Gastrointestinal Secretions — MCQs
Rebound increase in gastric acid secretion after stopping proton pump inhibitor therapy is due to?
Bilirubin conjugation with glucuronic acid has the following properties -
Cholecystokinin is produced from:
All of the following are features of Zollinger Ellison syndrome except:
Which of the following inhibits gastrin secretion?
What is the effect of cholecystokinin on the gastrointestinal tract?
Which cells are referred to as "Pacemaker cells" with relation to "BER"?
What is the primary function of the myenteric plexus?
Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
From which part of the gastrointestinal tract is glucose absorbed?
Gastrointestinal Secretions Indian Medical PG Practice Questions and MCQs
Question 1: Rebound increase in gastric acid secretion after stopping proton pump inhibitor therapy is due to?
- A. Parietal cell hyperplasia
- B. Increased histamine release
- C. Hypergastrinemia (Correct Answer)
- D. Hypersensitivity of Ach receptors
Explanation: ***Hypergastrinemia*** - Proton pump inhibitors (PPIs) create a state of **hypochlorhydria** (reduced stomach acid), which in turn stimulates the **G cells** in the stomach to produce more **gastrin**. - This elevated gastrin level leads to a compensatory increase in the number and activity of **parietal cells**, causing a rebound hypersecretion of acid when PPI therapy is discontinued. *Parietal cell hyperplasia* - While parietal cell hyperplasia can occur, it is a consequence of chronic **hypergastrinemia**, not the primary driver of rebound acid secretion. - The direct effect of increased gastrin stimulating existing parietal cells is more immediate and significant for the rebound phenomenon. *Increased histamine release* - Elevated histamine release from **enterochromaffin-like (ECL) cells** is a downstream effect of hypergastrinemia, as gastrin stimulates ECL cells. - While increased histamine contributes to acid secretion, the root cause for its increase in this context is the **hypergastrinemia** induced by PPIs. *Hypersensitivity of Ach receptors* - **Acetylcholine (Ach) receptors** on parietal cells are involved in direct neural stimulation of acid secretion. - There is no evidence that stopping PPIs causes an increased sensitivity of these receptors, or that this is the primary mechanism of rebound acid secretion.
Question 2: Bilirubin conjugation with glucuronic acid has the following properties -
- A. Hydrophilic to hydrophobic
- B. Able to cross cell membrane
- C. Lipid soluble
- D. Hydrophobic to hydrophilic (Correct Answer)
Explanation: ***Hydrophobic to hydrophilic*** - Conjugation with glucuronic acid makes **bilirubin more water-soluble (hydrophilic)**, allowing it to be excreted in bile and urine. - **Unconjugated bilirubin** is hydrophobic and tightly bound to albumin in the bloodstream. *Hydrophilic to hydrophobic* - This statement is incorrect as conjugation aims to make bilirubin **more polar and water-soluble**, not less. - Converting a hydrophilic substance to hydrophobic would hinder its excretion. *Able to cross cell membrane* - **Conjugated bilirubin** is less able to cross cell membranes because of its increased polarity, and it is actively transported across cell membranes via specific transporters. - **Unconjugated bilirubin** can cross cell membranes, especially in the brain, leading to neurotoxicity (kernicterus). *Lipid soluble* - This describes **unconjugated bilirubin**, which is lipid-soluble and can cross cell membranes. - **Conjugation with glucuronic acid** specifically reduces lipid solubility, making it water-soluble for excretion.
Question 3: Cholecystokinin is produced from:
- A. Hepatocyte
- B. Gastric mucosa
- C. Duodenal mucosa (Correct Answer)
- D. Epithelial cells of distal common bile duct
Explanation: ***Duodenal mucosa*** - **Cholecystokinin (CCK)** is primarily secreted by **I cells**, which are specialized enteroendocrine cells located in the **mucosa of the duodenum** and jejunum. - The release of CCK is stimulated by the presence of **fatty acids** and **amino acids** in the small intestine. *Hepatocyte* - **Hepatocytes** are the main functional cells of the liver, responsible for bile production, metabolism, and detoxification. - They **do not produce regulatory hormones** like cholecystokinin. *Gastric mucosa* - The **gastric mucosa** primarily produces **gastrin**, hydrochloric acid, and pepsinogen, which are involved in gastric digestion. - It does **not secrete cholecystokinin**, which is involved in stimulating gallbladder contraction and pancreatic enzyme release. *Epithelial cells of distal common bile duct* - The **epithelial cells of the common bile duct** are involved in bile transport and modification, but **not in hormone production**. - Their primary role is to line the duct and contribute to the composition of bile.
