Digestive Enzymes and Cell Types - MCAT Biological and Biochemical Foundations of Living Systems

The correct answer is parietal cells. Parietal cells are responsible for HCl secretion in the stomach, which lowers the overall pH of the stomach. Chief cells secrete pepsinogen, which is converted to pepsin and is responsible for digesting proteins. G cells secrete gastrin, which stimulates parietal cells.

The correct answer is carbohydrates.

Salivary amylase can only digest carbohydrates. Proteases further along in the digestive pathway breakdown proteins, while lipases digest fats. Amino acids are the product of digested proteins.

Pepsin and gastrin are secreted into the acidic environment of the stomach, while lipase, trypsin, and carboxypeptidase are secreted into the basic environment of the small intestine. Acidic chyme from the stomach must be neutralized in the duodenum before the enzymes in the small intestine can begin digestion, creating the basic environment for these enzymes to function.

Lipase does not function in an acidic environment.

Digestion of proteins begins in the stomach. The low pH of the stomach converts pepsinogen into pepsin, which is then used to break down proteins.

G cells secrete the large peptide hormone gastrin, which travels through blood to stimulate parietal cells to secrete hydrochloric acid.

Mucous cells produce mucus to protect the epithelial lining of the stomach from the harsh acidic environment. Chief cells are found in the exocrine glands and secrete pepsinogen, which is activated by the low pH of the stomach to become pepsin. Pepsin catalyzes the breakdown of protein into peptides.

In the stomach, food is broken down using a host of different cells and enzymatic processes. Chief cells release pepsinogen, making it the correct answer. Parietel cells, which release HCl, allow the conversion of pepsinogen (a zymogen) into pepsin. Pepsin actively digests proteins in the highly acidic environment of the stomach.

Goblet cells release mucus which lines the stomach for protection.

Pepsin is a protease that is secreted by the chief cells located in the stomach. All of the other choices are digestive enzymes secreted by the pancreas. Lipase helps to digest fats, carboxypeptidase and chymotrypsin both break down proteins, and trypsinogen is a zymogen of trypsin.

During digestion, the small intestine plays a major role in absorption and digestion of compounds. Because the contents of the stomach are extremely acidic, bicarbonate serves to neutralize hydrochloric acid, and raises the pH to an optimal level at which the enzymes can break down food.

Amylase is present in both saliva and the small intestine and breaks down starches and carbohydrates. Peptidase disrupts peptide bonds and digests proteins into amino acids. Lipase acts to hydrolyze lipids.

Lipase is the correct answer because it is the enzyme that is responsible for digesting fats in the small intestine. Trypsin, chymotrypsin, and pepsin digest protein. Amylase digests carbohydrates.

The answer to this question is cholecystokinin (CCK). CCK is responsible for the release of bile from the gallbladder. The bile is responsible for fat breakdown and absorption in the small intestine, as the bile acts to emulsify fats so that lipase can effectively digest them.

Gastrin and secretin are also digestive hormones, but serve different functions. Gastrin promotes acid release from parietal cells in the stomach, while secretin suppresses acid release. Renin is not involved in digestion, and is released in response to low blood pressure.

In order to stimulate digestion in the stomach G cells secrete gastrin, which stimulates parietal cells. Pepsinogen is released by chief cells. The parietal cells release hydrochloric acid into the stomach lumen. The lowered acidity cleaves pepsinogen and creates pepsin, which begins to degrade proteins.

Mucous cells have the nondigestive role of lubricating the stomach lumen and protecting the stomach epithelium from degradation by the highly acidic gastric juices.

Trypsin is created by the pancreas, and is responsible for the degradation of proteins in the lumen of the small intestine. More importantly, activated trypsin activates all of the other enzymes present in the small intestine. If trypsin is absent, virtually no digestion would take place.

Bile is released by the gallbladder due to secretion of cholecystokinin (CCK) in response to lipid digestion. Cholecystokinin is produced by I cells of the small intestine and has a number of digestive regulation effects, including pancreatic and liver stimulation. The liver produces bile, which is stored in the gall bladder until stimulation with CCK cause gall bladder contraction and bile release.

Secretin is released from the duodenum in response to an influx of chyme, containing digested food and stomach acid, from the antrum of the stomach. In order not to damage the walls of the small intestine, the pancreatic acinar cells produce and secrete bicarbonate to mediate the pH of the chyme entering the small intestine. Secretin stimulates this release of bicarbonate from the pancreatic cells.

Gastrin stimulates acid secretion in the stomach, trypsin breaks down amino acids, and cholecystokinin increases contraction of the gallbladder to expel bile salts into the lumen of the duodenum through the sphincter of Oddi.

Cholecystokinin (CCK), made by the I cells of the small intestine and secreted into the duodenum, serves to stimulate contraction of the muscular layer of the gallbladder. CCK is generally released within two to three minutes of ingesting food, especially foods that are high in fats and triglycerides. As the gallbladder contracts, it releases bile salts into the duodenum that help solubilize ingested fat for absorption in the jejunum of the small intestine.

Secretin stimulates release of bicarbonate from the pancreas, gastrin stimulates release of acid in the stomach, and chymotrypsin cleaves peptide bonds of ingested proteins.

Parietal cells are located in the body of the stomach, and are responsible for secreting acid when stimulated by a variety of hormones, including gastrin (from G cells) and histamine (from enterochromaffin-like (ECL) cells). The release of acid allows food particles to be broken down in the stomach before they are transported through the antrum to the small intestine.

Chief cells produce pepsinogen, trypsin is released from the pancreas into the small intestine, and ECL cells release histamine to stimulate parietal cells to secrete acid.

Enterochromaffin-like (ECL) cells are neuroendocrine cells in the body of the stomach that release histamine to stimulate the secretion of acid by parietal cells. They function in an indirect manner to decrease the pH of the stomach.

Chief cells release pepsinogen, which is activated to become pepsin by the acidic pH of the stomach and promotes protein breakdown. G cells release gastrin from the antrum of the stomach to encourage acid secretion by parietal cells.

Chief cells are responsible for secreting the zymogen pepsinogen into the lumen of the stomach. Once pepsinogen enters the acidic environment of the stomach, it auto-catalyzes its conversion into the fully functional enzyme pepsin, which serves to breakdown proteins into smaller amino acid units by cleaving peptide bonds. The reason that chief cells secrete the zymogen, rather than active pepsin, is to prevent the active enzyme from degrading the walls of the stomach.

Trypsin and trypsinogen are released from the pancreas and also help to break down proteins in the small intestine.

Parietal cells, in addition to secreting hydrochloric acid into the stomach lumen, also make intrinsic factor (IF) that serves to scavenge vitamin B-12 in the stomach and chaperone it to the ileum for absorption. IF is important because a lack of B-12 is implicated in numerous metabolic diseases and anemia.

The other enzymes listed are produced by different cells. Pepsinogen is released by chief cells of the stomach, and trypsin and amylase by the acinar cells of the pancreas.