Exchange Surfaces and Breathing: F211 1.2.1

Transport systems (e.g. lungs) are necessary because the body's SA:vol ratio is too small meaning diffusion will be too slow to provide enough oxygen.
1. Adaptations of the tissues of the lungs: alveoli are lined with squamous epithelium (short diffusion distance); the endothelium of capillaries (which line the alveoli is thin = short diffusion distance); alveoli have elastic fibres which stetch on inhalation and recoil on exhaltion to stop them from bursting; smooth muscle is present to constrict the airways when there are harmful substances in the air;; erythrocytes are constantly flowng to transport oxygen to the heart and maintain a concentration gradient; goblet cells (mucus to trap debris); ciliated cells (waft debris to throat); diaphragm and intercostals (maintain conc gradient to get oxygen into the blood). Cartilage holds open the trachea and stops it collapsing on itelf.
2. ALVEOLI - refreshing of the air is necessary to maintain a steep concentration gradient for oxygen to enter blood: increased partial pressure of oxygen in alveoli means higher conc of oxyegn in alveoli than blood so oxygen diffuses from alveoli to blood. The steep conc graient is further maintained by continuous blood flow.
3. Diaphragm and intercostals ensure conc gradient to get oxygen in and carbon dioxide out.
  1. Inhalation: intercostal muscles contract (moves the ribs up and out to increase volume in chest cavity); diaphragm contracts and flattens (further increases volume). This increase in voum means the pressue is less in the chest cavity than the outside air so air rushes in down a pressure gradient.
  2. Exhaltion: Intercostal muscles relax (moves ribs down and in to decreae volume in chest cavity); diaphragm relaxes and moves up (decrease volume further). This decrease in volume means the pressue is more in the chest cavity than the outside air so air rushes out.
Spirometer - used to measure vital capacity (largest volume of air that can be moved in/out of lungs in one breath); tidal volume (volume of air moved in/out of lungs in one breath); breathing rate; oxygen uptake
1. Chamber falls on inhalton; rises on exhaltion
2. Subject wears a nose clip to stop air escaping from the nose and breathes normally through the mouth. A trace is produced.
3. To measure tate of oxygen uptake: As oxygen is used up, the volume of the chamber decreases (carbon dioxide given out is absorbed by soda lime. So measure the decrease in the vol of the chamber and the time taken. Divide vol by time to get a rate.
4. Breathing rate. One breath = time from one peak to another. 60 divided by this time = breaths per minute.
5. Residual volume = air always left in lungs as you cannot compress lungs enough to expel it.

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Exchange Surfaces and Breathing: F211 1.2.1

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