Topic 6.1 Digestion
TOPIC 6.1 DIGESTION
The structure of the wall of the small
intestine allows it to move, digest and
absorb food.
Slide taken from Digestion power point by Stephen Taylor
You might try drawing a
digestive system that looks
something like this.
• Clearly show how and
where accessory organs
connect.
Skill 2: Plan Diagram of the small intestine
Slide taken from Absorption of Digestion power point by Stephen Taylor
Contraction of circular and longitudinal muscle of
the small intestine mixes the food with enzymes
and moves it along the gut
Epithelium
Submucosa
Mucosa
Circular Muscle
Smooth
muscle
layers
Longitudinal
Muscle
Serosa
Small Intestine:
Contains different regions
• Duodenum
• Jejunum
• ileum
• Chyme enters duodenum
• The pancreas secretes enzymes
into the duodenum.
• Pancreatic amylase & lipase
• Endopeptidases like trypsin
(break peptide bonds in the
center of polypeptide
molecules)
• Pancreas also secretes sodium
bicarbonate which neutralizes
the stomach acid.
• Pancreatic juice also contains
water
Does this look familiar?
This is the internal structure of a pancreas cell.
Rat Pancreas
Slide taken from Digestion power point by Stephen Taylor
Enzymes of the pancreas tend to act on
larger macromolecules to break them into
smaller monomers.
See your chart
Membrane bound enzymes:
• The epithelial lining of the small intestine also secretes enzymes
• Disaccharidases like maltase
• Dipeptidases
• The digestive enzymes in the epithelial cells of villi of the
duodenum are are attached to the cell membrane.
• They are peripheral proteins in the membrane
• They anchored in the membrane so NOT swept along in the
digestive process.
• If the whole cell detached the enzyme will continue to work in the
lumen of the GI tract.
Advantages:
• Products are released close to the membrane & easily
absorbed by blood
• Digestion of disaccharides takes place early in the small
intestine.
Villi of the Small Intestine:
small projections that cover the inner lining of
the small intestine.
• INCREASE
surface area
for the
absorption of
digested food.
Campbell Reese 9th edition, p887
Villi of the Small Intestine:
• Majority of digestion occurs in the duodenum
while much of the absorption occurs in the ileum.
Each villus contains:
• blood capillaries
• lymph capillaries
(the LACTEAL).
Amino acids &
glucose are absorbed
into the blood
glycerol and fatty
acids absorbed into
the lacteal.
Campbell Reese 9th edition, p887
Specific molecules absorbed by the
epithelium cells of the villi
•
•
•
•
•
Glucose, fructose, galactose,
Amino acids
Fatty acids, monoglycerides & glycerol
Bases from nucleotides
Mineral ions (Calcium, potassium,
sodium)
• Vitamins (vitamin c)
Absorption of Lipids through
epithelial cells
PASSIVE DIFFUSION: Water, fats, fat soluble
vitamins, Oxygen, CO2 & alcohol
Copy the link below into your browser to
see a video reviewing passive diffusion
http://nutrition.jbpub.com/resources/animations.cfm?id=5&debug=0
Campbell Reese 9th edition p888
Fructose absorption through the epithelium by
Faciliated Diffusion
• Fructose and other water-soluble molecules (such as
vitamins) move down the concentration gradient into
the epithelial cells.
• Integral protein channels
allow them to pass through
the hydrophobic
phospholipid bilayer
Copy link below to your browser to
see the video on facilitated diffusion
http://nutrition.jbpub.com/resources/animations.cfm?id=2&deb
ug=0
Absorption of Monosaccharides through the epithelium
(glucose & galactose)
Copy the link below into
your browser to see a video
http://nutrition.jbpub.com/resources/animations.cfm?id
=3&debug=0
http://nutrition.jbpub.com/resources/ani
mations.cfm?id=4&debug=0
Cellulose is a structural
polysaccharide found in
plant foods
Cellulose is digested by
cellulase
(humans can’t produce this)
Most cellulose is egested in the feces and
not broken down