Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 551: Gastric secretions are essential for absorption of -

A. Cobalamin (Correct Answer)
B. Fat
C. Thiamine
D. Folic acid

Explanation: ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].

Question 552: Which of the following statements regarding the lower esophageal sphincter is TRUE?

A. It relaxes in response to swallowing. (Correct Answer)
B. It remains contracted during swallowing to prevent regurgitation.
C. Its tone is primarily influenced by the myogenic properties of the smooth muscle.
D. It contracts in response to gastric distension.

Explanation: ***It relaxes in response to swallowing.*** - The **lower esophageal sphincter (LES)** normally maintains high resting tone to prevent gastroesophageal reflux but **relaxes completely during swallowing** to allow passage of food into the stomach. - This relaxation (called **receptive relaxation**) is mediated by **vagal nerve stimulation** through release of nitric oxide (NO) and vasoactive intestinal peptide (VIP). - The relaxation occurs **before the peristaltic wave arrives**, allowing coordinated transit of the bolus. *It remains contracted during swallowing to prevent regurgitation.* - This is **incorrect** - the LES must **relax during swallowing** to allow food passage into the stomach. - Failure of LES relaxation during swallowing is the pathophysiology of **achalasia**, leading to dysphagia. - The LES only maintains contraction between swallows to prevent reflux. *Its tone is primarily influenced by the myogenic properties of the smooth muscle.* - While the LES contains smooth muscle with intrinsic myogenic properties, its tone is **predominantly regulated by neural and hormonal factors**. - **Neural control:** Vagal cholinergic pathways (increase tone), non-adrenergic non-cholinergic (NANC) pathways with NO and VIP (decrease tone). - **Hormonal factors:** Gastrin increases tone, while progesterone, CCK, and secretin decrease tone. *It contracts in response to gastric distension.* - This is **incorrect** - gastric distension actually triggers **transient LES relaxations (TLESRs)**, which are the primary mechanism of physiological reflux. - TLESRs are vagally mediated reflex responses that allow venting of gastric air. - Increased LES contraction in response to gastric distension would be counterproductive.

Question 553: Which of the following receptors are missing from the surface of the intestine?

A. Pressure
B. Touch
C. Temperature (Correct Answer)
D. Distension

Explanation: ***Temperature*** - The intestine lacks **thermoreceptors** for sensing temperature changes, as its internal environment is tightly regulated and not subject to external temperature fluctuations. - While it responds to extreme temperatures via **pain receptors**, specific temperature sensation is not a primary function. *Pressure* - The intestine contains **mechanoreceptors**, including pressure receptors, which are vital for sensing the presence of contents and modulating motility. - These receptors contribute to reflex actions like peristalsis in response to luminal pressure. *Touch* - The intestine has **mechanoreceptors** that respond to tactile stimulation or light touch, although this sensation is not consciously perceived in the same way as external touch. - These receptors play a role in sensing the movement of chyme and initiating local reflexes. *Distension* - **Stretch receptors** or **distension receptors** are abundant in the intestinal wall, sensing changes in luminal volume. - These receptors are crucial for triggering intrinsic and extrinsic reflexes that regulate motility, secretion, and absorption.

Question 554: Basal electrical rhythm of the gastrointestinal tract is produced by?

A. Meissner plexus
B. Interstitial cells of Cajal (Correct Answer)
C. Smooth muscle at cardiac end of stomach
D. Myenteric plexus

Explanation: ***Interstitial cells of cajal*** - These cells are modified smooth muscle cells that act as **pacemaker cells** in the gastrointestinal tract, generating the **slow waves** or basal electrical rhythm. - They are critically involved in the **initiation and coordination of peristalsis** and segmentation contractions. *Meissner plexus* - Also known as the **submucosal plexus**, it primarily controls **glandular secretions** and local blood flow in the gastrointestinal tract. - It does not directly generate the electrical rhythm for muscle contraction. *Myenteric plexus* - Also known as **Auerbach's plexus**, it is located between the longitudinal and circular muscle layers and primarily controls **gastrointestinal motility** (contractions). - While it modulates the activity, it does not originate the basal electrical rhythm itself; it acts upon the rhythmic activity generated by the interstitial cells of Cajal. *Smooth muscle at cardiac end of stomach* - The smooth muscle cells in this region are involved in contraction and relaxation to control the passage of food, but they do not act as the primary **pacemaker** for the entire GI tract rhythm. - The **interstitial cells of Cajal** are found throughout the GI tract and are responsible for the overall basal electrical rhythm.

