6.1 Digestion and Absorption
Understanding:
- The contraction of circular and longitudinal
muscle layers of the small intestine mixes
the food with enzymes and moves it along
the gut
- The pancreas secretes enzymes into the
lumen of the small intestine
- Enzymes digest most macromolecules in
food into monomers in the small intestine
- Villi increase the surface area of epithelium
over which absorption is carried out
- Villi absorb monomers formed by digestion
as well as mineral ions and vitamins
- Different methods of membrane transport
are required to absorb different nutrients
Applications:
- Processes occurring in the small
intestine that result in the digestion of
starch and the transport of the
products of digestion to the liver
Skills:
- Production of an annotated diagram
of the digestive system
- Identification of tissue layers in
transverse sections of the small
intestine viewed with a microscope or
in a micrograph
Nature of science:
- Use models as representations f the
real world: dialysis tubing can be used
to model absorption in the intestine
The Digestive System
How do we get from this…
…to this?
Key stages
1. Ingestion – Eat the food
2. Digestion – Food converted into smaller
molecular form
3. Absorption – Small molecular forms
absorbed through cells of digestive system
and pass into blood system
4. Transport – Circulatory system delivers small
molecular nutrients to body cells
Digestion – why?
You are moving house…
Digestion – why?
You are moving house…
Digestion – Why?
Break down larger molecules that cannot be
absorbed into smaller molecules that can
Copy and complete the table:
Molecule ingested
Proteins
Lipids (triglycerides)
Carbohydrates (polysaccharides and
disaccharides)
Nucleic acids (DNA and RNA)
Molecular form after digestion
Digestion – Why?
Break down larger molecules that cannot be
absorbed into smaller molecules that can
Copy and complete the table:
Molecule Ingested
Molecular form after digestion
Proteins
Amino acids
Lipids (triglycerides)
Glycerol and fatty acids
Carbohydrates (polysaccharides and
disaccharides)
Monosaccharides
Nucleic acids (DNA and RNA)
Nucleotides
Structure of the digestive system
Create an annotated diagram of the digestive system:
1.
2.
Role of the digestive system
Organs
•
•
•
•
•
•
•
•
•
3.
4.
5.
Mouth
Esophagus
Stomach
Small intestine
Pancreas
Liver
Gall bladder
Large intestine
Anus
What does each organ do?
The process of peristalsis
Small intestine – the structure (4 layers)
What happens to a bolus of food once eaten?
Describe the
passage of the
bolus through
the digestive
system,
explaining
what happens
at every stage.
THE VERY
SIMPLE
BASICS!
The Digestive System
The mouth contains teeth.
These chew the food and
break it into smaller pieces.
The tongue pushes food to the
back of the mouth so you can
swallow it.
Enzymes (amylase) in saliva
The Digestive System
The oesophagus, or food pipe,
joins the mouth and the
stomach.
Food is squeezed along this
tube into the stomach.
The Digestive System
The stomach is a bag of acid.
The acid in the stomach, and
special chemicals called
enzymes break down the food
even more.
Bacteria and other pathogens
killed
The Digestive System
Pancreas secretes lipase,
amylase and protease
(enzymes)
The Digestive System
Liver secretes bile
Optimum pH for enzymes
Helps to break up lipids
Gall bladder stores the bile
The Digestive System
In the small intestine, the
broken down food gets
into the blood so the body
can use it.
Main area for digestion
The Digestive System
The large intestine is about
1.5 metres long.
In the large intestine, the
body absorbs a lot of
water back from the
digested food.
The Digestive System
At the end of the digestive
system, the left over stuff
that the body can’t use
leaves the body through
the anus when you go to
the toilet.
Faeces is held in the
rectum before.
Who can do a handstand?
