This document describes digestion that occurs in the mouth, esophagus, stomach, and small intestine. In the mouth, food is mechanically and chemically broken down by teeth and saliva enzymes. The chewed food or bolus is then swallowed through the esophagus using peristalsis. In the stomach, the bolus is further broken down by stomach muscles and enzymes in gastric juice. When fully digested, the liquid chyme exits the stomach into the small intestine where bile, pancreatic juice, and bicarbonate aid in further digestion before nutrients are absorbed in the jejunum and ileum.

1. Unit 2:
Digestion in The
Mouth &
Esophagus

2. (1) Digestive Organs
• Oral Cavity
• Esophagus
• Stomach
• Small Intestine
• Large Intestine

3. • Food is digested in the mouth both mechanically and chemically.
• Mechanically  Teeth chew and physically break down food into smaller units.|
• Chemically  Enzymes in your saliva help to break down biomolecules in food.
(2) What happens in the mouth?

5. • Saliva lubricates food for esophageal transfer.
• Saliva contains an enzyme called Amylase.
• Amylase breaks down polysaccharides
like starch into disaccharides.
(3) Chemical Digestion in the Mouth

6. • Once food is chewed up and mixed with saliva, it is
ready to travel down the esophagus.
• Chewed up food mixed with saliva is called “Bolus”.
• Bolus should be completely soft and moist.
(4) Mouth to Esophagus

7. • Deglutition is the proper term for swallowing.
• There are 2 Phases of Deglutition:
• The Buccal Phase 
• Voluntary
• The tongue moves the bolus into the pharynx and back of the throat.
• The Pharyngeal-Esophageal Phase 
• Involuntary
• The epiglottis closes over the larynx.
• Bolus is pushed down into the esophagus
(5) Swallowing

9. • The esophagus is the highway between the mouth and stomach.
• Food is pushed through the esophagus using Peristalsis.
• Peristalsis  Involuntary, wave-like contraction of muscle used to push softer /
more liquid-like substances through an organ.
(6) Traveling thru the Esophagus

10. Unit 2:
Digestion in
The Stomach

11. • The stomach can contain up to 1.5L of food comfortably.
• The stomach is composed of folds of excess tissue called “rugae”.
• Rugae in the stomach allow it to:
• Expand and enlarge as it fills with food and liquid.
• Secrete digestive solutions for food metabolism.
(1) Stomach Structure

12. • Food is broken down both mechanically and chemically in the stomach.
• Mechanical Digestion:
• Stomach muscles use peristalsis to break down bolus.
• Peristalsis is triggered by the release of a neurotransmitter called serotonin (from within the
rugae).
• Chemical Digestion:
• Gastric Juice is secreted from the rugae, to break down the bolus using enzymes and acid.
(2) Digestion in the Stomach

14. • Hydrochloric Acid
• Pepsin (an Enzyme that metabolizes Protein)
• Rennin (an Enzyme that metabolizes Protein)
• Muccin (an Enzyme that lubricates the food mass)
(3) Gastric Juice Composition

15. • The hormone Gastrin is released from the G-Cells in between the Rugae folds:
• Triggered by smell and taste.
• Triggered by the increase in pH when food drops into the stomach.
• Gastrin stimulates the release of Hydrochloric Acid from the rugae in the stomach:
• HCl decreases the pH in the stomach.
• HCl metabolizes proteins and carbohydrates.
• Gastrin stimulates peristaltic movement in the stomach, and small and large intestine.
(4) Gastric Juice Secretion

16. • Proteins are complex molecules which require a lot to be broken down.
• When proteins are metabolized, a large concentration of Hydrogen ions are
released (which decreases the pH of the stomach).
• The decrease in pH signals to the brain that the food is digested, and the G-Cells
in the stomach stop releasing gastrin.
(5) Protein Metabolism

17. • Once food is digested, the stomach stops churning and secreting gastric juice.
• Food them moves into small intestine.
• The liquefied mass leaving the stomach is called “Chyme”.
• Chyme exits out the Pyloric Sphincter into the small intestine.
(6) Leaving the Stomach

19. Unit 2:
Digestion in
The Small Intestine

20. • First Chamber = Duodenum (~10in long)
• Second Chamber = Jejunum (~7-8ft long)
• Third Chamber = Ileum (~12ft long)
(1) Small Intestine Regions

22. • The duodenum contains a solution used to metabolize any remaining
biomolecules from the stomach.
• The solution contains: Bile, Pancreatic Juice and Bicarbonate.
(2) The Duodenum

24. • Bile is a yellow-green solution produced by the liver, and stored in
the gallbladder.
• Bile contains salt compounds, lipids, and waste pigments from blood
cells.
• The function of bile is to emulsify lipids for better absorption…
• Lipids form micelles since they are polarized molecules.
• Bile helps break apart the micelles into individual lipids.
• This allows our bodies to more easily absorb them.
(3) Bile

26. • Pancreatic Juice is produced by and stored in the Pancreas.
• Contains:
• Carboxypeptidase and Chymotrypsin enzymes for metabolizing
protein.
• Amylase enzyme for further carbohydrate metabolism.
• Lipase enzymes for lipid metabolism.
• Nuclease enzymes for nucleic acid metabolism.
(4) Pancreatic Juice

27. • The presence of metabolized proteins and lipids in the duodenum
triggers the release of CCK (Cholecystokinin) into the blood stream.
• CCK stimulates the release of bile and pancreatic juice into the
duodenum.
• The solutions secrete out of an opening called the “Sphincter of
Oddi”.
(5) Releasing Bile & Pancreatic Juice

29. • Bicarbonate is a compound which balances out a solution’s pH by
absorbing and releasing hydrogen ions.
• The chyme that leaves the stomach is extremely acidic.
• Bicarbonate neutralizes the low pH.
• Bicarbonate is secreted from glands in the duodenum called
“Brunner’s Glands”.
(6) Bicarbonate

31. • Used to absorb all nutrients from food and liquid.
• Both contain microvilli:
• Microvilli are small finger-like projections used to absorb nutrients.
• They are directly connected to capillaries and the blood stream.
• Folds in between the microvilli are called the “Crypts of
Lieberkuhn”:
• These folds secrete Lysozymes to kill bacterial cells.
• The folds also secrete Muccin to further lubricate food.
(7) The Jejunum & Ileum