Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 511: A 30-year-old female experiences nausea and right upper quadrant abdominal discomfort after eating fatty meals. Which gastrointestinal hormone is most likely responsible for stimulating gallbladder contraction in response to dietary fat?

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

Explanation: ***Cholecystokinin*** - **Cholecystokinin (CCK)** is released by **I-cells in the duodenal mucosa** in response to **fat and protein** in the intestinal lumen. - Its primary actions include stimulating **gallbladder contraction** and **pancreatic enzyme secretion**, facilitating fat digestion and absorption. - CCK release after fatty meals causes **physiological gallbladder contraction**, which can provoke symptoms in individuals with **gallbladder pathology** (cholelithiasis, cholecystitis) due to mechanical obstruction. - This is the hormone directly responsible for postprandial gallbladder emptying. *Gastrin* - **Gastrin** is released by **G-cells in the gastric antrum** primarily in response to **protein**, **gastric distension**, and **vagal stimulation**. - Its main function is stimulating **gastric acid secretion** and promoting **gastric mucosal growth**. - Gastrin does not play a significant role in gallbladder contraction or fat-induced symptoms. *Secretin* - **Secretin** is released by **S-cells in the duodenum** in response to **acidic chyme** entering from the stomach. - It stimulates the **pancreas** to secrete **bicarbonate-rich fluid** to neutralize acid and inhibits gastric acid secretion. - Secretin does not directly stimulate gallbladder contraction in response to fat. *Motilin* - **Motilin** is released during the **fasting state** and regulates the **migrating motor complex (MMC)**, promoting intestinal motility between meals. - It is not involved in postprandial responses to dietary fat or gallbladder function.

Question 512: Which of the following acts as "Gatekeeper" in the GIT?

A. Na+ K+ ATPase (Correct Answer)
B. Na+-glucose cotransporter
C. Calcium channel
D. Na+-amino acid cotransporter

Explanation: ***Na+ K+ ATPase*** - The **Na+ K+ ATPase** maintains the **electrochemical gradient** across the cell membrane, creating a low intracellular Na+ concentration. - This gradient is essential for powering secondary active transporters, acting as a "gatekeeper" by enabling the absorption and secretion of various substances across the **gastrointestinal tract (GIT)**. *Na+-amino acid cotransporter* - This is a **secondary active transporter** that moves amino acids into the cell, driven by the Na+ gradient established by the **Na+ K+ ATPase**. It is not the primary gatekeeper. - It plays a role in amino acid absorption but does not directly control the overall movement of substances across the cell membrane in the same fundamental way as the ATPase. *Calcium channel* - **Calcium channels** regulate the influx of calcium ions into cells, primarily involved in muscle contraction, neurotransmission, and glandular secretion. - They are not directly involved in maintaining the primary electrochemical gradients or acting as a gatekeeper for general nutrient absorption in the **GIT**. *Na+-glucose cotransporter* - This is a **secondary active transporter (SGLT1)** that uses the Na+ gradient to absorb glucose and galactose into the enterocytes. - Similar to the Na+-amino acid cotransporter, its function is dependent on the **Na+ K+ ATPase**, which maintains the driving force for its activity.

Question 513: Site of short-chain fatty acid absorption is -

A. Ileum
B. Duodenum
C. Ascending colon (Correct Answer)
D. Rectum

Explanation: ***Ascending colon*** - The **ascending colon** is a primary site for the absorption of **short-chain fatty acids (SCFAs)**, which are produced by bacterial fermentation of dietary fiber. - This absorption is crucial for maintaining colonic health and providing an energy source for colonocytes. *Ileum* - The **ileum** is mainly responsible for absorbing **vitamin B12** and **bile acids**, as well as some remaining nutrients. - While some limited SCFA absorption might occur, it is not its primary role. *Duodenum* - The **duodenum** is the primary site for the digestion and absorption of most macronutrients such as **carbohydrates**, **proteins**, and **fats**. - Its role in SCFA absorption is negligible. *Rectum* - The **rectum** primarily functions as a storage site for stool before defecation and has limited absorptive capacity. - It does not significantly contribute to the absorption of short-chain fatty acids.

Question 514: Maximum fat absorption in GI tract occurs in?

