Digestive System PDF - Esophagus & Stomach

DIGISTIVE SYSTEM Esophagus & Stomach Dr. Olgu Enis TOK Kent University Faculty of Dentistry 2nd Class INTRODUCTION TO DIGESTIVE SYSTEM The digestive system consists of the alimentary canal (gastrointestinal tract) and its principal associated organs. Esophagus Stomach Small intestine Large intestine...

DIGISTIVE SYSTEM Esophagus & Stomach Dr. Olgu Enis TOK Kent University Faculty of Dentistry 2nd Class INTRODUCTION TO DIGESTIVE SYSTEM The digestive system consists of the alimentary canal (gastrointestinal tract) and its principal associated organs. Esophagus Stomach Small intestine Large intestine Tongue Teeth Salivary glands Pancreas Liver Gallbladder Functions of the digestive system: ▪ ▪ ▪ ▪ Transport of ingested water and food along the gastrointestinal tract; Secretion of digestive enzymes, fluids, electrolytes, hydrochloric acid, mucin, and antibodies; Digestion and absorption of digested products as well as vitamins, water, electrolytes, recyclable materials; ▪ Excretion of indigestible remains; ▪ Serves as a barrier to prevent the entry of antigens and pathogenic organisms; ▪ Immunologic protection. Lymphatic tissue within the mucosa serves as the body’s first line of immune defense. ❑ In the gastrointestinal tract, food is broken down physically and chemically so that the degraded products can be absorbed into the body via blood circulation. GENERAL ORGANIZATION OF THE GASTROINTESTINAL TRACT Mucosa Submucosa Muscularis externa Serosa (or Adventitia) ▪ The gastrointestinal tract extends as a single tube from the esophagus all the way to the distal portion of the anal canal. an oblique layer of smooth muscle cells (stomach) MUCOSA The mucosa forms the innermost layer of the tract. It encases the lumen and comes into direct contact with chyme (digested food). There are three layers to the mucosa: Epithelium: the innermost layer, forming a thin membrane where the majority of digestion, absorption and secretion occurs Lamina propria: a layer of connective tissue that lies within the mucosa, providing vascularisation and lymphoid drainage to the epithelium. The nutrients absorbed pass into the capillaries in this layer. Muscularis mucosae: a very thin double-layer of smooth muscle that allows for local peristalsis and catastalsis of the tract SUBMUCOSA ▪ ▪ ▪ ▪ ▪ a layer of loose connective tissue contains large blood vessels and large lymphatic vessels contains submucosal (Meisnner's) nerve plexus contains mucous-secreting glands anchors the mucosa to the muscularis externa MUSCULARIS EXTERNA ▪ a double layer of smooth muscle ▪ inner layer of circularly oriented smooth muscle ▪ outer layer of longitudinally oriented smooth muscle ▪ In the stomach, there is a third obliquely arranged layer. ▪ contains myenteric (Auerbach's) nerve plexus in between double layer of smooth muscle ▪ contraction causes peristalsis Differs in thickness along the tract: It is thicker in the large intestines as increased force is required to propel faecal matter It is thicker in the pylorus of the stomach to form the pyloric sphincter, which allows for the controlled release of chyme into the small intestine It is thinner in the small intestine as chyme is more liquid and requires less peristaltic force SEROSA or ADVENTITIA ▪ The outermost layer of the gastrointestinal tract is either serosa or adventitia and consists of several layers of connective tissue. ▪ Serosa covers intraperitoneal structures and is continuous with the parietal peritoneum. It is thin and consists of a double wall of simple squamous epithelium. ▪ Adventitia covers retroperitoneal structures. It is made of fibrous connective tissue and fixes structures in place. ▪ Serosa and adventitia both contain blood vessels, nerves and lymphatics. ESOPHAGUS The esophagus is a fixed muscular tube that delivers food and liquid from the pharynx to the stomach. As it enters the abdominal cavity, it is free for a short distance, approximately 1 to 2 cm. The overall length of the esophagus is about 25 cm. On cross-section, the lumen in its normally collapsed state has a branched appearance because of longitudinal folds. When a bolus of food passes through the esophagus, the lumen expands without mucosal injury. ▪ Esophageal cardiac glands (near pharynx & stomach) ▪ Produce mucus, lubricate & protect epithelium ▪ Occasional lymphoid nodules (MALT system) / EXTERNA Junction of Esophagus & Cardia of Stomach