In terms of oxygen transport, what does the term "saturation" refer to?

Saturation in the context of oxygen transport specifically refers to the proportion of available hemoglobin that is bound to oxygen. Hemoglobin is the protein in red blood cells responsible for oxygen transport, and its ability to bind oxygen is dependent on various factors, including the partial pressure of oxygen in the blood.

When we discuss saturation, we are typically referring to a percentage measurement that indicates how much of the hemoglobin present is currently carrying oxygen relative to its total carrying capacity. For example, if hemoglobin is 95% saturated, this means that 95% of the hemoglobin is engaged with oxygen molecules.

This concept is crucial for understanding how efficiently oxygen is being delivered to tissues and how various conditions, such as changes in pH or carbon dioxide levels (Bohr effect), can influence hemoglobin's affinity for oxygen. The other options provided—concentration of oxygen in the blood plasma, rate of oxygen consumption by tissues, and percentage of carbon dioxide in blood—do not accurately capture the specific meaning of saturation in terms of hemoglobin's oxygen binding capacity.