Which of these structures prevents food from entering the windpipe?

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: 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.

Correct Answer: D

Rationale: The correct answer is D, congenital pyloric stenosis. This condition typically presents in male infants around 3-6 weeks of age with projectile vomiting due to hypertrophy of the pyloric muscle, leading to obstruction at the pylorus. This causes the infant to forcefully vomit shortly after feeding. Meckel's diverticulum (A) presents with painless rectal bleeding. Esophageal atresia (B) presents with drooling and choking with feeding. Congenital diaphragmatic hernia (C) presents with respiratory distress and scaphoid abdomen due to herniation of abdominal organs into the chest cavity.

Correct Answer: B

Rationale: The correct answer is B: juvenile polyp. Juvenile polyps are benign growths commonly found in the colon and rectum of children. They have no significant tendency to undergo malignant transformation due to their non-neoplastic nature. They are typically small, solitary, and have a smooth surface. Familial polyposis (choice A) is a hereditary condition characterized by numerous polyps in the colon, which can progress to colorectal cancer. Villous adenomas (choice C) are precancerous lesions with a higher risk of malignant transformation. Carcinoid tumors (choice D) are neuroendocrine tumors that can be found in various parts of the body, including the gastrointestinal tract, and have the potential to be malignant.

Correct Answer: B

Rationale: The correct answer is B because HCl secretion is primarily carried out by parietal cells in the stomach lining. Parietal cells contain proton pumps that actively secrete HCl to aid in digestion. Chief cells secrete pepsinogen, not HCl (A is incorrect). Gastrin actually stimulates HCl secretion, so it doesn't inhibit it (C is incorrect). Acetylcholine (Ach) is a neurotransmitter that can stimulate, not inhibit, HCl secretion (D is incorrect). Therefore, option B is the correct choice based on the roles of parietal cells in HCl secretion.