Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 571: What is the physiological reflex responsible for post-meal defecation in children?

A. Gastro colic reflex (Correct Answer)
B. Gastro gastric reflex
C. Vasovagal reflex
D. Colonoileal reflex

Explanation: ***Gastro colic reflex*** - This reflex is a **physiological response** to stomach distention by food, leading to increased motility in the **colon**. - It explains why bowel movements, especially in infants and young children, often occur shortly **after eating**. *Gastro gastric reflex* - This reflex primarily involves communication **between different parts of the stomach**, controlling gastric motility and emptying. - It does not directly induce colonic contractions or defecation after a meal. *Vasovagal reflex* - The vasovagal reflex is a systemic response involving the **vagus nerve** that can cause a drop in heart rate and blood pressure, leading to fainting. - While it can be triggered by various stimuli, it is not the mechanism responsible for post-meal defecation. *Colonoileal reflex* - This reflex occurs when the colon is distended, slowing the movement of chyme from the **ileum into the colon**. - Its primary function is to prevent overloading the colon, not to stimulate post-meal defecation.

Question 572: All of the following have an inhibitory effect on the secretion of gastric acid, except:

A. VIP
B. Glucagon
C. Epinephrine (Correct Answer)
D. Acid in duodenum

Explanation: ***Epinephrine*** - **Epinephrine** primarily affects the cardiovascular system, respiratory system, and metabolism, preparing the body for "fight or flight." - It does not have a direct inhibitory effect on gastric acid secretion; rather, sympathetic activation can generally *reduce* overall gastrointestinal activity, but epinephrine itself isn't a direct inhibitor of acid secretion in the way other listed options are. *Acid in duodenum* - The presence of **acid in the duodenum** stimulates the release of **secretin** and **cholecystokinin (CCK)**, which in turn inhibit gastric acid secretion. - This is a crucial feedback mechanism preventing further acid entry into the duodenum until it is neutralized. *VIP* - **Vasoactive intestinal peptide (VIP)** is a neuropeptide that has a relaxant effect on gastrointestinal smooth muscle and inhibits gastric acid secretion. - It also stimulates **bicarbonate secretion** and can increase blood flow to the gut. *Glucagon* - **Glucagon**, an important metabolic hormone, is known to inhibit gastric acid secretion, particularly when administered exogenously. - While its primary role is in glucose homeostasis, it also has effects on gastrointestinal motility and secretion.

Question 573: 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 574: Which secretion is directly stimulated by histamine?

A. Gastrin secretion in the stomach
B. Secretion of HCl in the stomach (Correct Answer)
C. Secretion of amylase by salivary glands
D. Secretion of pancreatic enzymes

Explanation: **Secretion of HCl in the stomach** - **Histamine**, released from enterochromaffin-like (ECL) cells, acts on **H2 receptors** on **parietal cells** in the stomach. - This binding directly stimulates the parietal cells to secrete **hydrochloric acid (HCl)** into the gastric lumen. *Gastrin secretion in the stomach* - **Gastrin** is a hormone that stimulates **histamine release** from ECL cells and acts directly on parietal cells to stimulate HCl secretion. - Histamine is a downstream mediator of gastrin's action on parietal cells, not a direct stimulus for gastrin secretion itself. *Secretion of amylase by salivary glands* - **Amylase secretion** from salivary glands is primarily regulated by the **autonomic nervous system**, particularly **parasympathetic stimulation**. - Histamine does not play a direct role in the regulation of salivary amylase secretion. *Secretion of pancreatic enzymes* - **Pancreatic enzyme secretion** is primarily regulated by **cholecystokinin (CCK)** and **secretin**, hormones released in response to chyme in the duodenum. - While histamine can stimulate some pancreatic fluid and bicarbonate secretion indirectly, it is not a direct or primary stimulator of pancreatic enzyme secretion.

Question 575: Which of the following hormones primarily inhibits gastric emptying?

