Physiological Pharmaceutics

76 Physiological PharmaceuticsANATOMY AND PHYSIOLOGYThe stomach has several functions:1. it acts as a reservoir for food,2. it processes it into fluid chyme which facilitates the absorption of nutrients fromthe small intestine,3. it regulates the delivery of food to the small intestine where the nutrients areabsorbed,4. it produces acid which is bacteriostatic, since ingested food is not sterile, and it alsoproduces the correct pH for pepsin to function.The stomach is located in the left upper part of the abdomen immediately below thediaphragm. In front of the stomach are the liver, part of the diaphragm, and the anteriorabdominal wall. The pancreas, the left kidney, the left adrenal, the spleen and the colon arelocated behind it. When the stomach is empty, it contracts, and the transverse colon ascendsto occupy the vacated space. The size, shape, and position of the stomach can vary quiteconsiderably depending upon the extent of its contents as well as upon the tension in themuscles of its walls. The opening from the oesophagus into the stomach is thegastrooesophageal sphincter or junction. It is also known as the cardia. The pylorus is theoutlet from the stomach into the duodenum.Organisation of the stomachThe stomach can also be divided into three anatomical regions (Figure 5.1). The uppermostpart is the fundus, which after a meal is often seen to contain gas. It also produces slowsustained contractions which exert a steady pressure on the gastric contents graduallypressing them in an aboral direction. The largest part of the stomach is the body which actsas a reservoir for ingested food and liquids. The antrum is the lowest part of the stomach.It is almost funnel-shaped, with its wide end joining the lower part of the body of thestomach and its narrow end connecting with the pyloric canal. The pyloric portion (theantrum plus the pyloric canal) of the stomach tends to curve to the right and slightly upwardand backward and thus gives the stomach its J-shaped appearance.Figure 5.1 Structure of the stomach