Before traveling to the rest of the body, all absorbed nutrients or toxins must pass through the:

The liver is a crucial organ in the body's metabolic processes, primarily responsible for filtering blood coming from the digestive tract before it circulates to the rest of the body. This means that after nutrients or toxins are absorbed from the gastrointestinal tract, they are transported via the portal vein directly to the liver.

In the liver, these substances can undergo various processes such as detoxification, metabolism, and storage. Nutrients may be converted into forms that the body can use more effectively, while toxins are modified or broken down for excretion. This process is essential for maintaining homeostasis, regulating blood sugar levels, and ensuring that harmful substances are neutralized before they can affect other organs.

The other options, while important in various functions, do not play this specific role of filtering absorbed substances before they reach systemic circulation. The lungs primarily facilitate gas exchange, the spleen is involved in the filtration of blood and immune responses but not in processing absorbed nutrients and toxins, and the kidneys filter waste products from the blood but do so after substances have already circulated through the body. This mechanism highlights the liver's vital role in maintaining the body's overall health by managing what comes from the digestive tract.