# The Respiratory System: Gas Exchange and Regulation of Breathing

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The Respiratory System: Gas Exchange and Regulation of Breathing

O2 and CO2 Movement Figure 17.1

Partial Pressure Ptotal = P1 + P2 + P3 + … Pn
Partial pressure of a gas depends on Fractional concentration of the gas Total pressure of gas mixture Pgas = %gas x Ptotal Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Gas Composition of Air Pair = 760 mm Hg = PN2 + PO2
PN2 = 0.79 x 760 mm Hg = 600 mm Hg PO2 = 0.21 x 760 mm Hg = 160 mm Hg Air is only 0.03% carbon dioxide PCO2 = x 760 mm Hg = 0.23 mm Hg Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Composition of Air at 100% Humidity
Pair = 760 mm Hg = PN2 + PO2+ PH2O PN2 = x 760 mm Hg = 563 mm Hg PO2 = x 760 mm Hg = 149 mm Hg PH2O = x 760 mm Hg = 47 mm Hg PCO2 = x 760 mm Hg = 0.21 mm Hg Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Solubility: Henry’s Law
c = kP c = molar concentration of dissolved gas k = Henry’s Law constant P = partial pressure of gas in atmospheres Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Solubility of O2 Figure 17.3a

Solubility of CO2 Figure 17.3b

O2 and CO2 Partial Pressures
Figure 17.4 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

O2 and CO2 Partial Pressures
Table 17.1 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Pulmonary O2 Exchange Figure 17.5a

Pulmonary CO2 Exchange Figure 17.5b

Respiratory Terms Table 17.2

Oxygen Transport in the Blood
Oxygen not very soluble in plasma Thus only 3.0 mL/200 ml arterial blood oxygen dissolved in plasma (1.5%) Other 197 mL arterial blood oxygen transported by hemoglobin Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Forming Oxyhemoglobin
Figure 17.6a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Dissociation of O2 from Hemoglobin
Figure 17.6b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Saturation of Hemoglobin with O2
Arterial blood Hemoglobin is 98.5% saturated Figure 17.7a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Saturation of Hemoglobin with O2
Venous blood Hemoglobin is 75% saturated Figure 17.7b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Oxygen Dissociation Curve
Figure 17.8 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Effects of O2 Affinity Changes

Temperature Effects: O2 Saturation
Higher temperature Active tissues Shift right More O2 unloading in tissues More O2 delivery to tissues Figure 17.10a Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

pH Effects: O2 Saturation
Bohr effect Lower pH increases O2 unloading Active tissues Produce more acid pH decreases in tissues Decreased pH causes shift right in saturation curve More O2 is unloaded to tissues Figure 17.10b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Carbon Monoxide Hemoglobin has greater affinity for carbon monoxide (CO) than for oxygen Prevents oxygen from binding to hemoglobin Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

CO2 Transport in Blood Table 17.3

Carbon Dioxide Transport in Blood
The role of carbonic anyhdrase in carbon dioxide transport Carbon dioxide exchange and transport in systemic capillaries and veins Carbon dioxide exchange and transport in pulmonary capillaries and veins Effect of oxygen on carbon dioxide transport Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Carbon Dioxide Transport Mechanisms
Although carbon dioxide is more soluble in plasma than oxygen, it is still not very soluble 5–6% transported dissolved in plasma Carbon dioxide can bind to hemoglobin to form carbaminohemoglobin 5–8% transported bound to hemoglobin Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Carbon Dioxide Transport Mechanisms
Can be converted to bicarbonate by erythrocytes, then transported into plasma 86–90% transported dissolved in the plasma as bicarbonate Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

Carbonic Anhydrase CA CO2 + H2O  H2CO3  H+ + HCO3-
Enzyme that converts carbon dioxide and water to carbonic acid Law of Mass Action: An increase in CO2 causes an increase in bicarbonate and hydrogen ions CO2 + H2O  H2CO3  H+ + HCO3- CA Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.

CO2 Exchange: Tissues Figure 17.11a

CO2 Exchange: Lungs Figure 17.11b

PO2 Effect on CO2 Transport
Figure 17.12 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings.