Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 81: Gastric emptying is delayed by all except?

A. Fat in duodenum
B. Acid in duodenum
C. Gastrin (Correct Answer)
D. Secretin

Explanation: **Explanation:** Gastric emptying is regulated by a complex interplay of neural and hormonal signals aimed at ensuring the duodenum can effectively process the incoming chyme. **Why Gastrin is the Correct Answer:** Gastrin is primarily secreted by G-cells in the antrum of the stomach. Its main functions are to stimulate gastric acid secretion and promote **gastric motility**. By increasing the force of antral contractions and relaxing the pyloric sphincter, Gastrin actually **promotes/accelerates** gastric emptying. Therefore, it is the exception in this list. **Analysis of Incorrect Options (Factors that Delay Emptying):** * **Fat in Duodenum (A):** Fat is the most potent inhibitor of gastric emptying. It triggers the release of **Cholecystokinin (CCK)**, which slows gastric motility to allow sufficient time for fat emulsification and digestion. * **Acid in Duodenum (B):** Excess acidity in the duodenum triggers the **enterogastric reflex** and the release of Secretin. This prevents further acid from entering the duodenum until the existing acid is neutralized by pancreatic bicarbonate. * **Secretin (D):** Secreted by S-cells in response to low pH, Secretin inhibits gastric acid secretion and gastric motility, thereby delaying emptying. **High-Yield Clinical Pearls for NEET-PG:** * **Enterogastrone:** This is a collective term for hormones (CCK, Secretin, GIP) secreted by the duodenal mucosa that inhibit gastric secretions and motility. * **Osmolarity:** Hypertonic solutions in the duodenum delay gastric emptying to prevent osmotic diarrhea (Dumping Syndrome). * **Order of Emptying:** Carbohydrates (Fastest) > Proteins > Fats (Slowest). Liquids empty faster than solids. * **Vagus Nerve:** Stimulates gastric emptying; hence, a vagotomy (often done for peptic ulcers) leads to gastric stasis.

Question 82: Parietal cells secrete which of the following substances?

A. Pepsinogen
B. Hydrochloric acid (Correct Answer)
C. Mucus
D. Pepsin

Explanation: ### Explanation **Parietal cells** (also known as oxyntic cells) are primarily located in the body and fundus of the stomach. Their main physiological function is the secretion of **Hydrochloric acid (HCl)** and **Intrinsic Factor (Castle’s factor)**. #### Why the correct answer is right: * **Hydrochloric acid (HCl):** Parietal cells contain an H⁺/K⁺ ATPase pump (proton pump) that actively transports hydrogen ions into the gastric lumen. HCl is essential for activating pepsinogen into pepsin and providing the acidic pH required for protein digestion and the destruction of ingested pathogens. #### Why the other options are incorrect: * **A & D. Pepsinogen and Pepsin:** Pepsinogen is a proenzyme (zymogen) secreted by **Chief cells** (Peptic cells). It is converted into its active form, **Pepsin**, only in the presence of an acidic environment (pH < 3.5) created by HCl. * **C. Mucus:** This is secreted by **Mucous neck cells** and surface epithelial cells. Mucus, along with bicarbonate, forms the gastric mucosal barrier that protects the stomach lining from autodigestion by acid and pepsin. #### High-Yield Clinical Pearls for NEET-PG: 1. **Intrinsic Factor (IF):** Also secreted by parietal cells, IF is crucial for the absorption of **Vitamin B12** in the terminal ileum. Destruction of parietal cells (e.g., in Pernicious Anemia) leads to Vitamin B12 deficiency and Megaloblastic anemia. 2. **Stimulants of Secretion:** Parietal cell secretion is stimulated by three main secretagogues: **Gastrin** (via CCK2 receptors), **Histamine** (via H2 receptors), and **Acetylcholine** (via M3 receptors). 3. **Proton Pump Inhibitors (PPIs):** Drugs like Omeprazole irreversibly inhibit the H⁺/K⁺ ATPase pump, making them the most potent inhibitors of gastric acid secretion.

Question 83: Brunner's glands in the duodenum secrete what?

