36 clinical MCQs in Weekly Exam: Year 2: GIT Physiology. Which single statement below, about the stomach, is correct?. Kenya, Africa and global revision.
Q1. Which single statement below, about the stomach, is correct?
Answer: Pepsinogen and gastric lipase are secreted into the lumen of the stomach.
Explanation: Pepsinogen (precursor to pepsin) and gastric lipase are secreted by chief cells in the gastric glands into the lumen of the stomach. Carbonic anhydrase is involved in acid secretion, but not the primary stimulus. Peyer's patches are lymphoid tissue in the small intestine. The vagus nerve stimulates acid secretion during the cephalic and gastric phases.
Q2. Water transport can occur from the lumen of the intestine to the bloodstream, or vice versa. Which statement is correct?
Answer: Water absorption in the small intestine is primarily driven by osmotic gradients created by nutrient absorption.
Explanation: In the small intestine, the absorption of digested nutrients (like glucose and amino acids) creates an osmotic gradient that draws water from the lumen into the epithelial cells and then into the bloodstream. While solute transport is often coupled, water movement is primarily osmotic. Secretion of water into the lumen is often an active process or follows active solute secretion. Water movement against its osmotic gradient typically requires active solute transport.
Q3. Which statement about fat digestion and absorption is correct?
Answer: Triglycerides are broken down primarily by lingual lipase in the stomach.
Explanation: Lingual lipase, secreted in the mouth and activated in the stomach, begins the digestion of triglycerides. Short-chain fatty acids are absorbed directly into the portal circulation. Bile salts are essential for emulsifying fats and forming micelles, which aid in the absorption of long-chain fatty acids and monoglycerides, not free fatty acids and glycerol directly. Chylomicrons are assembled within the enterocytes.
Q4. Which statement about protein digestion is most correct?
Answer: Pepsinogen is activated by hydrochloric acid to pepsin.
Explanation: Pepsinogen, secreted by chief cells, is activated to pepsin by the acidic environment of the stomach. Trypsin is a key enzyme in the small intestine, but digestion starts in the stomach. Amino acids and small peptides are absorbed into the portal circulation. While small peptides can be absorbed, most protein digestion yields amino acids or very small peptides.
Q5. Which statement about dietary fibre is most correct?
Answer: Insoluble fibre absorbs water and softens stool, promoting regularity.
Explanation: Insoluble fibre adds bulk to stool and absorbs water, which helps to soften it and promote regular bowel movements. Dietary fibre is not digested by human enzymes. Soluble fibre can absorb water and form a gel, which can slow transit time in some cases, but its main effect is on stool consistency and fermentation. Fibre is crucial for colonic health and serves as a substrate for gut microbiota.
Q6. Which statement about absorption is most correct?
Answer: Iron absorption is regulated by dietary intake and body stores.
Explanation: Iron absorption is tightly regulated. When body stores are low, absorption increases, and when stores are high, it decreases. Fat-soluble vitamins are absorbed with fats into the lymph, while water-soluble vitamins are absorbed into the portal circulation. Significant nutrient absorption primarily occurs in the small intestine.
Q7. Which statement about the oral phase of digestion is INCORRECT?
Answer: The swallowing reflex is entirely voluntary and can be initiated at any time.
Explanation: The swallowing reflex, once initiated, becomes involuntary. While chewing and salivary enzymes begin digestion, and saliva aids in bolus formation, the reflex itself is not entirely voluntary.
Q8. Which statement about stomach lining cells is correct?
Answer: Goblet cells secrete mucus to protect the stomach lining.
Explanation: Goblet cells in the stomach epithelium secrete mucus, which forms a protective barrier against the acidic environment and digestive enzymes. Parietal cells secrete HCl and intrinsic factor. Chief cells secrete pepsinogen. ECL cells secrete histamine.
Q9. Which statement about pancreatic enzyme secretion is correct?
Answer: Secretin stimulates the secretion of bicarbonate-rich fluid from the pancreas.
Explanation: Secretin is a hormone released in response to acidic chyme in the duodenum, and it stimulates the pancreatic duct cells to secrete a bicarbonate-rich fluid, which neutralizes the stomach acid. Pancreatic amylase digests carbohydrates. CCK stimulates the secretion of both bicarbonate and digestive enzymes. Pancreatic enzymes like trypsinogen are secreted in inactive forms and activated in the duodenum.
Q10. Which statement about post-meal motility is correct?
Answer: Segmentation is the primary propulsive motility in the small intestine after a meal.
Explanation: Segmentation, characterized by mixing contractions, is the dominant motility pattern in the small intestine after a meal, facilitating digestion and absorption. The MMC is a pattern of motility that occurs during the fasting state. Gastric peristalsis increases after a meal to propel food into the duodenum. The gastrocolic reflex primarily affects colonic motility.
Q11. Which best describes colonic microbiota functions?
Answer: Synthesis of vitamin K and some B vitamins.
