1-Review the structure (anatomy) of the upper GI tract: 1-oesophagus: The oesophagus is a fibromuscular tube, approximately 25cm in length, that transports food from the laryngeal part of the pharynx to the stomach by peristalsis. It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice of the stomach (T11) it then enters the abdomen by theoesophageal hiatus. -Anatomical structure: 1-Adventitia:outer layer of connective tissue. 2-Muscle layer:external layer of longitudinal muscle and inner layer of circular muscle. 3-Submucosa 3-Mucosa: non-keratinised stratified squamous epithelium (contiuous with columnar epithelium of the stomach). Oesophageal Sphincters There are two sphincters present in the oesophagus, known as the upper and lower oesophageal sphincters. They act to prevent the entry of air and the reflux of gastric contents. Upper Oesophageal Sphincter The upper sphincter is an anatomical, striated muscle sphincter at the junction between the pharynx and oesophagus. It is produced by the cricopharyngeus muscle. Normally, it is constricted to prevent the entrance of air into the oesophagus Lower Oesophageal Sphincter The lower oesophageal sphincter is located at the gastro-oesophageal junction (between the stomach and oesophagus). During oesophageal peristalsis, the sphincter is relaxed to allow food to enter the stomach. Otherwise at rest, the function of this sphincter is to prevent the reflux of acidic gastric contents into the oesophagus. 2-Stomach: Thestomach, is an intraperitoneal digestive organ located betweenthe oesophagusand the duodenum. Divisions of the stomach:
The stomach hasfour main anatomical divisions; the cardia, fundus, body and pylorus: Cardia:surrounds the superior opening of the stomach at the T11 level. Fundus:the rounded, often gas filled portion superior to and left of the cardia. Body:the large central portion inferior to the fundus. Pylorus:This area connects the stomach to the duodenum. It is divided into the pyloric antrum, pyloric canal and pyloric sphincter. Greater and Lesser Curvatures The medial and lateral borders of the stomach are curved, forming the lesser and greater curvatures: Greater curvature- forms the long, convex, lateral border of the stomach. Lesser curvature- forms the shorter, concave, medial surface of the stomach. -sphincters of the stomach: There are two sphincters of the stomach, located at each orifice. They control the passage of material entering and exiting the stomach. Inferior Oesophageal Sphincter It allows food to pass through the cardiac orifice and into the stomach and is not under voluntary control. Pyloric Sphincter The pyloric sphincter lies between the pylorus and the first part of the duodenum. It controls of the exit of chyme (food and gastric acid mixture) from the stomach. In contrast to the inferior oesophageal sphincter, this is an anatomical sphincter. It contains smooth muscle, which constricts to limit the discharge of stomach contents through the orifice. 3-Duodenum: It is the most proximal portion of the small intestine runs from the pylorus of the stomach to the duodenojejunal junction. The duodenum can be divided into four parts: superior,
descending, inferior and ascending. Together these parts form a 'C' shape, that is around 25cm long, and which wraps around the head of the pancreas. - Superior (Spinal level L1) The first section of the duodenum is known as 'the cap'. It ascends upwards from the pylorus of the stomach. This area is most common site of duodenal ulceration. - Descending (L1-L3) The descending portion curves inferiorly around the head of the pancreas. It lies posteriorly to the transverse colon, and anterior to the right kidney. Internally the descending duodenum is marked by the major duodenal papilla. - Inferior (L3) The inferior duodenum travels laterally to the left, crossing over the inferior vena cava and aorta. It is located inferiorly to the pancreas, and posteriorly to the superior mesenteric artery and vein. - Ascending (L3-L2) After the duodenum crosses the aorta, it ascends and curves anteriorly to join the jejunum at a sharp turn known as the duodenojejunal flexure. It aids movement of the intestinal contents into the jejunum.