Transcript Lungs and Alveoli

Lungs and Alveoli
You must be able to draw the structure of the lungs and alveoli
http://www.people.eku.edu/ritchisong/301notes6.htm
Lung Anatomy
http://sprojects.mmi.mcgill.ca/resp/anatomy.
swf
Why and how do we breathe?
http://www.airinfonow.org/html/lungattack/lun
gplay.htm
The need to ventilate
• A ventilation system is needed to maintain concentration
gradients in the alveoli
• The steep concentration gradient across the respiratory
surface is maintained in two ways: by blood flow on one
side and by air flow on the other side. The ventilation
system replaces diffuses oxygen (keeping the
concentration high) and removes carbon dioxide
(keeping the concentration low).
• 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.
Alveoli and Pulmonary capillaries
Features of the alveoli
• large surface area: surface area of the
alveolar epithelium - 100 m2
• thin: single cell layer of epithelium across
which diffusion occurs
• moist: gasses need to dissolve before
passing membranes
• rich blood supply: extensive net of
capillaries for transport of gasses to and
from alveoli
Intercostal
muscles
contract.
Ribs move out
and ______
Diaphragm
contracts and
gets
____________
Inhalation
Volume _____________
Pressure ____________
Air enters the lungs
The lungs relax here and the pressure
inside and outside the lungs goes back
to normal atmospheric pressure 760mm Hg
Intercostal
muscles
______.
Ribs move ___
and ______
Diaphragm
_______ and
returns to its
dome shape
Exhalation
Volume _____________
Pressure ____________
Air _____ the lungs
Lowering of the diaphragm and rising of the ribs causes a
drop in air pressure of 4mm Hg
Gas exchhange
• Howstuffworks "Gas Exchange"
HL: Partial pressure
• In summary, gases move from a region of
higher partial pressure to a region of lower
partial pressure.
•
Animations partial pressure. Keep in mind
above summary.
Partial Pressures of O2 and CO2
in the body (resting)
• Alveoli
– PO2 = 100 mm Hg
– PCO2 = 40 mm Hg
• Alveolar capillaries
– Entering the alveolar capillaries
• PO2 = 40 mm Hg (relatively low because this blood has just
returned from the systemic circulation & has lost much of its
oxygen)
• PCO2 = 45 mm Hg (relatively high because the blood
returning from the systemic circulation has picked up carbon
dioxide)
How are oxygen & carbon
dioxide transported in the
blood?
• Oxygen is carried in blood:
1. bound to hemoglobin (98.5% of all
oxygen in the blood)
2. dissolved in the plasma (1.5%)
• Animation Quizzes hemoglobin
The graph below shows the Haemoglobin- Oxygen Association Curve. This shows
the % of oxygen in the blood (oxyhaemoglobin) and the partial pressure of O2 in the
environment.
Simply put it means that oxygen joins haemoglobin and stays joined at high partial
pressures of oxygen. When the level of oxygen is low (low partial pressure), the oxygen
molecules dissociate (jump off) the haemoglobin molecule. The more O2 a molecule of
Hb accepts, the easier it is to carry more, as it changes its shape.
Mammalian muscles also contain a chemical called Myoglobin. It is similar, but
smaller than haemoglobin. It holds onto oxygen much more tightly (higher
affinity) and only dissociates at much lower partial pressures- a store of oxygen
for difficult times.
In the developing foetus, the haemoglobin has a much higher affinity for
oxygen. This means that the baby can absorb oxygen efficiently across
the placenta at fairly low partial pressures.
The Bohr Shift: When there is lots of CO2 due to respiration, the
acidity of the blood increases slightly. This causes the whole graph to
shift to the right (and get steeper). This allows oxygen to unload at
these places even easier.
High altitudes
People who live at high altitude have to cope with having less O2
available for respiration. Their body compensates by making far
more haemoglobin. This increases the amount of oxygen that can
be carried. However, there is a downside: when there is too much
haemoglobin, blood becomes sticky and viscous and it is harder for
the heart to pump the blood around the body. This happens in
chronic mountain sickness.
Athletes often train at altitude- this can benefit
them when they return to run races, as they
have an improved exchange rate with more
haemoglobin
•CO2 produced in mitochondria
•Diffuses out into tissues and tissue fluid
•In rbc it combines with H20 forming carbonic acid
(H2CO3) using carbonic anhydrase.
•This splits (dissociates) into H ions and HCO3 ions
•Haemoglobin acts as a buffer and
takes the H ions to form Haemoglobonic
acid (H.Hb)
•The blood stays fairly neutral and can
absorb lots of CO2
•As the amount of HCO3 rises in the
rbc, they start to diffuse out down
the conc. gradient into the plasma
•This cannot be balanced, as the
cell stops ions like Na and K
•The cells would get more and more
positively charged (compared to the
plasma) and prevent O2 uptake
•Chloride ions are pumped in from
plasma to balance it- called the
chloride shift
•At the lungs the oxygen is taken up by dissolved H.Hb- forming Hb.O2
•H ions are released and combine with HCO3 forming carbonic acid- the CO2 then diffuses out
•The HCO3 content falls, so more moves in from the plasma, so more CO2 released
•The chloride shift moves ions into the plasma to maintain neutrality
What is asthma?
In asthma, the muscles lining the airways are very sensitive and
overreact to substances or events, known as triggers, that other
people tolerate without problem. Often pollen, dust, mould spores and
smoke can cause this, but often other allergens can trigger it too.
3 things generally happen:
1.
Tightening of the muscles lining the airways
2.
Mucus production
3.
Inflammation
Imagine having done 3 minutes exercise, then try to recover, but ONLY
breathing through a straw!!
http://video.about.com/asthma/Asthma.htm
http://kidshealth.org/misc/movie/cc/how-asthma-affects.html
Lung volumes
• Tidal volume – the amount of air breathed
in or out of the lungs in a normal breath.
This is about 500cm3
• Inspiratory reserve volume – extra lung
volume available if you breathe in as much
as you can. This is about 3000cm3
• Expiratory reserve volume – extra lung
volume available if you breathe out as
much as you can. This is about 1100cm3
Lung volumes
• Vital capacity – this is the TV + IRV + ERV
or the useable lung capacity. It is about
4500cm3
• Residual air – this is the amount of air that
needs to stay in your lungs to stop them
collapsing. It is about 1200cm3
Lung capacity practical
• Look at the instructions for how to use the
lung volume kit.
• Try to measure your own lung volume
• Plan an investigation into a factor that
could affect vital capacity.