Gas Exchange

Question 1

partial pressure

Answer 1

the pressure exerted by an individual gas in a mixture
the pressure a given gas would exert if it was the only gas in the container
small amounts of oxygen and carbon dioxide dissolve in arterial and venous blood, establishing the partial pressure

Question 2

in humans, gas movement is determined by

Answer 2

pressure differential: gas will move from an area of high pressure to low pressure
the solubility of the gas in the fluid: carbon dioxide > oxygen > nitrogen

Question 3

at rest (1)

Answer 3

gas exchange (alveolar gas-blood gas) equilibrium occurs in 0.25 s
the body does not rid itself of all carbon dioxide as carbon dioxide serves as the chemical basis for ventilatory control in the pons & medulla
alveolar gas composition remains considerably constant

Question 4

at rest (2)

Answer 4

carbon dioxide continually enters the alveoli from the blood
rapid transfer due to its high solubility in plasma

Question 5

at rest (3)

Answer 5

pressure differences between gases in plasma and tissue establish diffusion gradients
carbon dioxide flows from the cells and into the blood

Question 6

at rest (4)

Answer 6

air saturates with water vapor as it enters the nasal cavity, mouth, and respiratory tract
vapor dilutes the inspired air mixture

Question 7

at rest (5)

Answer 7

in the alveoli incoming most ambient air high in oxygen mixes with carbon dioxide returning to the alveoli from the blood

Question 8

at rest (6)

Answer 8

oxygen flows from the lungs into the blood for transport

Question 9

at rest (7)

Answer 9

pressure differences between gases in plasma and tissue establish diffusion gradients
oxygen leaves the blood and diffuse toward cells

Question 10

oxygen is transported in the blood

Answer 10

dissolved in the fluid portion of the blood
in combination with hemoglobin

Question 11

oxygen is transported in skeletal muscle

Answer 11

in combination with myoglobin

Question 12

oxygen has a low solubility so only a small amount of oxygen dissolves in blood

Answer 12

3 mL O2 dissolves per L of blood
cannot sustain life

Question 13

importance of oxygen transport dissolved in fluid

Answer 13

establishes the partial pressure of oxygen (PO2) of plasma
helps regulate breathing
determines oxygen loading of hemoglobin in the lungs and unloading from hemoglobin
the partial pressure of oxygen dissolved in physical solution dictates the oxygenation of hemoglobin to oxyhemoglobin

Question 14

hemoglobin

Answer 14

a globular protein composed of four subunit polypeptide chains; each polypeptide contains a single heme group with its single iron atom that acts as a magnet for oxygen
transports about 197 mL of O2 in each liter of blood
more hemoglobin = higher oxygen carrying capacity
females have 5-10% less hemoglobin than males
partly explains lower aerobic capacity of females

Question 15

cooperative binding

Answer 15

the union of oxygen with hemoglobin
explains hemoglobin oxygen saturation curve

Question 16

oxyhemoglobin dissociation curve

Answer 16

illustrates the saturation of hemoglobin with oxygen at various PO2 values in healthy individuals at sea level
hemoglobin achieves 98% of oxygen saturation with an alveolar/arterial PO2 of 100 mmHg
large drop in PO2 but not a large drop in saturation of hemoglobin (small dissociation)
the quantity of hemoglobin saturated with oxygen declines rapidly when PO2 drops below 60 mmHg
exercise conditions: large amount of oxygen is off loaded from hemoglobin and delivered to the skeletal muscle
a large drop in saturation of hemoglobin (large dissociation)

Question 17

Bohr effect

Answer 17

hemoglobin’s oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide
increases in metabolic heat, carbon dioxide, and acidity from blood lactate accumulation during intense exercise results in more oxygen release to tissues
dissociation curve shifts downward and to the right

Question 18

myoglobin

Answer 18

iron containing globular protein in skeletal and cardiac muscle that combines reversibly with oxygen
slow twitch muscle fibers are high in myoglobin content
facilitates oxygen transfer with the mitochondria when cellular PO2 declines
myoglobin’s oxygen-binding affinity is not affected by temperature, acidity, or carbon dioxide

Question 19

carbon dioxide is transported in the blood

Answer 19

1. dissolved in the fluid portion of the blood
   establishes the PCO2 of blood
   transports ~5% of CO2 formed during energy metabolism
2. in combination with hemoglobin within the red blood cells
   transports ~20% of CO2 formed during energy metabolism
3. as plasma bicarbonate
   transports 60-80% of CO2 formed during energy metabolism

Question 20

carbon dioxide transport: bicarbonate

Answer 20

1. carbonic anhydrase catalyzes the formation of carbonic acid from CO2 and water
2. carbonic acid is ionized into hydrogen atoms and bicarbonate ions
   hemoglobin provides the most important H+ acceptor to regulate the pH of the internal environment
3. plasma PCO2 decreases as CO2 leaves the blood via the lungs
   the reaction reverses and carbon dioxide exits the blood into the alveoli