Your digestive system works on the foods you eat for about:

Answer Explanation

d) all of the above

- Correct: All of the listed processes occur in the mouth:

a) Ingestion: The mouth is the entry point for food into the digestive system. Ingestion refers to the act of taking food or drink into the mouth.

b) Mechanical digestion: Mechanical digestion involves the physical breakdown of food into smaller pieces through actions such as chewing and mixing with saliva. In the mouth, the teeth tear and grind food into smaller particles, which increases the surface area for chemical digestion.

c) Chemical digestion: Chemical digestion involves the breakdown of food into smaller molecules by enzymes and other chemicals. In the mouth, salivary glands secrete saliva, which contains the enzyme amylase. Amylase begins the chemical breakdown of carbohydrates, converting starches into simpler sugars such as maltose.

Therefore, all of the processes listed—ingestion, mechanical digestion, and chemical digestion—occur in the mouth during the initial stages of digestion.

Answer Explanation

c) enteroendocrine cells

- Correct: Enteroendocrine cells are specialized cells located in the epithelium of the gastrointestinal tract that secrete hormones. These hormones play various roles in the regulation of digestion, nutrient absorption, and other physiological processes. Examples of hormones secreted by enteroendocrine cells include gastrin, secretin, cholecystokinin (CCK), and ghrelin.

a) parietal cells

- Incorrect: Parietal cells are found in the gastric glands of the stomach and secrete hydrochloric acid (HCl) and intrinsic factor, but they do not secrete hormones.

b) mucous neck cells

- Incorrect: Mucous neck cells are found in the gastric glands of the stomach and secrete mucus, which helps protect the stomach lining from the acidic environment, but they do not secrete hormones.

d) chief cells

- Incorrect: Chief cells are found in the gastric glands of the stomach and secrete pepsinogen, the precursor to the enzyme pepsin, which plays a role in protein digestion. Chief cells do not secrete hormones.

Answer Explanation

a) mouth

- Correct: The chemical digestion of starch begins in the mouth. Salivary amylase, an enzyme secreted by the salivary glands, initiates the breakdown of starch molecules into maltose and other smaller carbohydrate molecules. This process begins as soon as food enters the mouth and continues as it is mixed with saliva during chewing and swallowing.

b) esophagus

- Incorrect: The esophagus is not directly involved in the chemical digestion of starch. It serves primarily as a conduit for the passage of food from the mouth to the stomach via peristaltic contractions.

c) stomach

- Incorrect: While some minor digestion may occur in the stomach due to the presence of salivary amylase from swallowed saliva, the stomach is not the primary site of starch digestion. Its acidic environment inhibits the activity of salivary amylase, so significant starch digestion does not occur there.

d) small intestine

- Incorrect: Starch digestion continues in the small intestine, primarily in the duodenum, but it does not begin there. Enzymes such as pancreatic amylase and brush border enzymes further break down starch into simpler sugars in the small intestine.