Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 11: A patient undergoes a total gastrectomy because of a proximally located gastric cancer. After the surgery, which of the following digestive enzymes will be produced in inadequate amounts?

A. Amylase
B. Chymotrypsin
C. Lipase
D. Pepsin (Correct Answer)

Explanation: **Explanation:** **1. Why Pepsin is the Correct Answer:** Pepsin is the primary proteolytic enzyme of the stomach. It is secreted by the **Chief cells** (Peptic cells) of the gastric mucosa as an inactive proenzyme called **pepsinogen**. Pepsinogen is converted into active pepsin by the acidic environment (HCl) provided by Parietal cells. In a **total gastrectomy**, the entire gastric mucosa is removed, leading to a complete loss of Chief cells. Consequently, the production of pepsinogen ceases, making pepsin the enzyme produced in inadequate (zero) amounts. **2. Why Other Options are Incorrect:** * **A. Amylase:** Salivary amylase is produced by the salivary glands, and pancreatic amylase is produced by the pancreas. Neither is affected by the removal of the stomach. * **B. Chymotrypsin:** This is a pancreatic protease. Its precursor, chymotrypsinogen, is secreted by the exocrine pancreas and activated in the small intestine by trypsin. * **C. Lipase:** While a small amount of "lingual lipase" and "gastric lipase" exists, the most significant lipase for fat digestion is **pancreatic lipase**. Since the pancreas remains intact, lipase production remains largely functional. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vitamin B12 Deficiency:** The most critical long-term consequence of total gastrectomy is **Megaloblastic Anemia** due to the loss of **Intrinsic Factor** (secreted by Parietal cells), which is essential for B12 absorption in the terminal ileum. * **Digestion Post-Gastrectomy:** Despite the loss of pepsin, protein digestion remains relatively effective because pancreatic enzymes (trypsin, chymotrypsin) can compensate for the lack of gastric proteolysis. * **Dumping Syndrome:** A common post-gastrectomy complication where rapid emptying of hypertonic chyme into the small intestine causes vasomotor and GI symptoms.

Question 12: What is the approximate amount of bile produced per day in ml?

A. 100 - 500
B. 500 - 1000 (Correct Answer)
C. 1000 - 1500
D. 1500 - 2000

Explanation: **Explanation:** The liver is a vital metabolic organ that continuously secretes bile. In a healthy adult, the liver produces approximately **500 to 1000 ml** of bile per day. This bile is either stored and concentrated in the gallbladder or secreted directly into the duodenum to facilitate the emulsification and absorption of dietary lipids. * **Why Option B is correct:** Standard physiological texts (like Guyton and Ganong) establish that the daily hepatic secretion of bile ranges between 500–1000 ml. This volume is necessary to maintain the enterohepatic circulation of bile salts, which occurs 6–10 times a day. * **Why Option A is incorrect:** 100–500 ml is too low for daily production; however, it is important to note that the **gallbladder capacity** is much smaller (approx. 30–60 ml), achieving storage through significant concentration of the bile. * **Why Options C & D are incorrect:** Volumes exceeding 1000 ml are more characteristic of daily **salivary secretion** (approx. 1000–1500 ml) or **pancreatic juice** (approx. 1200–1500 ml), rather than bile. **High-Yield NEET-PG Pearls:** 1. **Composition:** Bile is composed of bile salts, bilirubin, cholesterol, lecithin, and electrolytes. It contains **no digestive enzymes**. 2. **Stimulus:** The most potent stimulus for gallbladder contraction and bile release is **Cholecystokinin (CCK)**, released from I-cells in the duodenum. 3. **Enterohepatic Circulation:** About 95% of bile salts are reabsorbed in the **terminal ileum** via active transport and returned to the liver. 4. **Specific Gravity:** Liver bile has a specific gravity of ~1.011, while gallbladder bile is more concentrated at ~1.040.

Question 13: What is the normal daily faecal fat excretion?

