Post on 28-Dec-2015
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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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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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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.