STOMACH ANATOMY + STOMACH WALL LAYERS скачать в хорошем качестве

STOMACH ANATOMY + STOMACH WALL LAYERS

The stomach is a hollow muscular organ of your gastrointestinal tract, with its contents contained by two sphincters – the lower oesophageal sphincter and the pyloric sphincter. The top of this organ lies against the diaphragm, and the bottom sits above the pancreas. Located between the oesophagus and the small intestine, the stomach is involved in the second stage of digestion, following mastication, or chewing. The stomach receives a bolus – a ball-like mixture of food and saliva - from the oesophagus and secretes digestive enzymes and gastric acid to further digest it. This process turns the bolus into what’s called “chyme” – a thick, acidic mixture. Then, the pyloric sphincter controls the passage of this chyme into the duodenum. The pyloric sphincter is an anatomical sphincter, while the oesophageal sphincter is a physiological sphincter. Basically, an anatomical sphincter has a thickened circular muscle which helps the sphincter action by reducing the lumen diameter. A physiological sphincter simply works through muscle contraction or relaxation. Surrounding the stomach are plexuses - networks of blood vessels and nerves. These regulate the secretory activity of the stomach and the movements of its muscles. Stomach emptying occurs intermittently due to intragastric pressure overcoming resistance of the pyloric sphincter. Gastric peristalsis moves chyme into the duodenum. The stomach is distensible, meaning it can expand. A relaxed, empty adult stomach can hold about 0.08 L and a feeling of fullness sets in at around 1 L’s worth of food consumption. When you go to an all you can eat restaurant, know that your stomach is at max capacity with around 3-4 L of food! Because the stomach is J-shaped, there are different names for the two curvatures of its shape – the greater and lesser curvatures. The greater curvature is 4-5 times longer than the lesser curvature. The stomach can be divided into four sections: the cardia, fundus, body, and pylorus. The cardia is where the oesophagus empties its contents. The fundus is the upper curved part. The body is the main, central region. Finally, the pylorus is the portion of the stomach that empties its contents into the duodenum. Like the rest of the gastrointestinal tract, the walls of the stomach consist of a serosa, a muscularis externa, an inner submucosa, and an outer mucosa. The muscularis externa is uniquely divisible into three layers – the inner oblique layer, the middle circular layer, and the outer longitudinal layer. Let’s briefly discuss the characteristics of each layer. The serosa is a smooth tissue membrane made of two layers of mesothelium. The purpose of this layer is to reduce friction during digestive movements. The muscularis externa, again, is made up of three layers. The outer longitudinal layer moves partially-digested food towards the pylorus. The middle circular layer controls the movement of chyme into the duodenum. It is constantly constricted and the muscle fibers run concentric to the longitudinal axis of the stomach. Between the outer longitudinal layer and the middle circular layer is the Auerbach’s plexus, which innervates both layers. Finally, the inner oblique layer creates the churning motion of the stomach which physically mushes up the food. The inner submucosa is a layer of connective tissue with blood vessels, nerves and lymphatics that branch into the layers immediately adjacent. Lastly, the outer mucosa , which is the innermost layer of the gastrointestinal tract, comes into contact with partially-digested food. It can be subdivided into three layers – the innermost being the epithelium, then the lamina propria, and then the muscularis mucosa. The epithelium is the source of the digestive juices, the lamina propria is a layer of connective tissue, and the muscularis mucosae is a thin layer of smooth muscle. One interesting characteristic of the mucosal and submucosal layers of the stomach wall are the gastric rugae – a series of ridges due to folding of the wall. These allow the stomach to expand when food enters and provide increased surface area for nutrient absorption during digestion. To close off, let’s discuss the stomach’s blood supply. The celiac trunk is the first major branch of the abdominal aorta, and supplies blood to the stomach, as well as the esophagus and duodenum, pancreas, liver, and spleen. The greater curvature of the stomach is supplied by the right and left gastroepiploic arteries, as well as the short gastric arteries. The lesser curvature is supplied by the right and left gastric arteries. The cardia is also supplied by the left gastric artery. Finally, the fundus is supplied by the short gastric arteries. 3D MODELS FROM: https://www.cgtrader.com/3d-models/ch... https://www.turbosquid.com/3d-models/...