Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 131: Which gastric enzyme is present in the stomach of infants but absent from the stomach of adults?

A. Pepsin
B. Rennin (Correct Answer)
C. Trypsin
D. Lipase

Explanation: **Explanation:** The correct answer is **Rennin** (also known as Chymosin). **1. Why Rennin is correct:** Rennin is a proteolytic enzyme secreted by the gastric glands (chief cells) in **infants**. Its primary function is the **curdling of milk**. It converts the soluble milk protein, casein, into insoluble calcium paracaseinate in the presence of calcium ions. This process slows down the passage of milk through the digestive tract, allowing more time for gastric proteases to act on it. Rennin is absent in the adult human stomach, where the function of milk curdling is taken over by Pepsin and Hydrochloric acid (HCl). **2. Why other options are incorrect:** * **Pepsin:** This is the primary proteolytic enzyme in the stomach of **both** infants and adults. It is secreted as the proenzyme pepsinogen. * **Trypsin:** This is a pancreatic enzyme, not a gastric one. It acts in the **small intestine** (duodenum) to digest proteins. * **Lipase:** Gastric lipase is present in both infants and adults. In fact, it plays a more significant role in infants for the digestion of milk fats (tributyrin) because pancreatic lipase is not yet fully developed. **3. Clinical Pearls & High-Yield Facts:** * **Spelling Tip:** Do not confuse **Rennin** (digestive enzyme) with **Renin** (hormone secreted by the juxtaglomerular cells of the kidney involved in blood pressure regulation). * **Chief Cells (Peptic Cells):** These cells secrete both Pepsinogen and Prorennin. * **pH Requirement:** Rennin works best at a pH of around 4.0, which is the typical gastric pH of a milk-fed infant, whereas Pepsin requires a more acidic pH (1.8–2.0) found in adults.

Question 132: During a fast, a brief phase of intense sequential contractions begins in the stomach and gradually migrates to the ileum. Release of which of the following intestinal hormones is most likely responsible for this observed effect?

A. Cholecystokinin
B. Gastrin
C. Gastrin-releasing peptide
D. Motilin (Correct Answer)

Explanation: ### Explanation The phenomenon described is the **Migrating Motor Complex (MMC)**, often referred to as the "housekeeper of the gut." **Why Motilin is Correct:** The MMC is a pattern of intense electrical and mechanical activity that occurs during the **inter-digestive state** (fasting). It consists of four phases, with Phase III being the period of maximal contraction. These contractions begin in the stomach and migrate down to the terminal ileum every 90–120 minutes to clear the gut of undigested food and bacteria. **Motilin**, a 22-amino acid peptide secreted by **M cells** in the duodenum and jejunum, is the primary hormonal mediator of these contractions. Plasma motilin levels fluctuate cyclically, peaking just before the onset of Phase III. **Why the Other Options are Incorrect:** * **Cholecystokinin (CCK):** Secreted by I cells in response to fatty acids and amino acids. It stimulates gallbladder contraction and pancreatic enzyme secretion but **inhibits** gastric emptying. * **Gastrin:** Secreted by G cells in the antrum. Its primary role is to stimulate gastric acid secretion and mucosal growth, typically during the fed state. * **Gastrin-releasing peptide (GRP):** A neurotransmitter released from vagal nerve endings that stimulates G cells to release gastrin; it does not coordinate inter-digestive motility. **High-Yield NEET-PG Pearls:** * **Erythromycin Connection:** Erythromycin acts as a **motilin agonist** by binding to motilin receptors. It is clinically used as a prokinetic agent in patients with gastroparesis. * **Feeding Effect:** The MMC is immediately abolished upon **ingestion of food**, replaced by the "fed pattern" of segmentation and peristalsis. * **Site of Origin:** Unlike most GI motility, the MMC starts in the stomach (not the esophagus) and ends at the ileum.

Question 133: Which one of the following statements regarding the regulation of gastrointestinal function is true?