A. 0-5 gm (Correct Answer)
B. 5-10 gm
C. 10-15 gm
D. 15-20 gm

Explanation: **Explanation:** The normal daily faecal fat excretion in a healthy adult consuming a standard diet (containing approximately 100g of fat) is **less than 5-7 grams per 24 hours**. **Why Option A is correct:** In a physiological state, the small intestine is highly efficient at absorbing dietary lipids. Most of the fat found in the stool of a healthy individual is not actually from undigested food, but rather derived from **shed intestinal epithelial cells, colonic bacteria, and biliary secretions**. A value of **0-5 gm/day** (or <7g in some texts) represents the standard reference range for normal fat malabsorption. **Why Options B, C, and D are incorrect:** * **5-10 gm:** While 5-7g is the upper limit of normal, values consistently above 7g are considered borderline or indicative of mild malabsorption. * **10-15 gm & 15-20 gm:** These ranges are definitively pathological. Excretion exceeding 7g/day is clinically defined as **Steatorrhea**, suggesting a failure in fat digestion (e.g., chronic pancreatitis) or absorption (e.g., Celiac disease). **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Test:** The **72-hour faecal fat estimation** (Van de Kamer method) is the definitive quantitative test for diagnosing steatorrhea. * **Coefficient of Fat Absorption (CFA):** Normal CFA is **>95%**. It is calculated as: *[(Fat Intake - Fat Excretion) / Fat Intake] × 100*. * **Clinical Presentation:** Steatorrhea is characterized by bulky, foul-smelling, oily stools that are difficult to flush. * **Screening:** The **Sudan III stain** is a common qualitative screening tool used to detect fat globules in a random stool sample.

Question 14: A patient who underwent extensive bowel resection is on total parenteral nutrition (TPN) for 1 month. Endoscopy done after one month reveals diffuse gastric mucosal atrophy. Which enzyme deficiencies are most likely responsible for gastric mucosal atrophy in this patient?

A. Gastrin and ghrelin
B. Secretin and cholecystokinin (CCK)
C. Gastrin and cholecystokinin (CCK) (Correct Answer)
D. Gastrin and secretin

Explanation: ### Explanation **Concept: The Trophic Effect of GI Hormones** The primary reason for gastric mucosal atrophy in patients on long-term Total Parenteral Nutrition (TPN) is the **lack of enteral stimulation**. When food does not enter the gastrointestinal tract, the physiological release of GI hormones is significantly diminished. **Why Gastrin and CCK are correct:** * **Gastrin:** Beyond its role in acid secretion, gastrin is a potent **trophic (growth-promoting) hormone**. It stimulates the proliferation of gastric mucosal cells (specifically parietal and ECL cells). Lack of oral intake leads to hypo-gastrinemia, resulting in disuse atrophy of the gastric mucosa. * **Cholecystokinin (CCK):** While CCK primarily acts on the gallbladder and pancreas, it also exerts a trophic effect on the **exocrine pancreas and the intestinal mucosa**. In the context of TPN, the absence of both gastrin and CCK leads to generalized atrophy of the digestive tract lining and associated glands. **Analysis of Incorrect Options:** * **Secretin:** Known as "nature's antacid," secretin primarily stimulates bicarbonate secretion. It does not have a significant trophic effect on the gastric mucosa; in fact, it inhibits gastric cell proliferation. * **Ghrelin:** While produced in the stomach and involved in hunger signaling, it is not the primary hormone responsible for maintaining the structural integrity (trophic maintenance) of the gastric lining. **High-Yield NEET-PG Pearls:** * **TPN Complication:** Long-term TPN leads to **biliary sludge and gallstones** because the lack of CCK release results in gallbladder stasis. * **Gastrinoma (Zollinger-Ellison Syndrome):** Excessive gastrin leads to the opposite effect—**hyperplasia** of the gastric mucosa and prominent rugal folds. * **Trophic Hierarchy:** Gastrin is the most important trophic hormone for the stomach, while CCK is the most important for the pancreas.

Question 15: Pancreatic juice becomes thick if it has impaired secretion?

