Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 311: Which protein is absent in saliva?

A. Lactoferrin
B. Amylase
C. Mucin
D. Intrinsic factor (Correct Answer)

Explanation: **Explanation:** The correct answer is **Intrinsic Factor (IF)**. Intrinsic factor is a glycoprotein essential for the absorption of Vitamin B12 (cobalamin) in the terminal ileum. It is synthesized and secreted by the **parietal cells** (oxyntic cells) of the gastric mucosa in the stomach, not by the salivary glands. **Analysis of Options:** * **Lactoferrin:** This is an iron-binding protein present in saliva. It exerts bacteriostatic effects by depriving bacteria of the iron required for their growth. * **Amylase (Ptyalin):** This is the primary digestive enzyme in saliva. It is secreted mainly by the parotid glands and initiates the breakdown of dietary starch into maltose and dextrins. * **Mucin:** Secreted by submandibular, sublingual, and minor salivary glands, mucins are glycoproteins that provide lubrication, protect the oral mucosa, and aid in bolus formation. **NEET-PG High-Yield Pearls:** 1. **R-Protein (Haptocorrin):** While saliva lacks Intrinsic Factor, it *does* contain R-protein. R-protein binds to Vitamin B12 in the stomach to protect it from acid degradation until it reaches the duodenum, where pancreatic proteases release B12 so it can bind to Intrinsic Factor. 2. **Parietal Cell Functions:** Parietal cells have two main secretions: Hydrochloric acid (HCl) and Intrinsic Factor. 3. **Clinical Correlation:** Destruction of parietal cells (as seen in Pernicious Anemia or Gastrectomy) leads to a deficiency of Intrinsic Factor, resulting in Vitamin B12 malabsorption and Megaloblastic Anemia. 4. **Saliva Composition:** Saliva is **hypotonic** compared to plasma and contains high concentrations of $K^+$ and $HCO_3^-$, but low concentrations of $Na^+$ and $Cl^-$.

Question 312: Which of the following is true about the Migrating Motor Complex (MMC)?

A. It occurs once every 90 minutes.
B. It occurs in the post-absorptive stage. (Correct Answer)
C. Phase 1 shows irregular contractions.
D. Motilin decreases MMC contraction.

Explanation: The **Migrating Motor Complex (MMC)** is a distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle during periods of fasting. ### **Explanation of the Correct Answer** **Option B** is correct because the MMC occurs exclusively during the **post-absorptive (fasting) state**. It begins roughly 2–3 hours after a meal once the stomach is empty. Its primary physiological role is the "interdigestive housekeeper" function—clearing the distal stomach and small intestine of residual undigested food, secretions, and bacteria to prevent bacterial overgrowth. ### **Analysis of Incorrect Options** * **Option A:** While the cycle repeats, it typically occurs every **90 to 120 minutes**, not strictly every 90 minutes. In a competitive exam context, the physiological state (fasting) is a more definitive characteristic than the exact timing. * **Option C:** Phase 1 is a period of **quiescence** (no contractions). It is **Phase 2** that shows irregular electrical activity and contractions. Phase 3 consists of regular, high-amplitude "explosive" contractions. * **Option D:** **Motilin**, a hormone secreted by M cells in the duodenum, is the primary **stimulator** of the MMC (specifically Phase 3). It increases contractions; it does not decrease them. ### **High-Yield Clinical Pearls for NEET-PG** * **Site of Origin:** 75% of MMCs originate in the stomach; 25% originate in the duodenum. * **Termination:** Feeding immediately terminates the MMC, replacing it with the "fed pattern" (segmentation and peristalsis). * **Regulation:** Regulated by Motilin and the Enteric Nervous System (ENS). Vagal innervation is not required for its propagation but can modulate it. * **Clinical Correlation:** Erythromycin acts as a motilin agonist and is used clinically to stimulate gastric emptying (prokinetic effect).

Question 313: Glucose absorption from the gut occurs by?