A. The main sympathetic nerve supply to the digestive tract is the vagus.
B. In general, sympathetic stimulation is excitatory to digestive activity.
C. Salivary secretion is stimulated by both branches of the autonomic nervous system, although not to the same degree. (Correct Answer)
D. Parasympathetic stimulation of the salivary glands produces a saliva rich in mucus.

Explanation: ### Explanation **1. Why Option C is Correct:** The regulation of salivary secretion is unique because it is stimulated by **both** the sympathetic and parasympathetic nervous systems. Unlike most other GI organs where the two branches are antagonistic, they act in a complementary manner here. * **Parasympathetic stimulation** (via CN VII and IX) produces a large volume of watery, enzyme-rich saliva. * **Sympathetic stimulation** (via superior cervical ganglion) produces a smaller volume of thick, viscous saliva rich in mucus. **2. Why the Other Options are Incorrect:** * **Option A:** The **vagus nerve (CN X)** is the primary **parasympathetic** supply to the GI tract (up to the proximal two-thirds of the transverse colon). The sympathetic supply originates from the thoracolumbar spinal cord (T5–L2). * **Option B:** In the GI tract, sympathetic stimulation is generally **inhibitory** (decreases motility and secretion) and causes vasoconstriction. Parasympathetic stimulation is typically excitatory. * **Option D:** This is the reverse of physiological reality. **Parasympathetic** stimulation produces **watery** saliva (serous), while **sympathetic** stimulation produces **mucus-rich**, viscous saliva (leading to the "dry mouth" sensation during stress). **3. NEET-PG High-Yield Clinical Pearls:** * **Salivary Control:** Salivary secretion is exclusively under **neural control**; there is no significant hormonal regulation (unlike gastric or pancreatic secretions). * **Atropine Effect:** Since parasympathetic activity is the dominant stimulus for volume, anticholinergic drugs like atropine cause significant xerostomia (dry mouth). * **Aldosterone:** While it doesn't initiate secretion, aldosterone acts on salivary ducts to reabsorb $Na^+$ and $Cl^-$ and secrete $K^+$, similar to its effect on the renal distal tubule.

Question 134: What is the approximate total daily fluid secretion by the salivary glands, stomach, and intestine in a human?

A. 3000 ml
B. 4000 ml
C. 5000 ml (Correct Answer)
D. 6000 ml

Explanation: ### Explanation The correct answer is **5000 ml**. This value represents the cumulative volume of secretions produced by the proximal segments of the gastrointestinal tract (GIT) before reaching the small intestine. **1. Why 5000 ml is correct:** The total daily fluid input into the GIT is approximately **9000 ml (9L)**. This is composed of 2000 ml of oral intake and **7000 ml** of endogenous secretions. The question specifically asks for the sum of secretions from the salivary glands, stomach, and intestine (small intestine): * **Saliva:** ~1500 ml * **Gastric Juice:** ~2000 ml * **Small Intestine (Succus Entericus):** ~1500 ml * **Total:** 1500 + 2000 + 1500 = **5000 ml**. **2. Why other options are incorrect:** * **A (3000 ml) & B (4000 ml):** These values are too low as they likely omit either the gastric or the intestinal component. * **D (6000 ml):** This value overestimates these three specific sources. If you were to add **Bile (500 ml)** and **Pancreatic juice (1500 ml)** to the 5000 ml, the total endogenous secretion would reach 7000 ml. **3. High-Yield Clinical Pearls for NEET-PG:** * **Absorption Efficiency:** Out of the 9L total fluid load, the **small intestine** absorbs the majority (~7-7.5L), while the colon absorbs about 1.4L. Only ~100-200 ml is excreted in feces. * **Maximum Colonic Capacity:** The colon can absorb a maximum of about 5-8 liters per day; exceeding this leads to diarrhea. * **Secretory Source:** Most intestinal secretion (Succus entericus) comes from the **Crypts of Lieberkühn**, while the **Brunner’s glands** specifically secrete alkaline mucus in the duodenum.

Question 135: Which hormone causes increased food intake?

