Question

What is the dissolved O2 in blood called?
1) PaCO₂
2) Hb
3) HCO₃
4) SaO2

Answer 1

The dissolved oxygen in blood that is bound to hemoglobin is called 4)
`SaO_(2)`, which is the correct answer to the student's question. Most oxygen in the blood is transported by hemoglobin, not dissolved directly into the plasma.

Step-by-step explanation:

The dissolved
`O_(2)` in blood is primarily called
`SaO_(2)`, which stands for arterial oxygen saturation.
`SaO_(2)` refers to the amount of oxygen that is bound to hemoglobin in the blood and is available for delivery to tissues throughout the body. Hemoglobin is a protein in red blood cells that is essential for transporting oxygen from the lungs to the rest of the body.

While a small amount of oxygen is dissolved directly into the plasma (about 1.5%), the vast majority of oxygen (98.5%) is bound to hemoglobin, denoted as Hb in option 2 of the question provided. The oxygen that has bound to hemoglobin is not referred to as dissolved, hence terms like
`PaCO_(2)` and
`HCO_(3)` reflect other components of blood gases, with
`PaCO_(2)` indicating the partial pressure of carbon dioxide and
`HCO_(3)` referring to bicarbonate ions in the bloodstream, respectively. Therefore, the most accurate answer is option 4.