Transcript Gas exchange File

SECTION II
– Structures and functions in
living organisms
Gaseous exchange
Syllabus
• understand the role of diffusion in gas
exchange
• describe the structure of the thorax,
including the ribs, intercostal muscles,
diaphragm, trachea, bronchi, bronchioles,
alveoli and pleural membranes
• understand the role of the intercostal
muscles and the diaphragm, in ventilation
Syllabus
• explain how alveoli are adapted for gas
exchange by diffusion between air in the
lungs and blood in capillaries
• understand the biological consequences of
smoking in relation to the lungs and the
circulatory system
• describe a simple experiment to
investigate the effect of exercise on
breathing in humans.
Terminology
• Gaseous exchange
– The exchange of gas (by diffusion) across a respiratory surface.
• Breathing (ventilation)
– the bodily process of inhalation and exhalation
– Muscular movements which keep the gaseous exchange
surfaces supplied with oxygen
• Respiration
– A series of chemical reactions which happen in all living cells.
– Food is broken down to release energy, usually by combining it
with oxygen.
• Respiratory system
– The organs, muscle and bones involved in the inhalation and
exhalation process.
Structures
• Lungs
– two organs
– extract oxygen from inhaled air and expel carbon
dioxide in exhaled air.
• Trachea
– Tube through which air passes from the nose to the
lungs (also known as the windpipe).
– Has rings of cartilage to keep it open.
– The rings are in a u shape to allow for the expansion of
the trachea during ventilation.
Structures
• Trachea
– Lined with two specialised
cells
Ciliated cells
• Ciliated cells
– Cells that have fine ‘hairs’ on
the surface of the cell.
– Their beating action carries the
mucus (containing microbes &
dust) away from the lung
surfaces.
• Goblet cells
– Produce mucus, that helps to
trap the microbes and dust that
is breathed in.
Goblet cells
Structures
• Larynx
– Voice box
• Location of vocal cords
• Bronchi
– The two main air passages into the lungs.
• Bronchioles
– A small tube carrying air to and from the alveoli in the
lungs.
• Alveoli
– Tiny air sacs
– The main site of gaseous exchange
Structures
• Nose and mouth
– Cavities where the air passes in and out of the
body
– Air becomes warm, filtered and moist if it flows
through the nasal cavity.
Structures
• Intercostal muscles
– Internal (go from the
front of the rib cage to
the back) & external
(go from the back to
the front)
– Thin sheets of muscle
between each rib that
expand and contract.
– Involved in breathing
Structures
• Diaphragm
– The main muscle used for breathing;
separates the chest cavity from the
abdominal cavity.
• Ribs
– Bones attached to the spine and central
portion of the breastbone, which support
the chest wall and protect the heart, lungs,
and other organs in the chest.
Structures
• Pleural membrane
– Covering the lung and lining the chest cavity,
this membrane has 2 thin layers.
• Pleural fluid
– The fluid inside the membranes lining the
lungs and chest cavity.
Features of gaseous
exchange surface
• Gas exchange surface
– The part of the organism through which gases
are exchanged.
• Properties of surfaces:
– Thin
• Allows gases to diffuse quickly
– Close to a transport system
• Takes gases to and from the cells which need
them.
Features of gaseous
exchange surface
• Properties of surfaces:
– Moist
• Stops the cells on the surface from drying out and
dying
– Large surface area
• Allows a lot of gas to diffuse across a surface at
the same time
– Supply of oxygen
• Is needed by the surface
Alveoli
• Is where gas
exchange occurs.
• Contains all the
features of a
respiratory surface:
– Close to a transport
system
– Thin
– Large SA
– Good supply of O2
Ventilation
• Also known as breathing
• Movement of air into and
out of the lungs.
• Air flows because of
pressure differences
between the atmosphere
and the gases inside the
lungs.
• This pressure difference
occurs because of
breathing movements we
undertake.
Source: http://www.stemnet.nf.ca/~dpower/resp/exchange.htm#Breathing, cited
16/11/06
Inhalation
• Also known as inspiration
• It is the process of taking air into the lungs.
• It is the active phase of ventilation
because the muscles are contracting.
• During inspiration:
– the diaphragm & intercostal muscles contract
– This increases the volume of the thoracic
cavity.
– This decreases the intraalveolar pressure so
that air flows into the lungs.
Exhalation
• Expiration (exhalation) is the process of
letting air out of the lungs during the
breathing cycle.
• During expiration:
– the diaphragm and intercostal muscles relax
– This decreases the thoracic volume and;
– increases the intraalveolar pressure
– Air is pushed out of the lungs.
