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Question 352
Physiology → Haematology
Classification
Question
SSBAQuestion Header
Two adults of equal body weight have substantially different proportions of adipose tissue. One then drinks a large volume of water.
Question Stem
Which statement most accurately describes the expected physiology of blood volume?
Options
A
Blood constitutes about 15% of body weight and is proportionally greater in people with more adipose tissue.
B
Blood constitutes about 7% of body weight, but drinking water does not alter blood volume.
C
Blood constitutes about 7% of body weight and forms a higher percentage of body weight in people with more adipose tissue.
D
Blood constitutes about 7% of body weight, forms a lower percentage in people with more adipose tissue, and blood volume rises after water is drunk.
E
Blood volume is independent of body composition and falls after water is drunk.
Explanation
Blood makes up about 7% of body weight. Blood volume forms a lower percentage of body weight in people with more fat than in thin people. Blood volume rises after water is drunk because absorbed water enters the blood.
Option Validity
A) Blood makes up about 7%, not 15%, of body weight, and its proportional contribution is lower rather than higher with greater adiposity.
B) The approximate 7% value is correct, but blood volume rises after water is drunk.
C) Blood volume forms a lower, not higher, percentage of body weight in people with more fat.
E) Blood volume varies with body composition and rises rather than falls after water is drunk.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Blood, p.67.