Download f211 exchange transport 1.2.1 exchange surfaces breathing

F211: Exchange &
transport
1.2.1 Exchange surfaces & breathing
(pulmonary system & ventilation)
By Mr. Wilson
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?
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).
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.
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
CO2
N2
H2O
Temp.
Notes
When inhaling & exhaling…
Inspiration/
Inhalation
External intercostal
muscles
Diaphragm
Thorax volume
Thorax pressure
(pressure on lungs)
Air movement
Expiration/
exhalation
Inhalation
Expiration
Measuring the volume of air in the
lungs




Lung volume/capacity (pulmonary activity) can
be measured using a SPIROMETER.
A KYMOGRAPH on a revolving drum can be
produced showing the volume of air entering and
leaving the lungs over time.
The TIDAL VOLUME is the volume of air
exchanged during normal breathing.
This is the volume of air in each breath in & out.
Usually around 0.4 - 0.5 dm3 per breath at rest.
Spirometers through the years

In the old days.

These days.
Lung volumes; inspiratory &
expiratory reserve volumes


IRV = Maximum
additional reserve
volume that can be
inspired on top of
tidal inspiration.
ERV = Maximum
additional volume
that can be expired
on top of tidal
expiration.
Lung volumes; vital capacity


Maximum
volume of air that
can be breathed in
(inspired) and
breathed out
(expired).
Q - Why is this
different for
different people?
Lung volumes; residual volume



Volume of air that cannot
be expired from the lungs
even after forced deep
expiration.
About 25cm3 for each Kg
of body mass.
RV + ERV = Functional
residual capacity (the
volume of air available
for gas exchange after
tidal expiration).
Ventilation rate (minute volume)




A measure of the volume of air taken into
the lungs in 1 minute (expressed
in dm3 min-1).
Breathing rate x tidal volume.
An increase on either side will produce
an overall increase in ventilation rate.
During exercise ventilation rate increases
as the tidal volume and then the breathing
rate increase.
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.