Lesson 3 of 7 / Nutrition in humans
Absorption, assimilation and the liver
What happens to glucose after it enters the blood?
I can trace absorbed nutrients through the hepatic portal vein and explain assimilation.
I can describe named digestive organs and ingestion, digestion, absorption, assimilation and egestion.Syllabus
Syllabus K224 / K225, Topic 4(a). Describe named digestive organs and ingestion, digestion, absorption, assimilation and egestion.
I can state the hepatic portal vein function.Syllabus
Syllabus K224 / K225, Topic 4(c). State the hepatic portal vein function.
I can state the five specified liver roles.Syllabus
Syllabus K224 / K225, Topic 4(d). State the five specified liver roles.
About 5 min
Make a guess. You are not marked.
Glucose has just been absorbed from your small intestine into the blood. Where does that blood go first?
Show the answer
To the liver, in the hepatic portal vein.
The hepatic portal vein takes nutrient-rich blood straight to the liver, which processes it before it goes on.
The key idea
The hepatic portal vein carries nutrient-rich blood from the small intestine to the liver. The liver processes nutrients before blood carries them onwards.
Hepatic means related to the liver. Follow glucose and amino acids in blood from the intestine; do not confuse this vessel with the duct that carries bile.
Explore the idea
Follow absorbed glucose to the liver
The hepatic portal vein delivers nutrient-rich blood to the liver. Converting absorbed glucose into glycogen is assimilation and storage.
Original flow diagram. Hormonal regulation is studied in homeostasis. Absorbed fat follows mainly the lacteal and lymph route, not this immediate portal route.
Explanation
Digestion makes small, soluble molecules that can pass through the wall of the small intestine. This is absorption. Glucose and amino acids go into the blood, which carries them away.
The hepatic portal vein carries this nutrient-rich blood from the small intestine to the liver. It is a blood vessel, not a bile duct. Bile travels the other way, from the liver to the intestine, in ducts.
Liver cells take some glucose out of the blood and turn it into glycogen to store it. When the body needs glucose, the liver breaks glycogen back down into glucose and releases it into the blood. Glycogen is a large storage molecule made of many glucose units.
Assimilation is what cells do with absorbed nutrients. Glucose can be used in respiration. Amino acids can be built into proteins for growth and repair. Absorption is getting nutrients into the blood; assimilation is using them.
Step by step
- 1
Absorb
Small soluble nutrients cross the intestinal wall into blood.
- 2
Transport
The hepatic portal vein takes nutrient-rich blood to the liver.
- 3
Assimilate
Cells use nutrients, for example by building proteins or storing glucose as glycogen.
Worked example
After a carbohydrate-rich meal
Glucose concentration rises in blood leaving the small intestine. Name the vessel taking it to the liver and describe one way the liver can store it.
One way to explain it
The hepatic portal vein takes the glucose-rich blood to the liver. Liver cells convert glucose into glycogen for storage. Glycogen can later be broken down to glucose when needed.
Why this answer works
- Give the precise vessel name.
- Use the correct direction: intestine to liver.
- Distinguish glucose from its storage molecule glycogen.
Watch out for this
A student says: "The hepatic portal vein carries bile from the liver to the intestine." What is wrong with this?
Show the answer
It carries blood from the intestine to the liver. Bile travels towards the intestine through bile ducts, which are not blood vessels.
Check your understanding
Which route and process are correctly paired?
Show the answer
Hepatic portal vein: nutrient-rich blood from the small intestine to the liver.
Glucose can then be assimilated, for example by conversion to glycogen in liver cells.
Quick recall
What happens to glucose after it enters the blood?