A. Sodium (Na) secretion
B. Chloride (Cl-) secretion (Correct Answer)
C. Sodium-Hydrogen (Na+/H+) exchange
D. Hydrogen (H+) secretion

Explanation: **Explanation:** The correct answer is **Chloride (Cl-) secretion**. The consistency of pancreatic juice is primarily regulated by the **CFTR (Cystic Fibrosis Transmembrane Conductance Regulator)** channel located on the apical membrane of pancreatic ductal cells. 1. **Mechanism:** Under normal conditions, Cl- is secreted into the ductal lumen via the CFTR channel. This Cl- is then exchanged for Bicarbonate (HCO3-) via the Cl-/HCO3- exchanger. The secretion of these ions creates an osmotic gradient that draws water into the duct. This water ensures that the pancreatic enzymes are diluted and the juice remains alkaline and fluid. 2. **Pathophysiology:** If Cl- secretion is impaired (as seen in **Cystic Fibrosis**), the exchange for HCO3- fails, and the osmotic drive for water secretion is lost. This results in the production of highly concentrated, protein-rich, and **viscid (thick) secretions** that plug the pancreatic ducts, leading to ductal obstruction and organ damage. **Analysis of Incorrect Options:** * **Option A & C:** Sodium (Na+) follows Cl- passively (paracellularly) to maintain electrical neutrality. While Na+ is present in the juice, the primary defect leading to "thick" secretions is the failure of the active transport of anions (Cl-). * **Option D:** Hydrogen (H+) secretion is characteristic of gastric parietal cells, not the pancreatic ductal cells (which focus on HCO3- secretion to neutralize gastric acid). **Clinical Pearls for NEET-PG:** * **Cystic Fibrosis (CF):** Caused by a mutation in the CFTR gene (most common: ΔF508). It presents with thick secretions in the lungs and pancreas. * **Secretin:** The hormone that stimulates the production of large volumes of watery, bicarbonate-rich pancreatic juice. * **Enzyme Secretion:** While ductal cells secrete water and electrolytes, **Acinar cells** secrete the digestive enzymes (stimulated by Cholecystokinin).

Question 16: A 35-year-old female, hospitalized after a motor vehicle accident, develops acute gastric stress ulcers. Increases in which of the following normal physiological parameters may have contributed to this condition?

A. Bicarbonate transport
B. Epithelial regenerative capacity
C. Mucosal blood flow
D. Pepsin production (Correct Answer)

Explanation: **Explanation:** The development of acute gastric stress ulcers (often called **Curling’s ulcers** in trauma/burn patients or **Cushing’s ulcers** in head injuries) results from an imbalance between **protective mucosal defenses** and **aggressive factors**. **Why "Pepsin production" is correct:** Pepsin is a potent proteolytic enzyme secreted as pepsinogen by gastric chief cells. In the setting of physiological stress, there is often a hypersecretion of gastric acid and an increase in **pepsin production**. Pepsin actively digests the mucosal proteins once the protective mucus-bicarbonate barrier is breached. This aggressive enzymatic digestion is a primary driver in the formation of acute erosions and ulcers in the gastric mucosa. **Why other options are incorrect:** * **A. Bicarbonate transport:** This is a protective mechanism. Bicarbonate neutralizes acid at the epithelial surface; an *increase* would prevent ulcers, not cause them. * **B. Epithelial regenerative capacity:** This is a defense mechanism. Rapid cell turnover helps heal the mucosa; a *decrease* in regeneration contributes to ulceration. * **C. Mucosal blood flow:** This is the most critical protective factor. It removes back-diffused H+ ions and provides nutrients for repair. Stress ulcers are typically caused by *decreased* (ischemic) blood flow, not an increase. **High-Yield Clinical Pearls for NEET-PG:** * **Curling’s Ulcer:** Associated with severe **burns** (due to reduced plasma volume and mucosal ischemia). * **Cushing’s Ulcer:** Associated with **increased intracranial pressure** (due to vagal overstimulation leading to massive ACh release and hyperacidity). * **Prophylaxis:** Critically ill patients in the ICU are routinely started on PPIs or H2 blockers to prevent these stress-induced lesions.

