In hemodialysis, what is the main function of the external machine?

In hemodialysis, the primary function of the external machine is to filter the blood. This machine acts as an artificial kidney, removing waste products, excess electrolytes, and fluids that build up in the blood when the kidneys are not functioning adequately. During the process, blood is drawn from the body, circulated through a dialyzer (the part of the machine that acts as the filter), and then returned to the body. This filtration process is crucial for maintaining the body's balance of fluids and electrolytes, which is often disrupted in individuals with kidney failure.

The other options do not align with the purpose of hemodialysis. For example, creating new blood cells is a function of bone marrow, while adding nutrients or removing excess glucose are not primary roles of the hemodialysis machine. Hemodialysis specifically targets the removal of waste and excess substances from the bloodstream, making filtration its main function.