Summary
Villi and microvilli provide a huge surface area for nutrient absorption into blood and lymph.
In depth
Folds, villi and microvilli increase area to about 250 square metres. Glucose and amino acids enter by active transport (with sodium) and facilitated diffusion, then the blood. Fatty acids are re-formed into triglycerides and enter lacteals.
Capillaries carry sugars and amino acids to the hepatic portal vein. Lacteals take up fats. Vitamin B12 needs intrinsic factor.
Remember: most absorption occurs in the small intestine, not the stomach.
The small intestine is about 6 m long and has three parts: duodenum, jejunum and ileum. Each villus has a capillary network and a lacteal. Glucose and galactose enter via SGLT1 (with sodium) and fructose by GLUT5 (facilitated diffusion), then all exit through GLUT2 to blood. Amino acids and small peptides use transporters; fatty acids and monoglycerides form micelles with bile salts, diffuse into cells, are repackaged into chylomicrons and enter lacteals. Water follows by osmosis. Bile salts are reabsorbed in the ileum (enterohepatic circulation), and B12 needs intrinsic factor.
In cholera, toxin causes massive chloride and water secretion, and oral rehydration solution uses glucose-sodium co-transport to restore fluids. Damage to villi in coeliac disease reduces absorption.
Key idea: the large surface area and short diffusion distance maximise absorption.
Frequently asked questions
What is Small Intestine Absorption?
Villi and microvilli provide a huge surface area for nutrient absorption into blood and lymph.
Which area of biology covers Small Intestine Absorption, and how advanced is it?
Small Intestine Absorption is one of the 51 topics in Human Physiology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Nephron Function, Digestive System, Digestive Enzymes.
Can you give an example of Small Intestine Absorption?
Coeliac disease flattens villi.
What should I learn before Small Intestine Absorption?
Work through the Beginner topics in Human Physiology first, such as Homeostasis, Tissues and Organs, Skeletal System, then return to Small Intestine Absorption. Intermediate topics assume the Beginner vocabulary.
What topics are related to Small Intestine Absorption?
The closest topics to Small Intestine Absorption are Nephron Function, Digestive System, Digestive Enzymes, Gas Exchange in Alveoli. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Small Intestine Absorption?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Small Intestine Absorption. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Small Intestine Absorption different from Nephron Function?
Small Intestine Absorption: Villi and microvilli provide a huge surface area for nutrient absorption into blood and lymph. Nephron Function: Filtration, selective reabsorption and secretion in the nephron form urine. Read both side by side and note what each one explains.
How should I study Small Intestine Absorption step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Nephron Function and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.