Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 181: What triggers the cephalic phase of gastric secretion?

A. Local hormones
B. Gastric distension
C. Nervous mechanism (Correct Answer)
D. Presence of food in stomach

Explanation: The gastric secretion process occurs in three distinct phases: **Cephalic, Gastric, and Intestinal.** ### 1. Why "Nervous mechanism" is correct: The **Cephalic phase** occurs *before* food enters the stomach. It is triggered by the sight, smell, thought, or taste of food. These sensory stimuli activate the cerebral cortex and the feeding center in the hypothalamus, which send impulses to the **Vagus nerve (Cranial Nerve X)**. The vagus nerve releases acetylcholine, stimulating parietal cells to secrete HCl and G-cells to secrete gastrin. Because this phase is mediated entirely via the central nervous system and the vagus nerve, it is strictly a **nervous mechanism**. ### 2. Why the other options are incorrect: * **B & D (Gastric distension / Presence of food):** These triggers define the **Gastric phase**. When food enters the stomach, it causes physical stretching (distension) and chemical stimulation (peptides), which trigger local enteric reflexes and the release of gastrin. * **A (Local hormones):** While hormones like Gastrin and Histamine play a role in amplifying secretion, the *trigger* for the cephalic phase is neural. Hormonal triggers are more characteristic of the Gastric and Intestinal phases. ### 3. NEET-PG High-Yield Pearls: * **Duration:** The cephalic phase accounts for approximately **20-30%** of total gastric secretion. * **Sham Feeding:** A classic experimental method used to study the cephalic phase (food is chewed but diverted before reaching the stomach). * **Vagotomy:** Surgical sectioning of the vagus nerve completely abolishes the cephalic phase, a fact historically used in treating peptic ulcer disease. * **Emotional State:** States like anger or hostility increase cephalic secretion, while fear or depression can inhibit it.

Question 182: What is the normal portal venous pressure?

A. 1-2 mmHg
B. 5-7 mmHg (Correct Answer)
C. 10-12 mmHg
D. 15-17 mmHg

Explanation: **Explanation:** The portal vein is a low-pressure system formed by the union of the superior mesenteric and splenic veins. Under normal physiological conditions, the **portal venous pressure ranges between 5 to 10 mmHg**, with **5–7 mmHg** being the most commonly cited baseline in clinical physiology. This pressure is slightly higher than the systemic venous pressure (Central Venous Pressure: 0–5 mmHg) to allow blood to flow through the hepatic sinusoids into the inferior vena cava. **Analysis of Options:** * **Option A (1-2 mmHg):** This is too low. Such low pressures are typically seen in the inferior vena cava or right atrium, but would not be sufficient to overcome the resistance of the hepatic sinusoidal bed. * **Option C (10-12 mmHg):** This represents the threshold for **Portal Hypertension**. Clinically, portal hypertension is defined as a portal venous pressure gradient (PVPG) > 5 mmHg or a total portal pressure > 10–12 mmHg. * **Option D (15-17 mmHg):** This indicates significant portal hypertension. At pressures above 12 mmHg, complications such as esophageal varices and ascites become highly likely. **High-Yield Clinical Pearls for NEET-PG:** 1. **Portal Hypertension Definition:** Sustained elevation of portal pressure above 10–12 mmHg. 2. **HVPG (Hepatic Venous Pressure Gradient):** The gold standard for measuring portal pressure. It is the difference between the wedged hepatic venous pressure (WHVP) and free hepatic venous pressure (FHVP). Normal HVPG is **1–5 mmHg**. 3. **Variceal Bleeding Risk:** The risk of variceal rupture increases significantly when the HVPG exceeds **12 mmHg**. 4. **Blood Supply:** The portal vein provides approximately 75% of the blood flow to the liver but only 50% of its oxygen supply.

Question 183: What is the effect of the gallbladder on the pH of bile?

A. Makes bile pH neutral.
B. Bile pH decreases from 8 - 8.6 to 7 - 7.6. (Correct Answer)
C. Bile pH increases from 7 - 7.6 to 8 - 8.6.
D. No effect on bile pH.

