The Stomach Cardiac Sphincter Image Source: http://refluxdefense.com/heartburn_GERD_articles/stomach-acid.html

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.

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

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

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

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 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

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

Stomach Video http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter26/animation__organs_of_digestion.html (Tip: To download this video and enlarge it, download this Firefox toolbar: http://www.sothinkmedia.com/web-video-downloader-firefox/index.htm Installation guide: http://www.sothinkmedia.com/guide/download-video.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 ulcer Most ulcers are due to a bacterial infection which impairs the cells to produce the protective mucus

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

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

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?