Final answer:
The average percentage of plasma in blood is 55%. For someone with a hematocrit of 42%, their blood plasma makes up approximately 58% of their blood, as plasma and erythrocytes (red blood cells) are the two main components of blood volume.
Step-by-step explanation:
The percentage of blood that is made up of plasma is approximately 55%. When considering a patient with a hematocrit of 42 percent, this is indicative of the volume percentage of erythrocytes (red blood cells) in the blood. Since erythrocytes make up about 45% of blood and plasma constitutes about 55%, the hematocrit value essentially indicates the proportion of red blood cells.
Given that plasma and erythrocytes are the two main components of blood volume, and knowing that the hematocrit measures red blood cells, one can conclude that the remaining percentage of blood volume must be plasma. Therefore, if a patient's hematocrit is 42%, this suggests that the patient's blood plasma would approximately be 100% - 42% = 58%, slightly higher than the average due to individual variability.
To summarize:
- Average plasma percentage = 55%
- Patient's erythrocytes (hematocrit) = 42%
- Patient's plasma percentage ≈ 100% - 42% = 58%