A. Simple diffusion
B. Facilitated diffusion
C. Primary active transport
D. Secondary active transport (Correct Answer)

Explanation: **Explanation:** Glucose absorption in the small intestine occurs primarily through **Secondary Active Transport** via the **SGLT-1 (Sodium-Glucose Co-transporter 1)** protein located on the apical (luminal) membrane of enterocytes. 1. **Mechanism (Why D is correct):** This process is "secondary" because it does not use ATP directly. Instead, it relies on the electrochemical gradient created by the **Na⁺-K⁺ ATPase pump** on the basolateral membrane, which pumps Na⁺ out of the cell. This creates a low intracellular Na⁺ concentration, driving the entry of Na⁺ from the gut lumen into the cell. Glucose "hitchhikes" with Na⁺ through SGLT-1 against its own concentration gradient. 2. **Why other options are incorrect:** * **Simple Diffusion (A):** Glucose is a large, polar molecule and cannot pass through the lipid bilayer unaided. * **Facilitated Diffusion (B):** While glucose *leaves* the enterocyte into the blood via facilitated diffusion (using **GLUT-2**), its initial absorption from the gut lumen is an active process. (Note: Fructose is absorbed solely by facilitated diffusion via GLUT-5). * **Primary Active Transport (C):** This involves direct ATP hydrolysis by the transport protein itself (e.g., the Na⁺-K⁺ pump), which is not the case for SGLT-1. **High-Yield Clinical Pearls for NEET-PG:** * **SGLT-1 vs. SGLT-2:** SGLT-1 is in the small intestine and renal tubules (S3 segment), while SGLT-2 is primarily in the kidney (S1 segment). * **Oral Rehydration Therapy (ORT):** The co-transport of Na⁺ and glucose is the physiological basis of ORS; glucose enhances the absorption of Na⁺ and, subsequently, water. * **GLUT-5:** Specifically transports **Fructose** via facilitated diffusion. * **GLUT-2:** A bidirectional transporter present on the basolateral membrane for all hexoses (Glucose, Galactose, Fructose).

Question 314: Which of the following is NOT a primary function of bile acids?

A. To promote bile flow
B. To solubilize cholesterol and phospholipids in bile
C. To enhance dietary lipid digestion and absorption
D. To facilitate reabsorption of bile acids in the ileum (Correct Answer)

Explanation: **Explanation:** The primary functions of bile acids are centered on their role as **amphipathic detergents** that assist in the digestion and excretion of lipids. The question asks for what is **NOT** a primary function. **Why Option D is the correct answer:** The reabsorption of bile acids in the terminal ileum is a **mechanism of conservation** (the Enterohepatic Circulation), not a functional goal of the bile acids themselves. The ileal reabsorption is facilitated by the **Apical Sodium-dependent Bile acid Transporter (ASBT)**. Bile acids do not "facilitate" their own reabsorption; rather, they are the substrates being actively transported to prevent loss in the feces. **Analysis of Incorrect Options:** * **Option A (Promote bile flow):** Bile acids are the primary osmotic driving force for bile secretion. As they are secreted into the canaliculi, they pull water and electrolytes with them (Bile acid-dependent flow). * **Option B (Solubilize cholesterol):** Bile acids, along with lecithin, form mixed micelles that keep water-insoluble cholesterol in a soluble state within the gallbladder. A deficiency in bile acids leads to cholesterol precipitation and gallstone formation. * **Option C (Lipid digestion/absorption):** Bile acids emulsify dietary fats, increasing the surface area for pancreatic lipase, and form micelles to transport the products of lipid digestion (monoglycerides and fatty acids) to the intestinal brush border. **High-Yield NEET-PG Pearls:** * **Rate-limiting enzyme:** 7-alpha-hydroxylase (inhibited by bile acids via feedback). * **Primary Bile Acids:** Cholic acid and Chenodeoxycholic acid (synthesized in the liver). * **Secondary Bile Acids:** Deoxycholic acid and Lithocholic acid (formed by bacterial action in the colon). * **Clinical Correlation:** Terminal ileal resection (e.g., in Crohn’s disease) leads to bile acid malabsorption, resulting in **steatorrhea** and **choleretic diarrhea**.

