Gastrointestinal System Practice Questions

Q: Gastric emptying is delayed by all except?

Gastrin. **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.

Q: Brunner's glands in the duodenum secrete what?

Alkaline mucus. **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.

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

Gastrin. **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.

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

Hexoses. **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.

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

CCKb receptor. **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.

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

Parietal cells. **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.

Q: Which of the following pancreatic function tests can be useful for estimation of bicarbonate as well as enzyme secretory activity of the pancreas?

CCK-secretin test. ### Explanation The **CCK-Secretin test** is considered the "Gold Standard" direct invasive test for assessing both the exocrine and ductal functions of the pancreas. **1. Why the Correct Answer is Right:** The test involves the intravenous administration of two hormones: * **Secretin:** Acts on the pancreatic ductal cells to stimulate the secretion of a large volume of juice rich in **bicarbonate**. * **Cholecystokinin (CCK):** Acts on the acinar cells to stimulate the secretion of **pancreatic enzymes** (like lipase, amylase, and trypsin). By intubating the duodenum and collecting pancreatic secretions after stimulation, clinicians can directly measure the bicarbonate concentration (ductal health) and enzyme output (acinar health). **2. Analysis of Incorrect Options:** * **CCK-PZ test:** While this stimulates enzyme secretion (via CCK/Pancreozymin), it lacks the secretin component required to adequately assess maximal bicarbonate secretory capacity. * **Bentiromide test:** This is an indirect, non-invasive test. It measures the ability of pancreatic chymotrypsin to cleave PABA from bentiromide, which is then measured in urine. It does not assess bicarbonate. * **D-xylose test:** This is a test for **intestinal mucosal absorption** (specifically in the proximal small intestine) and is used to differentiate malabsorption caused by intestinal disease from that caused by pancreatic insufficiency. **3. Clinical Pearls for NEET-PG:** * **Gold Standard:** The Secretin-CCK test is the most sensitive test for early chronic pancreatitis, though it is rarely used clinically due to its invasive nature. * **Fecal Elastase-1:** The most common non-invasive screening test for pancreatic insufficiency (highly specific). * **Secretin Stimulation:** In a healthy pancreas, bicarbonate concentration should rise above **80 mEq/L** following secretin administration.

Q: Which of the following decreases gastric acid secretion?

Secretin. **Explanation:** Gastric acid secretion is a tightly regulated process involving stimulatory and inhibitory pathways. The correct answer is **Secretin**, which acts as a primary "enterogastrone"—a hormone released from the duodenum that inhibits gastric activity. **Why Secretin is Correct:** Secretin is produced by **S-cells** in the duodenum in response to low pH (acidic chyme). Its primary physiological roles are to stimulate pancreatic bicarbonate secretion and to **inhibit gastric acid secretion** by the parietal cells. It also stimulates the release of Somatostatin and inhibits the release of Gastrin, further suppressing acidity to protect the duodenal mucosa. **Analysis of Incorrect Options:** * **Vagal Stimulation:** The Vagus nerve (Parasympathetic) is a potent **stimulator** of acid secretion. It acts via Acetylcholine on M3 receptors and by stimulating G-cells to release Gastrin. * **Proteins in Gastric Fluids:** Digested proteins and amino acids are the strongest chemical **stimulants** for G-cells in the antrum to secrete Gastrin, which in turn increases HCL production. * **Gastric Antral Distension:** Distension of the stomach triggers local (enteric) and central (vagovagal) reflexes that **increase** acid secretion to prepare for digestion. **High-Yield Clinical Pearls for NEET-PG:** * **Other Inhibitors:** Somatostatin (the "universal inhibitor"), GIP (Gastric Inhibitory Peptide), and CCK (Cholecystokinin). * **The "Alkaline Tide":** After a meal, high HCL secretion results in the release of bicarbonate into the bloodstream, temporarily increasing blood pH. * **Pharmacology Link:** Proton Pump Inhibitors (PPIs) like Omeprazole are the most potent inhibitors of gastric acid, acting on the $H^+/K^+$ ATPase pump.

Question 1

Which of the following is NOT a function of cholecystokinin?

Accepted Answer

Increased resistance of the sphincter of Oddi

Answer

Contraction of the gallbladder

Answer

Increased hepatic secretion of bile

Answer

Enhanced flow of biliary contents into the duodenum

Question 2

Gastric emptying is delayed by all except?

Accepted Answer

Gastrin

Answer

Fat in duodenum

Answer

Acid in duodenum

Answer

Secretin

Question 3

Brunner's glands in the duodenum secrete what?

Accepted Answer

Alkaline mucus

Answer

Acid

Answer

Pepsin

Answer

Gastrin

Question 4

Which of the following hormones does not act on the pancreas?

Accepted Answer

Gastrin

Answer

Secretin

Answer

CCK

Answer

GIP

Question 5

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

Accepted Answer

Hexoses

Answer

Pentose

Answer

Disaccharides

Answer

Polysaccharides

Question 6

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

Accepted Answer

CCKb receptor

Answer

G receptor

Answer

H receptor

Answer

M receptor

Question 7

The intrinsic factor of Castle is secreted by which cells?

Accepted Answer

Parietal cells

Answer

Chief cells

Answer

Enterochromaffin like cells

Answer

G-cells

Question 8

Which of the following pancreatic function tests can be useful for estimation of bicarbonate as well as enzyme secretory activity of the pancreas?

Accepted Answer

CCK-secretin test

Answer

CCK PZ test

Answer

Bentiromide test

Answer

D-xylose test

Question 9

Which of the following decreases gastric acid secretion?

Accepted Answer

Secretin

Answer

Vagal stimulation

Answer

Proteins in gastric fluids

Answer

Gastric antral distension

Question 10

Pacemakers of the GIT are present in all, EXCEPT:

Accepted Answer

Cardiac end of stomach

Answer

Pyloric end of stomach

Answer

Small intestine

Answer

Large intestine

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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