2Walls 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 layerThe 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.
3Mucosa 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 contentsHunger pains occur when an empty stomach churns2L of solids/liquidsSerosa
4Entering the StomachStores food/liquid (up to 2L!) and aids in digestionTerm 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
5Stomach Thick walled J-shaped organ lies on the left side of the body beneath the diagramMechanical Digestion/ProcessesCrushingChurningMoisteningAbsorption of liquidsAbsorption of simple sugars
6Stomach DigestionStomach mucosa has millions of gastric pits which lead into gastric glandsGastric glands produce Gastric JuiceGastric Juice contains:Hydrochloric acid (HCl)Pepsin (active form of enzyme)
8Gastric 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 PepsinInactive enzyme HCl active enzymeCreates pH of 2 in the stomach
9Gastric Juice Pepsin (active form of enzyme) From Pepsinogen (inactive enzyme)Is a protease - digests proteinsDigests protein in the bolus into smaller polypeptidesProtein shorter polypeptidePepsinOptimal pH of Pepsin: 2-3
10Stomach Video(Tip: To download this video and enlarge it, download this Firefox toolbar:Installation guide:
11Questions What does a pH of 2 indicate? Acidic - corrosiveWhat protects our stomach from this corrosive environment?A thick layer of mucus is present on the stomach wallsWhat 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
12Lab Activity Work in partners Must wear goggles Cleanup: Empty beakers into the designated containersEnsure your area is clean – no paper towels or liquidsIf you finish early start on the discussion questions
13Lab 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 stomachMimics 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
14Lab DiscussionThe 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?