We have learnt…

• 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

• 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

Stomach : FunctionsProtein 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

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

Stomach : Functions

Pepsin (protease)

• Digest proteins into polypeptides

proteins polypeptidespepsin

Pepsin does not digest proteins to amino acids!

• 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.

Stomach : Functions

Summary• Stomach

– Structure– Functions

Mechanical DigestionChemical 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 StarchCondition: pH 7Skills: • Tongue• Teeth • Saliva

Stomach

• 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 Questions2. Watch animation and complete the

worksheet