Which of these organs is not considered an accessory digestive structure?

Answer Explanation

b) propulsion

- Correct: Propulsion is the movement of food along the length of the alimentary canal, from the mouth to the anus. This process occurs throughout most of the alimentary canal and includes both swallowing (deglutition) and peristalsis. Swallowing moves food from the mouth to the esophagus, while peristalsis involves rhythmic contractions and relaxations of smooth muscles in the walls of the digestive organs, pushing food forward through the esophagus, stomach, and intestines.

a) Ingestion: Ingestion refers to the intake of food into the mouth, which occurs at the beginning of the alimentary canal.

c) Segmentation: Segmentation involves the mixing and churning of food within certain regions of the digestive tract, particularly the small intestine. It does not occur throughout most of the alimentary canal but rather in specific areas where mechanical digestion and absorption are optimized.

d) Absorption: Absorption is the process by which nutrients and water are taken up from the digestive tract into the bloodstream or lymphatic system. While absorption occurs primarily in the small intestine, it also occurs in other parts of the alimentary canal, particularly in the large intestine, but it is not a continuous process throughout most of the alimentary canal like propulsion.

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.

Answer Explanation

b) trypsin

- Correct: Trypsin is an enzyme involved in the chemical digestion of protein. It is secreted as trypsinogen by the pancreas and activated to its active form, trypsin, by enterokinase in the duodenum. Trypsin breaks down proteins into smaller peptides by cleaving peptide bonds between specific amino acids.

a) pancreatic amylase

- Incorrect: Pancreatic amylase is an enzyme involved in the digestion of carbohydrates (starches). It breaks down starch molecules into maltose and other simpler sugars.

c) sucrase

- Incorrect: Sucrase is an enzyme involved in the digestion of disaccharide sugars, specifically sucrose. It catalyzes the hydrolysis of sucrose into its constituent monosaccharides, glucose, and fructose.

d) pancreatic nuclease

- Incorrect: Pancreatic nuclease is an enzyme involved in the digestion of nucleic acids (DNA and RNA). It breaks down nucleic acid molecules into their component nucleotides.