1. The Stomach Cardiac Sphincter
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2. Walls of the Digestive Tract
The digestive tract wall has four layers:
Mucosa: mucous membrane – secretes digestive enzymes and mucus – inner most layer
Submucosa: loose connective tissue – houses blood and lymph vessels
Muscularis: two layers of smooth muscle - for peristalsis
Serosa: serous membrane – secretes serous fluid to prevent sticking – outermost layer
The serosa secretes a serous fluid that keeps the outer surface of the intestines moist so that the organs of the abdominal cavity slide against one another.

3. Mucosa Submucosa Muscularis Serosa
Source: Inquiry into Life , 10th edition by Sylvia S. Mader Ch. 12 pg.
These layers of muscle contract to churn and mix its contents
Hunger pains occur when an empty stomach churns
2L of solids/liquids
Serosa

4. Entering the Stomach
Stores food/liquid (up to 2L!) and aids in digestion
Term gastric always refers to the stomach
The wall of the stomach is protected by a thick layer of mucus
Food from the esophagus passes through the cardiac sphincter into the stomach
Muscular stomach wall churns (mechanical digestion) the bolus(food), mixing the food with gastric juice (chemical digestion)
Alcohol is absorbed but not food

5. Stomach Thick walled J-shaped organ
lies on the left side of the body beneath the diagram
Mechanical Digestion/Processes
Crushing
Churning
Moistening
Absorption of liquids
Absorption of simple sugars

6. Stomach Digestion
Stomach mucosa has millions of gastric pits which lead into gastric glands
Gastric glands produce Gastric Juice
Gastric Juice contains:
Hydrochloric acid (HCl)
Pepsin (active form of enzyme)

8. Gastric Juice Hydrochloric acid (HCl)
Kills most bacteria present in food
Does not digest food but breaks down the connective tissue of meat
Activates Pepsinogen to form Pepsin
Pepsinogen  Pepsin
Inactive enzyme HCl active enzyme
Creates pH of 2 in the stomach

9. Gastric Juice Pepsin (active form of enzyme)
From Pepsinogen (inactive enzyme)
Is a protease - digests proteins
Digests protein in the bolus into smaller polypeptides
Protein  shorter polypeptide
Pepsin
Optimal pH of Pepsin: 2-3

10. Stomach Video
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11. Questions What does a pH of 2 indicate?
Acidic - corrosive
What protects our stomach from this corrosive environment?
A thick layer of mucus is present on the stomach walls
What would happen if HCl penetrated the mucus wall?
The HCl would start to corrode the stomach wall creating an ulcer
Most ulcers are due to a bacterial infection which impairs the cells to produce the protective mucus

12. Lab Activity Work in partners Must wear goggles Cleanup:
Empty beakers into the designated containers
Ensure your area is clean – no paper towels or liquids
If you finish early start on the discussion questions

13. Lab Discussion What is a simulation?
What is the purpose of creating a digestive system simulation? Can you think of any examples?
Biomedical engineers have created the world’s first artificial stomach
Mimics many activities that take place in your body and can even throw up.
Allows scientists, doctors, and pharmacists to know what happens to our food or medicine after we swallow it

14. Lab Discussion
The two tablets you tested today were medication that is commonly used to relieve pain or fever – aspirin. What were the differences between the two tablets?
Why do you think there are these differences?
Why might it be a good idea to test new medicines in a simulated environment rather than on a real person?