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
bile
duct
bile
pancreatic juice
pancreatic
duct
• Neutralise the acidic chyme
• Provide a suitable alkaline medium
(~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
Enzyme
Product
Maltose
Maltase
Glucose
Polypeptide
Protease
(erepsin)
Amino acids
Fats
Lipase
Fatty acid
+glycerol
Duodenum
Pancreatic juice
• Function
Pancreatic juice contain enzymes
pancreatic amylase, pancreatic lipase
and trypsin
Pancreatic juice
Substrate
Enzyme
Product
Starch
Amylase
Maltose
Protein
Protease
(trysin)
Polypeptide
Fats
Lipase
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!
big drop
of fat
• In the small intestine, bile salts
emulsify fats.
+
bile salts
Bile salts emulsify fats into tiny
fat droplets.
big drop
of fat
• 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
Bile salts emulsify fats into tiny
fat droplets.
big drop
of fat
• 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
tiny fat
droplets
Bile salts emulsify fats into tiny
fat droplets.
big drop
of fat
• 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
• This causes the fats to break into
tiny fat droplets suspended in water,
forming an emulsion.
tiny fat
droplets
• Note that this is just a physical
break-up, but no chemical digestion
of fat molecules has occurred.
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.
tiny fat
droplets
+
lipase
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.
tiny fat
droplets
+
lipase
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.
tiny fat
droplets
+
lipase
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
Product
Lipase
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
Enzyme
Product/
Substrate
Proteins
Protease
(Trypsin)
Polypeptides
Enzyme
Product
Protease
(Erepsin)
Amino
acids
Small intestine
Region of Secretion
digestion
Source
Enzyme
Action
Small
intestine
Bile
Liver
-
Emulsifies fat
Pancreatic
juice
Pancreas
Amylase
Protease
(Trypsin)
Lipase
Starch  maltose
Proteins polypeptides
Fats fatty acids and glycerol
Intestinal
juice
Intestinal
glands
Maltase
Protease
(Erepsin)
Lipase
Maltose glucose
Polypeptides amino acids
Fats fatty acids and glycerol
Muddiest Point
• Any Question?