NS 3310 1st Edition Lecture 3Outline of Past LectureI. Overview of Digestive SystemII. Organs of the gastrointestinal tract (GI)Outline of Current LectureI. Layers of Digestive TractII. EsophagusIII. StomachCurrent LectureI. Layers of Digestive Tract- Four main layers compose the digestive tract-Mucosa: composed of epithelium, lamina propria and mucularis mucosa. It is the innermost mucous membrane layer and it produces/releases secretions needed for digestion-Submucosa: composed of connective tissue, lymphoid tissue and submucosal plexus. It contains blood and lymphatic vessels and nerves. The lymphoid tissue helps to fight bacteria that you intake-Muscularis externa: composed of circular and longitudinal smooth muscle. These muscles contract to cause a dynamic wave of movement to push bolus (chewed up food)down the GI tract (this is also known as peristalsis). This ensures the unidirectional flow of nutrients down the GI tract.-Serosa: composed of connective tissue and visceral peritoneum. This is the outer covering of the GI tract, which protects GI tract- There are also muscle fibers that run in different directions, which influences muscular movements of the GI tract. II. EsophagusThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Moves bolus from oral cavity to stomach by swallowing- Peristalsis occurs in esophagus, which is the action of moving bolus down the GI tract from the esophagus into the stomach- Gastroesophageal sphincter controls the entry of the food from the esophagus into the stomach-A sphincter is a circle of muscle that is present in-between structures that controls the flow of nutrients unidirectionally-Every time you eat, the gastroesophageal sphincter opens and when you are done, it closes so that food cannot come up- There are diseases that occur in the esophagus -One example is GERD (gastroesophageal reflux disease)III. Stomach- A little chemical digestion of nutrients occurs in the stomach- There are 4 main regions-Cardia region-Fundus-Body-Antrum or distal pyloric region: grinds food and mixes with gastric juices to form chime; has strong peristalsis for gastric emptying- The stomach has three layers of muscle: longitudinal, circular and diagonal. Forceful contractions of this muscle enables food to mix with gastric juice to form chyme- The lining of the stomach has many folds called rugae, which allow it to expand- Pyloric sphincter: regulates the flow of chyme from the stomach into the upper small