Surface area of the stomach is increased by

Correct Answer: A

Rationale: The correct answer is A: gastric pits. Gastric pits are invaginations in the stomach lining that contain specialized cells for secretion of gastric juices. These pits increase the surface area of the stomach by providing a larger area for nutrient absorption and digestion. Plicae circulares are folds in the small intestine, not the stomach. Villi and microvilli are found in the small intestine and further increase surface area for absorption, not in the stomach.

Correct Answer: A

Rationale: The correct answer is A: lacteals. Lacteals are specialized lymphatic capillaries found in the villi of the small intestine that absorb dietary fats and fat-soluble vitamins. They play a crucial role in the transport of these nutrients to the bloodstream. Peyer's patches (B) are lymphoid nodules in the small intestine involved in immune responses. Crypts of Lieberkuhn (C) are intestinal glands that secrete digestive enzymes. Microvilli (D) are small projections on the surface of intestinal cells that increase surface area for nutrient absorption but are not lymphatic capillaries.

Correct Answer: C

Rationale: The correct answer is C: local and mechanical stimulation. In the small intestine, movement of chyme is primarily regulated by local and mechanical stimulation, which triggers peristalsis and segmentation. This allows for the mixing and propulsion of chyme along the digestive tract. A: Secretin and cholecystokinin are hormones involved in regulating pancreatic and gallbladder secretions, not movement of chyme in the small intestine. B: The parasympathetic nervous system via the vagus nerve plays a role in stimulating digestive processes but is not the primary regulator of movement of chyme. D: The enterogastric reflex is related to regulating stomach emptying in response to irritating substances, not movement of chyme in the small intestine.

Correct Answer: A

Rationale: The correct answer is A because in the production of pancreatic juice, bicarbonate ions are actively transported into the intercalated duct to ensure the alkalinity of the pancreatic juice. Additionally, sodium ions are exchanged for hydrogen ions to maintain the pH balance. This process helps neutralize the acidic chyme entering the small intestine from the stomach. The other choices are incorrect because potassium ions are not directly involved in this specific process, and the exchange of sodium ions for potassium ions does not contribute to the regulation of pancreatic juice pH.

Correct Answer: B

Rationale: The correct answer is B because the teniae coli are bands of longitudinal smooth muscle in the colon. These bands contract to form haustra, which are the pouches that give the colon its segmented appearance. Choice A is incorrect because fat and epiploic appendages are not involved in the contraction of the colon. Choice C is incorrect because the teniae coli are smooth muscle, not skeletal muscle. Choice D is incorrect because the internal anal sphincter is not formed by the contraction of the teniae coli.