Excretion

This lesson covers: 

1. The role of the liver in excretion
2. How the liver breaks down excess amino acids
3. How the liver detoxifies harmful substances

What is excretion?

The liver plays a crucial role in metabolism, which involves many chemical reactions. These reactions generate waste products, including CO₂ and nitrogenous substances, which can harm cells if they accumulate.

Excretion is the process of removing metabolic waste from cells. This is essential for maintaining normal metabolism and homeostasis. For instance, CO₂ is excreted by cells following respiration and is then removed from the body by the lungs.

Many metabolic waste products, like urea, are metabolised in and excreted from the liver cells.

Function of the liver in detoxification

The liver breaks down toxic substances such as alcohol, medications, hormones, and excess amino acids. This detoxification process converts these substances into less harmful compounds that cells can excrete.

The liver breaks down amino acids through these steps:

1. Amine groups are removed from amino acids by deamination, producing ammonia and a keto acid.
2. Ammonia is highly toxic and soluble, interfering with metabolic processes and cell signalling, so it is converted to urea, which is less soluble and less toxic.
3. Urea is then excreted from liver cells, enters the blood plasma, and is filtered out of the body via the kidneys as a part of urine.