General anatomy of the Abdomen II_ part 1.pdf

16/02/24 General anatomy of the Abdomen II: part 1 Learning objective: describe the anatomy of the GI tract below the diaphragm – stomach, small bowel ( duodenum, jejunum and ileum ) and large bowel ( caecum, colon and rectum ). The GI tract: This is a hollow tube with different regions specialised...

16/02/24 General anatomy of the Abdomen II: part 1 Learning objective: describe the anatomy of the GI tract below the diaphragm – stomach, small bowel ( duodenum, jejunum and ileum ) and large bowel ( caecum, colon and rectum ). The GI tract: This is a hollow tube with different regions specialised to facilitate: 1. Mechanical digestion. 2. Chemical digestion. 3. Reabsorption of water. 4. Formation, storage and expulsion of faeces. Below the diaphragm: Muscular tube: oesophagus, stomach, small intestine and large intestine. Accessory organs: liver, gallbladder and pancreas. liver gallbladder small small intestine intestine The stomach: This is a J-shaped and highly distensible organ. It has 4 regions ( B, F, P and C ). 2 curvatures- lesser and greater. 2 sphincters- pyloric and oesophageal. Anatomical Physiological There are 2 types of sphincter in the body, the physiological sphincters and anatomical. The physiological sphincter prevents back ow due to a pressure difference, whereas the anatomical sphincter allows movement via a circular muscle ( which contracts ). 3 layers of smooth muscle: 1. Longitudinal. 2. Circular. 3. Oblique. mechanical digestion The stomach is lined by rugae. These increase the surface area and allow for stomach expansion. The stomach releases chyme into duodenum and this is controlled by the pyloric sphincter. Chyme = semi uid of partially digested food. The small intestine: Muscular tube with 3 parts: 1. Duodenum. 2. Jejunum. 3. Ileum. Muscle layers in the wall mix and move food during digestion. Circular folds ( equivalent to rugae ) increase surface area and help slow down the chyme. On top of these folds are villi and then microvilli which increases the surface area even more. Duodenum: Immobile and receives input from accessory organs. most occurs absorption here Jejunum and ileum: Quite similar but in different quadrants. Subtle vascular and internal differences. The circular folds change. terminal ileum The large intestine ( aka the colon ): Main function is to reabsorb water to create and excrete faeces. Runs from ileocaecal junction to the rectum. Regions: caecum ( appendix attached ), ascending colon, transverse colon, descending colon, sigmoid colon and rectum. 3 unique features: 1. Haustra ( large pouches ). 2. Taenia coli ( band of muscle ). 3. Fatty tags.