Gastrointestinal System Practice Questions

Q: All of the following inhibit gastric secretion except?

Histamine. **Explanation** The regulation of gastric acid secretion involves a balance between stimulatory and inhibitory factors. To answer this question, one must distinguish between substances that promote acid production and those that suppress it. **Why Histamine is the Correct Answer:** Histamine is a potent **stimulator** of gastric acid secretion. It is released by Enterochromaffin-like (ECL) cells in the gastric mucosa and binds to **H2 receptors** on parietal cells. This binding activates the adenylyl cyclase pathway, increasing intracellular cAMP, which ultimately activates the H+/K+ ATPase (proton pump) to secrete acid. Since the question asks for the factor that does *not* inhibit secretion, Histamine is the correct choice. **Analysis of Incorrect Options (Inhibitors):** * **Low pH (Antral pH < 3):** This acts as a negative feedback mechanism. When the stomach becomes too acidic, D-cells are stimulated to release somatostatin, which inhibits Gastrin release, thereby decreasing acid production. * **Somatostatin:** Known as the "universal endocrine off-switch," it is the most important physiological inhibitor of gastric acid. It acts directly on parietal cells and indirectly by inhibiting the release of Gastrin and Histamine. * **Prostaglandins (PGE2 and PGI2):** These are protective factors that inhibit acid secretion by decreasing cAMP levels in parietal cells and simultaneously stimulating mucus and bicarbonate secretion. **High-Yield NEET-PG Pearls:** * **The "Big Three" Stimulators:** Gastrin, Acetylcholine (Vagus), and Histamine. * **Potentiation:** Histamine significantly increases the response of parietal cells to Gastrin and Acetylcholine. This is why H2 blockers (e.g., Ranitidine) are effective even though they only block one pathway. * **Enterogastrones:** Hormones like Secretin, CCK, and GIP (released from the duodenum) also inhibit gastric acid secretion to prevent duodenal ulcers.

Q: Intrinsic factor is secreted by which cells of the stomach?

Parietal cells. **Explanation:** The correct answer is **Parietal cells** (also known as oxyntic cells) [1]. These cells are primarily located in the body and fundus of the stomach. They perform two critical secretory functions: the production of **Hydrochloric acid (HCl)** for digestion and the secretion of **Intrinsic Factor (IF)** [1]. Intrinsic factor is a glycoprotein essential for the absorption of Vitamin B12 (cobalamin) in the terminal ileum [2]. **Analysis of Options:** * **A. Mucous cells:** These are found in the gastric pits (neck cells) and surface epithelium. They secrete alkaline mucus and bicarbonate to protect the gastric mucosa from autodigestion by acid and pepsin. * **C. Chief cells:** Also known as peptic or zymogenic cells, these are located at the base of the gastric glands. They secrete **pepsinogen** (the inactive precursor to pepsin) and gastric lipase [1]. * **D. Goblet cells:** These are specialized simple columnar epithelial cells that secrete gel-forming mucins. While abundant in the respiratory tract and the **intestines**, they are not typically found in the normal gastric mucosa. **High-Yield Clinical Pearls for NEET-PG:** * **Pernicious Anemia:** This is an autoimmune condition where antibodies destroy parietal cells or neutralize Intrinsic Factor, leading to Vitamin B12 deficiency and megaloblastic anemia. * **Site of Absorption:** Remember the "Rule of B": Vitamin **B**12 is absorbed in the **B**ottom of the intestine (Terminal Ileum) [2]. * **Stimulants:** Parietal cell secretion is stimulated by **Gastrin, Acetylcholine (Vagus), and Histamine (H2 receptors)** [1]. * **Proton Pump Inhibitors (PPIs):** These drugs act directly on the $H^+/K^+$ ATPase pump located on the apical membrane of parietal cells [3].

Q: Bilirubin glucuronide in the urine in the absence of urobilinogen suggests which of the following conditions?