Question 4: All of the following are features of Zollinger Ellison syndrome except:
- A. Severe diarrhoea
- B. Beta cell tumours of the pancreas (Correct Answer)
- C. Very high acid output
- D. Intractable peptic ulcers
Explanation: ***Beta cell tumours of the pancreas*** - Zollinger-Ellison syndrome (ZES) is caused by **gastrinomas**, which are **neuroendocrine tumors** that typically arise from the **gastrin-producing G cells**, not the insulin-producing beta cells, of the pancreas or duodenum. - While pancreatic tumors are common in ZES, they are specifically **gastrinomas**, leading to excessive gastrin secretion. *Severe diarrhoea* - This is a common feature of ZES resulting from the **high acid output** reaching the small intestine. - The excessive acid inactivates pancreatic lipase, leading to **maldigestion** and stimulates fluid and electrolyte secretion, causing secretory diarrhea. *Very high acid output* - ZES is characterized by the **overproduction of gastrin**, which stimulates the parietal cells of the stomach to secrete large amounts of **hydrochloric acid**. - This leads to a significantly **increased basal and maximal acid output** in the stomach. *Intractable peptic ulcers* - The extremely high gastric acid secretion in ZES causes **multiple, recurrent, and often refractory peptic ulcers**, which can be located in atypical sites such as the jejunum. - These ulcers are typically difficult to treat with standard anti-ulcer medications due to the persistent gastric hypersecretion.
Question 5: Which of the following inhibits gastrin secretion?
- A. Intrinsic factor
- B. Histamine
- C. Gastrin
- D. Somatostatin (Correct Answer)
Explanation: ***Somatostatin*** - **Somatostatin** is a potent **inhibitor** of gastrin secretion, acting directly on **G cells** in the stomach via paracrine mechanisms. - It also reduces the secretion of other gastrointestinal hormones and **gastric acid**. - Somatostatin release is stimulated by **low gastric pH**, forming part of the negative feedback mechanism that regulates gastrin secretion. *Intrinsic factor* - **Intrinsic factor** is a glycoprotein essential for the absorption of **vitamin B12** in the small intestine. - It does not have a direct role in regulating the secretion of **gastrin**. *Histamine* - **Histamine** stimulates gastric acid secretion from **parietal cells** by binding to H2 receptors. - It does **not inhibit** gastrin secretion; histamine acts downstream of gastrin in the acid secretion pathway. - Histamine is released from **ECL cells** in response to gastrin stimulation. *Gastrin* - **Gastrin** is a hormone that **stimulates gastric acid secretion** from parietal cells. - Gastrin does not inhibit its own secretion; instead, it undergoes **negative feedback** regulation when the gastric pH drops below 3. - Low pH stimulates **somatostatin** release, which then inhibits further gastrin secretion.
Question 6: What is the effect of cholecystokinin on the gastrointestinal tract?
- A. Increases gastric acid secretion
- B. Increases gastric motility
- C. Relaxes gall bladder
- D. Increases small intestinal peristalsis (Correct Answer)
Explanation: ***Increases small intestinal peristalsis*** - **Cholecystokinin (CCK)** is released in response to fat and protein in the duodenum and plays a significant role in **digestion and absorption**. - One of its key functions is to enhance **small intestinal motility**, facilitating the mixing and propulsion of chyme for efficient digestion and nutrient absorption. *Increases gastric acid secretion* - **Gastrin** is the primary hormone responsible for increasing **gastric acid secretion**, stimulated by protein and amino acids in the stomach. - While CCK shares structural similarities with gastrin, its predominant effect on gastric acid is typically inhibitory, especially at physiological concentrations, to allow for intestinal processing. *Increases gastric motility* - CCK generally has an **inhibitory effect on gastric emptying and motility**, helping to slow down the rate at which food leaves the stomach. - This allows adequate time for the small intestine to process the incoming chyme, particularly rich in fats, by coordinating with **pancreatic enzyme** and **bile release**. *Relaxes gall bladder* - CCK is known for its potent ability to **contract the gallbladder**, leading to the expulsion of bile into the duodenum. - This action is crucial for **emulsifying dietary fats** and aiding in their digestion and absorption.
Question 7: Which cells are referred to as "Pacemaker cells" with relation to "BER"?
