Anatomy and Physiology / Unit 9: The Respiratory and Digestive Systems
9.7 Absorption in the Small Intestine
Notes
The small intestine's surface area is increased by circular folds, villi and microvilli (the brush border).
- Each villus has capillaries and a lymph capillary called a lacteal.
- Monosaccharides (glucose, galactose, fructose) and amino acids are absorbed into capillaries and travel via the hepatic portal vein to the liver. Fatty acids and monoglycerides form micelles with bile, enter cells, are reassembled into triglycerides and packaged into chylomicrons that enter the lacteals (lymph).
- Vitamins A, D, E and K are fat-soluble and are absorbed with fats. Vitamin B12 needs intrinsic factor from the stomach.
- Water is absorbed in the small intestine (most of it) and large intestine (rest) by osmosis.
- Example: celiac disease damages villi in response to gluten, reducing absorption.
Practice
Which structure inside a villus absorbs digested fats?
Chylomicrons enter the lymph capillary called the lacteal.
Absorbed glucose goes first to which organ?
Nutrient-rich blood from the intestine flows to the liver before the general circulation.
Why do villi and microvilli improve absorption?
More surface area allows more nutrients to be absorbed.
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