A. Gastrin
B. Cholecystokinin (Correct Answer)
C. Secretin
D. Vasoactive intestinal peptide

Explanation: ***Cholecystokinin (CCK)*** - **CCK** is released in response to **fat and protein** in the duodenum. - It slows gastric emptying to allow sufficient time for digestion and absorption of nutrients in the small intestine. *Gastrin* - **Gastrin** is primarily involved in **stimulating gastric acid secretion** and promoting gastric motility. - Its main effect is to increase, rather than inhibit, gastric emptying. *Secretin* - **Secretin** is released in response to **acid in the duodenum**. - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** and inhibit gastric acid secretion, but its effect on gastric emptying is less pronounced compared to CCK. *Vasoactive intestinal peptide (VIP)* - **VIP** functions as a **neurotransmitter** and hormone that causes **vasodilation**, relaxes smooth muscle, and inhibits gastric acid secretion. - While it can affect gut motility, its primary role is not the direct and significant inhibition of gastric emptying to the extent of CCK.

Question 576: Gastric acid secretion is stimulated during several phases associated with the ingestion and digestion of a meal. Which phase is primarily responsible for the majority of acid secretion?

A. Cephalic
B. Gastric (Correct Answer)
C. Intestinal
D. Interdigestive

Explanation: ***Gastric*** - The **gastric phase** is initiated by the presence of food in the stomach, leading to stomach distension and the presence of digested proteins and amino acids. - This phase accounts for approximately **60-70%** of total acid secretion, driven by local reflexes, vagovagal reflexes, and the release of gastrin. *Cephalic* - The **cephalic phase** is triggered by the **sight, smell, thought, or taste of food**, and accounts for about 20-30% of acid secretion. - It is mediated primarily by the **vagus nerve**, leading to the release of acetylcholine and gastrin. *Interdigestive* - The **interdigestive phase** refers to the period between meals when the stomach is empty. - During this phase, **basal acid secretion** is low and follows a circadian rhythm, primarily regulated by vagal tone and circulating gastrin. *Intestinal* - The **intestinal phase** begins once the chyme enters the small intestine and primarily functions to **inhibit** further gastric acid secretion. - While some stimulation can occur, inhibitory mechanisms, such as those from secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP), dominate to regulate gastric emptying and acid production.

Question 577: What factor delays gastric emptying?

A. Distension of stomach
B. Gastrin
C. Acid in duodenum (Correct Answer)
D. Vagal stimulation

Explanation: ***Acid in duodenum*** - The presence of **acid in the duodenum** stimulates the release of hormones like **secretin** and **cholecystokinin (CCK)**, which overall inhibit gastric motility and emptying to allow for neutralization and digestion. - This is a crucial feedback mechanism to protect the **duodenal mucosa** from acid damage and optimize nutrient absorption. *Distension of stomach* - **Stomach distension** generally *promotes* gastric emptying by activating stretch receptors that stimulate both local reflexes and vagal afferents, leading to increased gastric motility. - This reflex helps move food into the duodenum once the stomach has been filled sufficiently. *Gastrin* - **Gastrin** is a hormone primarily secreted in response to protein in the stomach and vagal stimulation; its main role is to *increase* gastric acid secretion and *stimulate* gastric motility, thus generally promoting rather than delaying emptying. - While high concentrations of gastrin can inhibit emptying in some contexts, its primary physiological effect on motility is typically stimulatory. *Vagal stimulation* - **Vagal stimulation** (parasympathetic innervation) generally *enhances* gastric motility and secretions, thereby promoting gastric emptying. - The **vagus nerve** plays a significant role in the cephalic and gastric phases of digestion, preparing the stomach for food and facilitating its processing.

Question 578: Maldigestion of protein and fat is manifested in chronic pancreatitis only if the damage to pancreatic tissue exceeds?

