Emergency Medical Technician (EMT) Intermediate Practice Exam

Which organ or system can survive the longest without oxygen?

1. Cardiac tissue

2. Brain

3. Skeletal muscles

4. Liver

The correct answer is: Skeletal muscles

Skeletal muscles are capable of surviving the longest without oxygen due to their unique ability to switch to anaerobic metabolism when oxygen levels are low. During intense physical activity or periods of limited oxygen supply, skeletal muscles can function for a relatively extended time by relying on stored energy sources like glycogen, converting it into lactic acid for energy production. This anaerobic process allows skeletal muscles to continue contracting and performing basic functions even in the absence of oxygen, although it is less efficient than aerobic metabolism. Over time, however, the accumulation of lactic acid and depletion of energy stores will lead to fatigue and decreased function. In contrast, cardiac tissue and the brain are highly dependent on a continuous supply of oxygen for their functioning. Cardiac muscle cells (myocytes) utilize aerobic metabolism almost exclusively and can suffer irreparable damage within minutes of oxygen deprivation. Similarly, the brain is extremely sensitive to low oxygen levels, with irreversible damage occurring within about five minutes of hypoxia. The liver also requires oxygen for its vital processes, though it has some anaerobic capacity; however, its cells can function for a shorter duration without oxygen compared to skeletal muscle. Therefore, the ability of skeletal muscles to utilize anaerobic metabolism allows them to outlast other organs and systems during