Explanation: Colonic microbiota are responsible for fermenting undigested carbohydrates and producing short-chain fatty acids, as well as synthesizing vitamin K and certain B vitamins. They do not digest all carbohydrates, nor do they absorb all essential minerals or produce enzymes for all macronutrients.
Q12. What explains fibre's protective effect against colon cancer?
Answer: Fibre leads to rapid transit of carcinogens through the colon.
Explanation: Dietary fibre, particularly insoluble fibre, can increase stool bulk and accelerate the transit of intestinal contents, including potential carcinogens, through the colon, thus reducing the duration of contact. Fibre does not directly kill cancer cells or promote only cancer-promoting bacteria. While fibre affects bile acid metabolism, its protective effect against colon cancer is more directly linked to transit time and dilution of carcinogens.
Q13. About some GIT hormones (true or false):
Answer: Gastrin is released as a result of stomach distension and vagal stimulation.
Explanation: Gastrin is released in response to stomach distension and vagal stimulation. Secretin primarily stimulates pancreatic duct cells to secrete bicarbonate. Pancreozymin is an older name for CCK, and CCK shares structural similarities with gastrin. Secretin inhibits gastric secretion and motility.
Q14. VIP causes (true or false):
Answer: VIP stimulates gastric acid secretion.
Explanation: Vasoactive intestinal peptide (VIP) is a potent vasodilator and relaxes gastrointestinal smooth muscle. It also stimulates intestinal secretion of water and electrolytes, and inhibits gastric acid secretion. Therefore, it generally promotes relaxation rather than increased motility.
Q15. Stimulation of Gastrointestinal Secretion include:
Answer: Sympathetic stimulation.
Explanation: Vagal stimulation (parasympathetic) generally increases gastrointestinal secretion. Sympathetic stimulation typically inhibits secretions. Somatostatin inhibits the release of many GI hormones and secretions. The enterogastric reflex, initiated by distension of the intestine or irritating stimuli, typically inhibits gastric secretion and motility.
Q16. The Secretin hormone:
Answer: Is released by S cells in the duodenum.
Explanation: Secretin is released by S cells in the duodenum in response to acidic chyme. It stimulates pancreatic duct cells to secrete bicarbonate and water. It inhibits gastric acid secretion and motility and has a weak effect on gallbladder contraction compared to CCK.
Q17. The GIT is controlled by:
Answer: All of the above.
Explanation: The gastrointestinal tract is controlled by a complex interplay of its own intrinsic nerve plexuses (enteric nervous system), extrinsic autonomic nerves (sympathetic and parasympathetic), and various hormones.
Q18. Inhibition of the myenteric plexus leads to which of the following?
Answer: Decreased motility.
Explanation: The myenteric plexus (Auerbach's plexus) is primarily responsible for controlling the tone, motility, and peristalsis of the GI tract. Inhibition of this plexus would lead to decreased motility.
Q19. The secretion of gastrin ceases (stops):
Answer: When the stomach pH drops below 2.
Explanation: Gastrin secretion is inhibited by a low gastric pH (below 2). It is stimulated by stomach distension, amino acids, and vagal activity. While chyme entering the duodenum can stimulate other hormones like secretin, it doesn't directly cause gastrin secretion to cease, and the cephalic phase stimulates gastrin release.
Q20. Stimulation of submucosal plexus results in an increase in which of the following?
Answer: Glandular secretion.
Explanation: The submucosal plexus (Meissner's plexus) primarily controls glandular secretions, blood flow, and some local muscle contractions within the mucosa and submucosa. The myenteric plexus is more involved in propulsive motility and peristalsis.
Q21. Secretin:
Answer: Stimulates pancreatic duct cells to secrete bicarbonate.
Explanation: Secretin, released from the duodenum in response to acid, primarily stimulates pancreatic duct cells to secrete bicarbonate-rich fluid. It inhibits gastric acid secretion and motility, and has no direct effect on gallbladder contraction.
Q22. About the GIT hormones affecting gastric function:
Answer: Gastrin stimulates gastric acid secretion.
Explanation: Gastrin is a primary stimulus for gastric acid secretion. CCK inhibits gastric acid secretion and motility (gastroileal reflex). Somatostatin generally inhibits gastric acid secretion. Secretin also inhibits gastric acid secretion and motility.
Q23. Cholecystokinin:
Answer: Is released from the duodenum in response to fats and proteins.
Explanation: Cholecystokinin (CCK) is released from duodenal I cells in response to fats and proteins. It stimulates gallbladder contraction, pancreatic enzyme secretion, and relaxation of the sphincter of Oddi. It also inhibits gastric emptying.
Q24. A major part of the gall bladder contractions are due to:
Answer: Cholecystokinin (CCK).
Explanation: Cholecystokinin (CCK) is the primary hormone responsible for stimulating the contraction of the gallbladder, which releases bile into the duodenum to aid in fat digestion.
