IB Biology Digestion and Absorption

1. 6.1: Digestion
and Absorption

2. UNDERSTANDINGS
The contraction of the circular and longitudinal
muscle 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/SKILLS
A: Processes occurring in the small intestine that
result in the digestion of starch and the transport of
the products of digestion to the liver.
A: Use of dialysis tubing to model absorption of
digested food in the intestine.
S: Production of an annotated diagram of the
digestive system.
S: Identification of tissue layers in transverse
sections of the small intestine viewed with a
microscope or micrograph.
Guidance
-Students should know that amylase, lipase, and
endopeptidase are secreted by the pancreas. The
name trypsin and the method used to activate it are
not required.
-Students should know that starch, glycogen, lipids,
and nucleic acids are digested into monomers and
that cellulose remains undigested.
-Tissue layers should include longitudinal and
circular muscles, mucosa, and epithelium.

3. Food Molecules
Molecule Type Molecular form ingested Form after digestion
Proteins Proteins Amino acids
Triglycerides
Polysaccharides, disaccharides,
monosaccharides
DNA, RNA
Complete the table

4. Order of Events
Ingestion- food is eaten
Digestion- food is converted into smaller and
smaller molecular forms
Absorption- molecular forms are absorbed by
cells in your digestive system and delivered to
blood or lymphatic vessels.
Transport- circulatory system delivers nutrients
to your body cells.
http://cmsnew.pdst.ie/node/2484

5. Role of Enzymes
Each enzyme is for a specific food type (ex: lipase is for lipids)
Remember: enzymes are catalysts that work by lowering the activation energy.
All digestion reactions are hydrolysis reactions.

6. The Alimentary Canal
The digestive system.
Basically a long tube that begins with the
mouth and ends with the anus.
Made of smooth muscle controlled by the
autonomic nervous system (not under
conscious control).

7. The Alimentary Canal
Two layers of smooth muscle: circular and
longitudinal
The action of the two layers together is
called peristalsis
◦ In the stomach=churning
◦ Everywhere else= muscle contraction to
keep the food moving through the canal

8. The Pancreas
Produces the hormones insulin and glucagon for glucose
metabolism.
Produces pancreatic juice for digestion
This is released into the first part of the small intestine
through a duct.
Enzyme Substrate Action
Lipase Lipids Lipids into fatty acids and
glycerol
Amylase Starch Starch into maltose
Endopeptidase Protein Long polypeptides into
smaller polypeptides
http://diabetesmelitusdisorder.blogspot.com/2010/10/gross-anatomy-of-pancreas_13.html
http://beyondthedish.files.wordpress.com/2012/07/pancreas.jpg

9. The Small Intestine
Pancreatic juice is sent into the first part (the duodenum).
pH in the small intestine is neutral to slightly alkaline.
Peristalsis moves the food through the lumen of the small intestine.
Hydrolytic reactions continue to occur.

10. Absorption into Villi
Cells in the inner lining of the small intestine
make up the mucosa.
The mucosa has many folds called villi which
absorb molecules from the lumen of the small
intestine.
The epithelial cells have membrane projections
called microvilli.
The purpose of villi and microvilli is to increase
surface area for absorption of nutrients.

11. The Villus
Each villus contains a capillary bed and a lacteal.
Capillary bed: for nutrient absorption and transport by the blood
stream; absorbs most monomers.
Lacteal: part of the lymphatic system; absorbs larger monomers,
such as fatty acids.
https://s.yimg.com/fz/api/res/1.2/4VoeZYbL9Q1Hyp2x9kDT6w--
/YXBwaWQ9c3JjaGRkO2g9Mjk3O3E9OTU7dz0yMzk-/http://drugline.org/img/term/intestinal-villu
8005_1.jpg

12. How is membrane transport involved in absorption of nutrients from the small intestine?
Method of transport Nutrients Outline
Simple diffusion Small molecules, non-polar molecules Fatty acids are non-polar and
therefore can pass freely through
hydrophobic core of the plasma
membrane into the epithelial cells
(down the concentration gradient )
Facilitated Diffusion Fructose, glucose, vitamins Water-soluble (hydrophilic) molecules
use channel proteins to pass
phospholipid bilayer
and enter the epithelial cells (down
the concentration gradient)
Active Transport Glucose, amino acids and mineral ions Protein pumps use ATP to move
molecules against the concentration
gradient into the epithelial cells
Endocytosis (Pinocytosis and
phagocytosis)
Antibodies from breast milk, other undigested
macromolecules
The plasma membrane folds inward
to form vesicles to absorb larger
molecules without digesting them

13. The digestion of starch and transport of the products
of digestion to the liver.
1. Glucose is transported into the epithelial cells of the villus.
2. Glucose moves by facilitated diffusion into the lumen of the villus.
3. Glucose then diffuses a short distance into the adjacent capillaries where it dissolves into the
blood plasma.
4. Blood in the capillaries moves to venules (small veins that collect blood from capillaries) then
to the hepatic portal vein which transports the glucose to the liver.
5. The liver absorbs excess glucose which it converts to glycogen for storage.

14. Dialysis tubing can be used to model absorption
https://ehumanbiofield.wikispaces.com/file/view/dialysis.jpg/32971865/dialysis.jpg
The tubing is semi-permeable and contains pores typically
ranging 1 – 10 nm in diameter
• How is the function of dialysis tubing similar to the small
intestine?
• What features of a real gut are missing from this model?
Test the solutions inside and outside the dialysis tubing
for starch and glucose before and after at least 15
minutes have elapsed

15. Produce an annotated diagram of the digestive system.

16. Homework
VOCAB
Alimentary canal, thoracic cavity, abdominal
cavity, autonomic nervous system, circular
muscle, longitudinal muscle, peristalsis,
pancreas, pancreatic juice, lipase, amylase,
endopeptidase, duodenum, lumen, maltase,
mucosa, villi (villus), microvilli, capillary bed,
lacteal
Exercises 1-3, pg 275