Page 904 - Fundamentals of anatomy physiology

Figure 23–23 A Summary of the Primary Gas Transport Mechanisms. Chapter 23 The Respiratory System 891

Plasma O2 pickup Pulmonary Systemic O2 delivery
Red blood cell capillary capillary Red blood cell

Hb Hb O2 Hb O2 O2 O2
O2 Cells in
O2 Hb O2 peripheral
Alveolar tissues
air space O2
Alveolar CO2
air space Cl– HCO3– Chloride Cells in
Hb HCO3–
CO2 Cl– shift peripheral
tissues
H+ + HCO3– H+ + HCO3–
H2CO3 Hb

Hb H+ H2O H2CO3
CO2 Hb H+

H2O

CO2 Hb Hb CO2

Hb CO2 Hb CO2

Pulmonary Systemic
capillary capillary

CO2 delivery CO2 pickup

Peripheral cells continuously absorb oxygen and generate Local Regulation of Gas Transport 23
carbon dioxide. Under normal conditions, the cellular rates and Alveolar Function
of absorption and generation are matched by the capillary
rates of delivery and removal. Both rates are identical to The rate of oxygen delivery in each tissue and the efficiency of
those of oxygen absorption and carbon dioxide excretion at oxygen pickup at the lungs are largely regulated at the local level.
the lungs. For example, when a peripheral tissue becomes more active,
the interstitial PO2 falls and the PCO2 rises. This change increases
If diffusion rates at the peripheral and alveolar capillar- the difference between the partial pressures in the tissues and
ies become unbalanced, homeostatic mechanisms intervene in the arriving blood. As a result, more oxygen is delivered and
to restore equilibrium. Such mechanisms involve (1) changes more carbon dioxide is carried away. In addition, the rising PCO2
in blood flow and oxygen delivery that are regulated at the levels cause the relaxation of smooth muscles in the walls of
local level and (2) changes in the depth and rate of respiration arterioles and capillaries in the area, increasing local blood flow.
under the control of the brain’s respiratory centers. The activi-
ties of the respiratory centers are coordinated with changes in At the lungs, local factors coordinate (1) lung perfusion,
cardiovascular function, such as fluctuations in blood pressure or blood flow to the alveoli, with (2) alveolar ventilation, or
and cardiac output. airflow. This local coordination takes place over a wide range