Peristalsis
Food does not move through your digestive
system using gravity
Peristalsis
Muscles control the movement of your food
throughout your digestive system
(Autonomic nervous system – you are unaware)
https://www.youtube.com/watch?v=o18UycWR
saA
Peristalsis
Draw the diagram:
Label the:
- Lumen
- Circular smooth muscle
- Longitudinal smooth muscle
- Villi
Enzymes
Specific enzymes for specific foods
Act as catalysts for reactions (reactions require
less energy when there are enzymes)
Most made by the pancreas in pancreatic juice
Secreted into the lumen of the small intestine
Starch molecules –
large and branched
Amylase – digestive
enzyme
Breaks down starch to
Maltose
Still too big!
Maltase in the small
intestine breaks down
maltose to glucose
units
Readily absorbed.
Proteins – large and branched
Amino acid
Amino
acid
Amino
acid
Amino acid
Trypsin from the pancreas
Amino acid
Amino
acid
Amino
acid
Amino acid
Breaks down proteins into
peptides.
Amino acid
Amino
acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino acid
Amino
acid
Still too big!
Amino
acid
Peptidase from the small
intestine
Amino acid
Amino
acid
Amino acid
Amino
acid
Amino
acid
Amino acid
Fats &
Oils
Fatty acids and
glycerol which is
easily absorbed.
Bile from the liver mixes
with the ‘fat’ to make
an emulsion
Lipase from the
pancreas breaks
down the fats to...
Enzymes
Enzyme
Lipase
Amylase
Maltase
Trypsin
Peptidase
Substrate
Action
Enzymes
Enzyme
Substrate
Action
Lipase
Lipids (fats and oils)
Breaks down lipids into
glycerol and fatty acids
Amylase
Starch
Breaks down starch into
maltose.
Maltase
Maltose
Breaks down maltose into
glucose.
Trypsin
Proteins (polypeptides)
Breaks down long
polypeptides into smaller
polypeptides.
Peptidase
Small polypeptides
Breaks down smaller
polypeptides into amino
acids
Super fun fact: How long is this boat?
Undigestables
Food takes hours to pass through the long small
intestine
Many molecules remain undigested
Human body cannot synthesize the necessary
enzymes
E.g. Cellulose: passes on to large intestine as the
main component of faeces
Small intestine
4
3
Four layers:
1. Serosa (outer coat)
2. Muscle layers
3. Sub-mucosa (blood and
lymph vessels)
4. Mucosa (Lining of small
intestine)
2
1
Villi
Draw a cross section of
an intestinal villus.
Label each part and
describe the function
-
Epithelium
Microvilli
Capillaries
Lacteal
Goblet cells
Absorption by villi
Epithelium must be
a barrier to
harmful substances
as well as be
permeable and
allow useful
nutrients to pass
through
Methods of absorption into villi
PASSIVE (No ATP):
- Simple diffusion
- Facilitated diffusion
ACITVE (ATP used):
- Active transport
- Exocytosis
Passive
Simple diffusion
- Follow concentration
gradient
- Small molecules/nonpolar molecules
- Fatty acids
Passive
Facilitated diffusion
- Down concentration
gradient
- Protein also used due
to size/polarity
- Glucose and amino
acids
Active
Active transport
- Uses membrane pumps
- Move against
concentration gradient
- Use ATP
- Glucose and amino
acids (under certain
circumstances)
Active
Endo/exocytosis
- Molecules trapped in
an infolding of the
membrane
- Pass through to the
other side as a vesicle
- Macromolecules that
have not yet been fully
digested
Villi recap
Three structures:
1. Epithelium is one cell thick
2. Many villi with microvilli = large surface area
3. Good blood supply
Why are each of these a good adaptation for the
villi to have?
What are these structures similar to somewhere
else in our body?
Surface areas
Small intestine is 5m long and 2.5cm diameter.
Surface area:
No villi= 0.5m2
With villi = 200m2
Villi
Spot the Difference
Coeliac small intestine
Some villi are lost, so the individual cannot
absorb the products of digestion properly
Modeling the small intestine
Write a simple method.
How can we use dialysis tubing to model absorption of
digested food in the intestine?
-
Title
Hypothesis
Equipment
Method
Results table template
We will
complete this
practical on
Monday