Digestive System
Topic 6 – Human Anatomy and
Physiology
Van Roekel – IB Biology 2
Bill
• What are some enzymes used in the digestive
system?
• Amylase – breaks down starch/carbohydrates
• Protease – breaks down proteins
• Lipase – breaks down lipids
• 6.1.1 Explain why digestion of large food molecules is essential.
• 6.1.2 Explain the need for enzymes in digestion. 3 The need for increasing
the rate of digestion at body temperature should be emphasized.
• 6.1.3 State the source, substrate, products and optimum pH
• conditions for one amylase, one protease and one lipase.
• Any human enzymes can be selected. Details of structure or mechanisms
of action are not required.
• 6.1.4 Draw and label a diagram of the digestive system.
• The diagram should show the mouth, esophagus,
• stomach, small intestine, large intestine, anus,
• liver, pancreas and gall bladder. The diagram
• should clearly show the interconnections between
• these structures.
• 6.1.5 Outline the function of the stomach, small intestine and
• large intestine.
• 6.1.6 Distinguish between absorption and assimilation.
• 6.1.7 Explain how the structure of the villus is related to its role
• in absorption and transport of the products of digestion.
Digestion Events
• Ingestion- eat the food
• Digestion – series of chemical reactions to
break food down into smaller and
smaller molecular forms
• Absorption – small molecules pass through
digestive cells and into blood
stream/lymphatic vessels
• Transport – circulatory system delivers molecules
to body cells to serve as nutrients
6.1.1 Explain why digestion of large
food molecules is essential.
• Most food molecules are large polymers and
insoluble
• They must first be digested to smaller soluble
molecules before they can be absorbed into
the blood
Molecule Type
Molecular Form
Ingested
Molecular Form
after Digestion
Protein
Protein
Amino acids
Lipids
Triglycerides
Glycerol and fatty
acids
Carbohydrates
Polysaccharides,
disaccharides,
monosaccharides
Monosaccharides
Nucleic Acids
DNA, RNA
Nucleotides
Catabolism for Anabolism
• Molecules are broken down into their smallest
components
• Small components can be used in anabolic
reactions to build large molecules, useful to
host organism.
Digestion of a Protein
• Eat egg whites that contain protein albumin
• Protein contains amino acid serine
• Inside stomach and small intestine, enzymes
break down albumin into monomers, such as
serine
• Serine diffuses through cells, into blood
stream, where it is brought to the pancreas
• Pancreatic cells build serine into hormone
insulin.
6.1.2 Explain the need for enzymes in
digestion.
• Enzymes are biological catalysts that increase
the rate of reaction
• Digestive enzymes are secreted into the lumen
of the gut
• Digestive enzyme increase the rate of reaction
of the hydrolysis of insoluble food molecules
to soluble end products
• Digestive enzymes increase the rate of
reaction at body temperature
Effect of an Enzyme on Reaction
• Notice that the normal
reaction requires a higher
activation energy which would
correspond to a high body
temperature. This is usually
not possible in living
organisms.
• The enzyme-catalysed reaction
has a lower activation energy.
This lower activation energy
would correspond to body
temperature but is only
possible in the presence of an
enzyme
6.1.3 State the source, substrate, products and optimum pH
conditions for one amylase, one protease and one lipase.
• EXAMPLE FOR Amylase
Conditions:
• Source is the Salivary
Gland
• Substrate is starch
(amylose)
• End product is the
disaccharide maltose
• Optimal pH 7.5-7.8
• Action: hydrolysis of 1-4
glycosidic bonds
Example 2 - Pepsin is a protease
produced in the stomach
Conditions:
• Source is the stomach
• Substrate is a polypeptide
chains of amino acids
• End product is amino
acids
• Optimal pH is 2-3
• Action is the hydrolysis of
peptide bonds within the
polypeptide chain
(endopeptidase).
