Transport in the lungs

My lung revision notes created for the OCR syllabus- unit 1

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  • Created on: 15-05-12 11:05
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Gas Exchange is effective in the lungs because of:
The Thin Barrier: Both alveoli and capillary are 1 cell thick. They both have SQAMUMOUS EPITHELIUM.
They are an in close contact with each other to reduce diffusion pathway. The barrier is less than 1um
thick. The capillaries are narrow so the blood is squeezed close to the alveolus reducing the rate the
flow past and ensuring faster gas exchange. (TSCN)
Large Surface Area: More space for molecules to diffuse across. Singularly each alveolus is about
100um across. Together they are over 70m meaning more space and more efficient exchange of
substances. (S)
The plasma membrane surrounding the thin cytoplasm of the cell form the barrier which is permeable
to both CO2 and O2 allowing exchange of both.
Maintained Concentration Gradient: The alveoli have a steep concentration gradient which is essential
for rapid diffusion. This is maintained by a good blood flow on one side and ventilation on the other
side. This allows oxygen to diffuse down its concentration gradient from the air to the blood while
allowing CO2 to diffuse down its concentration gradient simultaneously from blood to air. Consequently
maintaining the concentration gradient.
A thin layer of Moisture: This lines the alveoli and evaporates when breathing out. It comes from
cytoplasm to alveoli. Without this collapsing would occur. This is a problem in premature babies. This
layer of moisture produced by the lungs is a SURFACTANT. They are there to reduce the COHESIVE
FORCES between water molecules. Without this the alveoli would collapse due to the friction from the
COHESIVE FORCES between water lining air sacs.
Diaphragm contracts to become flatter and Diaphragm relaxes and is pushed up by
pushes digestive organs down displaced digestive organs
External intercostals muscles contract causing External intercostals muscles relax causing rib
rib cage to rise cage to fall
Volume of chest cavity increases Volume of chest cavity decreases
Pressure in chest drops below atmospheric Pressure in the chest increases and rises above
pressure atmospheric pressure
Air moves in Air moves out
All exchange surfaces have: Large surface area, thin permeable barriers and a maintained concentration gradient.
Examples of echange surfaces include lungs, liver, small intesetine, root hair in plants and hyphae in fungi.
Organisms exchange. FOCW ­ food, oxygen, carbon dioxide and waste. They either absorb them or make them
in the cytoplasm during metabloism.
Maisy the mouse: Small animals = diffusie directly. Big SA:VR
Harry the Hippo: Large animals = exchange systems because of small SA:VR, big transport distance, cells need
more supplies and outer surface is not enough to enable gas to enter fast enough.
Used to work out the rate of which a substance can diffuse.

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LUNG NOTES…read more

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Tissue in the lungs
TRACHEA, BRONCHUS, BRONCHIOLES: - allow passage of air. They are all large enough to allow
air to flow without any obstructions. They each divide into something smaller until they reach
the alveoli. They are strong enough to prevent collapsing when air pressure is low. They also
have to maintain flexibility for movement and be able to stretch and recoil.
Have a similar structure, but differ in size. Both walls are in layers and are very thick.…read more

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VENTILATION is the movement of air over the gas exchange system. In humans ventilation is a
TIDAL PROCESS because air enters and exits through the same way. Breathing rate usually is 12
xs per minute. However, when exercised or scared breathing becomes faster and deeper.…read more

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A SPIROMETER is an oxygen filled chamber with about 6dm3 of oxygen in it. It floats on a tank of water. It
counterbalanced so gas drawn out/in makes the chamber rise/fall.
Movements are recorded using a data logger or by a pen writing on a revolving drum (KYRMAGRAPH). This allows
a spirometer trace to be produced. The spirometer shows different breathing patterns.
BREATHING IN: Takes O2 from the chamber so the chamber sinks
BREATHING OUT: Pushes air into chamber so chamber rises.…read more

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Correct functioning equipment ­ such as hinges and chambers working properly.
Soda lime absorbs CO2 so over time total amount of gas in the spirometer will decline.
Volume of CO2 exhaled is equal to volume of O2 used up.
If a line could be straight line could be drawn through all the peaks of a trace in one period then it would show oxygen
consumption is at a constant rate.…read more

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Residual volume = (Expiratory Reserve X 6) ­ vital capacity
TISSUE: A group of similar cells that perform a particular function. Sometimes but not always attached together. An example
would be the nervous tissue in animals.
ORGAN: A collection of tissues that work together to perform a specific overall function or set of functions within a
multicellular organism.
SQUAMOUS EPITHELIUM: A lining of flat cells. An example would be the ciliated squamous epithelium of the cells in the
trachea.…read more

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FORCED EXPIRATION: Shows expiratory reserve volume. The abs contract, the internal intercostals muscles contract and a
larger and faster expiration occurs. Also used in exercise
SPIROMETER: A device that measures a person breathing. It's a chamber filled of medical grade oxygen 6dm3 which floats
on a tank of water. The person breathes through an attached mouthpiece into it. When breathing out tank rises, when
breathing in tank falls.…read more


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