Explanation: **Explanation:** The gallbladder does not merely store bile; it actively modifies its composition. Hepatic bile (secreted by the liver) is alkaline, with a pH ranging from **8.2 to 8.6**. This alkalinity is primarily due to the high concentration of bicarbonate ions. As bile is stored in the gallbladder, the mucosal lining actively reabsorbs water, sodium, and chloride. Crucially, the gallbladder mucosa also reabsorbs **bicarbonate ions** and secretes **hydrogen ions (H+)**. This acidification process serves two purposes: it prevents the precipitation of calcium salts (reducing the risk of gallstones) and neutralizes the alkaline hepatic bile. Consequently, the pH of gallbladder bile drops to a more acidic/neutral range of **7.0 to 7.6**. **Analysis of Options:** * **Option A:** While the pH moves toward 7.0, it is a specific decrease from an alkaline state rather than just "becoming neutral." * **Option C:** This is the opposite of the physiological process. Bile becomes more acidic, not more alkaline, during storage. * **Option D:** Incorrect, as the gallbladder significantly concentrates bile (up to 10-20 times) and alters its ionic composition. **High-Yield Facts for NEET-PG:** * **Concentration Power:** The gallbladder can concentrate bile salts, bilirubin, and cholesterol by 5 to 20 times by absorbing water and electrolytes. * **Major Components:** Bile contains bile salts, phospholipids (lecithin), cholesterol, and bile pigments (bilirubin). * **Cholecystokinin (CCK):** The primary hormone responsible for gallbladder contraction and the relaxation of the Sphincter of Oddi. * **Bile Acid Sequestrants:** Drugs like Cholestyramine bind bile acids in the gut, preventing enterohepatic circulation and lowering LDL levels.

Question 184: All of the following are true about secretin except:

A. Inhibits gastric emptying
B. Increases bicarbonate-rich pancreatic secretion
C. Potentiates the action of cholecystokinin (CCK)
D. Increases bile salt and bile acid secretion (Correct Answer)

Explanation: **Explanation:** Secretin is a hormone released by the **S-cells of the duodenum** in response to acidic chyme (pH < 4.5). Its primary role is to neutralize gastric acid in the duodenum to provide an optimal environment for pancreatic enzymes. **Why Option D is the Correct Answer (The False Statement):** Secretin does **not** increase the secretion of bile salts or bile acids. Bile salts are synthesized by hepatocytes and their secretion is primarily regulated by enterohepatic circulation. However, Secretin **does increase the secretion of bicarbonate-rich watery fluid** from the ductal cells of the liver (choleresis), which increases the total volume of bile but not the concentration of bile salts/acids. **Analysis of Other Options:** * **Option A (Inhibits gastric emptying):** Secretin acts as an "enterogastrone." It inhibits gastric acid secretion and slows down gastric emptying to ensure the duodenum has enough time to neutralize the incoming acid. * **Option B (Increases bicarbonate-rich pancreatic secretion):** This is the hallmark function of Secretin. It acts on the pancreatic ductal cells via cAMP to stimulate a watery, alkaline secretion high in $HCO_3^-$. * **Option C (Potentiates the action of CCK):** Secretin and CCK work synergistically. While CCK primarily stimulates enzyme-rich secretion from acinar cells, Secretin enhances this effect, and CCK conversely enhances Secretin’s bicarbonate-stimulating effect. **High-Yield NEET-PG Pearls:** * **Nature's Antacid:** Secretin is often called the "Antacid of the small intestine." * **First Hormone:** Secretin was the first hormone ever discovered (by Bayliss and Starling). * **Secretin Stimulation Test:** Used in the diagnosis of **Zollinger-Ellison Syndrome** (Gastrinoma). Paradoxically, secretin causes a marked increase in serum gastrin levels in these patients. * **Major Stimulus:** The most potent stimulus for Secretin release is **duodenal acidification**.

Question 185: What is the order of water absorption from the gastrointestinal tract?

