1. Digestive System Notes
Unit 1: Biochemistry and Digestion
Digestive System Notes
Biochemistry and Digestion

2. Unit 1: Biochemistry and Digestion
Food processing
Ingestion
Digestion (Mechanical vs. Chemical)
Absorption
Elimination

3. Unit 1: Biochemistry and Digestion
Food processing
OBJ 31/32
Ingestion
Digestion
Mechanical vs. Chemical

4. Unit 1: Biochemistry and Digestion
A molecule (like starch)
An enzyme

5. Unit 1: Biochemistry and Digestion
Why digest food?
It needs to be absorbed into your blood stream…
Ingested molecules are too big!
If they aren’t absorbed, they are eliminated
We use the smaller parts to build new molecules

6. Digestive System Overview
Unit 1: Biochemistry and Digestion
Digestive System Overview

7. Unit 1: Biochemistry and Digestion
Digestive Tract
vs. Digestive System

8. Unit 1: Biochemistry and Digestion
Mouth
Teeth
Mechanical digestion
Saliva
Wets food
Salivary amylase (enzyme that breaks down starch)
Kills bacteria
Tongue
Taste buds
Moves food around

9. Unit 1: Biochemistry and Digestion
Esophagus
Muscular tube
Moves food through peristalsis (wave-like muscle contractions)
Demo
Epiglottis prevents food from entering the trachea (to the lungs)

10. Unit 1: Biochemistry and Digestion
Stomach
Storage (2-3 hours)
Muscular walls
Churn stomach contents to liquify food (Mechanical Digestion)
Gastric juice
HCl – breaks down food, activates pepsin (pH 1-2)
Pepsin - enzyme that breaks apart proteins (only works at low pH)

11. Pancreas (NOT digestive tract)
Unit 1: Biochemistry and Digestion
Pancreas (NOT digestive tract)
Pancreatic Juice
Pancreatic amylase is an enzyme that breaks down starch
Other enzymes break down the other 3 organic macromolecules (what are they??)
Fig 21.10A

12. Unit 1: Biochemistry and Digestion
Pancreas
OBJ 33
Pancreas also
Produces insulin to lower blood glucose
Produces glucagon to raise blood glucose

13. Liver and Gallbladder (NOT digestive tract)
Unit 1: Biochemistry and Digestion
Liver and Gallbladder (NOT digestive tract)
Liver makes bile
Gallbladder stores bile
Increases lipid surface area by mechanical digestion
Fig 21.10A

14. The party’s in the small intestine!
Unit 1: Biochemistry and Digestion
The party’s in the small intestine!

15. Unit 1: Biochemistry and Digestion
Small Intestine
More than 6 m long and 2.5 cm in diameter
Pushes food through
Duodenum
1st section (25 cm or so)
Where hydrolysis finishes
Receives substances from liver/gallbladder, pancreas, and cells of the small intestine

16. Small Intestine - Duodenum
Unit 1: Biochemistry and Digestion
Small Intestine - Duodenum
OBJ 33
From liver via gallbladder – bile (breaks up lipids)
From pancreas – Pancreatic juice (breaks down starch, proteins, nucleic acids, and lipids)
PLUS – the small intestine makes its OWN enzymes!
Fig 21.10A

17. Small Intestine - Absorption
Unit 1: Biochemistry and Digestion
Small Intestine - Absorption
Absorption occurs here
Huge surface area (300 m2)
Lots of folds, villi, and microvilli

18. Small Intestine - Absorption
OBJ 33
Cell 1
Cell 2
Villi
Microvilli

19. Absorption in the small intestine
Unit 1: Biochemistry and Digestion
Absorption in the small intestine
Where do nutrients go from the small intestine?
How do they get into the blood stream?
Where do they go once they are in the blood stream?

20. Large Intestine or Colon
Unit 1: Biochemistry and Digestion
Large Intestine or Colon
What’s left?
Water
Cellulose (fiber)
Other nondigestible material
About 1.5 m long, 5 cm diameter
Absorbs water
E. coli live symbiotically and produce vitamins (vitamin K)
Feces stored in rectum

21. Where different types of chemicals are broken down chemically:
MOLECULES:
Carbohydrates
Proteins
Lipids
WHERE DIGESTED:
Mouth, small intestine
Stomach, small intestine
Small intestine

22. Gross Facts
Bacteria love the stuff we can’t break down…and gas & flatulence are caused by bacteria metabolizing these nutrients
99% of these gases are odorless
People actually study these gases to find out the 1% of these gases that cause the odors (great job!)
Feces is 1/2 bacteria by weight
Newborns don’t pass gas because they have no bacteria in their intestines yet
Beano breaks down some molecules the bacteria like
Lactaid breaks down lactose
Gas-X reduces the surface tension of gas bubbles, which makes you feel better….but the gas is still there
Passing gas in public in ancient Rome was against the law

23. Unit 1: Biochemistry and Digestion
The End

24. Unit 1: Biochemistry and Digestion
Essential Amino Acids

25. Unit 1: Biochemistry and Digestion
The breakdown…
Molecules
Where chemically digested
Carbohydrates
Mouth (to disaccharides)
Small Intestine (to disaccharides and
monosaccharides)
Proteins
Stomach (to smaller proteins)
Small Intestine (to smaller proteins and
amino acids)
Lipids
Small Intestine (to smaller lipids, then to
glycerol and fatty acids)
Nucleic Acids
Small Intestine (to nucleotides)

26. Unit 1: Biochemistry and Digestion
Why digest food?
Too big
Small enough
Polysaccharides (starch, etc)
Disaccharides (sucrose, etc)
Triglycerides
Proteins and polypeptides
Monosaccharides (glucose, fructose, etc)
Fatty acids
Glycerol
Amino acids
Water

27. Stomach – gastric ulcers
Unit 1: Biochemistry and Digestion
Stomach – gastric ulcers
OBJ 35

28. Unit 1: Biochemistry and Digestion
Cellulose digestion
OBJ 35

29. Where foods are broken down with enzymes
Unit 1: Biochemistry and Digestion
Where foods are broken down with enzymes
OBJ 36, 37

30. Questions to consider…
Unit 1: Biochemistry and Digestion
Questions to consider…
What is heartburn and why does it hurt?
What causes diarrhea? Constipation?
What prevents the stomach from being overly acidic? In your house or apartment, what keeps the furnace from overheating the building? Here, what characteristic of life pertains?

31. Think about the function of each food…
Unit 1: Biochemistry and Digestion
Think about the function of each food…
What would happen if you didn’t eat enough carbs?
Carbs are primarily used for what?
You would feel tired…
You would lose weight because your body is using stored reserves of energy…
Slow down digestion because of lack of fiber…
What would happen if you didn’t eat enough fat?
Some vitamins are fats...
Blood clotting, vision, bone growth would be affected…
Nervous system function would be impaired…

32. Think about the function of each food…
Unit 1: Biochemistry and Digestion
Think about the function of each food…
What would happen if you didn’t each enough protein?
Every body function would be affected… (No enzymes!!)
You might feel tired because you can’t produce enough hemoglobin…

33. Structure and Function in Digestion
Unit 1: Biochemistry and Digestion
Structure and Function in Digestion
OBJ 38
Mouth
Teeth – canines vs. molars
Esophagus
Tough, elastic connective tissue to stretch
Layers of smooth muscle for peristalsis
Stomach
Muscular walls for churning
Mucus lining to protect from acid and protease
Small Intestine
Long and folded, with villi for lots of absorption
Large Intestine
Size of cecum depends on diet