A. Leptin
B. Cart
C. Serotonin
D. Ghrelin (Correct Answer)

Explanation: **Explanation:** The regulation of food intake is controlled by the hypothalamus, specifically through the interplay of **orexigenic** (appetite-stimulating) and **anorexigenic** (appetite-suppressing) signals. **Why Ghrelin is Correct:** Ghrelin is a peptide hormone secreted primarily by the **P/D1 cells of the stomach fundus**. It is known as the "hunger hormone" because it is the only peripheral hormone that stimulates food intake (orexigenic). It acts on the **Arcuate Nucleus** of the hypothalamus to stimulate **NPY (Neuropeptide Y)** and **AgRP (Agouti-related peptide)** neurons, which increase appetite and growth hormone secretion. Ghrelin levels rise sharply before meals and fall immediately after eating. **Why Other Options are Incorrect:** * **Leptin:** Produced by adipocytes, it is a long-term satiety signal. It inhibits NPY/AgRP neurons and stimulates POMC neurons, thereby **decreasing** food intake. * **CART (Cocaine-and-Amphetamine-Regulated Transcript):** This is a potent **anorexigenic** neurotransmitter found in the hypothalamus that decreases appetite. * **Serotonin (5-HT):** In the CNS, serotonin acts as a **satiety signal**. Drugs that increase serotonin levels (like fenfluramine) were historically used to suppress appetite. **High-Yield Clinical Pearls for NEET-PG:** * **Prader-Willi Syndrome:** Characterized by hyperphagia and obesity due to pathologically **elevated Ghrelin levels**. * **Sleep Deprivation:** Increases Ghrelin and decreases Leptin, leading to weight gain. * **Vagus Nerve:** Ghrelin signals are also transmitted via the vagus nerve to the brainstem. * **Post-Gastric Bypass:** Weight loss is partly attributed to a significant **reduction in Ghrelin** levels due to the bypass of the stomach fundus.

Question 136: What is the migrating motility complex?

A. It occurs upon arrival of food in the stomach.
B. It begins in the lower part of the small intestine.
C. It is initiated by pacemaker cells in the intestine.
D. It occurs at a rate of 5 cm per minute from the stomach. (Correct Answer)

Explanation: The **Migrating Motility Complex (MMC)** is a distinct pattern of electromechanical activity observed in the gastrointestinal smooth muscle during the **interdigestive state** (fasting). ### **Explanation of the Correct Option** **Option D** is correct because the MMC acts as a "housekeeper" of the small intestine. It originates in the stomach and moves aborally (downward) toward the ileum. In the small intestine, these waves propagate at a velocity of approximately **5 cm per minute**, effectively clearing residual undigested food, secretions, and bacteria into the colon. ### **Analysis of Incorrect Options** * **Option A:** The MMC occurs during **fasting**. It is immediately **abolished by the arrival of food** in the stomach, which triggers the fed-state pattern (segmentation and peristalsis). * **Option B:** It begins in the **stomach** (specifically the body/antrum) and moves down to the terminal ileum; it does not start in the lower small intestine. * **Option C:** While basic electrical rhythm is controlled by pacemaker cells (Interstitial Cells of Cajal), the MMC specifically is regulated by the hormone **Motilin** and the enteric nervous system. ### **NEET-PG High-Yield Pearls** * **Hormonal Control:** **Motilin** is the primary mediator. Erythromycin (a motilin agonist) can be used to stimulate GI motility. * **Phases:** It consists of 4 phases; **Phase III** is the most active phase with intense contractions. * **Cycle Duration:** A complete cycle repeats every **90 to 120 minutes** during fasting. * **Function:** Prevents **Small Intestinal Bacterial Overgrowth (SIBO)** by sweeping bacteria into the large intestine.

Question 137: Which of the following segments of the gastrointestinal tract exhibits slow waves/basic electrical rhythm (BER) in increasing order?

