Gastrointestinal System Practice Questions

Q: Which protein is absent in saliva?

Intrinsic factor. **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 $Cl^-$.

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

It occurs in the post-absorptive stage.. 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).

Q: Glucose absorption from the gut occurs by?

Secondary active transport. **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).

Q: Which of the following hormones increases appetite?

Ghrelin. **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.

Q: Pepsin is activated by which of the following?

Hydrochloric acid (HCI). **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.

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

Hemolytic jaundice. ### 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.

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

Antrum. **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.

Q: Colipase is:

Encoded by the gene CLPS. **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.

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

Jejunum. **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).

Question 1

Which protein is absent in saliva?

Accepted Answer

Intrinsic factor

Answer

Lactoferrin

Answer

Amylase

Answer

Mucin

Question 2

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

Accepted Answer

It occurs in the post-absorptive stage.

Answer

It occurs once every 90 minutes.

Answer

Phase 1 shows irregular contractions.

Answer

Motilin decreases MMC contraction.

Question 3

Glucose absorption from the gut occurs by?

Accepted Answer

Secondary active transport

Answer

Simple diffusion

Answer

Facilitated diffusion

Answer

Primary active transport

Question 4

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

Accepted Answer

To facilitate reabsorption of bile acids in the ileum

Answer

To promote bile flow

Answer

To solubilize cholesterol and phospholipids in bile

Answer

To enhance dietary lipid digestion and absorption

Question 5

Which of the following hormones increases appetite?

Accepted Answer

Ghrelin

Answer

Leptin

Answer

Glucagon-like peptide 1 (GLP-1)

Answer

Peptide YY (PYY)

Question 6

Pepsin is activated by which of the following?

Accepted Answer

Hydrochloric acid (HCI)

Answer

Enterokinase

Answer

Uropepsinogen

Answer

Trypsinogen

Question 7

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

Accepted Answer

Hemolytic jaundice

Answer

Obstructive jaundice

Answer

Primary biliary cirrhosis

Answer

Extrahepatic biliary atresia

Question 8

Which one of the following is the primary site of production of gastrin?

Accepted Answer

Antrum

Answer

Pylorus

Answer

Pancreas

Answer

Small intestine

Question 9

Colipase is:

Accepted Answer

Encoded by the gene CLPS

Answer

Secreted by oxyntic cells

Answer

Secreted in the active form

Answer

Helps gastric lipase

Question 10

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

Accepted Answer

Jejunum

Answer

Stomach

Answer

Duodenum

Answer

Colon

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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