Exam I Study GuideI. Digestion and Absorption of Carbohydrates, Lipids and ProteinsA. Physiology of the gastrointestinal (GI) tract1. List the parts of the GI tract in the proper sequence and the purpose/function of each. Also list the accessory organs and their purpose/function in relation to digestion and absorption.GI tract: Oral Cavity, esophagus, stomach, (collectively upper digestive tract) small intestine & large intestine (lower digestive tract).Oral Cavity: mouth and pharynx, that provides the entry way to the digestive tract. On entering the mouth, mastication occurs - food is chewed by the teeth and jaw muscles to break down food. It is made ready for swallowing by mixing with secretions (saliva) released from the salivary glands which contain the enzymes, salivary amylase & lingual lipase.Salivary glands:Parotid: water, electrolytes (Na, K, Cl), and enzymes. Does NOT secrete mucus.Submandibular & Sublingual: water, electrolytes, enzymes, and MUCUS.Enzymes:Salivary amylase: responsible for the initial breakdown of carbohydratesLingual lipase: responsible for breaking down fats mainly triglycerides. Enzyme decreases with aging, really important enzyme for babies to break down triglycerides in the milk.20% of digestion of triglycerides is done by this enzyme!Lysozymes:Kill bacteriaImmunoglobulin A: kills microorganisms that you ingest with your food.Esophagus: From the mouth the food mixed with saliva (bolus) passes through the pharynx into the esophagus. As you swallow the epiglottis shifts upward this closes the glottis, preventing food from going into your trachea and then your lungs. The movement of the bolus through the esophagus is peristalsis (a progressive wave like motion, pushing the food down towards the stomach), it takes about 10 seconds.Upper esophageal sphincter: Voluntary contraction because of striated muscles.Lower esophageal sphincter: (gastroesophageal sphincter)Smooth muscle, non voluntary contraction. The pressure in this is higher than the pressure in the stomach. The pressure is what holds the sphincter closed, so it can impede passage of food from the esophagus into the stomach. When you swallow the pressure decreases in the sphincter, causing it to relax and let food go into the stomach.Gastro Esophageal Reflux Disease: When food is in the stomach the pressure in the lower esophageal sphincter is low or the muscle are weak. Therefore it relaxes when it is not suppose to, and the acid and food can go back to your esophagus and starts eroding the mucosa. This can cause irritation or ulcers, depending on severity.Esophagitus develops from acid erosion, later form of GERD.Treatments include:Taking anti-acids (basic) returns pH.Histamine blockers, target H2 (Pepcid AC, Zantac) are used. H2 blockers bind to the receptors of the parietal cells, decreasing HCl secretion.Proton pump inhibitors (Prilosec, Nexium) HCl can be released by proton pump, these medication inhibit the actions of proton pump, therefore H+ and Cl- cannot go into the stomach.Aggravating heartburn:Lower Pressure in sphincter: chocolate, high-fat foods, peppermint, alcohol.Increase acidity: coffee, caffeine, alcohol, calcium, tea.Irritants: spicy foods, citrus. Also coughing and weight lifting (abdominal pressure increases), lying down after eating.Stomach: Responsible for holding food, mechanical mixing and breaking down of food, gastric secretions, and the absorption of alcohol and Aspirin. The stomach extends from the Lower esophageal sphincter to the duodenum of the small intestine. The stomach contains four main regions: cardia, fundus, body, & pylorus.Cardia: receives the swallowed food from the esophagus. NO PARIETAL CELLSFundus: lies adjacent and above the cardia.Body: serves primarily as the reservoir for swallowed food and is the main production site of gastric juice. Empty holds 2oz, expands and when filled it can hold 50 oz.Pyloric: consists of the lower 1/3 of the stomach. Grinds and mixes food with the gastric juices, this is where the breakdown of food happens, forming chyme. Also provides peristalsis for gastric emptying through pyloric sphincter into the duodenum. NO CHIEF CELLSThe stomach has three kinds of muscles that begin the mixing of food with gastric juices, (circular, longitudinal & oblique). This mixing is when the breakdown of food begins in the stomach, to make it easier for the enzymes to act upon the nutrients. Several cell types that secrete different substances are found in the gastric gland.Neck Cells: secrete bicarbonate and mucus.Parietal Cells: secrete HCl and intrinsic factor. Intrinsic factor is needed for the absorption of vitamin B12. Have receptors for gastrin, acetylcholine, histamine.Chief Cells: secrete pepsinogen (inactive) form of enzyme & also gastric lipase.HCl activates it to pepsin (active), it can also activate itself (autocatalytic).Gastric lipase breaks down short chain and medium chain lipids.Enteroendocrine Cells (G cells): secrete a variety of hormones. Such as gastrin, this stimulates HCl and certain enzymes.Pyloric Sphincter: A circular muscular valve links the stomach to the duodenum of the small intestine. Regulates movement of food and acid from stomach to small intestine.Small Intestine: Represents the main site for nutrient digestion and absorption, is composed of the: Duodenum, Ileum & Jejunum.The small intestine has many folds which increase the surface area for the contact of the enzymes with the food.Duodenum: Proximal part of small intestine, linked to stomach through the pyloric sphincter. Mucus is important to protect mucosa when chyme (acid + food) enters, before bicarbonate can be released, it is more important than the bicarbonate in neutralizing the chyme.Large Intestine: The main purpose of this organ is the digestion of water and electrolytes, specifically Na & Cl.Accessory Organs: pancreas, liver & gallbladder. Provide or store secretions that ultimately are delivered to the lumen of the digestive tract and aid in the digestion & absorption process.Pancreas: Stimulated when sphincter relaxes and food comes in to the small intestine, releasing proteases, lipases, water, bicarbonate (neutralize acid pH) takes a long time for bicarbonate to be secreted, into the small intestine. Enzymes secreted in their inactive form so they do not break down the pancreas.Liver: Site for the synthesis of bile.Gallbladder: Stores and releases bile.2. Describe how the epithelial lining of the small intestine is structured to
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