Question 17: Which of the following is involved in peristalsis by causing relaxation?

A. Substance P
B. Acetylcholine
C. VIP (Correct Answer)
D. Norepinephrine

Explanation: **Explanation:** Peristalsis is a coordinated reflex involving a **contraction** of the circular muscle behind the food bolus and a **relaxation** of the muscle in front of it (the "receptive relaxation"). This process is mediated by the Myenteric (Auerbach’s) plexus. **1. Why VIP is correct:** **Vasoactive Intestinal Peptide (VIP)** and **Nitric Oxide (NO)** are the primary inhibitory neurotransmitters of the Enteric Nervous System. During the descending phase of peristalsis, these mediators are released to cause smooth muscle relaxation, allowing the bolus to move forward. **2. Why the other options are incorrect:** * **Substance P:** This is an excitatory neurotransmitter. Along with Acetylcholine, it causes the contraction of the smooth muscle proximal to the bolus. * **Acetylcholine (ACh):** The primary excitatory neurotransmitter of the GI tract. It acts on muscarinic receptors to increase motility and secretions. * **Norepinephrine:** While it generally causes GI relaxation, it is a sympathetic neurotransmitter that acts by inhibiting the enteric plexus or directly hyperpolarizing muscle cells. It is involved in the overall inhibition of digestion rather than the specific, coordinated reflex of a peristaltic wave. **Clinical Pearls for NEET-PG:** * **Law of the Gut:** Peristalsis always moves in an aboral direction (mouth to anus). * **Achalasia Cardia:** Caused by a deficiency of VIP and NO producing neurons in the lower esophageal sphincter (LES), leading to failure of relaxation. * **Hirschsprung Disease:** Absence of both Meissner’s and Auerbach’s plexuses in the distal colon, leading to a functional obstruction. * **Key Inhibitors:** VIP and NO (Relaxation); **Key Stimulators:** ACh and Substance P (Contraction).

Question 18: Which of the following processes is not a true component of swallowing?

A. Closure of the glottis.
B. Involuntary relaxation of the upper esophageal sphincter.
C. Movements of the tongue against the palate. (Correct Answer)
D. Esophageal peristalsis.

Explanation: ### Explanation The process of swallowing (deglutition) is divided into three stages: **Oral (Voluntary)**, **Pharyngeal (Involuntary)**, and **Esophageal (Involuntary)**. **Why Option C is the Correct Answer:** The question asks for the process that is **not** a true component of the swallowing reflex. Movements of the tongue against the hard palate constitute the **Oral Stage**. This stage is entirely **voluntary** and involves the conscious initiation of bolus movement toward the oropharynx. In medical physiology, the "swallowing reflex" strictly refers to the involuntary actions triggered once the bolus touches the tactile receptors in the pharynx. Therefore, while tongue movement is a precursor to swallowing, it is not part of the reflexive/involuntary component. **Analysis of Incorrect Options:** * **A. Closure of the glottis:** This is a vital part of the **Pharyngeal stage**. To prevent aspiration, the vocal cords adduct (closure of the glottis) and the epiglottis swings backward to cover the laryngeal opening. * **B. Involuntary relaxation of the UES:** During the pharyngeal stage, the Upper Esophageal Sphincter (UES) relaxes involuntarily to allow the bolus to enter the esophagus. * **D. Esophageal peristalsis:** This constitutes the **Esophageal stage**. Once the bolus enters the esophagus, primary and secondary peristaltic waves move it toward the stomach via involuntary smooth muscle contraction. **High-Yield Clinical Pearls for NEET-PG:** * **Deglutition Center:** Located in the **Medulla Oblongata** and lower **Pons**. * **Afferent Nerves:** Primarily the Glossopharyngeal (IX) and Vagus (X) nerves. * **Achalasia Cardia:** Failure of the Lower Esophageal Sphincter (LES) to relax due to loss of myenteric plexus (Auerbach’s). * **Passavant’s Ridge:** A ridge formed by the superior constrictor muscle that helps seal the nasopharynx during swallowing.

