3.1 - Exchange surfaces and breathing Flashcards
Why larger organisms need transport systems and specialised surfaces for exchange
- Large organisms are more active and so have higher demands for oxygen
- Larger organisms have smaller surface-area-to-volume-ratios.
- This means diffusion is too slow
- The diffusion distance is too great as many cells are deep in the body and not in contact with the environment
- Insufficient waste would be removed
Inspiration (breathing in)
- diaphragm contracts, flattens and moves downwards
- external intercostal muscles contract, internal intercostal muscles relax and move the ribs up
and out - this increases the volume inside the thorax and lungs
- this reduces the pressure inside the thorax and lungs below atmospheric pressure
- air moves into the lungs down a pressure gradient
Expiration (breathing out)
- diaphragm relaxes and moves upwards
- external intercostal muscles relax, internal intercostal muscles contract and ribs move down
and in - this decreases the volume inside the thorax and lungs
this induces the pressure inside the thorax and lungs above atmospheric pressure - air moves out of the lungs down a pressure gradient
Features of a good exchange surface
- Large surface area - more space for molecules to pass through – more efficient
- Thin barrier - shorter diffusion distance
- Fresh supply of molecules on one side and removal on the other - keeps concentration Gradient steep for quick diffusion
- Permeable to exchange molecule e.g. has carrier proteins in cell surface membrane
How lungs efficient exchange surfaces
- Large SA- millions of tiny alveoli give a huge S.A for more space for O2 and CO2 to diffuse
across (not SA:Vol)
Thin barrier - only two cells thick
- walls of alveoli are one cell thick
- walls of capillaries are one cell thick
- walls of alveoli and capillaries are made of squamous epithelial cells (very thin cells)
- capillaries and alveoli in close contact
- capillaries are so narrow that the RBCs are squeezed against wall, making them closer to the air in the alveoli and reducing the rate the flow past in the blood
- Permeable - Plasma membranes of the cells lining the alveoli and capillaries are fully
permeable to O2 and CO2
Tissues in the trachea and bronchi and bronchioles
C shaped rings of cartilage: (not in bronchioles)
- keep airways open and prevent collapse during inspiration when there is a low pressure in the thorax
- (also allows some flexibility to move neck without constricting airways)
Smooth muscle:
- contracts to constrict airways
- reduces flow of air (reduces harmful substances going into lungs)
Elastic fibres: DO NOT CONTRACT/RELAX
- stretch when smooth muscle contracts
- recoil (when smooth muscle relax) to help dilate the airway again
Goblet cells: (not in smallest bronchioles)
- secrete mucus which traps bacteria and other particles to be
removed from the lungs to reduce infection
Ciliated epithelium:
- waft to and fro to remove mucus from airways up to throat
Blood vessels:
- Supply lung tissue e.g. smooth muscle with oxygen for aerobic respiration
Tissues in the alveoli
Elastic fibres: DO NOT CONTRACT/RELAX
- stretch during inhalation to increase the lung volume and prevent the alveoli from bursting
- recoil during exhalation to expel more air from the alveoli
Squamous epithelium
- alveoli walls one cell thick to provide a short diffusion distance for gaseous exchange
Using a spirometer to measure mean tidal volume
- idea of not breathing through nose
- patient breathes normally
- measure height of waves (tidal volume) at least 3 waves from trace
- calculate mean (add volumes together and divide by number of breaths)
Why the volume of oxygen in the spirometer decreases over time
- When you exhale into the spirometer, the carbon dioxide is absorbed by the soda lime.
- This decreases the volume of gas in the spirometer and causes the trace line to fall gradually.
- This volume of carbon dioxide removed is equal to the volume of oxygen used by the person.
- We can use this to measure the rate of oxygen uptake.
