Digestive system
What is the purpose of digestion?
1.
Digestion helps break down food into tiny
particles that can be absorbed by our bodies.
2.
Digestion helps us obtain energy and nutrients.
Digestive System
Where is your food going when
you are eating? What organs will
be involved?
https://www.youtube.com/watch?v=_QYwscALNng
Label the organs

Go to echalk, search ‘digestive system’

Click the first resource

Label the organs in the body (do label the colon, appendix and anus!)
Modelling digestion

Aim: We aim to simulate the process of digestion from the mouth to
the small and large intestines, and to describe the major functions
and purpose of each step.

Materials
Methods
1.
Cut up food in to small pieces. (Simulate the action of your mouth.)
2.
Pour in a small amount of water.
3.
Add a little milk.
4.
Use a mortar and a pestle to mash the food and drink.
5.
Once you have mashed the food in to a liquidy slop then pour it in to a
bag to simulate the stomach.
6.
Add a little coke. (This simulates the stomach acid to help break down
food)
7.
Use your hands to squeeze the bag in order to mix the food and coke.
8.
Transfer the slurry to the nylon tube and squeeze. (small intestine)
9.
To simulate the large intestine, lay the nylon on multiple paper towels
and roll it up tightly. Squeeze and pat it as you can.
Questions (explanation of the model)
1.
2.
3.
4.
5.
Explain how step 1 to 4 are similar to what happens in your
mouth?
What happens in the stomach to break down the food further?
Step 5 to 7.
What does step 8 simulate? What happens at this stage of
digestion?
The large intestine is where faeces are forming. What does the
body remove from the material at this stage?
What is the material that is left at the end of digestion?
Mouth
Oesophagus
Liver
Stomach
Gallbladder
Pancreas
Duodenum
Transverse colon
Descending colon
Ascending colon
Appendix
Jejunum
Ileum
Anus
Rectum
Functions of organs
Organs
Mouth
Oesophagus (gullet)
Stomach
Liver
Gall bladder
Pancreas
Small intestine
Large intestine
Functions
Mouth

Teeth can break and grind the food into small pieces
(mastication or physical digestion)

Saliva moistens the food – make it easy to pass the
oesophagus

Salivary glands contain enzymes (amylase) to break
down starch into smaller molecules (chemical digestion)
Oesophagus (gullet)

Muscles in its wall push the food along
the oesophagus (peristalsis)

Peristalsis is an involuntary and
unidirectional prcoess
Stomach

The muscle of the stomach contracts and churns up the food with
gastric juices, forming chyme.

Protease in gastric juice (very acidic) breaks down proteins into
smaller molecules.

The tissue lining of the stomach is coated with mucus, protecting
the stomach from being ‘eaten’ by acidic gastric juices.

If the mucus is destroyed by certain bacteria, stomach ulcer can
occur.
Liver
 It
produces bile.
 Bile
passes through the bile duct into small
intestine.
 Bile
helps break down the fat molecules
into small droplets, which can be mixed
with the watery liquid - emulsification
Gallbladder
 It
stores the bile.
Gallstones
• Harderned deposits of bile in the
gallbladder
• Causes of gallstones: too much
cholesterol
Pancreas

Endocrine system
It secretes insulin to control blood glucose level.
Insulin

Blood glucose
diabetes
Exocrine system
It secretes digestive enzymes: protease, lipase, amylase (pancreatic
amylase)
Small intestine

Most digestion and absorption happens in small intestine.
Digestion
• Both bile juice and pancreatic juice
secrete into the duodenum, helping digest
carbohydrates, lipids and proteins.
• Small intestine itself also secretes some
digestive enzymes.
Absorption
Features of small intestine that allows maximum absorption:
1.
Length: 4-6 m long
2.
Narrowness: very thin (3-4 cm)–nutrients can easily pass through the
intestinal membrane into bloodstream
3.
Surface area: the membrane lining has finger-like projections on it,
called villi;
Villi themselves are further composed of fingers, called microvilli
Large intestine

The major fuction of large interstine is for water absorption.
BUT THIS DOES NOT MEAN THAT MOST OF THE WATER IS ABSORBED IN
LARGE INTESTINE! In fact most of the water is absorbed by SMALL
INTESTINE!

Flora in the large intestine synthesize vitamins and minerals.

The waste product which is faeces will be stored in the rectum before
it is excreted by anus.

Appendicitis: When appendix gets infecction or inflammation
Monomers of Carbohydrates

Glucose is the building blocks of starch and cellulose.

We can digest starch but not cellulose.
Cellulose-rich foods
Amylase

Amylase is the enzyme that breaks down big starch
molecules into maltose.

The further breakage of maltose into glucose is done by other
enzymes secreted by small intestine.
Starch

Amylase
maltose
＊Maltase (small
intestine)
glucose
Amylase is commonly secreted by salivary glands (salivary amylase)
and pancreas (pancreatic amylase).
Monomers of proteins

Amino acids are the basic units of proteins.
Protease

Pepsin is secreted in the stomach; trypsin is secreted in
the pancreas.

Protease breaks down proteins into peptides.
protein
protease
peptides
*peptidase
Amino acids
Composition of a fat molecule

Fat is made up of glycerol and three fatty acids.
Lipase

Lipase breaks down fats into glycerol and fatty acids.

Lipase is secreted by pancreas.
Fat
lipase
glycerol
+
Fatty acids