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

Explanation: ***Jejunum*** - The **jejunum** has a large surface area due to its numerous **plicae circulares (circular folds)**, villi, and microvilli, which are crucial for efficient nutrient absorption. - While digestion begins in the duodenum, the majority of **fat absorption**, along with most other nutrients, takes place in the jejunum after pancreatic enzymes and bile have emulsified and broken down fats. *Duodenum* - The **duodenum** is the primary site for **fat digestion** due to the entry of bile and pancreatic lipases, but not the primary site for maximal absorption. - While some absorption does occur here, it's more involved in **chemical breakdown** and initiation of absorption rather than the bulk uptake of fats. *Ileum* - The **ileum** is mainly responsible for the absorption of **bile salts** and **vitamin B12**, rather than the bulk of fat absorption. - Although it has absorptive functions, the **jejunum** is far more specialized for and efficient at absorbing fats and other digested nutrients. *Colon* - The **colon** is primarily involved in **water** and **electrolyte absorption**, and the formation and storage of feces. - It plays a minimal role in nutrient absorption, and virtually no fat absorption occurs here, as fats should have been fully absorbed in the small intestine.

Question 515: Which of the following statements is true regarding the basic rhythm of the gastrointestinal tract (GIT)?

A. Generated by the enteric nervous system
B. Fluctuate between -65 and -40 mV (Correct Answer)
C. Initiated by zymogen cells
D. Pacemaker cells are present only in the proximal stomach

Explanation: ***Fluctuate between -65 and -40 mV*** - The **basic electrical rhythm (BER)**, or **slow waves**, in GI smooth muscle are slow, undulating changes in the resting membrane potential, typically varying between **-65 mV** (resting potential) and **-40 mV** (threshold for action potentials). - These slow waves themselves do not cause muscle contraction but set the rhythm for action potentials, which are responsible for calcium influx and subsequent contraction. *Generated by the enteric nervous system* - While the **enteric nervous system (ENS)** plays a crucial role in modulating and coordinating GI motility, it does **not generate the basic electrical rhythm**. - The basic electrical rhythm is an intrinsic property of the **interstitial cells of Cajal (ICCs)**, which act as pacemaker cells. The ENS modulates this rhythm but does not initiate it. *Initiated by zymogen cells* - **Zymogen cells** (or chief cells) in the stomach primarily secrete **pepsinogen**, a precursor to pepsin, which is involved in protein digestion. They are not involved in initiating the basic electrical rhythm. - The basic electrical rhythm of the GI tract is initiated by specialized pacemaker cells called **interstitial cells of Cajal (ICCs)**. *Pacemaker cells are present only in the proximal stomach* - **Interstitial cells of Cajal (ICCs)**, the pacemaker cells of the GI tract, are found throughout the entire length of the GI tract, including the esophagus, stomach, small intestine, and large intestine. - While they are crucial for gastric motility, their presence is not limited to the proximal stomach; they are distributed to ensure coordinated contractions along the digestive tract.

Question 516: Hunger pangs are seen how long after starvation?

A. 6 hours
B. 48 hours
C. 24 hours
D. 12 hours (Correct Answer)

Explanation: ***12 hours*** - **Hunger pangs** typically become noticeable around **12 hours** after an individual's last meal, as the body transitions from post-absorptive to early fasting states. - This time frame represents a point where **glycogen stores begin to deplete**, prompting the body to signal for food intake through various hormonal and neural mechanisms. *6 hours* - At **6 hours** after a meal, the body is generally in a **post-absorptive state**, still utilizing absorbed nutrients, particularly glucose, from the digestive tract. - While initial feelings of hunger might just be starting for some individuals, true **hunger pangs** with significant stomach contractions are less common at this early stage. *24 hours* - By **24 hours** of starvation, hunger pangs may have *diminished*, as the body has significantly adapted to fasting, mobilizing **fat stores** and entering **ketosis**. - While the body still experiences hunger, the acute, painful "pangs" often peak earlier and then reduce as metabolic shifts occur. *48 hours* - At **48 hours** of starvation, the body is deeply in a **fasting state**, primarily relying on **fat and ketone bodies** for energy. - While physical and mental fatigue may be pronounced, the initial intense **hunger pangs** have typically subsided, replaced by a more sustained but less acute feeling of hunger.

Question 517: What is the main enzyme involved in the digestion of dietary fats?

