1. A Tour of the Digestive System

2. Where is the food now?
The duodenum

3. How broken down is it? Physical digestion: Chemical digestion:
Teeth and stomach churning broke it into pieces
Bile broke the fats into smaller globs
Chemical digestion:
Salivary amylase: starch  maltose
Pepsin in stomach: protein  peptides
Pancreatic amylase: starch  maltose
Trypsin from the pancreas: protein  peptides
Lipase from the pancreas: fats  glycerol + fatty acids

4. What still needs to be broken down?
FATS?
fats  glycerol + fatty acids
PROTEINS?
protein  peptides want AMINO ACIDS
CARBOHYDRATES?
starch  maltose want GLUCOSE
NUCLEIC ACIDS?
DNA / RNA  nucleotides  P + sugar + base

5. Digestive Enzymes from the Interstitial glands
Maltase
Glucose
Maltose
Peptidase
Amino Acids
Peptide

6. Cells in Small Intestine make enzymes
Interstitial glands…
Peptidases break down proteins
Amino acids
Maltase breaks down maltose
Glucose
Other disaccharides are also broken down, e.g. lactase breaks down lactose
Nucleosidases breaks down nucleotides
P, sugar, N base

7. Inside the small intestine
Increased surface area:
Large folds
Villi stick out from the folds
Microvilli stick out from the villi
~600m2 (size of a baseball diamond)

8. The Villi
Outer wall
Inner wall
Pathway for Food

9. Villi Layer of cells around villi (epithelium) Lacteal in the centre
lymphatic vessel
Blood capillaries surround the lacteal

10. Absorbing nutrients Fats enter the lacteal
Absorbed by lymphatic system
Lipase
Glycerol
Fatty Acid
Fatty Acid
Fatty Acid

11. Absorbing nutrients sugars and amino acids enter the blood
Capillaries join hepatic portal vein to the liver
How long is “food” here?
Up to 4 hours

12. A close up look at villi

13. A Tour of the Digestive System

14. Large Intestine Colon Rectum Anus ~1.5m long 3 parts: Last 20 cm
ascending
transverse
descending
Rectum
Last 20 cm
Anus
Sphincter at the end

15. Appendix a vestigial organ Caecum
pouch at the start of the large intestine
Appendix
a vestigial organ
(no current function)

16. What does the large intestine do?
Reabsorption of water
Absorption of some vitamins
Also contains:
bile pigments
heavy metals
billions of E. coli bacteria
break down some indigestible food
produce some vitamins, amino acids, and other growth factors

17. Indigestion? Disorders in the large intestine and symptoms
Overall review of digestion: