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Respiratory gases (O2 & CO2) are exchanged only by __
diffusion along their concentration gradients
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Gas exchange systems are made up of surfaces and the mechanisms that __ & __ those surfaces.
ventilate; perfuse
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__ is the concentration of a gas in a mixture.
Partial pressure
PO2 = 159 mm Hg
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The slow rate of diffusion of __ limits the size and shape of species without internal systems for gas exchange. These species have evolved __, or central cavities, or specialized respiratory systems.
- oxygen in water;
- larger surface area
(page 13 on slide)
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Oxygen is easier to obtain from __ than __.
air; water
- O2 content of air is higher than that of water.
- O2 diffuses much faster through air.
Air and water must be moved by the animal over its gas exchange surfaces - requires more energy to move water than air.
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Respiratory gas exchange is a 2-way process: __ diffuses out of the body as __ diffuses in.
CO2; O2
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The concentration gradient of CO2 from air-breathers to the environment is always __. CO2 is very__ in water and is easy for aquatic animals to exchange.
large; soluble
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Some respiratory systems have adaptations to maximize the exchange of O2 and CO2. From Fick's law of diffusion, this means __
- increased surface area (A)
- maximized partial pressure gradients (P1-P2)
- minimized diffusion path length (L)
- minimized diffusion that takes place in an aqueous medium (D)
rate of diffusion = Q = DA [ (P1-P2)/L ]
- P1: pressure of atm. To increase, breathe in more air. To decrease, climb a mountain.
- P2: capillaries: Decrease P2 by exercising.
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Surface area (A) can be increased by:
- external gills: also mimimize the diffusion path length (L) of O2 & CO2 in water
- internal gills: protected from predators and damage
- lungs: internal cavities for respiratory gas exchange with air
- tracheae: air-filled tubes in insects
(page 18 on slide)
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Air enters the human lung through the oral cavity or nasal passage, which joins the __. Below that, the __ leads to the lungs - at the beginning is the __, or voice box.
pharynx; trachea; larynx
(page 20 on slide)
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The trachea branches into 2 __, then into __, and then into __, the sites of gas exchange
bronchi; bronchioles; alveoli
(page 22 on slide)
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__ surround and lie between the alveoli - diffusion path (L) between blood and air is less than 2 micrometers.
Capillaries
Increasing surface area (A) of alveoli would increase the rate of diffusion (Q), while emphysema from smoking would destroy alveoli and decrease the surface area.
(page 24 on slide)
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O2 is picked up where its partial pressure is __ and is released where the partial pressure is __
high (in capillaries); lower (in tissues)
(page 28 on slide)
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One such O2 transporter is __ - a protein with _ polypeptide units. Each polypeptide surrounds a __ group that can bind a molecule of O2.
hemoglobin; 4; heme
One molecule of hemoglobin can bind up to 4 molecules of O2
(page 30 on slide)
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One subunit binds and changes shape making it easier for the next one to bind - the affinity for O2 is increased
positive cooperativity
When there is low PO2, one subunit binds to O2. When 3 subunits are bound, a larger increase in PO2 is needed.
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Myoglobin has a __ for O2, binds it at low PO2 values when hemoglobin molecules would release their O2. It provides a __ for high metabolic demand for O2.
higher affinity; reserve
Llamas and human fetuses also have a high affinity for O2
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The affinity of hemoglobin for O2 varies. 3 factors are:
- hemoglobin composition
- pH: in the Bohr effect, blood circulating through active tissues has a lower pH and H+ ions to bind to the hemoglobin molecule in place of O2
- 2,3-biphosphoglyceric acid (BPG) - also lowers affinity for O2 (byproduct of glycolysis)
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__ is transported away from the tissues after diffusing into the blood. In the blood plasma, it's slowly converted into __. In endothelial cells and red blood cells, __ speeds up the conversion.
CO2; HCO3-; carbonic anhydrase
Conversion of CO2 to HCO3- keeps PO2 low and facilitates diffusion away from the tissues.
(page 40 on slide)
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From blood capillaries to the lungs, the conversion reaction is from __ to __, which diffuses from the blood into the __ and is exhaled.
HCO3-; CO2; alveoli
(page 41 on slide)
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Breathing is controlled in the __.
medulla
(page 43 on slide)
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In mammals, the breathing rate is more sensitive to changes in __ than to __. The __ of blood is the primary metabolic feedback for breathing.
PCO2; PO2; PO2
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