Gastrointestinal System Practice Questions

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

Pancreatic lipase. ***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.

Q: Which of the following is passively absorbed in gut?

Lipids. ***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.

Q: Maximum water reabsorption in the gastrointestinal tract occurs in:

Jejunum. ***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.

Q: Gastric acid secretion is stimulated by all except-

Somatostatin. ***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.

Q: Tone of lower esophageal sphincter is increased by?

Acetylcholine. ***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.

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

2000-2500 ml. ***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.

Q: Pepsinogen is activated by?

H+. ***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.

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

Enterogastric. ***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.

Q: A young man met with a motorbike accident and had injuries to ileum and jejunum. Therefore the entire ileum and partial jejunum were resected. Which of the following would the patient suffer from

Vitamin B12 malabsorption due to ileal resection. **Vitamin B12 malabsorption due to ileal resection** - The **terminal ileum** is the primary site for the absorption of **vitamin B12** (cobalamin) complexed with intrinsic factor [3]. - Its resection would directly lead to the inability to absorb this vitamin, resulting in **B12 deficiency** and associated symptoms like macrocytic anemia [3]. *Atrophic gastritis unrelated to resection* - **Atrophic gastritis** is a chronic inflammatory condition of the stomach lining leading to loss of glandular tissue and often impaired production of **intrinsic factor**. - While it can cause B12 malabsorption, it is an independent condition and not a direct consequence of ileum and jejunum resection. *Constipation due to dietary changes* - Resection of the ileum and jejunum primarily impacts **nutrient absorption** and can lead to diarrhea due or **short bowel syndrome** [1], rather than constipation. - While diet changes can affect bowel habits, prolonged **severe gastrointestinal resection** is more likely to cause malabsorption-related diarrhea [1], [2]. *No significant symptoms* - The **ileum** and **jejunum** are crucial for the absorption of most nutrients, including vitamins, minerals, fats, and carbohydrates [4]. - Resection of these segments, especially a significant portion, would lead to **malabsorption syndromes** with various severe symptoms, potentially including weight loss, diarrhea, and nutritional deficiencies [1], [4].

Q: What is the primary hormonal action of cholecystokinin (CCK) in response to fat and protein in the duodenum?

Stimulates pancreatic enzyme secretion. ***Stimulates pancreatic enzyme secretion*** - **Cholecystokinin (CCK)** is released by **I cells** in the duodenum and jejunum in response to **fat and protein** in the small intestine. - CCK's primary actions include stimulating **pancreatic enzyme secretion** (amylase, lipase, proteases) and **gallbladder contraction** to release bile. - Both actions work synergistically to digest fats and proteins, making CCK essential for **enzymatic digestion and fat emulsification**. *Stimulates gallbladder contraction* - This is indeed a **major primary function** of CCK (cholecysto = gallbladder, kinin = movement). - CCK causes gallbladder contraction to release stored bile for fat emulsification. - Both pancreatic enzyme secretion and gallbladder contraction are co-equal primary functions; in exam context, pancreatic enzyme secretion is often prioritized as it reflects the broader digestive enzyme role. *Inhibits gastric emptying* - CCK does slow gastric emptying, but this is a **secondary regulatory effect** rather than a primary hormonal action. - This allows time for proper digestion of fats and proteins in the small intestine. *Increases gastric acid secretion* - **Incorrect.** CCK actually has an **inhibitory effect** on gastric acid secretion. - **Gastrin** is the primary hormone that increases gastric acid secretion from parietal cells.

Question 1

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

Accepted Answer

Pancreatic lipase

Answer

Lingual lipase

Answer

Gastric lipase

Answer

Phospholipase

Question 2

Which of the following is passively absorbed in gut?

Accepted Answer

Lipids

Answer

Glucose

Answer

Fructose

Answer

Amino acids

Question 3

Maximum water reabsorption in the gastrointestinal tract occurs in:

Accepted Answer

Jejunum

Answer

Colon

Answer

Stomach

Answer

Ileum

Question 4

Gastric acid secretion is stimulated by all except-

Accepted Answer

Somatostatin

Answer

Gastric distension

Answer

Gastrin

Answer

Smell of food

Question 5

Tone of lower esophageal sphincter is increased by?

Accepted Answer

Acetylcholine

Answer

Nitric Oxide

Answer

Norepinephrine

Answer

Vasoactive Intestinal Peptide

Question 6

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

Accepted Answer

2000-2500 ml

Answer

500-1000 ml

Answer

1000-1500 ml

Answer

3000-3500 ml

Question 7

Pepsinogen is activated by?

Accepted Answer

H+

Answer

Gastrin

Answer

Enterokinase

Answer

Trypsin

Question 8

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

Accepted Answer

Enterogastric

Answer

Gastroileal

Answer

Gastrocolic

Answer

Myenteric

Question 9

A young man met with a motorbike accident and had injuries to ileum and jejunum. Therefore the entire ileum and partial jejunum were resected. Which of the following would the patient suffer from

Accepted Answer

Vitamin B12 malabsorption due to ileal resection

Answer

Atrophic gastritis unrelated to resection

Answer

Constipation due to dietary changes

Answer

No significant symptoms

Question 10

What is the primary hormonal action of cholecystokinin (CCK) in response to fat and protein in the duodenum?

Accepted Answer

Stimulates pancreatic enzyme secretion

Answer

Stimulates gallbladder contraction

Answer

Inhibits gastric emptying

Answer

Increases gastric acid secretion

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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