Respiratory gases (O2 & CO2) are exchanged only by __
diffusion along their concentration gradients
Gas exchange systems are made up of surfaces and the mechanisms that __ & __ those surfaces.
__ is the concentration of a gas in a mixture.
PO2 = 159 mm Hg
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)
Oxygen is easier to obtain from __ than __.
- 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.
Respiratory gas exchange is a 2-way process: __ diffuses out of the body as __ diffuses in.
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.
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.
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)
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)
The trachea branches into 2 __, then into __, and then into __, the sites of gas exchange
bronchi; bronchioles; alveoli
(page 22 on slide)
__ surround and lie between the alveoli - diffusion path (L) between blood and air is less than 2 micrometers.
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)
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)
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)
One subunit binds and changes shape making it easier for the next one to bind - the affinity for O2 is increased
When there is low PO2, one subunit binds to O2. When 3 subunits are bound, a larger increase in PO2 is needed.
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
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)
__ 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)
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)
Breathing is controlled in the __.
(page 43 on slide)
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