Lesson 4 of 7 / Nutrition in humans
The liver processes more than glucose
Why does the liver have so many different jobs?
In this lesson: Explain the liver's roles in glucose storage, fat digestion, amino acid metabolism, urea formation and substance breakdown.
About 6 min
The key ideaThe liver stores and processes nutrients, produces bile, converts excess amino acid nitrogen into urea, and breaks down alcohol and hormones.
Metabolism means the chemical reactions in cells. Deamination is removal of the nitrogen-containing amino group from an amino acid.
Explore the idea
Name the change and its destination
The reverse conversion also occurs: glycogen is broken down to glucose when needed.
Original process summary. Each route highlights one liver role; the liver performs several roles at the same time.
Explanation
The liver helps regulate the supply of nutrients. It converts glucose to glycogen for storage and can convert glycogen back to glucose. This supports an available supply of glucose between meals, as well as providing a way to store some glucose after absorption.
The liver also produces bile for fat digestion. Bile is stored and concentrated in the gallbladder and then enters the duodenum. Emulsification by bile increases fat surface area for lipase; bile itself does not chemically digest the fat.
Amino acids are used to synthesise proteins, but an excess cannot be stored as a reserve of amino acids in the way glucose is stored as glycogen. In the liver, excess amino acids can be deaminated. Their nitrogen-containing amino groups are removed, and the nitrogen is converted into urea, a less toxic waste product.
Urea is released into the blood and carried to the kidneys, where it is removed into urine. The liver makes urea; the kidneys excrete it. The remaining carbon-containing parts of deaminated amino acids can be used in respiration or converted into other substances.
Liver cells also break down alcohol and hormones. Breaking down hormones helps prevent their effects from persisting indefinitely. Alcohol breakdown has limited capacity, and its processing does not prevent damage from excessive consumption. The liver's many roles explain why damage to it can affect several body functions.
Step by step
- 1
Separate nutrient routes
Glucose can become glycogen; amino acids can become proteins or be deaminated if in excess.
- 2
Track the nitrogen
The liver removes amino groups and forms urea. Blood transports it to the kidneys for excretion.
- 3
Include the other roles
Remember bile production, alcohol breakdown and hormone breakdown as distinct liver functions.
Worked example
An excess supply of amino acids
Amino acids are absorbed in excess of the amount needed for protein synthesis. Explain what happens to their nitrogen and name the organ that removes the resulting waste from blood.
One way to explain it
The excess amino acids are deaminated in the liver. Their nitrogen is converted into urea, which enters the blood. The kidneys remove urea from blood and excrete it in urine.
Why this answer works
- Place deamination and urea formation in the liver.
- Name blood as the transport medium.
- Assign removal into urine to the kidneys.
Is this true? "The kidneys turn amino acids into urea."
The liver forms urea after amino acid deamination. The kidneys remove the urea from blood and excrete it.