In respiration, air is inhaled into the lungs, which provide a large surface area for transport of oxygen, carbon dioxide, and water to or from the blood. The transported oxygen is delivered to body cells where it oxidizes glucose and fats from food to produce carbon dioxide, water, and thermal energy. The carbon dioxide and water are transported from the cells to the blood and back to the lungs, from which they are exhaled. The exhaled gas is at body temperature and saturated with water, some produced in the glucose and fat oxidation and some additionally drawn from moist lung tissue. Other water-containing streams— food, water, perspiration, and excreted waste streams—maintain the body’s level of hydration.

Suppose an individual inhales air at 20°C and 20%relative humidity, and 25%of the inhaled oxygen is consumed in the glucose oxidation reaction. (Under certain conditions, it is reasonable to neglect the oxidation of fats.) A flowchart of the respiration–metabolism process is shown below. The water in the exhaled gas equals the inhaled water plus the water produced by glucose oxidation plus additional water drawn from the lungs. Q_m represents only the heat transferred to or from the body as a consequence of the phenomena just described; not shown are heat and work transferred due to other bodily processes.

(a) Assume a basis of 1 mol bone-dry air (plus the water that goes with it) inhaled at 20°C. Draw and fully label a flowchart of the metabolic process, considering only breathing and glucose oxidation as components of the process. You don’t need to label the streams between the two units, since this problem will not require determining their masses or compositions. Do a degree of-freedom analysis of the overall system.

(b) Suppose all of the water and CO₂ produced from the glucose oxidation are transported to the lungs and exhaled, and calculate the masses of all components of all labeled streams.

(c) If the individual inhales an average of 500mL of air per breath and takes 12 breaths per minute, how much water (fluid ounces) must she drink per day to make up for the water she loses by breathing?

(d) Returning to the original basis, estimate the heat (kJ) transferred to or from the body as a consequence of breathing and glucose oxidation, assuming that the glucose is oxidized at 37°C and at that temperature ΔĤ_c = 2816 kJ/mol.

Transcribed Image Text:

Inhaled air 02 N2 H20 Exhaled gas O2 N2 CO2 H20 RESPIRATION (lungs) CO2 H20 O2 H,O (from lung tissue) МЕТАВOLISM C,H120, + 602 - 6CO2 + 6H,0 Glucose (from food) Om