Obstructive jaundice. ### Explanation The presence of **bilirubin glucuronide** (conjugated bilirubin) in the urine without **urobilinogen** is a classic laboratory hallmark of **Obstructive (Post-hepatic) Jaundice**. **1. Why Obstructive Jaundice is Correct:** In obstructive jaundice (e.g., gallstones or pancreatic cancer), the flow of bile into the intestine is physically blocked. * **Bilirubin in Urine:** Conjugated bilirubin (water-soluble) cannot enter the gut, so it regurgitates into the bloodstream and is excreted by the kidneys (bilirubinuria). * **Absence of Urobilinogen:** Urobilinogen is formed by the action of colonic bacteria on bilirubin. Since bile cannot reach the intestine, no urobilinogen is produced. Consequently, none is reabsorbed into the blood or excreted in the urine. **2. Why Incorrect Options are Wrong:** * **Hemolytic Jaundice:** There is an overproduction of unconjugated bilirubin (water-insoluble), which cannot be excreted in urine. However, increased bilirubin reaches the gut, leading to **increased** urinary urobilinogen. * **Hepatocellular Jaundice:** There is both conjugated hyperbilirubinemia and impaired re-excretion of urobilinogen by damaged hepatocytes. Therefore, both bilirubin and urobilinogen are typically **present** in the urine. **3. NEET-PG High-Yield Pearls:** * **Acholuric Jaundice:** Another name for Hemolytic Jaundice (because urine contains no bilirubin). * **Clay-colored stools:** Occurs in obstructive jaundice due to the absence of stercobilin. * **Van den Bergh Reaction:** * Direct Positive = Conjugated Bilirubin (Obstructive). * Indirect Positive = Unconjugated Bilirubin (Hemolytic). * Biphasic = Both (Hepatocellular). * **Urinary Urobilinogen:** It is normally present in trace amounts; its complete absence is the most sensitive indicator of total biliary obstruction.

Q: Which of the following increases appetite?

Neuropeptide Y. **Explanation:** The regulation of appetite occurs primarily in the **Arcuate Nucleus (ARC)** of the hypothalamus, which contains two distinct sets of neurons: **Orexigenic** (appetite-stimulating) and **Anorexigenic** (appetite-suppressing). **Why Neuropeptide Y (NPY) is correct:** NPY is a potent **orexigenic** neurotransmitter. It is co-released with **Agouti-related peptide (AgRP)** from the ARC neurons. When activated (e.g., during fasting or by the hormone Ghrelin), NPY stimulates the hunger centers in the lateral hypothalamus, leading to increased food intake and decreased energy expenditure. **Analysis of Incorrect Options:** * **Leptin:** Produced by adipose tissue, it is a long-term satiety signal. It inhibits NPY/AgRP neurons and stimulates POMC neurons, thereby **decreasing** appetite. * **$\alpha$-MSH (Alpha-Melanocyte Stimulating Hormone):** This is an **anorexigenic** peptide derived from Pro-opiomelanocortin (POMC). It acts on MC3 and MC4 receptors in the hypothalamus to reduce food intake. * **Insulin:** Similar to leptin, insulin acts as a satiety signal in the CNS. It crosses the blood-brain barrier to inhibit orexigenic neurons, resulting in **decreased** appetite. **High-Yield Clinical Pearls for NEET-PG:** * **Ghrelin:** The only major peripheral hormone that **increases** appetite ("Hunger hormone"). It is secreted by P/D1 cells of the stomach. * **Satiety Center:** Located in the **Ventromedial Nucleus (VMN)** of the hypothalamus. Lesions here lead to hyperphagia and obesity. * **Hunger Center:** Located in the **Lateral Hypothalamus (LHA)**. Lesions here lead to aphagia and weight loss. * **POMC Deficiency:** Can lead to early-onset severe obesity and adrenal insufficiency.

Q: Salivary amylase is inactivated by which of the following?

