ABSORPTION AND ASSIMILATION

Adaptation of Digestive System for Absorptiony Absorption of food takes place in small

intestine. yStart at duodenum yEnd at ileum

Adaptation of Digestive System for Absorption

yAlcohol, small amount of simple

sugars and water are also absorbed by the lining of the stomach.

Adaptation of Digestive System for Absorptiony The adaptation of small intestine: y Large surface area for absorption purpose y Small intestine is long y The wall of small intestine is folded inward y The inner surface of the small intestine is covered with villi y The epithelial cell of each villus are covered with microvilli

Adaptation of Digestive System for Absorptiony The epithelial cell covering the microvilli is one

cell thick, making it easy for digested food to pass through it. y A comprehensive network of blood capillaries within each villus to transport away the absorbed nutrients all over the body. y The lacteal within each villus transport away fatty acid, glycerol and fat-soluble vitamins.

G.I. Secretion & Absorption: the Balance Sheet

8.9 L Total absorbed by intestine

Intestinal Morphology

Intestinal Villus and Microvilli

CAPILLARY NETWORK

LYMPH VESSELStem cells

INTESTINAL GLANDSecretory cells

ONE CELL THICK

microvilli (brush border)

Functions of structures in a villusStructure Lacteal Intestinal gland Venule Function Absorb fatty acids, glycerol and fat-soluble vitamins (A, D, E, K) Secrete intestinal juice

Transport absorbed food from blood capillaries via the hepatic portal vein to the liver Network of blood Absorb amino acids, monosaccharides, vitamins B, C, capillaries mineral and water Arteriole Lymph vessel Supplies blood to the capillary network Transport fat droplets to the lymphatic system

Absorption takes pace when digested food pass through the epithelium of the villi and into the capillary network and lymph vessels. Nutrients that enter into blood capillaries are: Water Glucose Amino acids Vitamins B and C Nutrients that enter lymph vessels are: Fatty acids Glycerol Fat-soluble vitamins (A, D, E, K)