The Stomach

Cardiac Sphincter

Walls of the Digestive Tract

The digestive tract wall has four layers: Mucosa: mucous membrane – secretes digestive

enzymes and mucus – inner most layerSubmucosa: loose connective tissue – houses blood

and lymph vesselsMuscularis: two layers of smooth muscle - for

peristalsisSerosa: serous membrane – secretes serous fluid to

prevent sticking – outermost layer

Muscularis

Mucosa

Submucosa

Serosa

Entering the Stomach

Stores food/liquid (up to 2L!) and aids in digestion Term gastric always refers to the stomachThe wall of the stomach is protected by a thick layer

of mucusFood from the esophagus passes through the

cardiac sphincter into the stomachMuscular stomach wall churns (mechanical

digestion) the bolus(food), mixing the food with gastric juice (chemical digestion)

Alcohol is absorbed but not food

Stomach

Thick walled J-shaped organ lies on the left side of the body beneath the diagram

Mechanical Digestion/Processes1.Crushing2.Churning3.Moistening4.Absorption of liquids5.Absorption of simple sugars

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)

Gastric Juice

Hydrochloric acid (HCl)Kills most bacteria present in foodDoes not digest food but breaks down the

connective tissue of meatActivates Pepsinogen to form PepsinPepsinogen Pepsin

Inactive enzyme HCl active enzymeCreates pH of 2 in the stomach

Gastric Juice

Pepsin (active form of enzyme) From Pepsinogen (inactive enzyme) Is a protease - digests proteins Digests protein in the bolus into smaller

polypeptidesProtein shorter polypeptide

PepsinOptimal pH of Pepsin: 2-3

Stomach Video

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html

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

ulcerMost ulcers are due to a bacterial infection which

impairs the cells to produce the protective mucus

Lab Activity

Work in partnersMust wear gogglesCleanup:

Empty beakers into the designated containers Ensure your area is clean – no paper towels or

liquidsIf you finish early start on the discussion questions

Lab Discussion

1. What is a simulation?

2. 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

Lab Discussion

3. 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?

4. Why might it be a good idea to test new medicines in a simulated environment rather than on a real person?