heart
Alveoli
Ribs
Pleural cavity
Pleural Membrane
Diaphragm
Label as many parts as you can.
Video Clip
Lungs and breathing
Week 7
Capillary network over the surface of alveoli and details of gaseous exchange
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Can you say what is happening at each stage
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Week 7
Feature that make the lungs adapted to exchange
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Large surface area - An average adult
has about 600 million alveoli, giving a total
surface area of about 70m² (Half size of tennis
court)
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Permeable to O2 and CO2
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Thin barrier to reduce diffusion distance
1. The walls of the alveoli are composed of a
single layer of flattened epithelial cells, as
are the walls of the capillaries, so gases
need to diffuse through just two thin cells
(less than 1µm thick)
2. Both cells made of squamous cells
(meaning flattened or very thin cells)
3. Capillaries very close to alveolus wall
4. Narrow capillaries- RBCs squeezed
against cell wall
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Week 7
Feature that make the lungs adapted to exchange
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Water diffuses from the alveoli cells into
the alveoli so that they are constantly
moist.
Oxygen dissolves in this water before
diffusing through the cells into the blood,
where it is taken up by haemoglobin in the
red blood cells.
The water also contains a soapy
surfactant which reduces its surface
tension and stops the alveoli collapsing.
The alveoli also contain phagocyte cells to
kill any bacteria that have not been
trapped by the mucus
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The steep concentration gradient across the respiratory surface is
maintained in two ways:
1) by blood flow on one side
2) by air flow on the other side.
This means oxygen can always diffuse down its concentration
gradient from the air to the blood, while at the same time carbon
dioxide can diffuse down its concentration gradient from the
blood to the air.
The flow of air in and out of the alveoli is called ventilation and has
two stages: inspiration (or inhalation) and expiration (or
exhalation). Lungs are not muscular and cannot ventilate
themselves, but instead the whole thorax moves and changes
size, due to the action of two sets of muscles: the intercostal
muscles and the diaphragm.
Describe the stages of Inhalation and
exhalation
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Diaphragm
Intercostal muscles
Volume of chest cavity
pressure
Exhalation is a passive process, We breathe
out when our muscles relax
Breathing is a passive process
Inhalation
Exhalation
Diaphragm Contracts, moving
downwards increasing the volume
of the chest cavity and displacing
the organs beneath
The diaphragm relaxes, the
organs below move back into
place
The intercostal muscles contract
moving the ribcage up and out
The intercostal muscles relax, the
ribcage moves down and in
The volume of the chest cavity
increases decreasing the pressure
in the thorax below atmospheric
pressure
The volume of the chest cavity
decreases causing air pressure in
the lungs to increase above
atmospheric pressure
Air is sucked into the lungs as a
result
Air is forced out of the lungs as a
result
Week 7
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Describe the distribution of cartilage, ciliated epithelium, goblet cells, smooth
muscle and elastic fibres in the trachea, bronchi, bronchioles and alveoli of the
mammalian gaseous exchange system.
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Describe the functions of cartilage, cilia, goblet cells, smooth muscle and elastic
fibres in the mammalian gaseous exchange system.
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Week 7
(a) Bronchiole and (b) trachea in transverse section
What is the role of each tissue?
Cartilage
Smooth Muscle
Elastic fibres
Goblet cells and glandular
tissue
Cilliated epithelium
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Week 7
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Explain the meanings of the terms tidal volume and vital capacity.
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Describe how a spirometer can be used to measure vital capacity, tidal volume,
breathing rate and oxygen uptake.
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Analyse and interpret data from a spirometer.
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Removes CO2
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Total Lung Capacity- The maximum amount of air that the lungs can hold
Residual Volume- The volume of air that remains in the lungs after breathing
approx 1.5dm3
Vital Capacity- The maximum usable lung volume (total lung capacity minus the
residual volume). The average vital capacity is 4.5-5 dm3 for men and 3.5-4 for
women.
Tidal Volume- The volume of air that moves in and out of the lungs in each
breath (during normal breathing). In a normal adult this is about 0.5 dm3.
Inspiratory Reserve Volume- The amount of air that the lungs will hold after a
normal expiration (i.e. inspiratory reserve + tidal volume).
Expiratory Reserve Volume- The amount of air remaining in the lungs after a
normal quiet expiration (i.e. expiratory reserve volume + residual volume).
Exam questions
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