The Digestive System
Find words to do with
the human digestive
system.
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the key words from
the lesson score?
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highest score?
Extension – Find synonyms for the key words and work out their score.
Digestive system
• Glands, such as the pancreas and salivary glands, which
produce digestive juices
• The stomach and small intestine, where digestion occurs
• The liver, which produces bile
• The small intestine where the absorption of soluble food
occurs
• The large intestine, where water is absorbed from the
undigested food, producing feaces
Digestion
Digestion = the breaking down of food into smaller molecules.
Large molecules (proteins, carbohydrates & lipids) are too big to cross cell membranes,
meaning they cannot be absorbed from the gut into the blood.
These large molecules (polymers) are broken down into smaller molecules (monomers)
using hydrolysis reactions.
Proteins (polymers) are broken down into amino-acids (monomers)
Carbohydrates (polymers) are broken down into monosaccharides (monomers)
Lipids (polymers) are broken down into fatty acids and monoglycerides (monomers)
Digestive Enzymes
Digestive enzymes are produced by specialised cells in the digestive
systems of mammals. These enzymes are released and mix with
food in the gut.
Different enzymes are required to work with different foods, because
enzymes are specific to their substrates.
1.
2.
3.
4.
Amylase – is a digestive enzyme which catalyses starch into
maltose
Lipase – breaks down lipids into monoglycerides and fatty acids
Endopeptidases – hydrolyse peptide bonds within a protein
Exopeptidases – hydrolyse peptide bonds at the ends of protein
molecules
Protein
digestion
Maisie
Harris
Fat digestion
Beth
Will
Carbohydrate
digestion
Abi
Charlie
Questions to consider
1. Where does the digestion occur?
2. What are the enzymes involved, and where they are
produced?
3. How are the organs adapted for the digestion? (i.e. Villi
– finger-like projections – large surface area for
absorption)
4. What are the products of digestion?
5. How the products are absorbed into the blood?
6. Create a digestion pathway
Marketplace
Protein
digestion
Maisie
Harris
Fat digestion
Beth
Will
Carbohydrate
digestion
Charlie
Abi
Marketplace
Protein
digestion
Maisie
Harris
Fat digestion
Beth
Will
Carbohydrate
digestion
Charlie
Abi
Carbohydrate Digestion
Carbohydrates are broken down by
amylase and membrane-bound
disaccharides.
Amylase cataylses starch into maltose
through hydrolysis reaction of the
glycosidic bonds in the starch.
Membrane bound disaccharides are
enzymes that are attached to the cell
membranes of epithelial cells lining the
ileum. They help break down
disaccharides into monosaccharides,
using a hydrolysis reaction breaking
the glycosidic bonds.
Monosaccharides can be transported
across the cell membranes of the ileum
epithelial cells via specific transporter
proteins.
Amylase is
produced by
the salivary
glands and
the pancreas
Absorption Of Digested Carbs
Glucose is absorbed by
“active transport”
with sodium ions via
a co-transporter
protein.
Galactose is absorbed
in the same way
using the same cotransporter protein.
Fructose is absorbed
via facilitated
diffusion through a
different
transporter protein
Lipid Digestion
Lipids are broken down by lipases into fatty acids and monoglycerides, using a
hydrolysis reaction breaking the ester bonds in the lipids.
Lipids are made in the pancreas but work in the Small Intestine.
Bile salts produced by the liver emulsify the lipids (cause lipids to form small droplets).
This is really important in lipid digestion as smaller lipid droplets have a “larger
surface area” than a single large molecule. This increased surface area is
beneficial when the lipases work on them,
Once the lipid has been broken down into fatty acids and monoglycerides, they stick to
the bile salts to form “micelles”.
Micelles
Micelles help to move monoglycerides
and fatty acids towards the
epithelium.
Micelles constantly break up and
reform so they can release the
fatty acids and monoglycerides
allowing them to be absorbed.
Whole micelles are NOT taken up
across the epithelium.
Monoglycerides and fatty acids are
lipid-soluble, so can diffuse across
the epithelial cell membrane.
Lipid Digestion
Protein Digestion
Proteins are broken down by a combination of different proteases (or
peptidases).
These enzymes catalyse the conversion of proteins into amino-acids by
hydrolysing the peptide bonds between amino-acids.
Endopeptidases act by hydrolysing peptide
bonds within a protein
Exopeptidases act by hydrolysing
peptide bonds at the ends of
protein molecules.
Endopeptidases & Exopeptidases
Examples of Endopeptidases:
1.
2.
3.
Trypsin
Chymotrypsin
Pepsin
Trypsin and Chymotrypsin are synthesized in the
pancreas and secreted into the small
intestine.
Pepsin is released into the stomach by cells in the
stomach lining and only works in acidic
conditions, provided by the HCl in the
stomach.
Examples Of Exopeptidases
1.
Dipeptidases
Exopeptidases remove single amino-acids from
proteins.
Dipeptidases work specifically on dipeptides. They
separate two amino acids that make up a
dipeptide by hydrolysing the peptide bond
between them.
Dipeptidases are located in the cell-surface
membrane on epithelial cells in the small
intestine.
Amino-acids are absorbed in a similar way to glucose.
Amino-Acid Absorption
Amino acids are
absorbed in a
similar way to
glucose and
galactose.
Sodium ions are
actively
transported out of
the epithelial cells
into the ileum
itself. They then
diffuse back into
the cells through
sodium-dependent
transporter
proteins in the
epithelial cell
membranes,
carrying aminoacids with them.
Homework
List similarities and differences
between carbohydrate and
protein digestion