A. Duodenum > Jejunum > Ileum
B. Jejunum > Ileum > Colon (Correct Answer)
C. Jejunum > Colon > Rectum
D. Jejunum > Ileum > Rectum

Explanation: **Explanation:** The absorption of water in the gastrointestinal tract follows the osmotic gradient created by the absorption of nutrients and electrolytes. Approximately 9 liters of fluid enter the GI tract daily (2L from intake, 7L from secretions). **1. Why Jejunum > Ileum > Colon is correct:** * **Jejunum:** This is the primary site for water absorption (approx. 4–5 L/day). The tight junctions here are "leaky," allowing for high permeability. Water absorption is rapid as it follows the active transport of sugars and amino acids. * **Ileum:** Absorption continues here (approx. 3 L/day) but at a slower rate than the jejunum. The tight junctions are tighter, and water follows the absorption of NaCl. * **Colon:** Although the colon is highly efficient at absorbing water against large osmotic gradients, it handles a much smaller volume (approx. 1–1.5 L/day). **2. Analysis of Incorrect Options:** * **Option A:** The duodenum is primarily a site for osmotic equilibration. If chyme is hypertonic, water may actually enter the lumen; thus, it is not the site of maximal absorption. * **Options C & D:** While the rectum can absorb water (and certain drugs), its capacity is negligible compared to the proximal segments of the large intestine and the small intestine. **NEET-PG High-Yield Pearls:** * **Maximum Water Absorption:** Occurs in the **Jejunum**. * **Maximum Water Reabsorption Efficiency:** The **Colon** has the highest "tightness" of junctions, allowing it to concentrate feces effectively. * **Mechanism:** Water absorption is always **passive** (via Aquaporins) and follows solute movement (Solvent Drag). * **Daily Output:** Only about 100–200 ml of water is lost in feces daily; the rest is reabsorbed.

Question 186: Alcohol is maximally absorbed in which part of the gastrointestinal tract?

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

Explanation: **Explanation:** The correct answer is **Duodenum**. **Why Duodenum is Correct:** While alcohol is unique because its absorption begins in the stomach, the **small intestine** (specifically the duodenum and jejunum) is the site of maximal absorption. This is due to the massive surface area provided by the villi and microvilli and the high vascularity of the intestinal mucosa. Alcohol moves across biological membranes via simple diffusion; therefore, the larger the surface area, the faster the absorption. Even though the duodenum is shorter than the jejunum, it possesses the highest concentration of absorptive mechanisms per unit area for alcohol. **Why Other Options are Incorrect:** * **Stomach:** Approximately 20% of alcohol is absorbed here. While it is a significant site (and the reason alcohol effects can be felt quickly), the rate is much slower than in the small intestine. Gastric emptying is the rate-limiting step for alcohol absorption. * **Jejunum:** While a significant amount of alcohol is absorbed in the jejunum, the rate is slightly lower than in the duodenum due to the initial rapid transit and immediate absorption occurring as soon as the chyme exits the pylorus. * **Colon:** Very little alcohol reaches the colon under normal circumstances, as nearly 100% is absorbed in the proximal small intestine. **NEET-PG High-Yield Pearls:** 1. **Rate-Limiting Step:** Gastric emptying is the most important factor determining the peak blood alcohol concentration (BAC). 2. **Effect of Food:** Fatty foods delay gastric emptying, thereby slowing alcohol absorption and reducing the peak BAC. 3. **First-Pass Metabolism:** Alcohol is metabolized by **Gastric Alcohol Dehydrogenase (ADH)**. Women have lower levels of gastric ADH, leading to higher BACs compared to men for the same amount of ingestion. 4. **Order of Kinetics:** Alcohol metabolism follows **Zero-order kinetics** (a constant amount is eliminated per unit time).

Question 187: In Oral Rehydration Solution (ORS), what is the effect of glucose on sodium absorption?