- A. SA node
- B. AV node
- C. Interstitial cells of Cajal (Correct Answer)
- D. Pyramidal cells
Explanation: ***Interstitial cells of Cajal*** - The **Interstitial cells of Cajal (ICC)** are specialized cells in the gastrointestinal tract that act as the **pacemaker cells** for the **Basic Electrical Rhythm (BER)**. - They generate slow waves of **depolarization** and **repolarization**, which determine the frequency and rhythm of smooth muscle contractions. *SA node* - The **sinoatrial (SA) node** is the natural pacemaker of the **heart**, initiating the cardiac electrical impulse. - It controls the heart rate, not the **BER** of the gastrointestinal tract. *AV node* - The **atrioventricular (AV) node** is part of the heart's electrical conduction system, responsible for delaying and transmitting impulses from the atria to the ventricles. - It does not regulate the **BER** of the gastrointestinal system. *Pyramidal cells* - **Pyramidal cells** are a type of neuron found in various parts of the brain, particularly the cerebral cortex and hippocampus. - They are involved in cognitive functions and motor control, and have no role in generating the **BER** in the gut.
Question 8: What is the primary function of the myenteric plexus?
- A. Regulating GI secretion
- B. Regulating local blood flow
- C. Regulating motility (Correct Answer)
- D. Regulating absorption
Explanation: ***Regulating motility*** - The myenteric plexus, also known as **Auerbach's plexus**, is primarily responsible for coordinating the **rhythmic contractions** and **relaxation of the gastrointestinal (GI) smooth muscle**. - Its strategic location between the **longitudinal and circular muscle layers** allows it to directly influence the strength and frequency of peristalsis, thus regulating the movement of food through the digestive tract. *Regulating GI secretion* - While it has some indirect influence, the **submucosal plexus** (Meissner's plexus) is the primary neural network regulating **secretory functions** of the GI tract. - The myenteric plexus's main role is more directly related to muscle contraction and relaxation rather than glandular secretion. *Regulating local blood flow* - Local blood flow in the GI tract is primarily regulated by the **sympathetic and parasympathetic nervous systems**, along with local metabolic factors and hormones. - The myenteric plexus has a minimal direct role in the control of **GI blood vessel smooth muscle**. *Regulating absorption* - Absorption is primarily a function of the **intestinal epithelial cells** and is regulated by various transport mechanisms, hormones, and local factors. - While the enteric nervous system influences mucosal function indirectly, the myenteric plexus's primary role is **motor control** rather than directly regulating nutrient absorption processes.
Question 9: Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
- A. Disaccharides
- B. Polysaccharides
- C. Monosaccharides (Correct Answer)
- D. 5-carbon sugars
Explanation: ***Monosaccharides*** - **Monosaccharides**, like glucose and fructose, are the simplest forms of carbohydrates and do not require further digestion. - They are directly absorbed into the bloodstream from the intestinal lumen via specific **transporters** on the enterocyte membrane. *Disaccharides* - **Disaccharides**, such as sucrose and lactose, must first be broken down into their constituent monosaccharides by **brush border enzymes** (e.g., lactase, sucrase) before absorption can occur. - This additional enzymatic step makes their absorption less efficient than that of monosaccharides. *Polysaccharides* - **Polysaccharides**, including starch and glycogen, are complex carbohydrates requiring extensive digestion by enzymes like **amylase** in the mouth and small intestine. - This multi-step breakdown into monosaccharides is the least efficient process and takes the longest time. *5-carbon sugars* - While 5-carbon sugars (**pentoses**) like ribose and deoxyribose are monosaccharides and can be absorbed, they are not a primary energy source in the diet and are not absorbed as efficiently or in as large quantities as the metabolically more significant 6-carbon monosaccharides (hexoses like glucose). - The question asks which *type* of carbohydrate is most efficiently absorbed, and **monosaccharides** as a general category (including 6-carbon sugars) are the most efficient.
Question 10: From which part of the gastrointestinal tract is glucose absorbed?
- A. Stomach
- B. Colon
- C. Duodenum and jejunum (Correct Answer)
- D. Ileum
Explanation: ***Duodenum and jejunum*** - The **duodenum** and **jejunum** are the primary sites for nutrient absorption in the small intestine, including the majority of **glucose**. - Their large surface area, due to **villi** and **microvilli**, and abundant transport mechanisms facilitate efficient glucose uptake. *Stomach* - The stomach's primary role is **digestion**, particularly of proteins, with very little absorption of nutrients. - While some small, lipid-soluble substances like alcohol can be absorbed, significant **glucose absorption does not occur** here. *Ileum* - The **ileum** is mainly responsible for the absorption of **vitamin B12** and **bile salts**. - Although some remaining nutrients might be absorbed, the bulk of **glucose absorption** is completed in the upstream **duodenum and jejunum**. *Colon* - The **colon's** main functions are **water and electrolyte absorption** and the formation of feces. - It does not play a significant role in the absorption of **glucose** or other macro-nutrients.
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