Exchange Surfaces & Breathing Flashcards
Specialised Exchange Surfaces
UNICELLULAR ORGANISMS have…
- low oxygen demand
- low metabolic activity
- large SA:vol ratio
- ^ opposite for multicellular organisms
- gases can’t be exchanged fast enough or in large amounts for multicellular organisms to survive
Effective Exchange Surfaces
- increased surface area to overcome the limitations of a small SA:vol ratio
- thin layers to shorten the diffusion pathway
- good blood supply maintains a steep concentration gradient for diffusion
- ventilation to maintain diffusion gradient (for gases)
Human Gaseous Exchange & The Nasal Cavity
- mammals maintain body temperature independently
- mammals have high oxygen demand for cellular respiration
- the nasal cavity has a large SA
- ^ good blood supply that warms incoming air
- ^ hairy lining that secretes mucus to trap dust & bacteria
- moist surfaces that increase humidity of incoming air to reduce evaporation
Trachea
- supported by incomplete rings of cartilage to prevent collapsing
- incomplete rings allow food to move down oesophagus
- lined with ciliated epithelium and goblet cells inbetween
- cilia beat and move mucus along, towards the throat
Bronchus & Bronchioles
- Bronchi = divided trachea leading to the left & right lung
- bronchi divide into many small bronchioles
- bronchioles have no cartilage rings
- ^ walls contains smooth muscle
- lined with a layer of flattened epithelium making some gas exchange possible
Alveoli
- tiny air sacks of thin flattened epithelial cells, collagen & elastin fibres
- elastic tissues allow for elastic recoil when air is drawn in and out
- contains all adaptations for effective gas exchange
- ^ including good blood supply from network of capillaries
- inner surface covered in layer of water & lung surfactant that keep it inflated
- ^ oxygen dissolves in this water before it diffuses into blood
Lungs
- diaphragm = domed sheet of muscle at bottom of thorax
- thorax is lined w ‘pleural membranes’ that surround lungs
- pleural cavity = space between p. membranes filled with lubricating fluid
- ^ reduces friction between tissues in lungs making it easier to breathe
Ventilation (INSPIRATION)
active process
1. Diaphragm contracts (flattens)
2. External intercostal muscles contract so ribs move up and out
3. Volume of thorax increases (lungs inflate) so pressure decreases
5. Atmospheric pressure forces air into lungs until equilibrium
6. Gas exchange occurs in respiring cells
Ventilation (EXPIRATION)
passive process
7. Diaphragm relaxes and bounces back into its original “domed” shape
8. External intercostal muscles relax so ribs move down and in
9. Elastic fibres in alveoli return to normal length (elastic recoil)
10. Volume of thorax decreases (lungs deflate) so pressure increases
11. Atmospheric pressure forces carbon dioxide out of lungs until equilibrium
Active Expiration
- internal intercostal muscles contract
- ^ pulls ribs down hard and fast
- abdominal muscles contract to force diaphragm up
- ^ pressure in lungs increases rapidly
Measuring Lung Capacity
- Peak flow meters measure how much air is expelled from lungs
- Spirometers investigate lung volume & breathing patterns
They include…
- an airtight chamber filled with pure/medical oxygen above a “water level”
- soda lime CO2 absorber
- nose clip & mouthpiece
- a pen on the chamber lid that records the volume data on a ‘kymograph’
MLC definitions
- tidal volume = volume of air moving in/out of lungs during resting rate
- ^ 15% of vital capacity
- vital capacity = max vol. of air expelled after complete inhalation (vice versa)
- residual volume = air left in lungs after full exhalation
- inspiratory volume = max volume of air breathed in above normal inhalation
- expiratory volume = extra air forced out above normal tidal volume
- total lung capacity = vital + residual vol.
- ventilation rate = tidal vol. x breathing rate (per min)
Insect Gaseous Exchange
- tough chitin exoskeleton restricts gas exchange
- spiracles along thorax and abdomen allow air to enter and leave
- ^ water is lost in the process
- ^ sphincters act as “guard cells” to minimise loss
- spiracles are closed when oxygen demand is low
Insect Tracheae
- tracheae run along whole insect
- ^ acts as a delivery system that carries air into the its body
- lined with spirals of chitin to keep open
- ^ making it impermeable to gases
- tracheae branch into tracheoles that spread throughout tissues
Insect Tracheoles
- single elongated cell with no chitin lining
- ^ making it freely permeable to gases
- spread throughout tissue creating a short diffusion pathway
- ^ gas exchange takes place by diffusion
- many tracheoles to provide a large SA