A. Alkaline mucus (Correct Answer)
B. Acid
C. Pepsin
D. Gastrin

Explanation: **Explanation:** **Brunner’s glands** (also known as duodenal glands) are compound tubular submucosal glands found exclusively in the **duodenum**, primarily in the first part (proximal to the Sphincter of Oddi). 1. **Why Option A is Correct:** The primary function of Brunner’s glands is to secrete a thick, **alkaline mucus** (rich in bicarbonate). This secretion serves two vital purposes: * **Neutralization:** It neutralizes the highly acidic chyme entering the duodenum from the stomach. * **Protection:** It creates a protective mucosal barrier against gastric acid and pepsin, preventing duodenal ulcers. These glands secrete in response to tactile stimuli, vagal stimulation, and the hormone secretin. 2. **Why Other Options are Incorrect:** * **B (Acid):** Acid (HCl) is secreted by **Parietal cells** in the stomach, not the duodenum. * **C (Pepsin):** Pepsinogen (the precursor to pepsin) is secreted by **Chief cells** in the gastric mucosa. * **D (Gastrin):** Gastrin is a hormone secreted by **G-cells** located in the antrum of the stomach and the duodenum; it stimulates acid secretion rather than providing a protective alkaline coating. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Brunner’s glands are a key histological feature used to identify the duodenum because they are located in the **submucosa** (most GI glands are mucosal). * **Hypertrophy:** These glands may undergo hypertrophy in conditions like **Peptic Ulcer Disease (PUD)** as a compensatory mechanism to counter hyperacidity. * **Inhibition:** Sympathetic stimulation inhibits Brunner’s glands, which is why emotional stress can lead to duodenal peptic ulcers due to decreased protective mucus.

Question 84: Glucose transport occurs with the help of which ion during absorption in the gut?

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

Explanation: **Explanation:** The absorption of glucose in the small intestine occurs via **Secondary Active Transport**. This process is mediated by the **SGLT-1 (Sodium-Glucose Linked Transporter-1)** protein located on the apical (luminal) membrane of enterocytes. 1. **Mechanism (Why A is correct):** The transport of glucose is coupled with the movement of **Sodium (Na+)** ions. The **Na+-K+ ATPase pump** on the basolateral membrane pumps Na+ out of the cell, creating a low intracellular Na+ concentration (electrochemical gradient). SGLT-1 utilizes this gradient to "drag" glucose into the cell against its concentration gradient along with two Na+ ions. Once inside, glucose exits into the blood via facilitated diffusion through **GLUT-2** transporters. 2. **Why other options are incorrect:** * **B (K+):** Potassium is primarily involved in maintaining resting membrane potential and is pumped *into* the cell by the Na+-K+ ATPase, rather than driving nutrient co-transport. * **C (Ca+):** Calcium absorption occurs via distinct pathways (TRPV6 channels) and is regulated by Vitamin D (Calcitriol), not coupled with glucose. * **D (Cl-):** Chloride follows Na+ passively to maintain electrical neutrality or is exchanged for bicarbonate; it does not drive glucose transport. **High-Yield Clinical Pearls for NEET-PG:** * **Oral Rehydration Solution (ORS):** The physiological basis of ORS is the SGLT-1 transporter. Sodium and glucose are given together because their co-transport also promotes the osmotic absorption of water. * **SGLT-1 vs. SGLT-2:** SGLT-1 is primarily in the **gut**, while SGLT-2 is in the **proximal convoluted tubule (PCT)** of the kidney. * **Galactose:** Like glucose, galactose also uses SGLT-1 for absorption. Fructose, however, uses **GLUT-5** (facilitated diffusion).

Question 85: Which of the following hormones does not act on the pancreas?

A. Secretin
B. CCK
C. Gastrin (Correct Answer)
D. GIP

Explanation: **Explanation:** The pancreas is primarily regulated by hormones secreted from the duodenum and jejunum in response to chyme. While several gastrointestinal hormones influence pancreatic secretion, **Gastrin** is the correct answer because its primary physiological site of action is the **stomach**, not the pancreas. 1. **Why Gastrin is the correct answer:** Gastrin is secreted by G-cells in the antrum of the stomach. Its principal functions are to stimulate gastric acid (HCl) secretion from parietal cells and stimulate the growth of gastric mucosa. While it shares a structural similarity with CCK (same C-terminal pentapeptide), at physiological levels, it does not have a significant effect on pancreatic secretion. 2. **Analysis of incorrect options:** * **Secretin (Option A):** Known as "Nature's Antacid," it is the most potent stimulator of **bicarbonate-rich** pancreatic juice. It acts on pancreatic ductal cells. * **CCK (Option B):** Cholecystokinin acts on pancreatic acinar cells to stimulate the secretion of **enzyme-rich** pancreatic juice. It also causes gallbladder contraction. * **GIP (Option C):** Gastric Inhibitory Peptide (now called Glucose-dependent Insulinotropic Peptide) acts on the endocrine pancreas to stimulate **insulin secretion** in response to oral glucose (the Incretin effect). **High-Yield NEET-PG Pearls:** * **Potentiation:** Secretin and CCK show potentiation; when both are present, the total pancreatic secretion is much greater than the sum of their individual effects. * **S-cells:** Secretin source. * **I-cells:** CCK source. * **K-cells:** GIP source. * **The Incretin Effect:** Oral glucose causes a greater insulin response than intravenous glucose due to the action of GIP and GLP-1 on the pancreas.