Inspired vs expired air
Inspired
(inhaled)
21 %
Expired
(exhaled)
18 %
Carbon
dioxide
Nitrogen
0.04 %
3%
78 %
78 %
Water
Variable
saturated
Temperature
Variable
37 °C
Oxygen
Carbon dioxide test
• To determine whether
CO2 is being released in
exhalation, the limewater
test is used.
• Limewater
– (saturated calcium
hydroxide solution)
– Turns from clear to cloudy
when CO2 is present.
Physical activity and breathing
• Aims for investigations:
– The longer you exercise, the longer it
takes for your breathing rate to return to
normal.
– The more vigorously you exercise, the
longer it takes for your breathing rate to
return to normal.
Physical activity and breathing
• Rate and depth of breathing changes when
exercising.
– Oxygen is needed by cells, CO2 is produced as a
waste = cellular (aerobic) respiration
• Rate of breathing increases (more O2 in, more
CO2 out)
• Depth of breath changes, so that volume of
thoracic cavity is maximised (gets as large as
possible)
– Tidal volume
• Volume of air breathed in and out during a normal, resting
breath.
Physical activity and breathing
• More exercise = increased CO2
concentration = lowering of pH
• Blood & tissue pH becomes lower, as CO2
mixes with water in body resulting in
carbonic acid (H2CO3) being made.
Smoking and the respiratory
system
• In your teenage years your lungs are still
growing, and their ability to function is
supposed to increase.
• The smoke inhaled is:
– Hot
– has a drying effect
– Contains many harmful chemicals.
• Smoking damages your cilia, alveoli, and
bronchioles. These are part of the body’s
defense mechanism.
Smoking and the respiratory
system
• The lungs are one of the most vulnerable
parts of the body, as they have more
contact with the outside world than most
internal organs do.
• Anything that's in the air -- including dirt,
germs, and smoke -- can find its way into
your respiratory system.
Smoking and the respiratory
system
• To protect against these contaminants,
your body produces mucus, which helps to
trap and carry away irritating substances
from the air.
• The mucus-contaminant mixture is moved
through the respiratory system by tiny
hairs called cilia that move rapidly back
and forth.
Smoking and the respiratory
system
• Smoking decreases the rate of lung
growth and therefore decreases the level
of maximum lung function reached in the
late teens.
• This happens in both boys and girls, but
girls seem to be particularly susceptible to
smoking's effects on lung growth and
function.
Smoking and the respiratory
system
• Tar
– Sticks to cilia, thus they cannot remove the
contaminated mucus and causes extra mucus to be
produced. This travels down to the lungs with
contaminants within (eg. Bacteria) causing infections
& smokers cough, as the body tries to get rid of the
mucus.
– Irritates the lining of the lungs, making them inflamed,
causing bronchitis.
– Causes cells in respiratory system to multiply
uncontrollably, leading to lung cancer.
Smoking and the respiratory
system
• Carbon monoxide
– Displaces oxygen from haemoglobin, thus reduces oxygen
supply to cells.
• Nicotine
– Causes addiction
– Stimulant, causing blood pressure to increase, resulting in more
demand more oxygen = increased breathing rate.
Stop Smoking - timeline
• This is what happens to you when you stop smoking:
20 minutes
Blood pressure and pulse rate return to normal.
8 hours
Nicotine and carbon monoxide levels in the blood reduce by half, oxygen levels return
to normal.
24 hours
Carbon monoxide will be eliminated from the body. Lungs start to clear out mucus and
other smoking debris.
48 hours
There is no nicotine left in the body. Ability to taste and smell is greatly improved.
72 hours
Breathing becomes easier. Bronchial tubes begin to relax and energy levels increase.
2-12 weeks
Circulation improves.
3-9 months
Coughs, wheezing and breathing problems improve as lung function is increased by up
to 10%.
1 year
Risk of a heart attack falls to about half that of a smoker.
10 years
Risk of lung cancer falls to about half that of a smoker.
References
• wordnet.princeton.edu/perl/webwn, cited 6th Nov,
2006
• Jones, M & Jones, G 2002 Biology, Cambridge
University Press, Cambridge.
• http://people.eku.edu/ritchisong/301notes6.htm,
cited 16 Nov., 2006.
• http://thescooponsmoking.org/xhtml/effectsHom
e.php, cited 16 Nov., 2006
• Clegg, J, Price, G & Smith, M. 2006 Cambridge
IGCSE Biology, Collins Education, London.