The document summarizes the process of digestion. It defines key terms like enzymes, catalysts, and hydrolysis. It describes different enzyme assay methods and chemical tests to detect nutrients like sugars, starches, proteins, and fats. The roles of the tongue, larynx, gastroesophageal sphincter and bile in digestion are explained. The differences between segmentation and peristalsis in propelling food through the digestive tract are compared. Videos demonstrating selected chemical tests and digestive processes are also listed.

1. Practical 5 :Process of Digestion
Dr Shamshad
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2. Objectives
1. To recognize the variation between the types of enzymes
assays.
2. To perform the appropriate chemical tests to determine if
digestion of a particular food has occurred
3. To cite the function of bile in the digestive system
4. To define enzyme, catalyst, control substrate and hydrolase.
5. To explain why swallowing is both voluntary and a reflex
activity
6. To discuss the role of the tongue larynx and gastro-
esophageal sphincter swallowing
7. To compare and contrast segmentation and peristalsis as
mechanism of propulsion
• Physio Ex TM 9.0;Labrotatory simulations in physiology Peter Zao 2011.
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3. Enzymes assay : Either measure the consumption of substrate or
production of product over time.
Methods of quantitatively following enzyme reaction:
1. Fluorescence : Redox reactions; reduction reaction show blue
fluorescence.
2. Sampling : Withdrawing samples at intervals & estimating the
substrate or product by chemical methods.
3. Monomeric : Reaction with gas as component Ex: oxidases or
decarboxylase enzymes.
4. Electrode Reactions that involve acid production.
5. Polarimeteric : Isomerase that convert one isomer to another. 3

4. Food
sample
Reagent Method Initial color Color of +
result
Reducing
sugar
Benedict's Add Benedict's
reagent to the
food and boil in a
water bath
Blue Brick red
ppt
Starch Iodine Add iodine
reagent to the
food
Yellow -
brown
Blue to
black
Protein/AA Biuret
(mixture of
NaOH and
Cuso4
Add Biuret reagent
to the food
Blue Lilac
/purple
Fat Ethanol Add ethanol to the
food to dissolve
the fat then add
water
colorless White
emulsion
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5. Food
sample
Reagent Method Initial color Color of +
result
Reducing
sugar
Benedict's Add Benedict's
reagent to the
food and boil in a
water bath
Blue
Starch Iodine Add iodine
reagent to the
food
Yellow -
brown
Protein/AA Biuret(mixt
ure of
NaOH and
Cuso4
Add Biuret reagent
to the food
Blue
Fat Ethanol Add ethanol to the
food to dissolve
the fat then add
water
colorless
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6. Functions of bile
1:Bile salts :Helps in
 Digestion and absorption of fats
 Absorption of fat soluble vitamins.
2:Neutraliation of acid :
 Helps to neutralize the acidic chyme.
3:Excretion:
 Drugs, toxins, bile pigments and inorganic substances Ex:copper
,zinc and mercury
4: Solubility of cholestrol:
 Cholesterol in the bile are solubilized in micelles
Allow cholestrol to be transported without perception in bile via
Biliary tract to the intestine.
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7.  Enzymes /biological catalysts :
Increase the rate of a chemical reaction without becoming
part of the product.
 Hydrolytic enzymes (hydrolases):
• Need water to break down organic molecules to the
molecular bonds, under specific environmental condition.
• Cleave the bonds b/w the subunits /monomers
• Highly specific in its action
• Needs specific environmental conditions to function
optimally.
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8. Stages of Swallowing
• Voluntary Stage of swallowing:
When the food is ready for swallowing, it is “voluntarily”
squeezed or rolled posteriorly into the pharynx by pressure of
the tongue upward and backward against the palate.
• Involuntary Pharyngeal Stage of Swallowing:
swallowing becomes entirely automatic and ordinarily
cannot be stopped.
This slit performs a selective action, allowing food that has
been masticated sufficiently to pass with ease.
Pharyngeal stage of swallowing is principally a reflex act.
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9. Compare and contrast
segmentation and peristalsis
Peristalsis
• Basic propulsive movement
• A contractile ring appears around
the gut
• It is an inherent property
• Stimulus : Distention of the gut.
• Others :chemical/ physical
irritation of gut epithelial lining.
• Parasympathetic nervous signals.
• Requires active myenteric plexus.
• Peristaltic Waves Move Toward
the Anus With Downstream
Receptive Relaxation—“Law of
the Gut.”
Segmentation
• Forward progression of the
intestinal contents is blocked by a
sphincter: a peristaltic wave only
churns the intestinal contents.
• Stimulus: Intestinal wall elicits
localized concentric contractions
spaced at intervals
• Divide the intestine into spaced
segments.
• The segmentation contractions
“chop” the chyme 2-3 times /
minute.
• Promotes: progressive mixing of
the food with secretions of the
small intestine. 9

10. Iodine test for starch
https://youtu.be/CCq3rm6S2f8
Benedict's test for reducing sugars
https://youtu.be/QcQyuKsOvVE
Digestion of Starch by the Enzyme Amylase
https://youtu.be/ISf6ClTbg78
Digestion of protein
https://youtu.be/e9cAvWaK_no
Ethanol emulsion test for fats
https://youtu.be/_BcXylW7JFc
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