A. Increase in sodium absorption (Correct Answer)
B. Decrease in sodium absorption
C. Variable effect on sodium absorption
D. No effect on sodium absorption

Explanation: The correct answer is **A. Increase in sodium absorption**. ### **Explanation of the Underlying Concept** The effectiveness of Oral Rehydration Solution (ORS) is based on the **SGLT-1 (Sodium-Glucose Co-transporter 1)** mechanism located in the brush border of the small intestinal enterocytes. In this process, glucose and sodium are transported together across the apical membrane in a **1:1 stoichiometry**. The presence of glucose significantly enhances the absorption of sodium because the transporter requires both molecules to be present to function optimally. Once sodium is absorbed into the intercellular space, it creates an osmotic gradient that pulls water along with it (solvent drag), effectively rehydrating the patient even during secretory diarrheas like Cholera, where the cAMP-mediated chloride secretion remains active but the SGLT-1 pathway remains intact. ### **Why Other Options are Incorrect** * **B & C:** Glucose does not decrease or cause variable absorption; rather, it acts as a mandatory symport partner. Without glucose, sodium absorption via this specific pathway would be negligible. * **D:** Glucose has a profound synergistic effect on sodium; stating it has "no effect" ignores the physiological basis of oral rehydration therapy. ### **NEET-PG High-Yield Clinical Pearls** * **The "Coupled Transport" Principle:** This is the physiological "Gold Standard" for treating dehydration. * **WHO ORS Composition (Reduced Osmolarity):** The current recommended ORS has a total osmolarity of **245 mOsm/L**. * Sodium: 75 mmol/L * Glucose: 75 mmol/L (Note the 1:1 molar ratio for optimal SGLT-1 function) * Potassium: 20 mmol/L * Chloride: 65 mmol/L * Citrate: 10 mmol/L * **Trisodium Citrate:** Added to ORS to correct metabolic acidosis and enhance sodium/water absorption.

Question 188: What is the primary enzyme responsible for protein degradation in the stomach?

A. Trypsin
B. Pepsin (Correct Answer)
C. Chymotrypsin
D. Endopeptidase

Explanation: **Explanation:** **1. Why Pepsin is Correct:** Pepsin is the primary proteolytic enzyme of the stomach. It is secreted by the **Chief cells** (Peptic cells) of the gastric glands as an inactive zymogen called **pepsinogen**. The highly acidic environment of the stomach (pH 1.5–2.5), maintained by HCl from parietal cells, triggers the autocatalytic conversion of pepsinogen into active pepsin. Pepsin is an **endopeptidase** that specifically cleaves internal peptide bonds, particularly those involving aromatic amino acids (phenylalanine, tyrosine, and tryptophan), breaking large proteins into smaller peptides and peptones. **2. Why Other Options are Incorrect:** * **Trypsin (A) & Chymotrypsin (C):** These are potent proteolytic enzymes, but they are produced by the **pancreas** and act in the **duodenum** (small intestine). They require an alkaline pH to function and would be denatured by gastric acid. * **Endopeptidase (D):** While pepsin *is* a type of endopeptidase, "Endopeptidase" is a broad functional category of enzymes (including trypsin and elastase) rather than a specific enzyme name. In the context of the stomach, Pepsin is the specific primary enzyme. **3. High-Yield Clinical Pearls for NEET-PG:** * **Optimal pH:** Pepsin is most active at a pH of **2.0** and becomes irreversibly inactivated when the pH rises above 5.0 (e.g., in the duodenum). * **Vagal Stimulation:** The Cephalic phase of gastric secretion (via the Vagus nerve) is a potent stimulator of pepsinogen release. * **Rennin (Chymosin):** In infants, the stomach also secretes Rennin, which curdles milk (casein) to prolong its retention for digestion; this should not be confused with Renin (from the kidney). * **Achlorhydria:** Patients with a lack of gastric acid (e.g., Atrophic Gastritis) will have impaired protein digestion because pepsinogen cannot be activated.

Question 189: What is the function of hepatic Kupffer cells?

