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.

Therefore, the Correct Answer is B.

Q #1: Which phase of deglutition involves contraction of the longitudinal muscle layer of the muscularis?

A. voluntary phase

B. buccal phase

C. pharyngeal phase

D. esophageal phase

Answer Explanation

a) voluntary phase

- Correct: The voluntary phase of deglutition (swallowing) involves the initial voluntary movement of food from the mouth into the pharynx. During this phase, the tongue pushes the food bolus backward toward the oropharynx. Contraction of the longitudinal muscle layer of the muscularis propels the food bolus into the pharynx, which is part of the voluntary control of swallowing.

b) buccal phase

- Incorrect: The buccal phase of deglutition involves the initial formation of the food bolus and its movement toward the oropharynx by the coordinated action of the tongue and muscles of the cheeks. It does not involve contraction of the longitudinal muscle layer of the muscularis.

c) pharyngeal phase

- Incorrect: The pharyngeal phase of deglutition is involuntary and occurs when the food bolus reaches the pharynx. It involves the sequential contraction of muscles in the pharyngeal wall to propel the food bolus downward toward the esophagus. The contraction of the longitudinal muscle layer of the muscularis is not a significant component of the pharyngeal phase.

d) esophageal phase

- Incorrect: The esophageal phase of deglutition involves the passage of the food bolus through the esophagus and into the stomach. Peristaltic waves of contraction and relaxation of the muscularis propels the food bolus along the length of the esophagus. The contraction of the longitudinal muscle layer of the muscularis primarily occurs during the voluntary phase of deglutition, not the esophageal phase.
Q #2: During the process of absorption, nutrients from food go from:

A. the intestines into the bladder

B. the blood into the organs

C. the intestines into the bloodstream

D. the mouth into the stomach

Answer Explanation

c. the intestines into the bloodstream

- Correct: During the process of absorption, nutrients from food pass from the intestines into the bloodstream. After food is broken down into its constituent nutrients through digestion in the stomach and small intestine, these nutrients are absorbed across the lining of the small intestine into the bloodstream. The small intestine is highly specialized for absorption, with villi and microvilli increasing the surface area available for nutrient absorption. Once absorbed into the bloodstream, nutrients are transported to various organs and tissues throughout the body to provide energy, support growth and repair, and maintain overall health.

a. the intestines into the bladder

- Incorrect: The bladder is part of the urinary system and is responsible for storing urine produced by the kidneys. Absorption of nutrients does not involve passage into the bladder.

b. the blood into the organs

- Incorrect: While nutrients absorbed into the bloodstream are indeed transported to various organs and tissues throughout the body, absorption itself occurs in the intestines, not directly from the blood into the organs.

d. the mouth into the stomach

- Incorrect: The mouth and stomach are primarily involved in the initial stages of digestion, including mechanical breakdown of food and the initiation of chemical digestion of carbohydrates and proteins. Absorption of nutrients occurs primarily in the small intestine, not from the mouth into the stomach.
Q #3: Where does the chemical digestion of starch begin?

A. mouth

B. esophagus

C. stomach

D. small intestine

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.

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In which part of the alimentary canal does most digestion occur?

More Questions on TEAS 7 Science

Q #1: Which phase of deglutition involves contraction of the longitudinal muscle layer of the muscularis?

Answer Explanation

Q #2: During the process of absorption, nutrients from food go from:

Answer Explanation

Q #3: Where does the chemical digestion of starch begin?

Answer Explanation

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