Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 521: Pepsinogen is activated by?

A. H+ (Correct Answer)
B. Gastrin
C. Enterokinase
D. Trypsin

Explanation: ***H+*** - **Pepsinogen**, a zymogen, is activated by the **acidic environment** created by the secretion of **hydrochloric acid (H+)** in the stomach. - The H+ ions cause a conformational change in pepsinogen, leading to the autocatalytic cleavage of a small peptide segment, forming the active enzyme **pepsin**. *Enterokinase* - **Enterokinase** is an enzyme found in the brush border of the small intestine that activates **trypsinogen to trypsin**. - It plays a crucial role in the activation of pancreatic proteases, not gastric pepsinogen. *Gastrin* - **Gastrin** is a hormone that stimulates the secretion of **hydrochloric acid (HCl)** and pepsinogen by the stomach's parietal and chief cells, respectively. - While it *promotes* the conditions for pepsinogen activation, it does not directly activate pepsinogen itself. *Trypsin* - **Trypsin** is a protease found in the small intestine, formed from **trypsinogen** through the action of enterokinase. - Its primary role is to digest proteins and activate other pancreatic zymogens, not gastric pepsinogen.

Question 522: Tone of lower esophageal sphincter is increased by?

A. Acetylcholine (Correct Answer)
B. Nitric Oxide
C. Norepinephrine
D. Vasoactive Intestinal Peptide

Explanation: ***Acetylcholine*** - **Acetylcholine** is the **primary excitatory neurotransmitter** that **increases the tone** of the lower esophageal sphincter (LES) by binding to muscarinic (M3) receptors on smooth muscle cells. - Increased LES tone prevents the reflux of gastric contents into the esophagus. - This is the **main mechanism** for maintaining basal LES tone. *Nitric Oxide* - **Nitric oxide** is a potent **inhibitory neurotransmitter** that causes **relaxation** of the LES. - Its release is crucial during swallowing to allow the passage of food into the stomach. *Norepinephrine* - **Norepinephrine** has dual effects on the LES depending on receptor type: - **Alpha-adrenergic receptors**: Cause **contraction** and increased tone (predominant effect) - **Beta-adrenergic receptors**: Cause relaxation and decreased tone - While it can increase LES tone via alpha receptors, **acetylcholine remains the primary neurotransmitter** responsible for maintaining basal LES tone. *Vasoactive Intestinal Peptide* - **Vasoactive Intestinal Peptide (VIP)** is an **inhibitory neurotransmitter** that acts to **relax** the LES. - It works synergistically with nitric oxide to facilitate LES relaxation during swallowing.

Question 523: Which of the following is passively absorbed in gut?

A. Glucose
B. Lipids (Correct Answer)
C. Fructose
D. Amino acids

Explanation: ***Lipids*** - **Short-chain fatty acids** and **diglycerides** can be directly absorbed into epithelial cells via **passive diffusion** due to their lipid solubility. - **Micelles**, formed from longer-chain fatty acids and monoglycerides, diffuse across the unstirred water layer and release their contents, allowing these products to passively diffuse across the cell membrane. *Glucose* - **Glucose absorption** in the gut primarily occurs via **active transport** mechanisms, specifically the **SGLT1 transporter** (Na+-glucose cotransporter) and **GLUT2 transporter**. - While GLUT2 can facilitate some passive diffusion at very high concentrations, it is mainly involved in facilitated diffusion and overall glucose absorption is energy-dependent. *Fructose* - **Fructose absorption** primarily occurs through **facilitated diffusion** via the **GLUT5 transporter** in the small intestine. - This process is still a form of passive transport, but it requires a carrier protein and is not simple diffusion, making it distinct from the direct passive absorption of lipids. *Amino-acids* - **Amino acid absorption** predominantly involves **active transport systems** that are specific for different groups of amino acids (e.g., neutral, basic, acidic). - These transporters require energy (often co-transport with sodium) to move amino acids against their concentration gradient into intestinal cells.

Question 524: What is the average amount of gastric juice secreted by the human stomach in a day?

A. 500-1000 ml
B. 1000-1500 ml
C. 2000-2500 ml (Correct Answer)
D. 3000-3500 ml

Explanation: ***2000-2500 ml*** - The human stomach typically secretes a significant volume of gastric juice daily to facilitate **digestion**. - This range represents the average output of fluids like **hydrochloric acid, enzymes, and mucus** under normal physiological conditions. *500-1000 ml* - This volume is significantly **lower** than the typical daily gastric juice production. - Such a low secretion might indicate **hypochlorhydria** or other gastrointestinal issues. *1000-1500 ml* - While a considerable amount, this range is still generally **below the average** daily secretion for a healthy adult. - It does not account for the high demands of continuous digestion throughout the day. *3000-3500 ml* - This volume is generally **higher** than the average daily gastric juice production. - Secretion at this level might suggest conditions like **Zollinger-Ellison syndrome**, characterized by excessive acid production.

Question 525: What is the reflex in which there is inhibition of gastric emptying when there is acid and hypertonic solution in the duodenum?

