Chapter 20: The Gastrointestinal System

Gastrin is a hormone that is released by the stomach in response to the presence of food. It stimulates the secretion of acid by the stomach, which helps in the digestion of food. Therefore, the correct answer is "stimulates".

Bile salts are necessary for the proper functioning of lipases. Lipases are enzymes responsible for the breakdown of fats into smaller molecules that can be absorbed by the body. Bile salts help in emulsifying fats, breaking them down into smaller droplets, which increases the surface area for lipases to act upon. This allows lipases to efficiently break down fats into fatty acids and glycerol, facilitating their digestion and absorption in the small intestine. Without bile salts, the activity of lipases would be significantly impaired, leading to poor fat digestion and absorption.

Cholecystokinin is a hormone that is released in response to the presence of food in the small intestine. It stimulates the contraction of the gallbladder, which in turn releases bile into the small intestine. Bile is important for the digestion and absorption of fats. Secretin, on the other hand, is another hormone that is released in response to the acidity of the chyme in the small intestine. It stimulates the release of bicarbonate from the pancreas to neutralize the acidity. While both secretin and cholecystokinin play important roles in the digestive process, it is cholecystokinin that specifically stimulates the contraction of the gallbladder.

Blockage of the flow of bile into the duodenum interferes with the digestion of lipids only. Bile is produced by the liver and stored in the gallbladder, and it plays a crucial role in the digestion and absorption of lipids. Bile emulsifies fats, breaking them down into smaller droplets and increasing their surface area for enzymes to act upon. This allows lipases to efficiently break down lipids into fatty acids and glycerol, which can then be absorbed by the small intestine. Without bile, the digestion and absorption of lipids are impaired, leading to difficulties in processing and utilizing dietary fats.

Brush border enzymes are responsible for breaking down disaccharides into monosaccharides. These enzymes are located on the brush border of the small intestine and include enzymes such as sucrase, lactase, and maltase. They hydrolyze the bonds between the sugar molecules in disaccharides, converting them into their individual monosaccharide components. This process allows for the absorption of monosaccharides into the bloodstream for energy production. Pancreatic enzymes, on the other hand, primarily break down proteins, fats, and carbohydrates into smaller molecules but do not specifically target disaccharides.

An increase in the osmolarity of duodenal contents and the entry of stomach acid into the duodenum both tend to inhibit acid secretion by the stomach. When the osmolarity of duodenal contents increases, it signals the stomach to slow down acid secretion in order to prevent further increase in osmolarity. Similarly, when stomach acid enters the duodenum, it triggers a negative feedback mechanism that inhibits further acid secretion. Therefore, both a and b are true statements that explain factors inhibiting acid secretion by the stomach.

Amylase is an enzyme that breaks down starch into smaller sugar molecules. One of the main products of amylase digestion is maltose. Maltose is a disaccharide composed of two glucose molecules linked together. Therefore, maltose is the correct answer as it is a digestion product of amylase.

If the salivary glands fail to secrete amylase, it would not affect the digestion of any of the mentioned substances. Amylase is an enzyme responsible for breaking down starch into simpler sugars. However, the question states that the failure of salivary glands to secrete amylase would make it impossible to digest "none of the above," indicating that amylase is not required for the digestion of proteins, fats, disaccharides, or starch.