What are some main functions of the liver?

The liver plays a crucial role in numerous physiological processes, making it one of the most vital organs in the body. One of its primary functions is bilirubin excretion, which is essential for the breakdown of hemoglobin from red blood cells. The liver processes bilirubin, a byproduct of this breakdown, converting it into a form that can be excreted in bile and ultimately eliminated from the body.

In addition to bilirubin excretion, the liver is integral to drug metabolism. It modifies and detoxifies various substances, including medications and toxins, transforming them into forms that can be more easily eliminated. This function is critical for drug efficacy and safety, as it helps to prevent potentially harmful accumulations in the bloodstream.

Another essential function is protein metabolism, where the liver synthesizes various proteins, including blood-clotting factors and albumin, which helps maintain oncotic pressure and transport substances in the blood. The liver also plays a role in the regulation of amino acids and the overall metabolism of nitrogen, promoting the synthesis and breakdown of proteins based on the body's needs.

Given these diverse yet interconnected functions, the correct answer encompasses all of the proposed functions of the liver, highlighting its critical role in maintaining metabolic homeostasis and overall health.