Question 555: Enterogastric reflex is stimulated by all except:

A. Alkaline content of small intestine (Correct Answer)
B. Distension of duodenum
C. Hyperosmolarity of chyme
D. None of the options

Explanation: ***Alkaline content of small intestine*** - The **enterogastric reflex** is primarily stimulated by factors indicative of digestive activity in the duodenum, such as **acidic chyme** (low pH), high fat content, and hypertonicity. - An **alkaline environment** in the small intestine would typically inhibit the reflex, as it suggests efficient neutralization of gastric acid and thus less need to slow gastric emptying. *Hyperosmolarity of chyme* - **Hyperosmolarity** (e.g., from digested carbohydrates or proteins) in the small intestine is a strong stimulus for the enterogastric reflex. - This helps to slow down gastric emptying, allowing enough time for water to move into the intestinal lumen and equalize the osmotic pressure, preventing **dehydration** and promoting efficient digestion and absorption. *Distension of duodenum* - **Distension of the duodenum** by chyme is a direct mechanical stimulus for the enterogastric reflex. - This physical stretching of the duodenal wall indicates a sufficient amount of chyme has entered, signaling the stomach to slow down further emptying. *None of the options* - This option is incorrect because there is one option (alkaline content of small intestine) that does not stimulate the enterogastric reflex. - This reflex is crucial for coordinating gastric emptying with duodenal processing capacity.

Question 556: The maximum motility of the colon is seen in which part of the colon?

A. Ascending colon
B. Sigmoid colon (Correct Answer)
C. Transverse colon
D. Descending colon

Explanation: ***Sigmoid colon*** - The **sigmoid colon** exhibits the **maximum motility** among all colonic segments, characterized by high-amplitude propagating contractions (mass movements). - These powerful contractions efficiently propel fecal matter into the rectum, occurring several times daily with significant force. - The sigmoid acts as a **propulsive pump** with the strongest and most frequent muscular activity in the colon. *Ascending colon* - Exhibits the **slowest motility** among colonic segments, with predominantly mixing movements. - Primary function is **water and electrolyte absorption** rather than propulsion. - The slow motility facilitates the absorption process and allows chyme to be retained for adequate fluid extraction. *Transverse colon* - Demonstrates **intermediate motility** with both mixing and slow propulsive contractions. - Serves as a transition zone where continued **water absorption** occurs and chyme progressively solidifies. - Less active than the sigmoid but more active than the ascending colon. *Descending colon* - Has **moderate motility** with regular segmental contractions for propulsion. - Functions to transport formed stool toward the sigmoid colon. - While exhibiting coordinated contractions, its overall motility is less than that of the sigmoid colon.

Question 557: Which part of the gastrointestinal tract exhibits the highest frequency of peristaltic contractions?

A. Stomach
B. Ileum
C. Duodenum (Correct Answer)
D. Jejunum

Explanation: ***Correct Option: Duodenum*** - The **duodenum** has the highest frequency of peristaltic contractions in the gastrointestinal tract, approximately **12 contractions per minute**. - This high frequency is determined by the **basic electrical rhythm (BER)** or slow waves generated by the **interstitial cells of Cajal** in the proximal duodenum, which acts as the intestinal pacemaker. - The duodenum's rapid contractions facilitate **mixing of chyme** with pancreatic enzymes and bile, optimizing digestion and absorption. *Incorrect Option: Jejunum* - The jejunum has a frequency of approximately **9-11 contractions per minute**, which is lower than the duodenum. - The contraction frequency **decreases progressively** along the length of the small intestine from the duodenum. - While the jejunum is the primary site for nutrient absorption, it does not have the highest contraction frequency. *Incorrect Option: Ileum* - The ileum has the **lowest** frequency of small intestine contractions, approximately **7-9 contractions per minute**. - Its main functions include absorption of **vitamin B12**, **bile salts**, and completion of nutrient absorption. - The slower transit time allows for optimal absorption of these specialized nutrients. *Incorrect Option: Stomach* - The stomach has approximately **3 contractions per minute**, the lowest among all options. - Gastric contractions are primarily designed for **churning**, **mixing**, and **gastric emptying** rather than rapid propulsion. - These slower contractions allow adequate time for mechanical and chemical digestion of food.

Question 558: A 45-year-old patient with chronic pancreatitis is suffering from malnutrition and weight loss secondary to inadequate pancreatic exocrine secretions. Which of the following is true regarding pancreatic secretions?

