D313 Anatomy and Physiology II - Set 2 - Part 3

Correct Answer: Oral cavity, small intestine, large intestine

Option a is correct because carbohydrate digestion begins in the oral cavity with salivary amylase, continues in the small intestine with pancreatic amylase and brush border enzymes, and finishes via large intestine fermentation. Option b is incorrect because the stomach is not a significant carbohydrate digestion site. Salivary amylase is deactivated by the acidic gastric environment, and no major carbohydrate-digesting enzymes are secreted in the stomach. Option c is incorrect because this list omits the large intestine, where bacterial fermentation of remaining dietary fibers represents the final stage of carbohydrate processing within the entire digestive tract pathway. Option d is incorrect because the stomach does not significantly digest carbohydrates. The acidic environment inactivates salivary amylase, and the stomach focuses on protein digestion using pepsin and hydrochloric acid instead.

Correct Answer: Stomach and small intestine

Option d is correct because protein digestion starts in the stomach with pepsin breaking peptide bonds and continues in the small intestine with trypsin and brush border enzymes completing breakdown into absorbable amino acids. Option a is incorrect because the oral cavity does not perform protein digestion at all. Salivary amylase targets carbohydrates only, and protein digestion does not begin until food reaches the acidic stomach and encounters pepsin. Option b is incorrect because neither the oral cavity nor the large intestine performs significant protein digestion. Protein breakdown is handled exclusively by the stomach and small intestine, not the structures listed here. Option c is incorrect because this reverses the correct anatomical order and includes the wrong organ. Protein digestion starts in the stomach and finishes in the small intestine, not in the large intestine at all.

Correct Answer: Small intestine

Option b is correct because the small intestine is where significant lipid digestion occurs after bile emulsifies fat into smaller droplets. Pancreatic lipase then performs chemical digestion, breaking fats into absorbable fatty acid components. Option a is incorrect because the stomach contributes only minor lipid digestion through gastric lipase. Most fat digestion requires bile emulsification and pancreatic lipase, both of which act within the small intestine. Option c is incorrect because the oral cavity does not perform lipid digestion. No lipase enzymes are active in the mouth, and fat digestion does not begin until food reaches the stomach for minor breakdown. Option d is incorrect because the large intestine does not perform significant lipid digestion at all. By the time material reaches the large intestine, fat digestion and absorption have been completed in the small intestine.

Correct Answer: On microvilli of epithelial cells

Option c is correct because brush border enzymes are embedded in the membranes of microvilli, the tiny hair-like extensions on intestinal epithelial cell surfaces. They perform final breakdown of carbohydrates and proteins into monomers. Option a is incorrect because the base of villi is where crypts of Lieberkuhn are located. Brush border enzymes are found on microvilli surfaces along the villi tips and surfaces, not at their structural base. Option b is incorrect because crypts of Lieberkuhn are glands at the villi base that secrete lysozyme for antimicrobial defense. Brush border enzymes are on the microvilli surfaces above, not within these crypt gland structures. Option d is incorrect because the submucosa is a connective tissue layer beneath the mucosa that contains blood vessels and nerves. Brush border enzymes are on the mucosal surface within the microvilli cell membranes above.

Correct Answer: Trypsin

Option a is correct because trypsin is the key pancreatic protease that digests proteins directly and activates other proteases in the small intestine. Its absence disrupts the entire protease activation cascade. Option b is incorrect because pancreatic amylase digests carbohydrates in the small intestine and has no role in protein digestion. It does not activate other enzymes in any protease cascade within the duodenal environment. Option c is incorrect because gastric lipase is a stomach enzyme contributing only to minor fat digestion. It operates in the stomach and has no involvement in protein digestion or enzyme activation in the intestine. Option d is incorrect because salivary amylase initiates carbohydrate digestion in the oral cavity only. It does not digest proteins or activate any other enzymes within the small intestinal protease activation cascade.

Correct Answer: Cerebral cortex and hypothalamus

Option d is correct because the cerebral cortex and hypothalamus trigger gastric secretions during the cephalic phase. They process sensory input such as the smell and thought of food and then signal the stomach. Option a is incorrect because the pons and medulla oblongata house the salivary nuclei that control saliva production. They are important brainstem structures but do not initiate gastric secretions during the cephalic phase. Option b is incorrect because the thalamus is a sensory relay center and the cerebellum coordinates motor movement and balance. Neither is directly responsible for triggering gastric secretions during the anticipatory cephalic phase. Option c is incorrect because while the brainstem participates in autonomic functions, the spinal cord is not a primary cephalic phase initiator. The cerebral cortex and hypothalamus are the specific structures identified in this role.

Correct Answer: Pons and medulla oblongata

Option c is correct because the salivary nuclei are in the pons and medulla oblongata of the brainstem. They receive input from chewing muscles and conditioned reflexes then signal salivary glands to produce saliva. Option a is incorrect because the cerebral cortex handles higher-order thinking and the thalamus relays sensory information to the cortex. Neither structure houses the salivary nuclei that directly control salivary gland activation. Option b is incorrect because the hypothalamus regulates homeostatic functions and the cerebellum coordinates movement. The salivary nuclei are specifically found in the pons and medulla oblongata, not in these brain structures. Option d is incorrect because the spinal cord transmits signals between brain and body while the midbrain handles visual and auditory reflexes. Neither contains the salivary nuclei that control salivary gland secretion activity.

Correct Answer: Stretch receptors in the stomach wall

Option a is correct because stretch receptors in the stomach wall detect distension when food enters during the gastric phase. They send signals stimulating increased gastric secretions and enhanced motility to process the food. Option b is incorrect because chemoreceptors in the duodenal lining detect chemical composition of chyme in the small intestine. They participate in the intestinal phase, not the gastric phase triggered by stomach distension. Option c is incorrect because baroreceptors in the aortic arch monitor blood pressure changes within the cardiovascular system. They have no involvement in detecting stomach distension or regulating gastric secretory activity. Option d is incorrect because thermoreceptors detect temperature changes in swallowed food or surrounding tissue. They do not detect mechanical stretching of the stomach wall that triggers the gastric phase of regulation.

Correct Answer: Contents volume and specific food molecules

Option b is correct because the gastric phase is driven by stomach contents volume causing wall distension and the presence of specific food molecules that stimulate G-cells to release gastrin for continued secretion. Option a is incorrect because brain signals primarily drive the cephalic phase before food enters the stomach. Intestinal hormones are part of the intestinal phase triggered by chyme entering the duodenum, not the gastric phase. Option c is incorrect because salivary reflexes are controlled by brainstem salivary nuclei and involve saliva production in the mouth. Esophageal contractions move food downward but neither stimulus drives gastric phase activity. Option d is incorrect because duodenal pH and bile salt concentration are factors relevant to the intestinal phase of regulation occurring in the small intestine. The gastric phase is driven by stimuli within the stomach.

Correct Answer: The thought or smell of food

Option d is correct because the cephalic phase is triggered by sensory inputs like the thought, sight, or smell of food. These activate the cortex and hypothalamus, which signal the stomach via the vagus. Option a is incorrect because stretching of the stomach wall is the stimulus that triggers the gastric phase, not the cephalic phase. The cephalic phase specifically occurs before food physically enters the stomach cavity. Option b is incorrect because acidic chyme entering the duodenum triggers the intestinal phase of gastric regulation. This event occurs after food has been processed in the stomach and moved into the small intestine. Option c is incorrect because bacterial fermentation in the large intestine occurs at the end of the digestive process. It is not a sensory stimulus that triggers any phase of gastric regulation in the stomach.