Multiple Choice
Blood vessel spasms (vascular spasm) immediately following an injury are stimulated primarily by which of the following?
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17. The Blood
Platelets: Hemostasis
Multiple Choice
In a healthy adult, platelets (thrombocytes) make up approximately what percentage of total blood volume?
A
About 5%
B
About 45%
C
About 20%
D
Less than 1%
Verified step by step guidance1
Understand that blood volume is composed of plasma and formed elements, which include red blood cells, white blood cells, and platelets.
Recall that red blood cells make up about 45% of total blood volume, known as the hematocrit.
Recognize that white blood cells and platelets together make up the remaining portion of the formed elements, but white blood cells are very few in number compared to red blood cells and platelets.
Know that platelets are much smaller and less numerous than red blood cells, so their volume percentage is very small, typically less than 1% of total blood volume.
Therefore, the percentage of platelets in total blood volume is less than 1%, which is significantly lower than the other given options.
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