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Learning OutcomesTo explain what digestion isTo label all the major organs of the digestive system

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The body carries out digestion of food to convert large insoluble food molecules into smaller soluble ones.

Carbohydrate

Protein

Lipid

Small food molecules can pass through the walls of the small intestine and then dissolve into the blood stream. Large food molecules cannot do this.

What is Digestion ?

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Dig

est

ive

Syst

em Salivary

Glands

Tongue

Teeth

Oesophagus

Liver

Gall Bladder

Pancreas

Small Intestine Large Intestine Rectum

Stomach

Anus

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Ingestion – into the mouth Digestion – large to small

molecules Absorption – taken into the blood

stream Assimilation – food is used for

jobs Egestion – faeces out of the body

Key words to learn

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In the Mouth Digestion begins in the mouth

where food is broken down by the teeth. This is called physical breakdown.

The small parts of food are mixed with saliva and swallowed.

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In the Mouth Saliva contains enzymes that start

to chemically breakdown some of the starch and fats in the food.

Enzymes are biological catalysts that speed up chemical reactions.

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Enzymes in Action

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Amylase and Starch

Amylase breaks the long starch chains into glucose molecules.

How long can you keep a piece of bread in your mouth?

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Enzymes are specific

This means that they will only work in certain conditions.

The mouth is slightly alkaline so amylase works best at pH 7-8

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Enzyme Function Optimum

Condition

Amylase &

Salivary Amylase

Break down carbohydrates into

glucose

Neutral

pH ~ 7

Protease

(Pepsin)

Breaks down protein into amino acids

Acidic

pH < 7

Lipase Breaks down lipids (fats and oils) into

fatty acids and glycerols

Weak Basic

pH ~ 8

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The Journey So Far...

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Down to the Stomach

Food then passes the epiglottis, a flap of skin and cartilage that prevents food from entering the trachea (air tube).

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Down to the Stomach The food is moved

down the oesophagus with the help of wave like contractions, a process called peristalsis.

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In the Stomach The stomach is a

hollow muscular sac with a variety of functions.

a) It stores and churns food before moving to the duodenum

b) Produces hydrochloric acid (pH 2) and the enzyme pepsin for chemical breakdown of proteins

Mucus prevents the acid digesting the wall of

the stomach

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Mmmmmm… Bile! Bile – a greeny-yellow substance

made by the liver but stored in the gall bladder which emulsifies fats to allow absorption. It also neutralizes the chyme.

The bile is released just after food leaves the stomach in the duodenum

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As the food goes through the duodenum, it is mixed with:

1. Bile - produced by the liver

Bile assists lipase breaking down lipid molecules and also neutralises the acid from the stomach

2. Pancreatic juice - produced by the pancreas

Pancreatic juice contains digestive enzymes like lipase (breaks down lipids) and amylase (breaks down carbohydrates)

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1. Name of liquid in stomach?2. pH of the stomach3. Name of enzyme in the stomach4. What food group is digested in

the stomach?5. What protects the stomach from

the acid?6. Name of green liquid made by

liver?7. What is the job of the liquid?

Quick recap

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Small Intestine The nutrients diffuse into the

blood stream though the wall of the small intestine.

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Villi

The walls of the small intestine are not smooth.

They are covered in villi which increases the surface area

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You must be able to describe how the small intestine is adapted for maximum absorption of nutrients!!!

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Large surface area

Large blood supply

Thin surface to move across

Blood has low concentration of nutrient which increases the rate of diffusion

How it is maximised….

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Large Intestine After the long trip

through the small intestine, the remains enter the large intestine.

Here remains are fermented by the action of gut bacteria, excess water is absorbed and faeces is stored until released.

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Label the Diagram

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Digestion Summary

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Anagrams

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Digestion Quiz