A. Lingual lipase
B. Gastric lipase
C. Pancreatic lipase (Correct Answer)
D. Phospholipase

Explanation: ***Pancreatic lipase*** - **Pancreatic lipase** is the primary enzyme responsible for the digestion of dietary **triglycerides** in the small intestine. - It hydrolyzes triglycerides into **monoglycerides** and **fatty acids**, which can then be absorbed by the intestinal lining. *Lingual lipase* - **Lingual lipase** is secreted in the mouth and begins the digestion of some dietary fats, particularly **short-chain** and **medium-chain triglycerides**. - Its activity is limited and contributes only a small percentage to overall fat digestion, primarily in the stomach due to its acid stability. *Gastric lipase* - **Gastric lipase** is produced in the stomach and primarily digests **short-chain** and **medium-chain triglycerides**, especially important for infants. - While it initiates some fat digestion, its contribution to the overall breakdown of dietary fats is minor compared to pancreatic lipase. *Phospholipase* - **Phospholipase** is an enzyme that specifically breaks down **phospholipids** (not triglycerides) into fatty acids and other lipophilic substances. - It plays a role in the digestion of membrane lipids, but not the bulk of dietary triglycerides.

Question 518: Maximum water reabsorption in the gastrointestinal tract occurs in:

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

Explanation: ***Jejunum*** - The **jejunum** is the site of **maximum water absorption** in the gastrointestinal tract by volume. - Approximately **5-6 liters of water** are absorbed daily in the jejunum, which is the largest absolute amount of any GI segment. - While the jejunum is known primarily for nutrient absorption (carbohydrates, proteins, fats), it handles the bulk of fluid absorption due to the large volume of secretions (saliva, gastric juice, bile, pancreatic juice) entering the upper GI tract. *Colon* - The **colon** absorbs approximately **1-2 liters of water** daily, which is significantly less than the jejunum. - However, the colon is crucial for **concentrating feces** and has high efficiency in water reabsorption (absorbs ~90% of water entering it). - It plays a vital role in final water conservation, but not maximum absolute volume absorption. *Ileum* - The **ileum** absorbs approximately **2-3 liters of water** daily, along with bile acids and vitamin B12. - Its water absorption capacity is important but less than the jejunum. *Stomach* - The **stomach** has minimal water absorption capacity. - Only small amounts of water and certain substances like alcohol are absorbed here. - The stomach primarily functions in digestion and mixing food with gastric secretions.

Question 519: Gastric acid secretion is stimulated by all except-

A. Gastric distension
B. Gastrin
C. Smell of food
D. Somatostatin (Correct Answer)

Explanation: ***Somatostatin*** - **Somatostatin** is a **peptide hormone** that **inhibits** gastric acid secretion by suppressing the release of gastrin and histamine. - It acts as a **negative feedback mechanism** to regulate stomach acid. *Gastric distension* - **Gastric distention** during the **gastric phase** of digestion stimulates the release of **gastrin**, which in turn promotes acid secretion. - This is a local reflex mediated by the **enteric nervous system** and vagal reflexes. *Gastrin* - **Gastrin** is a hormone secreted by **G cells** in the stomach, which directly stimulates **parietal cells** to secrete hydrochloric acid. - It also promotes the growth of the gastric mucosa. *Smell of food* - The **smell of food** initiates the **cephalic phase** of digestion, mediated by the **vagus nerve**. - This **vagal stimulation** directly stimulates parietal cells to secrete acid and also releases **acetylcholine**, which promotes gastrin release.

Question 520: Which of the following statements about iron absorption is false?

A. Major site of absorption is duodenum
B. Absorbed in ferrous form
C. Stored as Ferritin
D. Pancreatic secretions improve the absorption (Correct Answer)

Explanation: ***Pancreatic secretions improve the absorption*** - This statement is **false** because **pancreatic secretions reduce iron absorption** by increasing the pH and contributing to the formation of insoluble iron complexes, making iron less available for mucosal uptake. - Additionally, exocrine pancreatic insufficiency can lead to **iron deficiency**, further supporting the inhibitory role of pancreatic enzymes in high concentrations or altered functionality. *Major site of absorption is duodenum* - The **duodenum** is indeed the **primary site of iron absorption** due to its acidic environment and high concentration of iron transporters. - Iron absorption efficiency progressively decreases distal to the duodenum in the small intestine. *Stored as Ferritin* - Iron is primarily stored in the body, particularly in the liver, spleen, and bone marrow, in the form of **ferritin**, which is a protein complex that sequesters iron. - This storage mechanism prevents **iron toxicity** while allowing for controlled release when needed for erythropoiesis or other metabolic functions. *Absorbed in ferrous form* - Dietary non-heme iron (Fe3+) must be reduced to its **ferrous form (Fe2+)** by **duodenal cytochrome B (Dcytb)** on the brush border for optimal absorption into the enterocyte. - Heme iron, found in meat, is absorbed directly as a porphyrin ring and then broken down, but the majority of dietary iron is non-heme and requires reduction to Fe2+ for uptake.

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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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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