The Lumen of Which of the Following Systems is Part

Question

The lumen of which of the following systems is part of the internal environment?
A) gastrointestinal and urinary systems
B) respiratory system
C) gastrointestinal system
D) urinary system
E) cardiovascular system

Accepted Answer

The lumen of the cardiovascular system is considered part of the internal environment because it contains blood, which circulates throughout the body, delivering nutrients and oxygen to cells and removing waste products. This system directly interacts with and supports the internal environment of the body. In contrast, the lumens of the gastrointestinal, urinary, and respiratory systems are technically outside the body proper and interface with the external environment.