Gas Exchange
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Explain the variety of gas exchange surfaces using different examples.
• entire body can be gas exchange surface • spiracles present in tracheae to help increase SA:V ratio • can have external gills, however these are more vulnerable to damage • suck water over gills and have internal gills which increase SA:V ratio • can have internal lungs which are highly protected but it’s more difficult to get gas exchange medium IN
Describe the key features of a gas exchange surface.
• Large SA:V ratio • Very thin barrier (small diffusion distance between air and blood) • Concentration gradient (in order to avoid equilibrium by by allowing movement of internal and external media) • Selectively permeable (to ensure only the target molecules pass through)
What is Fick’s Law?
Rate of gas exchange = (surface area x concentration gradient x diffusion coefficient) / diffusion distance
How is gas exchange maximised?
• increase area • increase pressure difference • decrease diffusion distance
Describe the advantages and disadvantages of breathing air versus water.
• oxygen diffuses 8000x more rapidly in air than in water • water is harder to move as it is 800x denser and 50x more viscous than air • more CO2 in water because is is 20x more soluble in water than in air
How are CO2 and O2 transported across the alveolar membrane?
• capillary transports CO2 to alveolus - alveolus transports O2 to capillary
How is increased surface area in the lung achieved?
• branching of bronchioles - many alveoli
Why is water inside alveoli an issue? Explain using an animal example.
Water is sticky and can cause alveoli to stick together; therefore cannot breathe. E.g fish when out of water cannot breathe bc gills contain water and stick together bc of surface tension
What is used to disrupt surface tension within alveoli and lungs?
Surfactant. It is phospholipoprotein.
Why are premature babies unable to breathe?
They don’t have surfactant to disrupt surface tension in alveoli
What type of exchange flow occurs in gills? How does it work?
Counter-current flow. H2O and blood travelling opposite to each other across gills
What is co-current and counter-current flow? Which one maximises gas exchange more and how is this done?
Co-current flow: oxygen in water travels in same direction as oxygen in haemolymph. Pressure difference is not maintained Counter current flow: oxygen in water travels in opposite direction to oxygen in haemolymph. Maintains pressure difference and therefore maximises gas exchange.
What factors affect solubility of oxygen in water?
• salinity • temperature • pressure
What is eutrophication?
• applies to still moving water where pressure gradient is not maintained • in summer, algal growth occurs which lead to O2 depletion, bad for fish. • in winter, decay occurs leading to O2 depletion again
What is diaphragm movement in lung controlled by?
Controlled by phrenic nerves
Describe the pleural pressure and what the lungs look like when inhaling. Describe the same when exhaling.
Negative plural pressure, keeps lung stuck to thoracic wall. Movement of diaphragm, releases When exhaling, pleural pressure is equal to atmospheric pressure. Lungs are no longer stuck to thoracic wall. Lung is collapsedi. Produces pneumothorax which is presence of air between lung and chest wall, causing collapse of lung
What are the two reserves in a human lung? What are the two volumes?
Reserves: inspiration to and expiratory Volumes: tidal and residual
Why is there always air left in our lungs even after we breath all the air out?
Can’t breathe everything out otherwise lung system would collapse. This is residual volume
What is eupnea?
Normal breathing
Describe the properties of alveolar air.
It is fairly stagnant and has lower %O2 than air. Still higher level than in the blood though
What is haemoglobin?
Main vertebrate respiratory pigment
Why does O2 binding cause colour change?
Due to metal ion in pigment leg haemocyanin turns blood bluish
What is haemoglobin composed of? What does each heme group contain?
4 globin protein subunits, each containing a heme group. Therefore 4 heme units. Each heme group contains an iron ion which binds to O2.
Compare the colours of oxygenate vs deoxygenate blood.
Oxygenated blood is lighter red than deoxygenated blood.