Download HW 11 and 12

Gas Exchange 42.5 and 42.6
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What is gas exchange?
Why does an organism need O2?
How are O2 and CO2 moved across respiratory surfaces?
How can rate of diffusion be increased?
What else is needed?
If you don’t have enough surface area or you’re too “thick” what do you do?
Gills:
Fig. 42.20
- Outfoldings of body surface suspended in water.
- Water keeps cells moist.
- BUT, O2 concentration low in water so gills have to be very efficient.
- Improved by ventilation of gills Ex. crayfish.
-Fig. 42.21
- Fish ventilate gills by water flow through mouth and over gills and out.
- Need lots of energy as H2O denser and less O2 cf air.
- So, have capillaries in gills and blood flow is opposite to movement of water.
- Countercurrent exchange. Maintain difference in O2 along length of capillary so 80% of
O2 removed from water.
Land:
- Higher O2 amounts and faster diffusion BUT more energy needed so ventilation.
- Respiratory surfaces INSIDE body and openings to atmosphere through tubes.
a) Trachea
- Fig. 42.22
- Insects have air tubes (tracheae) throughout body. Air sacs near organs needing
more O2.
b) Lungs
- One location.
- Have a circulatory system to transport gases.
- Spiders, snails, vertebrates (amphibians have small lungs, use moist skin).
Mammals:
- Fig.42.23
- Lungs like a sponge
Air
Nostrils
Pharynx
Epiglottis
Lungs
Bronchioles
Alveoli
Glottis
Larynx
Trachea
Air moistened, filtered, warmed, and sampled in nostrils
Epiglottis closes off entry to larynx when swallowing
Vocal cords stretched to different tensions and exhaled air makes noises.
Alveoli have about 100m2 area in average lung for O2 and CO2 diffusion.
Q: How do you get the air to the lungs?
Bronchi
A: Ventilation by breathing.
Amphibians use POSITIVE pressure breathing.
- Muscles lower the floor of the oral cavity and air drawn in through nostrils.
- Nostrils and mouth then closed and oral cavity rises (positive pressure) forcing air
down trachea.
- Recoil of lungs and pushing of muscular body wall force air out of lungs.
Mammals use NEGATIVE pressure breathing. Fig. 42.24.
- Like a suction pump.
- Contraction of diaphragm muscle the rib cage muscles creates a vacuum (negative
pressure), in the chest cavity and air moves in to fill this negative pressure.
- Relaxation of the diaphragm muscle and the rib cage muscles forces air out of the
lungs as the volume of the chest cavity is reduced.
Q: How is breathing regulated?
A: Two parts of the brain (Medulla oblongata and Pons). Fig. 42.26.
- Sensors in the aorta and carotid artery detect levels of CO2 in the blood. CO2
dissolves in the blood to form carbonic acid which reduces the pH (more acidic).
When the pH drops below a certain level the brain speeds up breathing and
circulation.
- This is an automatic response – you don’t consciously think about it.
Q: How are O2 and CO2 loaded and unloaded?
A: Diffusion along concentration gradients.
Fig. 42.27.