Low pH of the stomach. **Explanation:** Salivary amylase (also known as **ptyalin**) is an enzyme secreted by the salivary glands that initiates the digestion of dietary starches into maltose and dextrins. **Why the correct answer is right:** Salivary amylase functions optimally at a near-neutral pH (approximately **6.7 to 7.0**). When the food bolus reaches the stomach, it encounters gastric juice, which has a very **low pH (1.5 to 2.5)** due to the presence of hydrochloric acid (HCl). This high acidity denatures the protein structure of salivary amylase, rendering it completely inactive. While some starch digestion continues within the center of a food bolus for a short period, the enzyme is eventually inactivated as the bolus mixes with gastric secretions. **Why the incorrect options are wrong:** * **A. Enteropeptidase:** Also known as enterokinase, this enzyme is located in the duodenal brush border. Its specific role is to convert trypsinogen into active trypsin; it has no inhibitory effect on amylase. * **C. High pH of the intestine:** The intestine actually has a slightly alkaline pH (around 7.0 to 8.0), which is favorable for amylase activity. In fact, starch digestion is completed in the small intestine by **pancreatic amylase**, which functions optimally in this environment. **High-Yield Facts for NEET-PG:** * **Chloride ions ($Cl^-$):** These are essential activators for salivary amylase. * **Site of action:** Salivary amylase accounts for only about 5% of total starch digestion in the mouth but can contribute up to 30-40% before being fully inactivated in the stomach. * **Lingual Lipase:** Unlike amylase, lingual lipase is acid-stable and remains active in the stomach, beginning lipid digestion.

Q: Which class of carbohydrates is absorbed fastest in the intestine?

Hexoses. **Explanation:** The absorption of carbohydrates in the small intestine is a highly specific process that occurs only in the form of **monosaccharides**. **1. Why Hexoses are correct:** Hexoses (6-carbon monosaccharides) like **Glucose and Galactose** are absorbed the fastest because they are the final products of carbohydrate digestion. They do not require further enzymatic breakdown. They are rapidly transported across the apical membrane of enterocytes via **SGLT-1** (Secondary active transport with Sodium) and across the basolateral membrane via **GLUT-2** (Facilitated diffusion). Fructose, another hexose, is absorbed via GLUT-5. Since they are already in their simplest absorbable form, their uptake is immediate. **2. Why other options are incorrect:** * **Disaccharides (e.g., Lactose, Sucrose):** These cannot be absorbed directly. They must first be hydrolyzed into monosaccharides by "brush border enzymes" (Lactase, Sucrase) before transport can occur. * **Oligosaccharides & Polysaccharides (e.g., Starch, Glycogen):** These are complex molecules that require extensive luminal digestion by salivary and pancreatic **alpha-amylase** followed by brush border enzymes. This multi-step process makes their overall absorption rate significantly slower than that of free hexoses. **High-Yield Clinical Pearls for NEET-PG:** * **Rate of Absorption:** Galactose > Glucose > Fructose. * **SGLT-1:** This transporter is the physiological basis for **Oral Rehydration Therapy (ORT)**; sodium absorption is enhanced in the presence of glucose. * **Diagnostic Test:** The **D-Xylose test** is used to distinguish between malabsorption due to mucosal disease (low absorption) and pancreatic deficiency (normal absorption), as D-xylose is a pentose that does not require pancreatic enzymes for breakdown.

Q: What is the normal lower esophageal sphincter pressure?

10-25 mm of Hg. **Explanation:** The **Lower Esophageal Sphincter (LES)** is a specialized segment of circular smooth muscle located at the gastroesophageal junction. Unlike anatomical sphincters, it functions as a **physiological high-pressure zone** that prevents the reflux of acidic gastric contents into the esophagus. **Why Option B is Correct:** The normal resting pressure of the LES typically ranges between **10 to 25 mm Hg** (some texts cite 10–30 mm Hg). This pressure must remain higher than the intragastric pressure (usually 5–10 mm Hg) to maintain a competent barrier. During swallowing, the LES undergoes "receptive relaxation" mediated by Nitric Oxide (NO) and Vasoactive Intestinal Peptide (VIP), allowing food to enter the stomach. **Analysis of Incorrect Options:** * **Option A (5-8 mm Hg):** This pressure is too low. A resting pressure below 10 mm Hg is considered **hypotensive**, leading to Gastroesophageal Reflux Disease (GERD). * **Option C (25-40 mm Hg):** While the upper limit of normal can occasionally reach 30-35 mm Hg, a sustained pressure in this range is borderline hypertensive. * **Option D (>40 mm Hg):** This indicates a **hypertensive LES**. Pressures exceeding 45 mm Hg are characteristic of motility disorders like **Achalasia Cardia**, where the sphincter fails to relax. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hormonal Control:** Gastrin increases LES pressure, while Secretin, Cholecystokinin (CCK), and Glucagon decrease it. 2. **Achalasia Cardia:** Characterized by high resting LES pressure and failure of relaxation due to loss of myenteric (Auerbach’s) plexus. 3. **GERD:** Often caused by "Transient Lower Esophageal Sphincter Relaxations" (TLESRs) or a hypotensive LES. 4. **Pharmacology:** Calcium channel blockers and Nitrates are used to decrease LES pressure in Achalasia.

