Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 561: Which of the following is a major synthetic function of the liver?

A. Bile production
B. Hormone regulation
C. Detoxification
D. Protein synthesis (Correct Answer)

Explanation: ***Protein synthesis*** - The liver is the central organ for synthesizing crucial **plasma proteins**, including **albumin** (maintains oncotic pressure), **coagulation factors** (II, VII, IX, X), and various **transport proteins**. - Albumin constitutes approximately 60% of total plasma protein and is exclusively synthesized by hepatocytes. - Loss of hepatic synthetic function leads to **hypoalbuminemia** and **coagulopathy**, which are key indicators of liver failure. *Bile production* - While the liver produces **500-1000 mL of bile daily**, this is primarily a **secretory and excretory function** rather than a synthetic one. - Bile contains bile salts, cholesterol, phospholipids, and bilirubin for fat emulsification and waste excretion. *Hormone regulation* - The liver metabolizes hormones such as **insulin**, **thyroid hormones**, and **steroid hormones** but does not primarily synthesize them. - This represents a **metabolic and regulatory function** rather than a synthetic function. *Detoxification* - The liver detoxifies drugs and toxins through **Phase I (cytochrome P450)** and **Phase II (conjugation)** reactions. - This is a **metabolic function** involving biotransformation rather than synthesis of new functional proteins.

Question 562: Which of the following most significantly increases gastric motility?

A. Distension of stomach (Correct Answer)
B. Tryptophan in duodenum
C. Fatty food in stomach
D. Acid in duodenum

Explanation: ***Distension of stomach*** - **Stomach distension** activates stretch receptors (mechanoreceptors), leading to increased gastric motility and gastric emptying via **vagovagal reflexes** and local enteric nervous system responses. - The distension triggers both **extrinsic reflexes** (vagal afferents to the brainstem and back via vagal efferents) and **intrinsic reflexes** (local enteric nervous system), which increase the force and frequency of gastric contractions. *Acid in duodenum* - The presence of **acid in the duodenum** triggers the release of **secretin**, which primarily inhibits gastric motility and acid secretion. - This mechanism ensures that the duodenal contents are adequately neutralized before more acidic chyme enters, protecting the duodenal lining. *Tryptophan in duodenum* - **Tryptophan** (an amino acid) and other amino acids/peptides in the duodenum primarily stimulate the release of **cholecystokinin (CCK)**, which slows gastric emptying. - CCK's primary role is to promote the digestion and absorption of fats and proteins by stimulating pancreatic enzyme secretion and gallbladder contraction. *Fatty food in stomach* - The presence of **fatty acids** in the stomach and particularly in the duodenum stimulates the release of **cholecystokinin (CCK)** and **gastric inhibitory peptide (GIP)**. - Both CCK and GIP act to **slow down gastric emptying** and motility, allowing more time for fat digestion and absorption in the small intestine.

Question 563: 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 564: Digestion of proteins is initiated by:

A. Amylase
B. Sucrase
C. Chymotrypsin
D. Pepsin (Correct Answer)

Explanation: ***Pepsin*** - **Pepsin** is the primary enzyme responsible for initiating **protein digestion** in the **stomach**. - It cleaves proteins into smaller polypeptides, functioning optimally in the highly **acidic environment** of the stomach. *Amylase* - **Amylase** is responsible for the digestion of **carbohydrates**, breaking down starch into simpler sugars. - It is found in both saliva (salivary amylase) and pancreatic secretions (pancreatic amylase), and does not act on proteins. *Sucrase* - **Sucrase** is an enzyme located in the **small intestine** and is responsible for breaking down the disaccharide **sucrose** into glucose and fructose. - It plays no role in protein digestion. *Chymotrypsin* - **Chymotrypsin** is a proteolytic enzyme secreted by the **pancreas** that acts in the **small intestine** to further digest polypeptides into smaller peptides. - While it digests proteins, it is not the *initiating* enzyme; protein digestion is already underway by the time chymotrypsin acts.

Question 565: What is the typical range of bile production per day in milliliters?

A. 0 - 500 mL
B. 500 - 1000 mL (Correct Answer)
C. 1000 - 1500 mL
D. 1500 - 2000 mL

Explanation: ***500 - 1000 mL*** - The liver typically produces between 0.5 to 1 liter (500-1000 mL) of **bile** per day to aid in the digestion and absorption of fats. - This production rate is sufficient to emulsify dietary lipids and excrete waste products effectively. *0 - 500 mL* - This range is generally considered **too low** for normal physiological bile production. - Insufficient bile production within this range would likely impair **fat digestion** and vitamin absorption. *1000 - 1500 mL* - While bile production can sometimes reach the lower end of this range in certain conditions, it is generally **higher than the typical daily average**. - Consistent production at this level might indicate increased metabolic activity or certain disease states rather than a normal baseline. *1500 - 2000 mL* - This range represents an **excessively high** amount of bile production, which is not typical for healthy individuals. - Such high volumes could be associated with specific pathological conditions or significant alterations in liver function.

Question 566: Through which of the following means of transport is folic acid absorbed in the proximal jejunum?

