Unit 2: Digestion in The Mouth & Esophagus

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

(2) What happens in the mouth? 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.

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

(4) Mouth to Esophagus 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.

(5) Swallowing 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

(6) Traveling thru the Esophagus 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.

Unit 2: Digestion in The Small Intestine

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

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

(3) Bile 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.

(4) Pancreatic Juice 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.

(5) Releasing Bile & Pancreatic Juice 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 Oddi”.

(6) Bicarbonate 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”.

(7) The Jejunum & Ileum 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.

Unit 2: Digestion in The Stomach

(1) Stomach Structure 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.

(2) Digestion in the Stomach 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.

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

(4) Gastric Juice Secretion 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.

(5) Protein Metabolism 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.

(6) Leaving the Stomach 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.