A. Jejunum > Sigmoid colon > Stomach
B. Jejunum < Sigmoid colon < Stomach
C. Stomach > Sigmoid colon > Jejunum
D. Stomach < Sigmoid colon < Jejunum (Correct Answer)

Explanation: ### Explanation **Concept of Basic Electrical Rhythm (BER)** Slow waves, or the Basic Electrical Rhythm (BER), are spontaneous rhythmic fluctuations in the membrane potential of gastrointestinal smooth muscle cells. They are generated by the **Interstitial Cells of Cajal (ICC)**, which act as the GI pacemakers. The frequency of these waves determines the maximum frequency of contractions in that segment. **Why Option D is Correct:** The frequency of slow waves varies significantly across different segments of the GI tract, generally increasing as we move from the stomach to the small intestine, and then decreasing in the large intestine. * **Stomach:** ~3 cycles per minute (cpm) — The slowest rate. * **Sigmoid Colon:** ~8–9 cycles per minute. * **Jejunum:** ~10–11 cycles per minute (Duodenum is the highest at ~12 cpm). Therefore, the increasing order is: **Stomach (3) < Sigmoid Colon (8-9) < Jejunum (10-11).** **Analysis of Incorrect Options:** * **Option A & C:** These suggest the stomach has a higher frequency than the jejunum, which is physiologically incorrect. The stomach always has the lowest BER frequency. * **Option B:** While it correctly places the stomach lower than the colon, it incorrectly suggests the colon has a higher frequency than the jejunum. The small intestine (duodenum/jejunum) maintains the highest frequency in the entire tract. **High-Yield Facts for NEET-PG:** * **Pacemaker Cells:** Interstitial Cells of Cajal (ICC) are located between the longitudinal and circular muscle layers. * **Ionic Basis:** Slow waves are primarily due to the cyclic opening of **calcium channels** (influx) and **potassium channels** (efflux). * **Highest Frequency:** Duodenum (~12 cpm). * **Lowest Frequency:** Stomach (~3 cpm). * **Clinical Note:** Slow waves do not cause contractions by themselves; they require **spike potentials** (triggered by ACh or distension) to reach the threshold for mechanical contraction.

Question 138: Which ion is present in higher concentration in gastric secretions compared to blood?

A. Cl- (Correct Answer)
B. HCO3-
C. K+
D. Na+

Explanation: ### Explanation The primary function of gastric secretion is the production of Hydrochloric Acid (HCl) by the parietal (oxyntic) cells. This process results in a unique ionic profile compared to plasma. **1. Why Cl- is the Correct Answer:** Chloride (Cl-) is the most abundant anion in gastric juice. During acid secretion, Cl- is actively transported from the cytoplasm of parietal cells into the gastric lumen via chloride channels. To maintain electrical neutrality, it follows the actively secreted H+ ions. Consequently, the concentration of Cl- in gastric juice (approx. 120–160 mEq/L) is significantly **higher** than its concentration in blood/plasma (approx. 100–105 mEq/L). **2. Analysis of Incorrect Options:** * **HCO3- (B):** Bicarbonate is virtually absent in pure gastric acid. In fact, for every H+ ion secreted into the stomach, one HCO3- ion is released into the blood, leading to the **"Post-prandial Alkaline Tide."** * **K+ (C):** While K+ concentration in gastric juice is higher than in plasma (approx. 10–20 mEq/L vs. 4–5 mEq/L), **Cl- remains the ion with the highest absolute concentration difference** and total volume in the secretion. In the context of standard NEET-PG questions, Cl- is the hallmark ion of gastric juice. * **Na+ (D):** The concentration of Na+ in gastric juice is significantly **lower** than in plasma (approx. 40–60 mEq/L vs. 140 mEq/L). As the rate of secretion increases, Na+ concentration further decreases while H+ increases. **3. Clinical Pearls for NEET-PG:** * **Inverse Relationship:** In gastric juice, as the secretory rate increases, the concentration of **H+ and Cl- increases**, while the concentration of **Na+ decreases**. * **Vomiting Complications:** Persistent vomiting leads to loss of gastric juice rich in H+, Cl-, and K+. This results in the classic metabolic profile: **Hypochloremic, Hypokalemic, Metabolic Alkalosis with Paradoxical Aciduria.** * **Proton Pump:** The H+/K+ ATPase pump is the final common pathway for gastric acid secretion.

