What is the primary function of the liver in the human body?

The liver is the body’s chemical processing plant. Its main job is detoxification and the metabolism (breaking down and building up) of nutrients and drugs. Poisonous substances such as alcohol, old medicines and ammonia from broken-down protein are changed in the liver into safer forms — for example, ammonia is turned into urea, which the kidneys then remove in urine.

The liver also handles the food you absorb from the gut. It stores extra glucose as glycogen and releases it when blood sugar falls, it deals with fats and amino acids, and it makes bile that helps digest fat. All of this is metabolism of nutrients, which is why that answer fits best.

The other choices belong mainly to other organs or are only side roles. Blood pressure is mostly controlled by the heart, blood vessels and kidneys. Hormones are made mainly by endocrine glands such as the pituitary, thyroid and adrenal glands — the liver makes proteins and enzymes, not hormones as its main work. Body temperature is regulated by the skin and the hypothalamus in the brain; the liver’s heat is only a by-product of its chemical work.