H Pylori Symptoms

Digestion actually begins with the brain. Close your eyes and imagine yourself eating your favorite meal. What do you feel? If you’re like most people, your mouth begins to water and your stomach begins to rumble as you think about your first bite. These are the anticipatory reactions that your brain sets in motion to jump-start the process of digestion, and these occur before you even take your first bite.

Environmental signals prime the digestive process before food reaches the mouth. The sight, smell, or thought of food begins the flow of saliva and the secretion of stomach acid and enzymes, thereby preparing the digestive system to receive food. Saliva, an essential component of digestion, is produced by the salivary glands, located under the tongue near the lower part of the jaw. Not only does saliva lubricate food and facilitate chewing and swallowing, it also contains digestive enzymes, which are proteins that aid in the chemical breakdown of food.

As children, we’re all taught to chew our food thoroughly. This practice is not only good manners, it’s also important for digestion. Chewing grinds and shreds food, vastly increasing the surface area upon which salivary enzymes can work in breaking food down. These enzymes include salivary amylase—which begins the breakdown of carbohydrates— and lingual lipase—which aids the breakdown of fats. Thorough chewing also ensures that the food is well lubricated with saliva, making it easier to swallow. The stomach is a large, muscular organ into which contents of the esophagus pass to undergo further processing. The stomach secretes a number of substances that aid in digestion, including hydrochloric acid and digestive enzymes. The stomach also agitates and churns food like a washing machine, mixing it with digestive acid and enzymes that, together, chemically break the food into small particles.

Cells in the lining of the stomach produce a number of substances that promote digestion. Upon stimulation by the brain and/or the arrival of food in the stomach, cells in the stomach begin to secrete hormones, acid, and enzymes. G cells (Figure 2.9), located near the bottom of the stomach, produce a hormone called gastrin. Gastrin is absorbed into the blood stream and carried to other secretory cells of the stomach, stimulating these cells to increase the production of stomach acid and digestive enzymes. Stomach acid is produced by a special type of cell located in the lining of the stomach’s body called the parietal cell. This acid acts directly to break down food, but also acts  indirectly by activating pepsinogen, an enzyme produced by chief cells (also located in the lining of the stomach body), which is involved in the breakdown of protein. Pepsinogen, secreted as an inactive enzyme, is converted to its active form, called pepsin, by exposure to stomach acid.

Secretion of an inactive enzyme is a protective mechanism in the stomach, as its inactive nature protects the pepsinogenproducing cells from being digested by their own secretions. Chief cells, like all cells, contain protein and would be degraded were pepsinogen produced as an active enzyme. The lining of the stomach itself is further protected by a thick layer of mucus, which is produced by mucous cells in the stomach lining. This mucus layer is often lacking in people who have ulcers.As we will see in later chapters, this reduction in mucus leads to auto-digestion of the stomach lining and the formation of ulcers, a phenomenon that occurs in people who are infected with H. pylori. After food is sufficiently broken down by the churning and mixing with acid and enzymes, it flows into the duodenum. The duodenum regulates the flow of chyme from the stomach into the small intestine. It takes approximately two to six hours for the stomach to empty its contents into the duodenum. The amount and composition of the chyme are both important in determining the rate of stomach emptying. High protein content and high acidity of the chyme slows stomach emptying, whereas low protein content and high volume promote emptying. High protein content triggers secretion of gastrin by cells in the duodenum, which reduces the rate of stomach emptying, affording high protein foods a longer stay in the bath of digestive enzymes.

The duodenum is also the receptacle for digestive enzymes produced by the pancreas, and for bile produced by the liver. The pancreas and liver are connected to the duodenum via a single tube-like structure called the common bile duct, through which bile from the liver and gallbladder, and enzymes from the pancreas, flow. The pancreas produces numerous powerful digestive enzymes; however, because these enzymes are inactivated by acid, pancreatic enzymes are secreted in a highly alkaline liquid. This liquid rapidly neutralizes the highly acidic chyme, allowing the pancreatic enzymes to quickly digest the food.

The pancreas secretes enzymes that digest many types of foods. Pancreatic proteases such as trypsin, chymotrypsin, and carboxypeptidase digest proteins; pancreatic amylase is responsible for digestion of carbohydrates (sugars and starches) and pancreatic lipase digests lipids (fats and oils). These enzymes are similar to, but more potent than, the enzymes found in saliva: salivary amylase and lingual lipase. Bile is a substance produced continuously by the cells of the liver and stored in the gallbladder. Bile performs a detergent- like function, acting somewhat like dish soap in a sink full of greasy dishwater. It emulsifies, or breaks, large globules of fat into smaller globules. By breaking the fat into small droplets, a greater surface area is exposed to digestive enzymes, thereby increasing the efficiency of fat digestion by the pancreatic lipase enzyme.

Once fully mixed with bile and digestive enzymes, chyme moves down the intestinal tract, where it is taken up by the microvillus cells of the small intestine and passed to the capillaries and into the bloodstream. The microvilli themselves also contain digestive enzymes on the surface of the cells that break down incompletely digested nutrients while the nutrients are being drawn into the tissue. On or adjacent to the cell membranes are enzymes that act on simple sugars to break them into individual sugar molecules; peptidases, which break down short fragments of proteins, called peptides, into individual amino acids; and lipases, which break down small fat molecules into their components: fatty acid and glycerol.