Question 139: Acinar cells of the Exocrine Pancreas secrete which of the following?

A. Glucagon
B. Lysozyme
C. Insulin
D. Proteases (Correct Answer)

Explanation: **Explanation:** The pancreas is a dual-function gland consisting of endocrine and exocrine components. The **exocrine pancreas** is composed of **acinar cells** and ductal cells. Acinar cells are responsible for synthesizing, storing, and secreting digestive enzymes. These include **proteases** (such as trypsinogen, chymotrypsinogen, and procarboxypeptidase), lipases, and amylases. These enzymes are secreted as inactive proenzymes (zymogens) to prevent autodigestion of the gland and are activated in the duodenum by enterokinase. **Analysis of Incorrect Options:** * **A & C (Glucagon and Insulin):** These are hormones produced by the **endocrine pancreas** (Islets of Langerhans). Specifically, Alpha cells secrete glucagon and Beta cells secrete insulin. They are released directly into the bloodstream, not into the pancreatic ducts. * **B (Lysozyme):** While lysozyme is an antibacterial enzyme found in saliva and the secretions of **Paneth cells** in the small intestine, it is not a primary secretion of pancreatic acinar cells. **High-Yield Clinical Pearls for NEET-PG:** * **Ductal Cells:** Unlike acinar cells, ductal cells secrete a large volume of juice rich in **Bicarbonate ($HCO_3^-$)**, stimulated primarily by the hormone **Secretin**. * **CCK (Cholecystokinin):** This is the primary stimulus for **acinar cells** to release digestive enzymes. * **Trypsin Inhibitor:** Acinar cells also secrete a trypsin inhibitor to prevent the premature activation of trypsin within the pancreatic ducts, a key protective mechanism against **Acute Pancreatitis**.

Question 140: Which of the following factors increases gastric motility?

A. Acid in the duodenum
B. Fatty food in the stomach
C. Carbohydrates in the stomach
D. None of the above (Correct Answer)

Explanation: ### Explanation The rate of gastric emptying and motility is primarily regulated by the nature of the chyme entering the duodenum. The correct answer is **None of the above** because all the listed factors actually **inhibit** or delay gastric motility rather than increase it. #### Why the options are incorrect: * **Acid in the duodenum (Option A):** When acidic chyme (pH < 3.5–4.0) enters the duodenum, it triggers the **enterogastric reflex** and the release of **Secretin**. Both mechanisms potently inhibit gastric motility to protect the duodenal mucosa and allow time for neutralization by pancreatic bicarbonate. * **Fatty food in the stomach (Option B):** Fats are the slowest macronutrients to empty. The presence of fat in the duodenum stimulates the release of **Cholecystokinin (CCK)** and **Gastric Inhibitory Peptide (GIP)**, which significantly decrease gastric emptying to ensure adequate time for emulsification and digestion. * **Carbohydrates in the stomach (Option C):** While carbohydrates empty faster than proteins and fats, they do not *increase* motility beyond the basal rate. In fact, hypertonic solutions (like concentrated sugars) in the duodenum trigger osmoreceptors that slow down gastric emptying. #### High-Yield NEET-PG Pearls: * **Order of Gastric Emptying:** Carbohydrates > Proteins > Fats (Slowest). * **Liquids vs. Solids:** Isotonic liquids empty the fastest; solids must be ground to particles < 2mm (antral mill) before passing the pylorus. * **Key Inhibitors:** CCK is the most potent inhibitor of gastric emptying triggered by fat. * **Stimulant:** The only major factor that increases gastric motility is **Gastrin** (and physical distension of the stomach via the vago-vagal reflex). * **Clinical Correlation:** **Gastroparesis** (delayed emptying) is common in Diabetes Mellitus due to autonomic neuropathy, while **Dumping Syndrome** occurs after gastric surgery due to rapid emptying of hypertonic chyme.

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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Hepatobiliary Physiology

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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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