Cambridge O Level Biology · Syllabus 5090 · Human Nutrition
Liver
What is Liver?
A large organ associated with the digestive system that produces bile, which is stored in the gall bladder and released into the duodenum to emulsify lipids. The liver also receives most of the absorbed nutrients directly from the ileum through the hepatic portal vein, and stores excess glucose as glycogen.
This definition is part of the Human Nutrition chapter in Cambridge O Level Biology.
Common mistakes with Liver
- “Bile is an enzyme.” Why it is wrong Bile contains no enzyme, catalyses no reaction and breaks no chemical bond. Write instead "Bile is an alkaline liquid made by the liver. It contains no enzymes."
- “Enzymes are made where they act.” Why it is wrong Pancreatic amylase is made in the pancreas and acts in the small intestine; bile is made in the liver and acts in the duodenum. Questions ask for both columns precisely because they differ. Write instead "Amylase is produced by the salivary glands and the pancreas, and acts in the mouth and the small intestine."
- “The hepatic portal vein carries food from the stomach to the liver.” Why it is wrong Two errors. It carries blood, containing absorbed molecules and ions, not food; and it starts at the capillaries of the ileum, not the stomach. Write instead "The hepatic portal vein carries most of the molecules and ions absorbed in the ileum to the liver."
Questions students ask about Liver
What does the hepatic portal vein carry, and where?
It carries most of the molecules and ions absorbed in the ileum — glucose, amino acids, mineral ions and water — in blood, from the capillaries of the small intestine directly to the liver. It is unusual among veins because it runs from one capillary network to another instead of returning blood to the heart. The products of lipid digestion are the exception: they enter the lacteals and travel through the lymphatic system, joining the blood later.