A. Formation of sinusoids
B. Vitamin-A storage
C. Increases blood perfusion
D. Phagocytosis (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Phagocytosis** **Mechanism:** Hepatic Kupffer cells are specialized **fixed macrophages** located within the lumen of the liver sinusoids. They belong to the Mononuclear Phagocyte System (Reticuloendothelial system). Their primary function is to filter the blood arriving from the portal circulation. They perform **phagocytosis** to remove particulate matter, aged red blood cells, and, most importantly, gut-derived bacteria and endotoxins that cross the intestinal barrier. This prevents systemic bacteremia and protects the liver from injury. **Analysis of Incorrect Options:** * **A. Formation of sinusoids:** Sinusoids are lined by **fenestrated endothelial cells**, not Kupffer cells. Kupffer cells are simply attached to the inner surface of these endothelial walls. * **B. Vitamin-A storage:** This is the specific function of **Stellate cells (Ito cells)** located in the Space of Disse. In pathology, these cells are also responsible for liver fibrosis when they transform into myofibroblasts. * **C. Increases blood perfusion:** Blood perfusion is regulated by the hepatic artery, portal vein, and pre-capillary sphincters. Kupffer cells do not have a primary hemodynamic role. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Kupffer cells are found on the luminal side of sinusoidal endothelium. * **Origin:** Like all macrophages, they originate from circulating **monocytes**. * **Immune Role:** They are the largest population of tissue-resident macrophages in the body. * **Pathology:** In conditions like alcoholic liver disease, Kupffer cells release inflammatory cytokines (TNF-α, IL-6) that contribute to hepatocyte damage. * **Marker:** CD163 is a common immunohistochemical marker for Kupffer cells.

Question 190: A 40-year-old woman underwent surgical ileal resection due to perforation caused by severe Crohn's disease. Which of the following physiological changes occurs?

A. A decrease in the absorption of amino acids
B. An increase in the absorption of iron
C. An increase in the concentration of bile acid in the enterohepatic circulation
D. An increase in the water content of the faeces (Correct Answer)

Explanation: **Explanation:** The **terminal ileum** is the primary site for the active reabsorption of **bile salts** and **Vitamin B12** (complexed with intrinsic factor). **Why Option D is correct:** When the ileum is resected, bile salts are not reabsorbed and instead pass into the colon. These unabsorbed bile salts exert an **osmotic effect** and stimulate the colonic mucosa to secrete water and electrolytes (secretory diarrhea). Additionally, the loss of bile salts leads to fat malabsorption; unabsorbed fatty acids are converted by colonic bacteria into hydroxy-fatty acids, which further stimulate fluid secretion. This results in **increased water content in the feces** (diarrhea and steatorrhea). **Analysis of Incorrect Options:** * **Option A:** Amino acid absorption primarily occurs in the **duodenum and jejunum**. While the ileum can absorb them, the proximal small intestine usually compensates, making a significant decrease unlikely. * **Option B:** Iron is predominantly absorbed in the **duodenum**. Ileal resection does not increase its absorption. * **Option C:** Since the ileum is responsible for the enterohepatic circulation of bile acids, its removal leads to a **decrease** in the bile acid pool, as the liver cannot synthesize bile acids fast enough to compensate for the fecal loss. **High-Yield Clinical Pearls for NEET-PG:** * **B12 Deficiency:** Ileal resection >100 cm almost always leads to Megaloblastic anemia due to B12 malabsorption. * **Choleretic Enteropathy:** Small resections (<100 cm) cause watery diarrhea (bile acid-induced). * **Steatorrhea:** Large resections (>100 cm) cause fat malabsorption because the bile salt pool is depleted. * **Oxalate Stones:** Ileal disease leads to increased absorption of dietary oxalate in the colon, causing **calcium oxalate nephrolithiasis**.

Practice by Chapter

Gastrointestinal Motility

Practice Questions

Gastrointestinal Secretions

Practice Questions

Digestion and Absorption

Practice Questions

Gastrointestinal Hormones

Practice Questions

Hepatobiliary Physiology

Practice Questions

Pancreatic Exocrine Function

Practice Questions

Gastrointestinal Circulation

Practice Questions

Intestinal Immune System

Practice Questions

Gut Microbiome

Practice Questions

Regulation of Food Intake

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free