Question 19: Which of the following inhibits both gastric acid secretion and motility?

A. Vasoactive intestinal polypeptide (VIP)
B. Gastric inhibitory peptide (GIP) (Correct Answer)
C. Somatostatin
D. Ghrelin

Explanation: **Explanation:** The correct answer is **Gastric Inhibitory Peptide (GIP)**, also known as Glucose-dependent Insulinotropic Polypeptide. **1. Why GIP is correct:** GIP is a hormone secreted by the **K-cells** of the duodenum and jejunum in response to the presence of glucose, amino acids, and fatty acids. Its primary physiological actions include: * **Inhibition of Gastric Acid Secretion:** It acts directly on parietal cells to decrease H+ secretion. * **Inhibition of Gastric Motility:** It slows gastric emptying, ensuring sufficient time for intestinal digestion. * **Insulinotropic effect:** It stimulates insulin release from pancreatic beta cells (hence its modern name). **2. Why other options are incorrect:** * **Vasoactive Intestinal Polypeptide (VIP):** Primarily functions as a neurotransmitter. While it inhibits acid secretion, its main GI effect is stimulating the secretion of water and electrolytes into the intestine and **relaxing GI smooth muscle** (sphincters), rather than specifically inhibiting overall gastric motility in this context. * **Somatostatin:** Known as the "universal inhibitor," it strongly inhibits gastric acid secretion (via paracrine action). However, its effect on motility is complex and less specific compared to the classic "enterogastrone" profile of GIP. * **Ghrelin:** Secreted by the stomach P/D1 cells, it **stimulates** food intake and **increases** gastric motility and acid secretion (the "hunger hormone"). **Clinical Pearls for NEET-PG:** * **Enterogastrone Reflex:** GIP, Secretin, and Cholecystokinin (CCK) collectively act as "enterogastrones"—hormones released by the duodenum that inhibit gastric activity. * **Oral vs. IV Glucose:** Oral glucose leads to a higher insulin spike than intravenous glucose because oral glucose triggers **GIP release**, which augments insulin secretion (the Incretin effect). * **Stimulus:** Fat is the most potent stimulus for GIP release.

Question 20: During deglutition, which structure limits the size of the swallowed bolus?

A. Soft palate
B. Posterior pharyngeal pillars (Correct Answer)
C. Upper esophageal sphincter
D. Larynx

Explanation: **Explanation:** The process of deglutition (swallowing) is divided into oral, pharyngeal, and esophageal stages. The correct answer is **Posterior pharyngeal pillars** (palatopharyngeal arches). **Why it is correct:** During the voluntary stage of swallowing, the tongue forces the bolus backward into the pharynx. The posterior pharyngeal pillars are mucosal folds containing the palatopharyngeus muscle. These pillars move medially toward each other, forming a **sagittal slit** through which the food must pass. This slit acts as a "selective filter," allowing only sufficiently masticated food and small boluses to pass into the posterior pharynx while impeding large, unchewed masses. **Analysis of incorrect options:** * **Soft palate:** Its primary role is to elevate and seal off the nasopharynx to prevent the reflux of food into the nasal cavity. It does not regulate bolus size. * **Upper esophageal sphincter (UES):** Also known as the cricopharyngeal muscle, it relaxes to allow the bolus into the esophagus and prevents air from entering the stomach. It acts as a gateway rather than a size-limiting filter. * **Larynx:** During swallowing, the larynx moves upward and forward, and the epiglottis covers the glottis to protect the airway. It is involved in airway protection, not bolus sizing. **High-Yield NEET-PG Pearls:** * **Swallowing Center:** Located in the **Medulla Oblongata** and lower Pons. * **Deglutition Apnea:** The temporary arrest of breathing during the pharyngeal stage of swallowing to prevent aspiration. * **Pharyngeal Stage:** This is an "all-or-none" involuntary reflex; once the bolus touches the epithelial swallowing receptor areas (especially on the tonsillar pillars), the reflex is triggered.

Practice by Chapter

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