Q: Antegrade peristalsis is due to which neurotransmitter?

Vasoactive intestinal peptide. **Explanation:** Peristalsis is a reflex response that occurs when the gut wall is stretched by the contents of the lumen. This reflex involves a coordinated wave of contraction behind the bolus and relaxation in front of it, known as the **Law of the Gut**. **Why Vasoactive Intestinal Peptide (VIP) is correct:** Antegrade movement (forward propulsion) requires the segment of the intestine ahead of the bolus to relax. This **receptive relaxation** is mediated by inhibitory motor neurons of the myenteric plexus. The primary inhibitory neurotransmitters responsible for this relaxation are **Vasoactive Intestinal Peptide (VIP)** and **Nitric Oxide (NO)**. Without this relaxation, the bolus cannot move forward. **Analysis of Incorrect Options:** * **Acetlycholine (ACh) & Substance P:** These are the primary **excitatory** neurotransmitters. They cause the contraction of the circular muscle *behind* the bolus (proximal segment) to push it forward. While essential for the peristaltic reflex, they do not mediate the "antegrade" relaxation phase. * **Serotonin (5-HT):** This is released by enterochromaffin cells in response to mucosal stretch. It acts as a sensory trigger to initiate the peristaltic reflex by stimulating IPANs (Intrinsic Primary Afferent Neurons), but it is not the effector molecule for relaxation. **NEET-PG High-Yield Pearls:** * **Law of the Gut:** Distension initiates contraction proximal to the bolus and relaxation distal to it. * **Myenteric (Auerbach’s) Plexus:** Primarily controls GI motility. * **Hirschsprung Disease:** Caused by the absence of the myenteric plexus, leading to a failure of relaxation (lack of VIP/NO) and functional obstruction. * **Key Inhibitors:** VIP and NO (Relaxation); **Key Excitators:** ACh and Substance P (Contraction).

Question 1

All of the following inhibit gastric secretion except?

Accepted Answer

Histamine

Answer

Low pH

Answer

Somatostatin

Answer

Prostaglandin

Question 2

Intrinsic factor is secreted by which cells of the stomach?

Accepted Answer

Parietal cells

Answer

Mucous cells

Answer

Chief cells

Answer

Goblet cells

Question 3

Bilirubin glucuronide in the urine in the absence of urobilinogen suggests which of the following conditions?

Accepted Answer

Obstructive jaundice

Answer

Hemolytic jaundice

Answer

Hepatocellular jaundice

Answer

None of the above

Question 4

Which of the following increases appetite?

Accepted Answer

Neuropeptide Y

Answer

Insulin

Answer

Leptin

Answer

a-MSH

Question 5

In newborns, at which site is the absorption of antibodies maximally achieved?

Accepted Answer

Ileum

Answer

Duodenum

Answer

Jejunum

Answer

Colon

Question 6

Salivary amylase is inactivated by which of the following?

Accepted Answer

Low pH of the stomach

Answer

Enteropeptidase

Answer

High pH of the intestine

Answer

None of the above

Question 7

Kupffer cells in the liver are:

Accepted Answer

Phagocytic cells

Answer

Endothelial cells

Answer

Secretory cells

Question 8

Which class of carbohydrates is absorbed fastest in the intestine?

Accepted Answer

Hexoses

Answer

Disaccharides

Answer

Oligosaccharides

Answer

Polysaccharides

Question 9

What is the normal lower esophageal sphincter pressure?

Accepted Answer

10-25 mm of Hg

Answer

5-8 mm of Hg

Answer

25-40 mm of Hg

Answer

>40 mm of Hg

Question 10

Antegrade peristalsis is due to which neurotransmitter?

Accepted Answer

Vasoactive intestinal peptide

Answer

Serotonin

Answer

Acetylcholine

Answer

Substance P

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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