Chapter 35: Gas Transport & pH Regulation

Gas Transport & pH Regulation begins by explaining how oxygen and carbon dioxide move along partial pressure gradients, emphasizing the indispensable role of hemoglobin in increasing the blood's carrying capacity for oxygen. The text details the cooperative binding of oxygen to the four subunits of hemoglobin, describing the transition from a tense configuration with low affinity to a relaxed state with high affinity. This relationship is graphically represented by the sigmoid-shaped oxygen-hemoglobin dissociation curve, which is influenced by factors such as blood temperature, pH levels, and the concentration of 2,3-diphosphoglycerate. The Bohr effect is highlighted to show how increased acidity facilitates oxygen release in tissues. In contrast, carbon dioxide transport is explained through its dissolution in plasma, its binding to proteins as carbamino compounds, and its primary conversion into bicarbonate via the enzyme carbonic anhydrase within red blood cells. This process involves the chloride shift, where bicarbonate ions are exchanged for chloride to maintain electrical balance. The chapter also provides an in-depth analysis of acid-base balance, defining the arterial pH of 7.4 and the critical buffering systems, including the carbonic acid-bicarbonate system and the buffering capacity of hemoglobin and plasma proteins. It distinguishes between respiratory and metabolic forms of acidosis and alkalosis, outlining how the body utilizes rapid respiratory compensation through altered ventilation and slower renal compensation through the secretion of hydrogen ions or reabsorption of bicarbonate. Furthermore, the discussion extends to the various classifications of hypoxia, such as hypoxemic, anemic, ischemic, and histotoxic types, and explores the clinical implications of carbon monoxide poisoning, which severely impairs oxygen delivery. Finally, the chapter examines the human body's remarkable ability to adapt to high altitudes through acclimatization processes, including increased erythropoietin production to stimulate red blood cell formation and shifts in the ventilatory response to manage low atmospheric oxygen levels.