Question 86: The rate of absorption of sugars by the small intestine is highest for which of the following?

A. Pentose
B. Disaccharides
C. Hexoses (Correct Answer)
D. Polysaccharides

Explanation: **Explanation:** The absorption of carbohydrates in the small intestine occurs exclusively in the form of **monosaccharides**. Among these, **Hexoses** (6-carbon sugars) like glucose and galactose have the highest rate of absorption. **Why Hexoses are correct:** Hexoses are absorbed via highly efficient, specialized transport mechanisms. **Glucose and Galactose** are absorbed through **Secondary Active Transport** via the **SGLT-1** (Sodium-Glucose Co-transporter 1) on the apical membrane. This process is rapid because it is driven by the sodium gradient maintained by the Na⁺-K⁺ ATPase pump. **Fructose**, another hexose, is absorbed via facilitated diffusion through **GLUT-5**. Once inside the enterocyte, all hexoses exit into the blood via **GLUT-2**. **Why other options are incorrect:** * **Pentoses (A):** While pentoses (5-carbon sugars) are absorbed, they move across the intestinal mucosa by **simple diffusion**. This process is significantly slower and less efficient than the active transport used by hexoses. * **Disaccharides (B) & Polysaccharides (D):** The human intestinal mucosa lacks transport proteins for complex sugars. Polysaccharides (starch/glycogen) and disaccharides (lactose/sucrose) must first be hydrolyzed into monosaccharides by salivary/pancreatic amylase and brush border enzymes (disaccharidases) before absorption can occur. **High-Yield Clinical Pearls for NEET-PG:** * **Rate of absorption:** Galactose > Glucose > Fructose > Pentoses. * **SGLT-1 Deficiency:** Leads to Glucose-Galactose Malabsorption, but fructose absorption remains normal (as it uses GLUT-5). * **Oral Rehydration Salt (ORS):** Its efficacy is based on the SGLT-1 mechanism, where sodium transport is coupled with glucose, enhancing water absorption via osmosis.

Question 87: In gastric secretion, gastrin acts on which receptor on parietal cells?

A. G receptor
B. H receptor
C. CCKb receptor (Correct Answer)
D. M receptor

Explanation: **Explanation:** The secretion of hydrochloric acid (HCl) by gastric parietal cells is regulated by three primary secretagogues: **Gastrin, Histamine, and Acetylcholine.** **Why CCKb is correct:** Gastrin is a peptide hormone produced by G-cells in the antrum. It stimulates parietal cells through two pathways: an indirect pathway (stimulating histamine release from ECL cells) and a **direct pathway**. In the direct pathway, Gastrin binds to the **Cholecystokinin-B (CCKb) receptor** on the basolateral membrane of the parietal cell. This receptor is a G-protein coupled receptor (Gq) that activates the Phospholipase C pathway, increasing intracellular calcium to trigger the H+/K+ ATPase pump. **Analysis of Incorrect Options:** * **A. G receptor:** This is a distractor. While Gastrin is produced by **G-cells**, the receptor it binds to is classified based on its affinity for the CCK family of peptides. * **B. H receptor:** Histamine acts on **H2 receptors** (G-protein coupled to cAMP) on parietal cells. H1 receptors are typically involved in allergic reactions. * **C. M receptor:** Acetylcholine, released via the Vagus nerve, acts on **M3 (Muscarinic)** receptors on parietal cells to stimulate acid secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Receptor Synergy:** The combined effect of Gastrin, Histamine, and ACh is greater than the sum of their individual effects (Potentiation). * **CCKa vs. CCKb:** CCKa ("Alimentary") receptors have high affinity for CCK only; **CCKb ("Brain/Body")** receptors have high affinity for both Gastrin and CCK. * **Proton Pump Inhibitors (PPIs):** These act on the "final common pathway" (H+/K+ ATPase), making them more effective than H2 blockers which only block one receptor type.

Question 88: Glucose is absorbed in the intestine along with:

A. 1 Na+ (Correct Answer)
B. 2 Na+
C. 1 K+
D. 2 K+

Explanation: **Explanation:** The absorption of glucose in the small intestine occurs via **Secondary Active Transport**. This process is mediated by the **SGLT-1 (Sodium-Glucose Co-transporter 1)** protein located on the apical (luminal) membrane of enterocytes. **Why Option A is Correct:** The SGLT-1 transporter functions by coupling the movement of glucose against its concentration gradient with the movement of sodium down its electrochemical gradient. For every **one molecule of glucose** (or galactose) transported into the cell, **one sodium ion (Na+)** is co-transported. This mechanism relies on the low intracellular sodium concentration maintained by the Na+-K+ ATPase pump on the basolateral membrane. **Why Other Options are Incorrect:** * **Option B (2 Na+):** While the **SGLT-2** transporter (found primarily in the S1 segment of the renal proximal tubule) transports glucose with 1 Na+, and some literature previously debated stoichiometry, the standard physiological consensus for intestinal **SGLT-1** is a 1:1 ratio for glucose and sodium. * **Options C & D (K+):** Potassium is not involved in the co-transport of glucose. In fact, the Na+-K+ ATPase pump moves potassium *into* the cell while pumping sodium *out* to create the driving force for glucose absorption. **High-Yield Clinical Pearls for NEET-PG:** * **SGLT-1 vs. SGLT-2:** SGLT-1 is mainly in the **intestine** (and late proximal tubule), while SGLT-2 is the major transporter in the **kidney** (targeted by Gliflozins for Diabetes). * **GLUT-2:** Once inside the enterocyte, glucose exits into the blood via **facilitated diffusion** through the GLUT-2 transporter. * **Oral Rehydration Therapy (ORT):** The principle of ORS is based on this 1:1 Na-Glucose co-transport; glucose is added to ORS to enhance the absorption of sodium and, consequently, water. * **Galactose** uses the same SGLT-1 transporter, whereas **Fructose** is absorbed via **GLUT-5** (facilitated diffusion).

Question 89: What is the primary function of the proximal part of the stomach?

A. Secretion
B. Digestion
C. Motility
D. Storage (Correct Answer)

Explanation: ### Explanation The stomach is functionally divided into two parts: the **proximal stomach** (fundus and upper body) and the **distal stomach** (lower body and antrum). **Why Storage is Correct:** The primary function of the proximal stomach is **storage**. When food enters the stomach, the proximal region undergoes **receptive relaxation** (mediated by the vagus nerve and VIP/Nitric Oxide). This allows the stomach to accommodate large volumes of food (up to 1.5 liters) with very little increase in intragastric pressure. This reservoir function ensures that food is held until it can be processed and moved into the duodenum. **Analysis of Incorrect Options:** * **Secretion:** While the proximal stomach contains oxyntic glands that secrete HCl and intrinsic factor, secretion is a shared function across most of the gastric mucosa and is not the *primary* functional role of the proximal region compared to its unique storage capacity. * **Digestion:** Gastric digestion (mainly of proteins via pepsin) occurs throughout the stomach, but the proximal part lacks the heavy muscular machinery required for the mechanical breakdown of food. * **Motility:** While the stomach exhibits motility, the **distal stomach** is the primary site for vigorous peristalsis and "antral milling." The proximal stomach exhibits slow, sustained tonic contractions rather than the phasic motility required for mixing. **NEET-PG High-Yield Pearls:** * **Vagotomy:** Loss of receptive relaxation occurs after a vagotomy, leading to increased intragastric pressure and "early satiety." * **Pacemaker of the Stomach:** Located in the greater curvature of the **mid-body**; it generates the Basal Electrical Rhythm (BER) of 3 cycles/minute. * **Gastric Emptying:** Liquids empty faster than solids; fats empty the slowest due to CCK release.

Question 90: The intrinsic factor of Castle is secreted by which cells?

A. Chief cells
B. Parietal cells (Correct Answer)
C. Enterochromaffin like cells
D. G-cells

Explanation: **Explanation:** The **Parietal cells** (also known as oxyntic cells), located primarily in the body and fundus of the stomach, are responsible for secreting two vital substances: **Hydrochloric acid (HCl)** and **Intrinsic Factor (IF) of Castle**. Intrinsic factor is a glycoprotein essential for the absorption of Vitamin B12 (cobalamin) in the terminal ileum. Without IF, Vitamin B12 cannot be absorbed, leading to Pernicious Anemia. **Analysis of Incorrect Options:** * **Chief cells (Peptic cells):** These cells secrete **Pepsinogen** (the inactive precursor of pepsin) and gastric lipase. They do not produce intrinsic factor. * **Enterochromaffin-like (ECL) cells:** These are neuroendocrine cells located in the gastric mucosa that secrete **Histamine**, which subsequently stimulates parietal cells to release HCl. * **G-cells:** Located primarily in the antrum of the stomach, these cells secrete the hormone **Gastrin** into the bloodstream to stimulate gastric acid secretion and mucosal growth. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Absorption:** While IF is secreted in the **stomach**, the IF-B12 complex is absorbed in the **terminal ileum**. * **Pernicious Anemia:** This is an autoimmune condition where antibodies destroy parietal cells or block IF, leading to B12 deficiency and megaloblastic anemia. * **Post-Gastrectomy:** Patients undergoing total gastrectomy require lifelong Vitamin B12 injections because the source of Intrinsic Factor (parietal cells) has been removed. * **Stimulants:** Parietal cell secretion is stimulated by Acetylcholine (Vagus), Gastrin, and Histamine.

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