Nutrition in Man

Recap!

Crossword puzzle!

Lesson Objectives

• By the end of the lesson, you should be able to: • State the 3 parts of the small intestine.

• Describe the functions of the duodenum in terms of digestion by stating the enzymatic reaction that takes place.

• Explain the role of bile in the process of fats digestion in the small intestine.

Structure of the small intestine

Parts of Small Intestine

Three parts: 1) Duodenum 2) Jejunum 3) Ileum

Structure

6 metres long!!!

Structure

Lining of the walls the small intestine contains intestinal glands which secrete digestive enzymes

Structure

• Walls contain villi and microvilli, and single-cell epithelium, blood and lymph capillaries for absorption of digested food particles

Duodenum

Duodenum

• Structure • Receive pancreatic juice from pancreas via pancreatic duct.

• Receive intestinal juice from the intestinal gland • Receive bile (produced from liver , stored in gall bladder and released via bile duct

Small intestine (Duodenum)

• All three fluids are alkaline • Neutralise the acidic chyme • Provide a suitable alkaline medium bile duct bile pancreatic juice pancreatic duct (~pH 8.5) for the action of the pancreatic and intestinal enzymes intestinal juice

Functions Secretion of Intestinal Juice

• Functions • Intestinal juice contain digestive enzymes : maltase, protease (erepsin) and lipase

Intestine juice

• Functions – enzymes

Substrate

Maltose

Enzyme

Maltase Polypeptide Fats Protease (erepsin) Lipase

Product

Glucose Amino acids Fatty acid +glycerol

Duodenum Pancreatic juice

• Function Pancreatic juice contain enzymes pancreatic amylase , pancreatic lipase and trypsin

Pancreatic juice

Substrate

Starch

Enzyme

Amylase Protein Fats Protease (trysin) Lipase

Product

Maltose Polypeptide Fatty acid +glycerol

Bile

• Liver cells secrete bile • Alkaline greenish-yellow liquid •

Has no enzymes

so cannot digest food • Aid in digestion of fats • Bile stored temporarily in gall bladder • When gall bladder contracts, bile flows into duodenum via bile duct

Simulate action of Bile

• • • Add a small amount of oil to a beaker of water Shake it Add liquid detergent to simulate bile.

Observe!

• In the small intestine, bile salts

emulsify

fats. + bile salts big drop of fat

Bile salts emulsify fats into tiny fat droplets.

• In the small intestine, bile salts emulsify fats. • They lower the surface tension of the fats, that is, they reduce the attractive forces between the fat molecules. + bile salts big drop of fat

Bile salts emulsify fats into tiny fat droplets.

• In the small intestine, bile salts emulsify fats. • They lower the surface tension of the fats, that is, they reduce the attractive forces between the fat molecules. • This causes the fats to break into tiny fat droplets suspended in water, forming an emulsion.

+ bile salts big drop of fat tiny fat droplets

Bile salts emulsify fats into tiny fat droplets.

• In the small intestine, bile salts emulsify fats. • They lower the surface tension of the fats, that is, they reduce the attractive forces between the fat molecules. • This causes the fats to break into tiny fat droplets suspended in water, forming an emulsion.

• Note that this is just a physical break-up, but no chemical digestion of fat molecules has occurred.

+ bile salts big drop of fat tiny fat droplets

Bile salts emulsify fats into tiny fat droplets.

• Emulsification increases the surface area to volume ratio of the fats, speeding up their digestion by lipase. tiny fat droplets

Bile salts emulsify fats into tiny fat droplets.

• Emulsification increases the surface area to volume ratio of the fats, speeding up their digestion by lipase . + lipase tiny fat droplets

Bile salts emulsify fats into tiny fat droplets.

• Emulsification increases the surface area to volume ratio of the fats, speeding up their digestion by lipase. • Emulsified fats are digested by lipases to fatty acids and glycerol.

+ lipase tiny fat droplets

Bile salts emulsify fats into tiny fat droplets.

• Emulsification increases the surface area to volume ratio of the fats, speeding up their digestion by lipase. • Emulsified fats are digested by lipases to fatty acids and glycerol.

+ lipase tiny fat droplets fatty acids and glycerol

Bile salts emulsify fats into tiny fat droplets.

Summary

Small intestine

Carbohydrate digestion Substrate Enzyme Product/ Substrate Enzyme Product

Starch Pancreatic amylase Maltose Maltase Glucose

Small intestine

Fat digestion

• Bile emulsifies fats and breaks them up into minute fat globules • Enlarges surface area of fats • Speed up digestion • End products are fatty acids and glycerol

Substrate

Fats

Enzyme

Lipase

Product

Fatty acids and Glycerol

Small intestine

Protein digestion

• Some digested in the stomach • Undigested proteins enter small intestine • Converted to polypeptides by protease (trypsin)

Substrate Proteins Enzyme Protease (Trypsin) Product/ Substrate Enzyme Product Polypeptides Protease (Erepsin) Amino acids

Small intestine

Region of digestion

Small intestine

Secretion

Bile Pancreatic juice

Source Enzyme

Liver Pancreas Amylase Protease (Trypsin) Lipase Intestinal juice Intestinal glands Maltase Protease (Erepsin) Lipase

Action

Emulsifies fat Starch  Proteins  maltose polypeptides Fats  fatty acids and glycerol Maltose  glucose Polypeptides  amino acids Fats  fatty acids and glycerol

Muddiest Point

• Any Question?