9.3 - Absorption

Adaptations of the Ileum and Villi for Absorption

• Simple molecules from digested food are absorbed in the ileum.

Structural Adaptations of the Ileum

• The ileum is long.
• Its internal layer is folded and covered with villi, providing a large surface area for nutrient absorption.

Adaptations of a Villus

• One-cell-thick epithelial layer accelerates nutrient absorption.
• Goblet cells secrete mucus to aid digestion.
• Blood capillary network transports digestive products throughout the body.
• Lacteal carries droplets of fatty acids and glycerol.
• Intestinal glands secrete intestinal juices containing digestive enzymes.
• Microvilli on the villus epithelium provide a large surface area, increasing the rate of nutrient absorption.

Methods of Nutrient Absorption

Digested food	Method and destination
Fructose	Facilitated diffusion into blood capillaries
Glucose and galactose	Active transport into blood capillaries
Amino acids	Active transport into blood capillaries
Vitamins B and C	Absorbed with water into blood capillaries
Water	Osmosis into blood capillaries
Fatty acids and glycerol	Simple diffusion; recombine by condensation into tiny lipid droplets in epithelial cells, then enter the lacteal
Vitamins A, D, E and K	Simple diffusion; dissolve in lipid and enter the lacteal