We have learnt…
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What are the 4 stages of nutrition?
Why must we digest our food?
What are the two types of digestion?
What is the structure and function of:
– Mouth
– Oesophagus
Question 1
What is the enzyme that is produced by the
mouth?
(A)Protease
(B) Lipase
(C) Amylase
(D)Cellulase
Question 2
What is the process of moving food down the
oesophagus
(A)By gravity
(B) Absorption
(C) Excretion
(D)Peristalsis
Question 3
Digestion is present in the oesophagus.
True/False
Question 4
Which of the following is not one of the stages
of holozoic nutrition?
(A)Absorption
(B) Egestion
(C) Ingestion
(D)Digestion
Lesson Objective
• Describe the structure and the main functions
of the stomach in relation to digestion.
• Holiday Assignment
The Stomach
Stomach : Structure
• Thick muscular bag with
thick muscle walls
• At the end of the
stomach, there is a
muscular valve called
pyloric sphincter
• Controls the entry of food
from the stomach into the
intestines
Stomach : Functions
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Mechanical Digestion
Peristalsis in the stomach helps to mix and churn the food
Digestion of proteins.
Storage of food, where the partly digested food particles becomes
liquefied chyme .
Stomach : Functions
Protein digestion begins in the stomach
• Proteins  polypeptides
• Protein digestion in the stomach requires the gastric
juice
• Food in the stomach stimulates the gastric glands to
secrete gastric juice
Gastric Juice
• Gastric juice is a dilute solution of:
– Hydrochloric acid (~pH 2)
– Pepsin
– Rennin
Gastric Juice
Stomach : Functions
Functions of dilute HCl:
• Denatures salivary amylase
• Activates inactive enzyme, Pepsin
• Provide slightly acidic for action of gastric
enzymes
• Kills potentially harmful microorganisms
Stomach : Functions
Pepsin (protease)
• Digest proteins into polypeptides
proteins
pepsin
polypeptides
Pepsin does not digest proteins to amino acids!
Stomach : Functions
• Function of Rennin (for your information):
Rennin curdles milk proteins
– converts the soluble caseinogen found in milk to
insoluble casein
– caseinogen (soluble)
casein
(insoluble)
– this process requires Ca2+
• This allows the insoluble casein to remain in the stomach
long enough for digestion by pepsin.
Summary
• Stomach
– Structure
– Functions
Mechanical Digestion
Chemical Digestion
• Hydrochloric acid (~pH 2)
• Pepsin
• Rennin
Remember your job application?
Let us assess without you will get the job!
Mouth
Applying for job : Digestion of Starch
Condition: pH 7
Skills:
• Tongue
• Teeth
• Saliva
Stomach
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Applying for job: Digestion of protein
Condition: pH2
Skills:
Mechanical Digestion
Chemical Digestion (Gastric Juice)
Hydrochloric acid
Pepsin
Rennin
Holiday Assignment
1. Ten Years Series Questions
2. Watch animation and complete the
worksheet