Video Transcript
What substance, or substances, is
urea formed by the breakdown of?
This question is asking us about
urea, which is a waste product excreted in the urine. Before answering our question,
let’s first describe what the excretory system is.
Metabolism is the sum of all
chemical reactions in the body. These reactions are important for
almost every process ranging from the breakdown of food molecules for energy to the
synthesis of biological macromolecules. These chemical reactions can
produce products that aren’t always useful for the human body, or are sometimes
toxic. These are known as waste
products. Here are some examples of waste
products produced by the body. Carbon dioxide, as you might
recall, is produced as a by-product of cellular respiration, which produces energy
from the breakdown of glucose.
The process of removing waste from
the body is called excretion, and many organs are involved in this process. Some of these organs include the
lungs, liver, and kidneys. These organs make up the excretory
system, although they also belong to other organ systems as well.
Urea is excreted by the kidneys and
is the result of the breakdown of amino acids from proteins. You’ll recall that amino acids are
the monomer subunits of proteins. When amino acids are broken down,
the amino group is converted into a toxic substance called ammonia. The liver is responsible for
converting toxic substances, like ammonia, into less toxic ones. Ammonia is actually converted into
urea by the liver.
Urea is a major component of the
urine, which is formed by the filtering actions of the kidneys. The kidneys are able to filter the
blood’s contents, carrying waste and excess ions away to make urine, while only
allowing useful compounds to be reabsorbed into the body.
Getting back to our question, amino
acids are the substances that are broken down to form urea.