Q25. Which of the following statements is FALSE?
Answer: Longest intestinal transit time occurs in the ascending colon.
Explanation: While sodium is actively reabsorbed in the colon and significant water reabsorption occurs, leading to stool formation, the longest intestinal transit time actually occurs in the transverse and descending colon, where the most water is absorbed and material is compacted.
Q26. Which tissue layer provides for primary digestive motility?
Answer: Muscularis externa
Explanation: The muscularis externa, composed of inner circular and outer longitudinal smooth muscle layers, is responsible for the propulsive movements (peristalsis) and mixing movements (segmentation) that constitute primary digestive motility.
Q27. Which statement about bile is true?
Answer: Bile salts are synthesized in the liver and reabsorbed in the ileum.
Explanation: Bile salts are synthesized from cholesterol in the liver and are crucial for fat digestion and absorption. They are actively reabsorbed in the terminal ileum and returned to the liver via the enterohepatic circulation. Bile primarily aids in fat digestion and emulsification, not carbohydrate digestion. Bile secretion is stimulated by parasympathetic activity and hormones like CCK.
Q28. Which statement regarding the swallowing reflex is false?
Answer: It is entirely voluntary.
Explanation: While the oral phase of swallowing is voluntary, the pharyngeal and esophageal phases are involuntary reflex actions. The epiglottis covers the glottis to prevent aspiration of food into the trachea, and respiration is temporarily inhibited.
Q29. Which of the following statements is TRUE?
Answer: The lower esophageal sphincter relaxes to allow food into the stomach.
Explanation: The pyloric sphincter relaxes to regulate the controlled release of chyme from the stomach into the duodenum. The lower esophageal sphincter relaxes to allow food into the stomach but contracts to prevent reflux. The sphincter of Oddi controls the flow of bile and pancreatic juice into the duodenum. The internal anal sphincter is under involuntary control, while the external anal sphincter is voluntary.
Q30. What is false about tonic contractions?
Answer: They are primarily responsible for peristalsis.
Explanation: Tonic contractions are sustained contractions that are important for maintaining closure of sphincters and regulating blood flow. Peristalsis, on the other hand, involves a wave of coordinated contraction and relaxation, not a sustained contraction.
Q31. Which of the following is characteristic of the segmenting movements in the small intestine?
Answer: Mixing of chyme with digestive juices.
Explanation: Segmenting movements are characterized by localized contractions and relaxations of the circular muscles in the small intestine. These contractions mix the chyme with digestive juices and facilitate contact with the absorptive surfaces, thus aiding digestion and absorption. They do not primarily propel chyme aborally (peristalsis does this).
Q32. Secretion of saliva increases in all of the below except
Answer: Sympathetic stimulation.
Explanation: Parasympathetic stimulation is the primary driver of increased salivary secretion, whether through direct stimulation or conditioned reflexes. Chewing also stimulates saliva production. Sympathetic stimulation generally leads to a thicker, more viscous saliva and can inhibit secretion, rather than increase it significantly.
Q33. Defecation is a reflex action
Answer: That involves relaxation of the internal and external anal sphincters.
Explanation: Defecation is a complex reflex involving both involuntary (rectosphincteric reflex) and voluntary components. It involves the relaxation of the internal anal sphincter (involuntary) and the external anal sphincter (voluntary). Parasympathetic stimulation facilitates defecation, while sympathetic stimulation can inhibit it. Therefore, it's not solely voluntary and is actually facilitated by parasympathetic activity.
Q34. In the stomach
Answer: Protein digestion begins with pepsin.
Explanation: Protein digestion begins in the stomach with the enzyme pepsin, which is activated by the acidic environment. While some minimal fat digestion by gastric lipase occurs, most fat digestion happens in the small intestine. Carbohydrate digestion by salivary amylase is inhibited by the acidic pH. Nutrient absorption is minimal in the stomach; the small intestine is the primary site for this.
Q35. Intestinal secretions contain
Answer: All of the above.
Explanation: Intestinal secretions, from glands like Brunner's glands and the intestinal crypts, contain bicarbonate ions to neutralize stomach acid, mucus for lubrication and protection, and enzymes (e.g., disaccharidases, peptidases, enterokinase) that complete the digestion of carbohydrates and proteins. While some fat digestion occurs, many fat-digesting enzymes come from the pancreas.
Q36. A 55-year-old man with chronic alcohol consumption presents with nonspecific complaints of dyspepsia. Examination reveals destruction of gastric glands. This predisposes him to
Answer: Vitamin B12 deficiency.
Explanation: Chronic alcohol consumption can damage gastric glands, leading to atrophic gastritis. This can impair the secretion of intrinsic factor by parietal cells, leading to vitamin B12 deficiency (pernicious anemia). Gastric acid secretion would likely be decreased, and protein digestion would be less efficient due to reduced pepsinogen secretion.