Example 3: Pancreatic lipases:
•
•
•
•
•
Source is the pancreas
The substrate is a triglyceride lipid
The product is glycerol and fatty acid chains
The optimal pH is 7.2
The action of pancreatic lipases also requires
the presence of bile salts that emulsify the
lipid. This emulsification has two effects:
– Increases the surface area of the lipid for the
digestion of fat
– Exposes the glycerol 'head' structure to the
enzyme
• Action: hydrolysis of ester bonds between
the glycerol molecules and the fatty acid
chains.
6.1.4 Draw and label a diagram of the
digestive system
• Use your IB Text to get
the exact Drawing.
BILL
• Label the parts of the digestive system on the board to the
left.
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•
•
•
•
•
•
•
•
A - Mouth
B – Esophagus
C – Stomach
D – Pancreas
E – Large Intestines
F – Small Intestines
G – Gall Bladder
H – Liver
I – Rectum
6.1.5 Outline the function of the stomach,
small intestine and large intestine.
• Food brought to stomach by esophagus, using
smooth muscle contractions called peristalsis
• Once in stomach, food is held to mix with gastric
juices, consisting of:
– Pepsin – protease enzyme
– Hydrochloric acid – degrades and breaks down food,
creates acidic condition for pepsin
– Mucus – lines stomach to prevent damage from HCL
• Muscular wall churns mixture
Stomach
• The stomach stores the food from a
meal and begins protein digestion
• (a) Lumen of the stomach which
stores the food from a meal
• (b) Gastric pits from which mucus ,
enzymes and acid are secreted
• (c) Mucus secreting cells. Mucus
protects the surface of the stomach
from auto-digestion
• (d) Parietal cells that produce HCL
which kills microorganism that
enter the digestive system (food &
tracheal mucus). This also converts
inactive pepsinogen to active
pepsin
• (e) Chief cells: produces
pepsinogen a protease enzyme
Small Intestine
• In the small intestine digestion is completed
and vast majority of absorption occurs.
• Uses:
– Bile from Liver
– Trypsin, lipase, amylase, and bicarbonate from
pancreas
• The products of digestion are absorbed into
the blood stream.
Small Intestine
• (a) Villus which increase the
surface area for absorption of the
products of digestion
• (b) Microvilli border of the
epithelial cell increases the
surface are for absorption.
• (c) Lacteals are connect to the
lymphatic system for the
transport of lipids.
• (d) In the wall of the small
intestine are the capillary
beds/blood vessels to transport
absorbed products to the general
circulation,
• There are also the muscle to
maintain peristalsis
Large Intestine (Colon)
(a) The lumen of the colon
(b) The mucus producing goblet cells
(b) Muscular walls to maintain peristalsis
• The colon is responsible
for the reabsorption of
water from the gut.
• Contains large number
of E. Coli – synthesize
Vitamin K and maintain
Healthy environment
• Any undigested food is
eliminated as feces
BILL
• Complete the DBQ you received at the door.
6.1.7Explain how the structure of the villus is related to its role
in absorption and transport of the products of digestion.
• Villi increases surface area of digestive system
• Each villus contains a capillary bed and lacteal
– Capillary bed is a small vessel for circulatory
system – absorbs most nutrients except fatty acids
– Lacteal is a small vessel of the lymphatic system –
absorbs fatty acids
6.1.7Explain how the structure of the villus is related to its role
in absorption and transport of the products of digestion.
(a) folds increase SA:VOL ration by X 3
(b) Villi project into the lumen of the gut increasing the
surface area by X 10
(c) Microvilli are outward folds of the plasma membrane
increasing the surface area another X10
Absorption vs. Assimilation
• Absorption: digested nutrients are absorbed
through digestive cells, into the blood stream
or lymphatic system
• Assimilation: Movement of nutrients into
body cell to be used for energy (glucose) or to
build larger molecules (amino acids)
Absorption vs. Assimilation
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