Where is the majority of absorption of nutrients in the digestive tract?

Correct Answer: B

Rationale: The majority of absorption of nutrients occurs in the small intestine. This is because the small intestine has a large surface area due to its villi and microvilli, which increase the absorption capacity. Additionally, the small intestine contains specialized cells that facilitate the absorption of nutrients into the bloodstream. In contrast, the stomach's main function is to break down food, the large intestine primarily absorbs water and electrolytes, and the mouth is responsible for initial digestion through chewing and saliva production. Therefore, choice B is correct as it aligns with the anatomical and physiological functions of the digestive system.

Correct Answer: A

Rationale: The correct answer is A: liver. Bile is produced in the liver and stored in the gallbladder before being released into the small intestine to aid in digestion. The liver plays a crucial role in bile production, whereas the pancreas is primarily responsible for producing digestive enzymes. The gallbladder stores and concentrates bile but does not produce it. The small intestine is where bile acts to break down fats. Therefore, the liver is most associated with bile due to its production and regulation of bile.

Correct Answer: A

Rationale: The correct answer is A: Epiglottis. The epiglottis is a flap of tissue that covers the opening to the trachea (windpipe) during swallowing, preventing food from entering the airway. This action ensures that food goes down the esophagus to the stomach. The other choices (B, C, D) are involved in controlling the flow of food in the digestive system at different points, but they do not specifically prevent food from entering the windpipe like the epiglottis does.

Correct Answer: B

Rationale: The correct answer is B because bile salts are essential for the digestion and absorption of fats, not carbohydrates. Cellulose cannot be digested by human amylases, making choice A incorrect. Starch digestion starts in the mouth with salivary amylase, not one-third in the mouth and two-thirds in the small gut, so choice C is incorrect. Carbohydrate digestion can occur simultaneously with protein digestion, so choice D is also incorrect. Bile salts aid in emulsifying fats, facilitating their digestion and absorption in the small intestine.

Correct Answer: B

Rationale: The correct answer is B: Entropeptidase. Pancreatic exocrine secretion is primarily stimulated by hormones like CCK and the presence of food in the stomach. Vagal stimulation can also trigger pancreatic secretion. However, enteropeptidase is an enzyme that activates trypsinogen to trypsin in the small intestine, not a direct stimulator of pancreatic exocrine secretion. Therefore, choice B is the exception among the given options.