A. Enterogastric (Correct Answer)
B. Gastroileal
C. Gastrocolic
D. Myenteric

Explanation: ***Enterogastric*** - The **enterogastric reflex** is initiated when the duodenum detects the presence of acid and hypertonic solutions, signifying that the chyme is not yet ready for further digestion and absorption. - This reflex inhibits **gastric emptying** to allow more time for the stomach to process its contents and for the duodenum to neutralize the acid and dilute the hypertonic solution. *Gastroileal* - The **gastroileal reflex** increases motility in the ileum when the stomach is distended, facilitating the movement of chyme into the large intestine. - This reflex does not primarily involve the inhibition of gastric emptying due to duodenal contents. *Gastrocolic* - The **gastrocolic reflex** increases the motility of the colon in response to the stretching of the stomach by food. - Its main function is to prepare the large intestine for upcoming chyme and does not directly inhibit gastric emptying. *Myenteric* - The **myenteric plexus** (Auerbach's plexus) is a network of neurons located between the longitudinal and circular layers of the muscularis propria throughout the gastrointestinal tract. - While it plays a crucial role in controlling gut motility and is involved in numerous reflexes, it refers to a neural plexus rather than a specific reflex mechanism for inhibiting gastric emptying due to duodenal stimuli.

Question 526: Vitamin D absorption is decreased by ?

A. Proteins
B. Acid
C. Lactose
D. Fat malabsorption (Correct Answer)

Explanation: ***Fat malabsorption*** - **Vitamin D** is a **fat-soluble vitamin**, meaning it requires dietary fat for proper absorption in the small intestine. - Conditions causing **fat malabsorption**, such as **cystic fibrosis**, **celiac disease**, or **pancreatic insufficiency**, significantly reduce the uptake of vitamin D. *Proteins* - **Proteins** do not directly decrease vitamin D absorption; in fact, some dietary proteins can enhance vitamin D binding and transport in the bloodstream. - Their primary role is in structural and enzymatic functions, not impeding fat-soluble vitamin uptake. *Acid* - **Gastric acid** is important for the absorption of some nutrients, but it generally does not directly hinder the absorption of **fat-soluble vitamins** like vitamin D. - Conditions like **achlorhydria** primarily affect the absorption of minerals and vitamin B12, rather than vitamin D. *Lactose* - **Lactose** is a sugar found in milk, and its malabsorption (lactose intolerance) primarily causes gastrointestinal symptoms like bloating and diarrhea. - It does not directly interfere with the absorption of **fat-soluble vitamins**; rather, it affects carbohydrate digestion.

Question 527: Secretion of bile out of hepatocytes occurs via?

A. Passive diffusion
B. Facilitated diffusion
C. Osmosis
D. Active transport (Correct Answer)

Explanation: ***Active transport*** - Bile secretion by hepatocytes is an **energy-dependent process** against concentration gradients, requiring specific transporter proteins. - This active mechanism ensures efficient bile flow and prevents reflux, crucial for processes like **fat digestion and absorption**. *Passive diffusion* - **Passive diffusion** involves substances moving down their concentration gradient without energy expenditure. - Bile components, like bile salts, are highly concentrated within hepatocytes and need to be moved against this gradient. *Facilitated diffusion* - This type of diffusion utilizes **transmembrane proteins** to move substances down their concentration gradient, but still does not directly consume ATP. - Bile components are often transported against their concentration gradient, which is not facilitated diffusion. *Osmosis* - **Osmosis** specifically refers to the movement of water across a semipermeable membrane from a region of higher water concentration to a region of lower water concentration. - While water is a component of bile, the primary mechanism of moving bile solutes out of the hepatocyte is not osmosis.

Question 528: 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 529: Lower esophageal sphincter pressure is increased by all of the following substances, EXCEPT:

A. Motilin
B. Gastrin
C. Substance P
D. Secretin (Correct Answer)

Explanation: ***Secretin*** - **Secretin** is a gastrointestinal hormone that *decreases* lower esophageal sphincter (LES) pressure - This hormone is released from S cells in the duodenum in response to acidic chyme - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** to neutralize acidic chyme entering the duodenum - By decreasing LES pressure, it facilitates the passage of gastric contents into the duodenum during digestion *Gastrin* - **Gastrin** is a hormone that *increases* lower esophageal sphincter (LES) pressure - This helps prevent gastroesophageal reflux when the stomach is distended - It also stimulates the secretion of **gastric acid** by parietal cells in the stomach - Released from G cells in the gastric antrum in response to protein ingestion *Motilin* - **Motilin** is a peptide hormone that *increases* lower esophageal sphincter (LES) pressure - It initiates the **migrating motor complex (MMC)** during the interdigestive period - Stimulates gastric and intestinal motility - Released from M cells in the duodenum and jejunum *Substance P* - **Substance P** is a neuropeptide that *increases* lower esophageal sphincter (LES) pressure - Functions as both a neurotransmitter and neuromodulator in the enteric nervous system - Plays a role in **smooth muscle contraction** and gastrointestinal motility - Also involved in pain transmission and inflammatory responses

Question 530: 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.

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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