A. 30%
B. 50%
C. 90% (Correct Answer)
D. 75%

Explanation: ***90%*** - **Maldigestion** of protein and fat in chronic pancreatitis typically occurs when there is extensive damage to the pancreatic tissue, specifically affecting more than **90%** of its functional capacity. - This threshold is critical because the pancreas has a significant reserve capacity for enzyme production, meaning a large portion must be damaged before **exocrine insufficiency** becomes clinically apparent. *30%* - Damage to only **30%** of pancreatic tissue is generally below the threshold for significant clinical manifestations of maldigestion. - The remaining **70%** of functional tissue can still adequately produce digestive enzymes to prevent widespread nutrient malabsorption. *50%* - While **50%** damage is substantial, it usually does not lead to overt clinical symptoms of maldigestion, particularly fat malabsorption (**steatorrhea**). - The body's compensatory mechanisms and the remaining functional pancreatic mass can still maintain relatively normal digestion at this stage. *75%* - Although **75%** damage represents significant pancreatic loss, it often does not fully manifest as severe maldigestion of protein and fat. - Significant **steatorrhea** and **protein malabsorption** typically require an even greater reduction in exocrine function.

Question 579: The primary hormone secreted by duodenal cells in response to dietary fats and proteins is:

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

Explanation: ***Correct Answer: CCK (Cholecystokinin)*** - **Cholecystokinin (CCK)** is primarily released from the **duodenal I-cells** in response to the presence of **fats and proteins** in the chyme entering the duodenum. - Its main functions include stimulating **gallbladder contraction** (releasing bile for fat emulsification) and **pancreatic enzyme secretion** (for nutrient digestion). *Incorrect: Secretin* - **Secretin** is primarily released in response to **acidic chyme** entering the duodenum, not directly by fats and proteins. - Its main roles are to stimulate the pancreas to release **bicarbonate-rich fluid** to neutralize gastric acid and to inhibit gastric acid secretion. *Incorrect: Gastrin* - **Gastrin** is secreted by **G-cells** in the stomach and duodenum, primarily in response to food (especially proteins) and vagal stimulation. - Its main function is to stimulate **gastric acid secretion** by parietal cells, not directly to dietary fats and proteins as a primary duodenal response. *Incorrect: Motilin* - **Motilin** is released from the small intestine during the **interdigestive period** (when fasting). - It plays a key role in initiating the **migrating motor complex (MMC)**, which sweeps undigested food and bacteria from the stomach and small intestine into the colon.

Question 580: What is the approximate total volume of saliva secreted daily by an adult?

A. 3-3.5 L
B. 2-2.5 L
C. 1-1.5 L (Correct Answer)
D. 0.75-1 L

Explanation: ***1-1.5 L*** - The **average daily saliva production** in healthy adults typically ranges from **1000 mL to 1500 mL** (1-1.5 liters). - This is the **standard physiological range** cited in major textbooks including **Guyton & Hall** and **Ganong's Review of Medical Physiology**. - This volume is essential for **digestion** (salivary amylase initiates carbohydrate breakdown), **oral hygiene** (antibacterial properties), **lubrication**, and **speech**. *0.75-1 L* - This range represents the **lower end** of normal salivary production. - While some individuals may produce this amount, it is **below the typical average** cited in standard physiology references. - This volume might be seen during periods of **reduced stimulation** or mild **dehydration**. *2-2.5 L* - This range represents a **significant overestimation** of normal daily saliva volume. - Such excessive production would be **beyond the physiological range** and could indicate **pathological hypersalivation** (sialorrhea). *3-3.5 L* - This volume is **substantially higher** than normal salivary secretion. - Production at this level would be indicative of a **pathological condition** such as **mercury poisoning**, **organophosphate toxicity**, or **severe neurological disorders** affecting salivary control.

Practice by Chapter

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Gastrointestinal Secretions

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Digestion and Absorption

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Pancreatic Exocrine Function

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Regulation of Food Intake

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