Question 315: Which of the following hormones increases appetite?

A. Leptin
B. Glucagon-like peptide 1 (GLP-1)
C. Peptide YY (PYY)
D. Ghrelin (Correct Answer)

Explanation: **Explanation:** The regulation of appetite is controlled by the arcuate nucleus of the hypothalamus, which balances **orexigenic** (appetite-stimulating) and **anorexigenic** (appetite-suppressing) signals. **Correct Option: D. Ghrelin** Ghrelin is the only major peripheral hormone that is **orexigenic**. It is secreted primarily by the P/D1 cells in the fundus of the stomach and epsilon cells of the pancreas. Ghrelin levels rise during fasting (pre-prandially) and stimulate the **NPY/AgRP neurons** in the hypothalamus to increase hunger and food intake. **Incorrect Options:** * **A. Leptin:** Produced by adipocytes, leptin is a long-term satiety signal. It inhibits NPY/AgRP neurons and stimulates POMC/CART neurons to **decrease** appetite. * **B. GLP-1:** Secreted by L-cells of the ileum and colon in response to food, it stimulates insulin secretion and acts as a potent **satiety** signal. * **C. Peptide YY (PYY):** Also secreted by L-cells of the distal small intestine and colon, it reduces appetite by inhibiting NPY release. **High-Yield Facts for NEET-PG:** * **"Hunger Hormone":** Ghrelin (G for "Growl" of the stomach). * **Sleep Deprivation:** Increases Ghrelin and decreases Leptin, leading to weight gain. * **Prader-Willi Syndrome:** Characterized by hyperphagia and obesity due to pathologically high Ghrelin levels. * **Vagus Nerve:** Ghrelin also acts via the vagal afferents to signal the brain. * **Bariatric Surgery:** Gastric bypass often leads to weight loss not just by restriction, but by significantly lowering Ghrelin production.

Question 316: Pepsin is activated by which of the following?

A. Hydrochloric acid (HCI) (Correct Answer)
B. Enterokinase
C. Uropepsinogen
D. Trypsinogen

Explanation: **Explanation:** The conversion of pepsinogen to its active form, **pepsin**, is a critical step in protein digestion within the stomach. **1. Why Hydrochloric acid (HCl) is correct:** Pepsin is secreted by the **Chief cells** (Peptic cells) of the gastric mucosa as an inactive zymogen called **pepsinogen**. This inactive form prevents the autodigestion of the gastric wall. When pepsinogen is released into the gastric lumen, it encounters **Hydrochloric acid (HCl)** secreted by the **Parietal cells**. The low pH (1.8 to 3.5) induced by HCl triggers a conformational change in pepsinogen, causing it to cleave itself to form active pepsin. Once a small amount of pepsin is formed, it further activates more pepsinogen molecules—a process known as **autocatalysis**. **2. Why the other options are incorrect:** * **Enterokinase (Enteropeptidase):** This enzyme is secreted by the duodenal mucosa. Its specific role is to activate **trypsinogen into trypsin** in the small intestine. * **Uropepsinogen:** This is simply pepsinogen that has entered the bloodstream and is excreted in the urine. It is a diagnostic marker, not an activator. * **Trypsinogen:** This is an inactive pancreatic zymogen. It does not activate pepsin; rather, its active form (trypsin) activates other pancreatic enzymes like chymotrypsinogen and procarboxypeptidase. **NEET-PG High-Yield Pearls:** * **Optimal pH for Pepsin:** It is most active at a pH of **1.8 to 3.5**. It becomes irreversibly inactivated if the pH rises above 5.0. * **Vagal Stimulation:** The Cephalic phase of gastric secretion (via the Vagus nerve) stimulates both Gastrin and HCl, which indirectly increases pepsin activation. * **Achlorhydria:** In conditions like Pernicious Anemia (where parietal cells are destroyed), the lack of HCl leads to a failure in pepsin activation, severely impairing protein digestion.