A. Secretin releases fluid rich in enzymes.
B. Secretin releases fluid rich mainly in electrolytes and bicarbonate. (Correct Answer)
C. Cholecystokinin releases fluid, predominantly rich in electrolytes, and bicarbonate.
D. All pancreatic enzymes are secreted in an inactive form.

Explanation: ***Secretin releases fluid rich mainly in electrolytes and bicarbonate.*** - **Secretin** is stimulated by an acidic pH in the duodenum and primarily promotes the secretion of **bicarbonate-rich fluid** from the pancreas, which neutralizes gastric acid. - This bicarbonate-rich fluid helps create an optimal pH environment for digestive enzymes in the small intestine. *All pancreatic enzymes are secreted in an inactive form.* - While many pancreatic enzymes, particularly proteases like **trypsinogen** and **chymotrypsinogen**, are indeed secreted as inactive zymogens to prevent auto-digestion of the pancreas. - Some enzymes, such as **lipase** and **amylase**, are secreted in their active forms. *Secretin releases fluid rich in enzymes.* - Secretin primarily stimulates the release of **bicarbonate-rich fluid** to neutralize acidic chyme. - Enzyme rich secretions are primarily stimulated by **cholecystokinin (CCK)**. *Cholecystokinin releases fluid, predominantly rich in electrolytes, and bicarbonate.* - **Cholecystokinin (CCK)** mainly stimulates the secretion of **enzyme-rich pancreatic fluid** and contraction of the gallbladder. - The release of fluid rich in electrolytes and bicarbonate is primarily regulated by **secretin**.

Question 559: All of the following cause the secretion of gastric juice during the cephalic phase EXCEPT:

A. Thought of food
B. Food in mouth
C. Sight of food
D. Food in stomach (Correct Answer)

Explanation: ***Food in stomach*** - The presence of **food in the stomach** primarily stimulates the **gastric phase** of digestion, which occurs after the cephalic phase. - This phase involves stimuli like **stomach distension** and the presence of digested proteins, leading to further gastric juice secretion. *Food in mouth* - The taste and chewing of **food in the mouth** stimulate the **cephalic phase** through neural signals to the brainstem. - This initiates anticipatory gastric juice secretion via the vagus nerve. *Sight of food* - The **sight of food** is a powerful sensory input that triggers the **cephalic phase** of digestion. - This visual stimulus sends signals to the cerebral cortex, which then activates the vagus nerve to stimulate gastric secretion. *Thought of food* - The **thought of food**, even without direct sensory contact, can initiate the **cephalic phase**. - This cognitive stimulation reflects a conditioned reflex, where the brain anticipates a meal and prepares the digestive system, including gastric secretion.

Question 560: What is the primary physiological role of the cyclo-oxygenase-1 (COX-1) isoenzyme?

A. Is involved in gastric mucosal protection
B. Is involved in the inflammatory response
C. Is NOT primarily involved in gastric mucosal protection
D. Is the predominant isoenzyme involved in gastric mucosal protection (Correct Answer)

Explanation: ***Is the predominant isoenzyme involved in gastric mucosal protection*** - **COX-1** is constitutively expressed in many tissues, including the **gastric mucosa**, where it produces **prostaglandins** that protect the stomach lining. - These protective prostaglandins enhance **mucus and bicarbonate secretion**, maintain **mucosal blood flow**, and promote **epithelial repair**. *Is involved in gastric mucosal protection* - While COX-1 *is involved* in gastric mucosal protection, this option is less precise than stating it is the *predominant isoenzyme* for this role. - Omitting the word "predominant" makes this statement true but less accurate in highlighting its primary importance. *Is involved in the inflammatory response* - This role is primarily attributed to **COX-2**, which is an **inducible enzyme** largely expressed during inflammation. - While COX-1 can contribute to inflammation in some contexts, it is not its **primary physiological role**. *Is NOT primarily involved in gastric mucosal protection* - This statement is incorrect, as **COX-1** is indeed primarily and constitutively involved in **gastric mucosal protection**. - Inhibiting COX-1 often leads to adverse effects like **gastrointestinal ulcers** due to the loss of this protection.

Practice by Chapter

Gastrointestinal Motility

Practice Questions

Gastrointestinal Secretions

Practice Questions

Digestion and Absorption

Practice Questions

Gastrointestinal Hormones

Practice Questions

Hepatobiliary Physiology

Practice Questions

Pancreatic Exocrine Function

Practice Questions

Gastrointestinal Circulation

Practice Questions

Intestinal Immune System

Practice Questions

Gut Microbiome

Practice Questions

Regulation of Food Intake

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free