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The alimentary canal, or digestive tract, is made up of the:

A. pancreas, liver, and gallbladder

B. esophagus, stomach, and intestines

C. colon, rectum, and anus

D. mouth, esophagus, and stomach

Answer Explanation:

b. esophagus, stomach, and intestines

- Correct: The alimentary canal, or digestive tract, is made up of the esophagus, stomach, and intestines (both small and large). These organs form a continuous tube that extends from the mouth to the anus and is responsible for the digestion and absorption of food and the elimination of waste. The esophagus transports food from the mouth to the stomach through peristaltic contractions, while the stomach and intestines further digest food and absorb nutrients.

a. pancreas, liver, and gallbladder

- Incorrect: While the pancreas, liver, and gallbladder are important accessory organs that produce digestive enzymes and substances involved in digestion (such as bile), they are not part of the alimentary canal itself. Instead, they secrete their products into the alimentary canal to aid in digestion.

c. colon, rectum, and anus

- Incorrect: The colon, rectum, and anus are parts of the large intestine, which is a component of the alimentary canal. However, the alimentary canal is not solely composed of these organs; it also includes the esophagus, stomach, and small intestine.

d. mouth, esophagus, and stomach

- Incorrect: While the mouth, esophagus, and stomach are indeed part of the alimentary canal, they do not represent the entirety of it. The alimentary canal includes additional organs such as the small and large intestines, which are also involved in the digestion and absorption of food.

Therefore, the Correct Answer is B.

Q #1: Which of the following organs has 3 layers of smooth muscle in its muscularis externa?

A. small intestine

B. esophagus

C. stomach

D. large intestine

Answer Explanation

C. stomach

- Correct: The stomach has three layers of smooth muscle in its muscularis externa, which is the muscular layer of the gastrointestinal tract responsible for peristalsis and mixing of food. These muscle layers are arranged in longitudinal, circular, and oblique orientations, allowing for the mechanical processing of ingested food and the propulsion of food through the digestive tract. This muscular arrangement contributes to the stomach's ability to churn and mix food with gastric juices during digestion.

A. small intestine

- Incorrect: While the small intestine does have smooth muscle in its muscularis externa, it typically has two layers of smooth muscle: an inner circular layer and an outer longitudinal layer.

B. esophagus

- Incorrect: The esophagus also has smooth muscle in its muscularis externa, but it typically has two layers of smooth muscle: an inner circular layer and an outer longitudinal layer.

D. large intestine

- Incorrect: The large intestine, like the small intestine, typically has two layers of smooth muscle in its muscularis externa: an inner circular layer and an outer longitudinal layer.
Q #2: Pancreatic juice ________.

A. deactivates bile.

B. is secreted by pancreatic islet cells.

C. buffers chyme.

D. is released into the cystic duct.

Answer Explanation

c) buffers chyme.

- Correct: Pancreatic juice contains bicarbonate ions, which act as buffers to neutralize the acidic chyme entering the duodenum from the stomach. This neutralization is essential for maintaining the optimal pH for the activity of digestive enzymes in the small intestine.

a) deactivates bile.

- Incorrect: Pancreatic juice does not deactivate bile. Bile is not deactivated in the digestive process; instead, it aids in the emulsification and digestion of fats in the small intestine.

b) is secreted by pancreatic islet cells.

- Incorrect: Pancreatic juice is secreted by exocrine cells called pancreatic acinar cells, not by pancreatic islet cells. Pancreatic islet cells secrete hormones such as insulin and glucagon, which regulate blood glucose levels.

d) is released into the cystic duct.

- Incorrect: Pancreatic juice is released into the duodenum through the pancreatic duct, not the cystic duct. The cystic duct connects the gallbladder to the common bile duct, allowing bile to be released into the duodenum when needed for digestion.
Q #3: In which part of the alimentary canal does most digestion occur?

A. stomach

B. proximal small intestine

C. distal small intestine

D. ascending colon

Answer Explanation

b) proximal small intestine

- Correct: Most digestion occurs in the proximal small intestine, specifically in the duodenum. The duodenum receives chyme from the stomach and plays a crucial role in digestion by mixing the chyme with digestive enzymes and bile. Digestive enzymes from the pancreas, including amylase, lipase, and proteases, break down carbohydrates, fats, and proteins, respectively, in the duodenum. Bile, produced by the liver and stored in the gallbladder, emulsifies fats to aid in their digestion and absorption.

a) stomach

- Incorrect: While digestion begins in the stomach, where proteins are broken down by pepsin and fats are emulsified to some extent by gastric lipase, the majority of digestion occurs in the small intestine, particularly in the duodenum.

c) distal small intestine

- Incorrect: The distal small intestine, including the jejunum and ileum, is primarily involved in nutrient absorption rather than digestion. Although some digestion continues in these regions, the majority of digestive processes have already occurred in the proximal small intestine.

d) ascending colon

- Incorrect: The ascending colon is part of the large intestine and is not directly involved in digestion. Its main function is to absorb water and electrolytes from the indigestible residue of food (feces) before it is excreted from the body.

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