Question 317: In which cause of jaundice is there no bilirubin excretion in the urine?

A. Obstructive jaundice
B. Primary biliary cirrhosis
C. Extrahepatic biliary atresia
D. Hemolytic jaundice (Correct Answer)

Explanation: ### Explanation The presence or absence of bilirubin in urine depends on whether the circulating bilirubin is **conjugated** or **unconjugated**. **1. Why Hemolytic Jaundice is the Correct Answer:** In hemolytic jaundice, there is excessive breakdown of RBCs, leading to an overproduction of **unconjugated bilirubin (UCB)**. UCB is hydrophobic and travels in the blood bound to albumin. Because it is bound to a large protein, it cannot be filtered by the renal glomerulus. Therefore, despite high serum levels, no bilirubin appears in the urine. This is why hemolytic jaundice is clinically referred to as **"acholuric jaundice"** (jaundice without bile in urine). **2. Why the Other Options are Incorrect:** * **Obstructive Jaundice (A), Primary Biliary Cirrhosis (B), and Extrahepatic Biliary Atresia (C):** All three conditions involve an obstruction to bile flow (cholestasis). In these cases, the liver successfully conjugates the bilirubin, but it cannot be excreted into the intestine. This **conjugated bilirubin (CB)** leaks back into the systemic circulation. Unlike UCB, conjugated bilirubin is water-soluble and not bound to albumin, allowing it to be easily filtered by the kidneys and excreted in urine (dark-colored urine). **3. NEET-PG High-Yield Pearls:** * **Urine Bilirubin:** Only conjugated bilirubin appears in urine. * **Urine Urobilinogen:** Increased in hemolytic jaundice; absent in complete obstructive jaundice (since no bilirubin reaches the gut for conversion). * **Van den Bergh Reaction:** * Indirect Positive = Unconjugated Hyperbilirubinemia (Hemolysis). * Direct Positive = Conjugated Hyperbilirubinemia (Obstruction). * Biphasic = Mixed (Hepatitis). * **Stool Color:** "Clay-colored" stools are characteristic of obstructive jaundice due to the absence of stercobilin.

Question 318: Which one of the following is the primary site of production of gastrin?

A. Pylorus
B. Antrum (Correct Answer)
C. Pancreas
D. Small intestine

Explanation: **Explanation:** **1. Why Antrum is Correct:** Gastrin is a peptide hormone primarily secreted by **G-cells**. These cells are predominantly located in the **gastric antrum** (the distal part of the stomach). While G-cells are found in other areas, the antral mucosa is the most significant site of production. Gastrin’s primary physiological role is to stimulate gastric acid secretion by parietal cells and promote the growth of the gastric mucosa. **2. Why Other Options are Incorrect:** * **Pylorus:** While the pylorus is anatomically adjacent to the antrum, the term "Antrum" is the more specific physiological site for G-cell concentration. In many contexts, the "pyloric antrum" is considered the source, but "Antrum" is the standard textbook answer. * **Pancreas:** In a healthy adult, the pancreas does not produce significant amounts of gastrin. However, it can become a site of gastrin production in pathological states, such as a **Gastrinoma** (Zollinger-Ellison Syndrome). * **Small Intestine:** G-cells are present in the duodenum (producing "enteric gastrin"), but this accounts for only a small fraction of total gastrin production compared to the antrum. **3. High-Yield Facts for NEET-PG:** * **Stimuli for Gastrin:** Gastric distension, peptides/amino acids (phenylalanine and tryptophan), and **Vagal stimulation** (via Gastrin-Releasing Peptide/GRP). * **Inhibition:** Gastrin secretion is inhibited by a luminal pH < 1.5 and by **Somatostatin**. * **Trophic Effect:** Gastrin has a significant trophic (growth) effect on the gastric mucosa; hypergastrinemia leads to mucosal hyperplasia. * **Zollinger-Ellison Syndrome:** Characterized by a gastrin-secreting tumor (usually in the gastrinoma triangle) leading to refractory peptic ulcers.

