Dr Swapnil Pawar
Notes by Dr Madhuri Anupindi
Outline the physiology of swallowing:
There are three phases of swallowing; voluntary, pharyngeal, and oesophageal.
Describe the composition and regulation of gastric secretions
The stomach produces approximately 1.5 – 2.5L of gastric secretions a day. These secretions aid in digestion and help to protect the stomach. At rest, the lining of the stomach is coiled into folds called gastric rugae which contain microscopic invaginations known as gastric pits. Each gastric pit opens into several gastric glands which come in two varieties, oxyntic glands which make up 75% of the total number of glands, and pyloric glands which form the remainder. The entire surface of the stomach also contains surface mucus cells which secrete a large amount of alkali mucus that coats and lubricates the gastric surface. This helps to protect the gastric epithelium from hydrochloric acid, pepsin and other insults. Production is stimulated by contact with food or any chemical irritation.
Oxyntic glands are present in the fundus and proximal region of the stomach and contain:
Pyloric glands are structurally similar to oxyntic glands but have few peptic cells and almost no parietal cells. They are located in the pylorus and the antrum. They contain
There are three phases of gastric secretion:
Describe the control of gastric emptying
Gastric emptying is a complex sequence of events that is controlled by myogenic, neural, hormonal and physicochemical mechanisms.
The stomach can be functionally divided into two regions:
List the physiological factors that prevent gastro-oesophageal reflex
Briefly outline the digestion and fate of dietary triglycerides.
Triglycerides consist of 3 fatty acids bound to glycerol. A small amount of digestion of triglyceride occurs in the stomach by gastric lipase but the majority occurs in the small intestine.
The first step of triglyceride digestion is emulsification by bile acids and lecithin. This breaks the fat into smaller pieces allowing for increased mixing with digestive enzymes. This begins to occur in the stomach via agitation and then continues in the duodenum through the action of bile which contains bile salts and lecithin. The next step is digestion via lipase produced by the pancreas which digests triglycerides into free fatty acids and 2-monoglyceride. The bile salts combine with monoglycerides and fatty acids to form micelles which transfer the fat to the intestinal epithelial cells where they enter the enterocytes. Within the enterocytes, the fatty acids and monoglyceride are transported into the endoplasmic reticulum where they are packaged with cholesterol and lipoproteins to form chylomicrons. A small number of fatty acids are absorbed directly into the portal blood and bound to albumin. The chylomicrons are then transported in the lymphatics to the liver or to muscle and adipose tissue. These tissues contain lipoprotein lipase which hydrolyses the triglycerides in the chylomicron, thus releasing fatty acids and glycerol which can be used as energy – the glycerol can enter the glycolytic pathway to form glucose, and the fatty acids can undergo beta-oxidation to form acetyl CoA and then enter the citric acid cycle. If excess acetyl CoA is produced it can be used for fatty acid synthesis, cholesterol formation, protein acetylation or formation of ketone bodies.