Transcript Digestive System

Learning Outcomes
To explain what digestion is
To label all the major organs
of the digestive system
1 of 27
What is Digestion ?
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.
2 of 27
Digestive System
Teeth
3 of 27
Tongue
Salivary
Glands
Oesophagus
Liver
Gall Bladder
Stomach
Pancreas
Small Intestine
Large Intestine
Rectum
Anus
Key words to learn
 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
4 of 27
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.
5 of 27
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.
6 of 27
Enzymes in Action
7 of 27
Amylase and Starch
 Amylase
breaks the long
starch chains into glucose
molecules.
 How
long can you keep a
piece of bread in your
mouth?
8 of 27
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
9 of 27
10 of 27
Enzyme
Function
Optimum
Condition
Neutral
pH ~ 7
Amylase &
Salivary
Amylase
Break down
carbohydrates into
glucose
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
The Journey So Far...
11 of 27
Down to the Stomach
 Food
then passes the
epiglottis, a flap of
skin and cartilage
that prevents food
from entering the
trachea (air tube).
12 of 27
Down to the Stomach
 The
food is moved down
the oesophagus with the
help of wave like
contractions, a process
called peristalsis.
13 of 27
In the Stomach
 The
stomach is a
hollow muscular sac
with a variety of
functions.
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
a)
14 of 27
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
15 of 27
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)
16 of 27
Quick recap
1.
2.
3.
4.
5.
6.
7.
17 of 27
Name of liquid in stomach?
pH of the stomach
Name of enzyme in the stomach
What food group is digested in the
stomach?
What protects the stomach from the
acid?
Name of green liquid made by liver?
What is the job of the liquid?
Small Intestine
 The
nutrients diffuse into the blood
stream though the wall of the small
intestine.
18 of 27
Villi
The walls of the
small intestine are
not smooth.
They are covered in
villi which increases
the surface area
19 of 27
You must be able to describe
how the small intestine is
adapted for maximum
absorption of nutrients!!!
20 of 27
How it is maximised….

Large surface area

Large blood supply

Thin surface to move across

Blood has low concentration of
nutrient which increases the rate of
diffusion
21 of 27
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.
22 of 27
Label the Diagram
23 of 27
Digestion Summary
24 of 27
25 of 27
26 of 27
Anagrams
27 of 27
Digestion Quiz
28 of 27