section 1: exchange & transport - topic 3: ventilation in mammals Flashcards
what is ventilation?
ventilation consists of inspiration and expiration.
what is ventilation controlled by?
the movements of the diaphragm, intercostal muscles, and ribcage.
what happens during inspiration?
the external intercostal and diaphragm muscles contract.
this causes the ribcage to move upwards and outwards, and the diaphragm to flatten, increasing the volume of the thorax (the space where the lungs are).
as the volume of the thorax increases, the lung pressure decreases (to below atmospheric pressure).
this causes air to flow into the lungs.
inspiration is an active process - it requires energy.
what happens during expiration?
the external intercostal and diaphragm muscles relax.
this causes the ribcage to move downwards and inwards, and the diaphragm to become curved again.
the thorax volume decreases, causing the air pressure to increase (to above atmospheric pressure).
air is forced out of the lungs.
normal expiration is a passive process - it doesn’t require energy.
expiration can be forced though (i.e. blowing out candles), during this - the internal intercostal muscles contract, pulling the ribcage down and in.
what is a spirometer?
a machine that can be used to investigate breathing.
what can a spirometer give readings of?
- tidal volume.
- vital capacity.
- breathing rate.
- oxygen uptake.
what is tidal volume?
the volume of air in each breath - usually about 0.4 dm^3.
what is vital capacity?
the maximum volume of air that can be breathed in or out.
what is breathing rate?
how many breaths are taken per unit time.
what is oxygen uptake?
the rate at which a person uses up oxygen.
how do you use a spirometer?
a spirometer has an oxygen-filled chamber with a movable lid.
the person using it breathes through a tube connected to the oxygen chamber.
as the person breathes in and out, the lid of the chamber moves up and down.
these movements are recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace (or it can be hooked up to a motion sensor, which will use the movements to produce electronic signals, which are picked up by a data logger).
the soda lime in the tube the subject breathes into absorbs carbon dioxide.
the total volume of gas in the chamber decreases over time because the air that’s breathed out is a mixture of oxygen and carbon dioxide.
as the carbon dioxide is absorbed by the soda lime, only oxygen is in the chamber the subject inhales from.
as this oxygen gets used up by respiration, the total volume decreases.
how do you get a valid reading from a spirometer?
the person using it must be wearing a nose clip - ensures they can only breathe in and out through their mouth (so all the air they breathe goes through the spirometer).
the machine must be airtight.
