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
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
Structure of the digestive system
Create an annotated diagram of the digestive system:
1. Role of the digestive system
2. Organs
•
•
•
•
•
•
•
•
•
Mouth
Esophagus
Stomach
Small intestine
Pancreas
Liver
Gall bladder
Large intestine
Anus
3. What does each organ do?
4. The process of peristalsis
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 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.
Enzyme (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
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
Creates 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
absorbed 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 overs 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.
Can you swallow if you are upside
down?
Peristalsis
Food does not move through your digestive
system using gravity
Peristalsis
Muscles control the movement of your food
throughout your digestive system
Oesophagus, stomach and intestines
(Autonomic nervous system – you are unaware)
https://www.youtube.com/watch?v=o18UycWRsaA
Small Intestine
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)
Firstly from pancreas
Then from walls of small intestine
Enzymes Round 1 from pancreas
Enzyme
Amylase
Lipase
Phospholipase
Protease
Substrate
Action
Enzymes Round 1 from pancreas
Enzyme
Substrate
Action
Amylase
Starch
Breaks down starch to
maltose
Lipase
Triglycerides
Broken down to fatty
acids and glycerol
Phospholipase
Phospholipids
Broken down to fatty
acids, glycerol and
phosphate
Protease/endopeptidases
Proteins/polypeptides
Broken down to shorter
peptides
Some of these products are still too big to be absorbed so need to
be broken down more by different specific enzymes
Enzymes Round 2 from wall of small intestine
Enzyme
Nuclease
Maltase
Lactase
Sucrase
Exopeptidases
Dipeptidases
Substrate
Action
Enzymes Round 2 from wall of small intestine
Enzyme
Substrate
Action
Nuclease
DNA/RNA
Breaks down into
nucleotides
Maltase
Maltose
Breaks down into glucose
Lactase
Lactose
Breaks down to glucose and
galactose
Sucrase
Sucrose
Breaks down into glucose
and fructose
Exopeptidases
Peptides
Break down into single
amino acids (leaves
dipeptides)
Dipeptidases
Dipeptides
Break down 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
Villi Summary
Three key points:
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?
Surface areas
A small intestine that is 5m long and 2.5cm diameter.
Surface area:
No villi= 0.5m2
With villi = 200m2
Spot the Difference
Coeliac small intestine
Some villi are lost, so the individual cannot
absorb the products of digestion properly
Methods of absorption into villi
PASSIVE (No ATP):
- Simple diffusion
- Facilitated diffusion
ACITVE (ATP used):
- Active transport
- Exocytosis
1. Triglycerides
1. Must be digested before being absorbed,
producing fatty acids and monoglyceride
1. Triglycerides
2. Can be absorbed by simple diffusion as they can
pass between phospholipids in plasma
membrane
1. Triglycerides
3. Fatty acids also
absorbed by
facilitated
diffusion using
fatty acid
transporters
(proteins in
membrane of
microvilli)
1. Triglycerides
4. Once through the membrane and inside the
epithelium cells, fatty acids are combined with
monoglycerides to produce triglycerides, which
cannot diffuse back again
1. Triglycerides
5. These triglycerides join with cholesterol to form
droplets. These then become coated in
phospholipids and protein
1. Triglycerides
6. These lipoproteins are released from epithelial
cells into either the capillary of lacteal by
exocytosis
2. Glucose
1. Glucose cannot pass through the plasma
membrane by simple diffusion because it is polar
(therefore hydrophilic)
2. Glucose
2. Sodium potassium pumps pump sodium ions by
active transport from the cytoplasm inside the
villus to the intestinal lumen. Pumps potassium
ions the other way. Sodium concentration builds
up.
2. Glucose
3. Sodium glucose co-transporter proteins transfer
a sodium ion and glucose molecule together into
epithelium cells. (Facilitated diffusion = passive)
2. Glucose
4. Glucose channels allow glucose to move by
facilitated diffusion into the villus and on into the
blood capillaries.
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
Friday
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