Chapter 24

• The four chemical classes of respiratory pigments are all metalloproteins.
• Respiratory pigments bind reversibly with oxygen at specific oxygen-binding sites associated with the metal atoms in their molecular structures.
• In hemoglobins, the unit molecule consists of heme bonded with protein.
• The heme structure is an iron porphyrin that is identical in all hemoglobin.
• Globin varies widely among species and among different molecular forms of hemoglobin within any single species.
• Hemoglobins are the most common and widespread respiratory pigments.
• Virtually all vertebrates have blood hemoglobin.
• The blood-hemoglobin molecules of vertebrates always occur in red blood cells.
• Hemocyanins are the second most common of the respiratory pigments, they turn bright blue when oxygenated.
• Respiratory pigments increase the oxygen-carrying capacity of blood, meaning the total amount of oxygen that can be carried by each unit of volume.
• When respiratory pigments are combined with oxygen, they are considered oxygenated.
• When respiratory pigments release oxygen, they are deoxygenated.
• The oxygen equilibrium curve of a respiratory pigment shows the relation between the extent of oxygen binding by the pigment and the oxygen partial pressure.
• The shape of the oxygen equilibrium curve depends on the degree of cooperativity among oxygen-binding sites on respiratory-pigment molecules.
• The Bohr effect is a reduction in oxygen affinity caused by a decrease in pH and/or an increase in CO2 partial pressure.
• The Bohr effect typically enhances oxygen delivery because it promotes oxygen unloading in systemic tissues while promoting loading in the breathing organs.
• Elevated blood temperatures often decrease the oxygen affinity of respiratory pigments.
• Organic molecules and inorganic ions frequently serve as allosteric modulators of respiratory-pigment function.
• Respiratory pigments are diverse in their functional properties.
• Respiratory pigments can potentially perform oxygen transport, facilitate CO2 transport, transport other substances, blood buffer, and store oxygen.
• Blood respiratory pigments typically become well oxygenated in breathing organs, and when animals are at rest, they typically release only a modest fraction of their oxygen to the systemic tissues.
• During exercise, oxygen delivery is enhanced by increases in both the extent of pigment unloading and the rate of blood flow.
• The oxygen affinities of respiratory pigments are often critical for pigment function.
• When oxygen is transferred from one respiratory pigment to another in an individual animal, the pigment receiving the oxygen has a higher oxygen affinity.
• Respiratory-pigment physiology undergoes acclimation, as by changes in pigment amounts, synthesis of new molecular forms, or modulation of preexisting forms.
• The carbon dioxide equilibrium curve shows the relation between the total carbon dioxide concentration of blood and the CO2 partial pressure.
• In water breathers, the CO2 partial pressures of both systemic arterial blood and systemic venous blood are typically low.
• In air breathers, blood CO2 partial pressures tend to be far higher and therefore on the flatter portion of the curve.
• Most CO2 carried in blood is typically in the form of bicarbonate.
• Bicarbonate formation depends on blood buffers and determines the shape of the carbon dioxide equilibrium curve.
• Carbonic anhydrase facilitates the uptake and loss of CO2 from the blood.
• The neutral pH varies with temperature, being higher at low temperatures than at high ones.
• In animals with variable body temperatures, the normal blood pH often varies in parallel with the neutral pH, being displaced in the alkaline direction to a constant extent.
• Acidosis and alkalosis are categories of acid-base disturbance.
• Within their range of acid-base regulation, animals correct chronic acid-base disturbances by modulating the elimination of CO2, H+, and bicarbonate in regulatory ways.
• Blood concentration as a function of oxygen partial pressure.

  
• Oxygen delivery by human blood at rest and during vigorous exercise.

  
• As the oxygen partial pressure of blood falls, less and less of a drop in partial pressure is required to cause unloading of 5 ml of oxygen from each 100 ml of blood.

  
• The partial pressure of oxygen at which a pigment is 50% saturated shifts.

  
• The Bohr effect: affinity for oxygen decreases as pH decreases or CO2 partial pressure increases.