A. Facilitated diffusion
B. Both active and passive transport (Correct Answer)
C. Active transport
D. Passive transport

Explanation: ***Both active and passive transport*** - **Folic acid** absorption in the **proximal jejunum** occurs through **both active and passive mechanisms**. - At **low physiological concentrations**, an **active carrier-mediated transport** system is primarily responsible, while at **higher concentrations** (e.g., from supplements), **passive diffusion** also plays a significant role. *Facilitated diffusion* - While a type of passive transport, **facilitated diffusion** alone does not fully encompass the entirety of folic acid absorption, especially at low concentrations. - It relies on a **concentration gradient** and **carrier proteins** but does not require metabolic energy. *Active transport* - **Active transport** is crucial for absorbing folic acid when its concentration is low in the gut lumen. - This process requires **energy** and specific **carrier proteins**, like the **reduced folate carrier (RFC)**, to transport folate against a concentration gradient. *Passive transport* - **Passive transport**, specifically **simple diffusion**, contributes to folic acid absorption but primarily at **high lumen concentrations**, such as after taking large doses of supplements. - It occurs down a **concentration gradient** and does not require energy or specific carriers.

Question 567: What is the most important site for gastrin-producing cells?

A. Cardia
B. Fundus
C. Antrum (Correct Answer)
D. Duodenum

Explanation: ***Antrum*** - The **G cells**, which produce gastrin, are most concentrated in the gastric **antrum**. - **Gastrin** plays a crucial role in stimulating parietal cells to secrete hydrochloric acid and promoting gastric motility. *Cardia* - The cardia is the entry point of the esophagus into the stomach and contains mostly **mucus-secreting cells** for protection against reflux. - It has a minimal number of gastrin-producing G cells compared to the antrum. *Fundus* - The **fundus** is primarily responsible for storing food and contains abundant parietal cells for **acid secretion** and chief cells for **pepsinogen production**. - While it does contain some endocrine cells, it is not the main site for gastrin production. *Duodenum* - The **duodenum** contains some G cells, but they are less abundant than in the gastric antrum. - Its primary role is digestion and absorption, with major secretions including **cholecystokinin** and **secretin**.

Question 568: Which of the following is least important in the maintenance of normal fecal continence?

A. Anorectal angulation
B. Rectal innervation
C. Internal sphincter
D. Haustral valve (Correct Answer)

Explanation: **Haustral valve** - The **haustral valve** (or redundant mucosal folds within the haustra) primarily functions to *increase surface area* for water absorption and slow the passage of contents through the colon. - While critical for digestive function, it plays a *negligible direct role* in the mechanisms preventing involuntary stool leakage. *Anorectal angulation* - The **anorectal angle**, formed by the pull of the **puborectalis muscle**, creates a sharp bend that acts as a flap valve, significantly contributing to continence. - Loss of this angle (e.g., due to injury or structural changes) substantially impairs continence. *Rectal innervation* - **Intact innervation** of the rectum provides crucial sensory feedback regarding rectal distension and stool consistency, allowing for conscious control of defecation. - It also mediates the **rectoanal inhibitory reflex** and the ability to voluntarily contract external anal sphincters, both vital for continence. *Internal sphincter* - The **internal anal sphincter** is an *involuntary smooth muscle* responsible for approximately 70-80% of the resting anal tone, providing continuous passive continence. - Damage to this sphincter leads to substantial impairment in continence, particularly against flatus and liquid stool.

Question 569: Glucose is primarily absorbed from which part of the small intestine?

A. Proximal part of the small intestine (Correct Answer)
B. Distal part of the small intestine
C. Cecum
D. Colon

Explanation: ***Proximal part of the small intestine*** - The majority of nutrient absorption, including **glucose**, occurs in the **duodenum** and **jejunum**, which constitute the proximal small intestine. - Glucose absorption mechanisms, such as **SGLT1** and **GLUT2** transporters, are highly concentrated and active in this region. - This is where the surface area is maximized with villi and microvilli for optimal absorption. *Distal part of the small intestine* - The **ileum**, which is the distal part, is primarily responsible for absorbing **vitamin B12** and **bile salts**, not the bulk of glucose. - While some minimal glucose absorption might occur, it is not the primary site. *Cecum* - The cecum is the beginning of the **large intestine** and is involved in **water** and **electrolyte** absorption and microbial fermentation. - It is not involved in significant nutrient absorption like glucose. *Colon* - The colon is part of the **large intestine** and primarily absorbs **water** and **electrolytes**. - By the time contents reach the colon, virtually all glucose has already been absorbed in the small intestine.

Question 570: Which of the following is the PRIMARY mechanism that prevents gastroesophageal reflux?

A. Mucosal folds at gastroesophageal junction
B. Angle made by the oesophagus with stomach
C. Circular muscle fibres of GE sphincter (Correct Answer)
D. Looping fibres of crus of diaphragm

Explanation: ***Circular muscle fibres of GE sphincter*** - The **lower esophageal sphincter (LES)**, primarily composed of **circular smooth muscle**, is the main physiological barrier preventing reflux. - Its tonic contraction maintains a higher pressure in the distal esophagus than in the stomach, effectively **blocking retrograde flow** of gastric contents. *Looping fibres of crus of diaphragm* - The **right crus of the diaphragm** forms a sling around the gastroesophageal junction, providing an **extrinsic compressive force**. - While it contributes to the anti-reflux barrier, it is secondary to the intrinsic tone of the LES. *Mucosal folds at gastroesophageal junction* - These folds might act as a **flap valve** under certain conditions, but their contribution to preventing reflux is generally considered minor. - They are not the primary anatomical or physiological mechanism for reflux prevention. *Angle made by the oesophagus with stomach* - The acute angle (angle of His) between the esophagus and the gastric fundus creates a **flap-valve mechanism**, especially during increased intra-abdominal pressure. - This anatomical arrangement aids in preventing reflux but is a supportive mechanism, not the primary Sphincter.

Practice by Chapter

Gastrointestinal Motility

Practice Questions

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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