Question 319: Colipase is:

A. Secreted by oxyntic cells
B. Secreted in the active form
C. Helps gastric lipase
D. Encoded by the gene CLPS (Correct Answer)

Explanation: **Explanation:** **Colipase** is a small protein co-enzyme required for the optimal activity of pancreatic lipase. It is essential for fat digestion in the small intestine. 1. **Why Option D is correct:** Colipase is indeed a protein product of the **CLPS gene** located on chromosome 6. It functions by binding to the C-terminal domain of pancreatic lipase, anchoring it to the surface of lipid droplets. 2. **Why Option A is incorrect:** Colipase is synthesized and secreted by the **pancreatic acinar cells**, not the oxyntic (parietal) cells of the stomach (which secrete HCl and Intrinsic Factor). 3. **Why Option B is incorrect:** It is secreted as an inactive precursor called **procolipase**. It must be activated (cleaved) in the intestinal lumen by **trypsin** to become functional colipase. 4. **Why Option C is incorrect:** Colipase specifically assists **pancreatic lipase**, not gastric lipase. Its primary role is to prevent the inhibitory effect of bile salts. Bile salts normally displace lipase from the fat droplet; colipase "clears" a path through the bile salts, allowing pancreatic lipase to bind to its substrate. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Colipase shifts the pH optimum of pancreatic lipase from 8.0–9.0 back to 6.0–7.0, which is the actual pH of the duodenum. * **Ratio:** Pancreatic lipase and procolipase are secreted by the pancreas in a **1:1 ratio**. * **Clinical Significance:** In cases of severe pancreatic insufficiency, fat malabsorption (steatorrhea) occurs because lipase cannot function without its co-factor in the presence of bile salts.

Question 320: Maximum water and nutrient absorption occurs in which part of the intestine?

A. Stomach
B. Duodenum
C. Jejunum (Correct Answer)
D. Colon

Explanation: **Explanation:** The **Jejunum** is the primary site for the absorption of the majority of water, electrolytes, and nutrients (including carbohydrates, proteins, and water-soluble vitamins). This is due to its specialized anatomy, featuring prominent **plicae circulares** (valves of Kerckring) and long villi, which significantly increase the surface area available for transport. * **Why Jejunum is Correct:** While the duodenum begins the process, the jejunum has a higher density of transport proteins and a more "leaky" epithelium compared to the distal segments, allowing for massive osmotic water movement following the active transport of solutes like glucose and amino acids. Approximately 7–9 liters of fluid enter the small intestine daily; the jejunum absorbs the largest fraction (approx. 4–5 liters). * **Why other options are incorrect:** * **Stomach:** Absorption is minimal, limited to highly lipid-soluble substances like alcohol and certain drugs (e.g., Aspirin). * **Duodenum:** Although it is the shortest segment and the site where iron and calcium are primarily absorbed, its total surface area is much smaller than the jejunum. * **Colon:** Its primary role is the absorption of remaining water and electrolytes (about 1–1.5 liters) and the storage of feces. It has no villi. **Clinical Pearls for NEET-PG:** * **Iron** is absorbed primarily in the **Duodenum**. * **Vitamin B12 and Bile Salts** are absorbed in the **Terminal Ileum**. * **Water absorption** follows the "standing gradient" osmotic model. * In cases of **Short Bowel Syndrome**, the loss of the jejunum is better tolerated than the loss of the ileum because the ileum can adapt to absorb nutrients, but the jejunum cannot perform the specialized functions of the ileum (B12/Bile acid recycling).

Practice by Chapter

Gastrointestinal Motility

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Gastrointestinal Secretions

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Digestion and Absorption

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Gastrointestinal Hormones

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Pancreatic Exocrine Function

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Gastrointestinal Circulation

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Intestinal Immune System

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Gut Microbiome

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Regulation of Food Intake

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