Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 581: Which of the following is not a function of the liver?

A. Metabolism of drugs
B. Detoxification of ammonia
C. Production of albumin
D. Production of vitamin K (Correct Answer)

Explanation: ***Production of vitamin K*** - The **liver** is essential for activating **vitamin K** and producing **vitamin K-dependent clotting factors**, such as factors II, VII, IX, and X. - However, the liver itself does not *produce* vitamin K. Instead, **intestinal bacteria** synthesize vitamin K, which is then absorbed. *Production of albumin* - The liver is the primary site for the synthesis of **albumin**, a crucial plasma protein. - **Albumin** plays a vital role in maintaining **oncotic pressure**, transporting hormones, and carrying drugs in the bloodstream. *Detoxification of ammonia* - The liver is responsible for detoxifying **ammonia** by converting it into **urea** through the urea cycle. - This process is essential as **high levels of ammonia** are neurotoxic. *Metabolism of drugs* - The liver is the main organ for **drug metabolism** through various enzyme systems, including the cytochrome P450 system. - This process transforms drugs into more water-soluble compounds, facilitating their excretion from the body.

Question 582: Which GI hormone is classified as an incretin and primarily responsible for the glucose-dependent stimulation of insulin secretion?

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

Explanation: ***GIP*** - **Glucose-dependent insulinotropic polypeptide (GIP)** is a hormone with **incretin** activity produced in the duodenum and jejunum. - Its primary role is to stimulate **insulin secretion** from pancreatic beta cells in a glucose-dependent manner, meaning insulin release is enhanced when blood glucose levels are high. *Gastrin* - **Gastrin** is a hormone primarily secreted by G cells in the stomach and duodenum. - Its main function is to stimulate the secretion of **gastric acid (HCl)** by parietal cells, playing a key role in digestion, not insulin secretion. *Secretin* - **Secretin** is released by S cells in the duodenum in response to acidic chyme entering the small intestine. - It primarily stimulates the pancreas to release **bicarbonate-rich fluid** to neutralize stomach acid, and it inhibits gastric acid secretion, with no direct role as an incretin. *CCK* - **Cholecystokinin (CCK)** is secreted by I cells in the duodenum and jejunum, mainly in response to fats and proteins. - CCK primarily stimulates the contraction of the **gallbladder** to release bile and the secretion of **pancreatic enzymes**, and it also promotes satiety.

Question 583: What is the primary site for active iron absorption in the gastrointestinal tract?

A. Duodenum (Correct Answer)
B. Proximal ileum
C. Terminal ileum
D. Stomach

Explanation: ***Duodenum*** - The **duodenum** is the primary site for **iron absorption** in the gastrointestinal tract due to its specialized transport mechanisms. - Iron absorption is an **active process** mediated by specific transporters, such as **DMT1 (divalent metal transporter 1)** on enterocytes, which are highly expressed in the duodenum. *Terminal ileum* - The **terminal ileum** is the main site for the absorption of **vitamin B12** and **bile salts**, not iron. - While some passive absorption of other nutrients can occur, it is not specialized for active iron uptake. *Proximal ileum* - The **proximal ileum** is a major site for the absorption of many nutrients, including **carbohydrates, fats, and proteins**, but it is secondary to the duodenum for iron. - The abundance of specific iron transporters is highest in the duodenum. *Stomach* - The **stomach** primarily plays a role in **gastric acid secretion**, which helps in the release of iron from food, and aids in the conversion of ferric iron (Fe3+) to the more absorbable ferrous iron (Fe2+). - However, the stomach itself does not actively absorb significant amounts of iron.

Question 584: From which part of the gastrointestinal tract is glucose absorbed?

A. Stomach
B. Colon
C. Duodenum and jejunum (Correct Answer)
D. Ileum

Explanation: ***Duodenum and jejunum*** - The **duodenum** and **jejunum** are the primary sites for nutrient absorption in the small intestine, including the majority of **glucose**. - Their large surface area, due to **villi** and **microvilli**, and abundant transport mechanisms facilitate efficient glucose uptake. *Stomach* - The stomach's primary role is **digestion**, particularly of proteins, with very little absorption of nutrients. - While some small, lipid-soluble substances like alcohol can be absorbed, significant **glucose absorption does not occur** here. *Ileum* - The **ileum** is mainly responsible for the absorption of **vitamin B12** and **bile salts**. - Although some remaining nutrients might be absorbed, the bulk of **glucose absorption** is completed in the upstream **duodenum and jejunum**. *Colon* - The **colon's** main functions are **water and electrolyte absorption** and the formation of feces. - It does not play a significant role in the absorption of **glucose** or other macro-nutrients.

Question 585: Which of the following hormones stimulates HCl secretion in the stomach?

A. Histamine
B. Secretin
C. Gastrin (Correct Answer)
D. Somatostatin

Explanation: ***Gastrin*** - **Gastrin** is a hormone produced by **G cells** in the stomach antrum in response to food, particularly proteins. - It directly stimulates parietal cells to secrete **hydrochloric acid (HCl)** and indirectly increases HCl secretion by promoting histamine release. *Secretin* - **Secretin** is released from the duodenum in response to acidic chyme entering the small intestine. - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** and to inhibit gastric acid secretion, counteracting gastrin's effect. *Histamine* - While **histamine** is a potent stimulator of HCl secretion, it is a **paracrine** substance produced by enterochromaffin-like (ECL) cells, not a hormone that circulates in the blood to exert its effect. - It acts locally on parietal cells via **H2 receptors** to increase acid production. *Somatostatin* - **Somatostatin** is a hormone released by **D cells** in the stomach and duodenum. - It acts as an inhibitory hormone, **decreasing** or stopping the secretion of gastrin, secretin, and histamine, thereby reducing gastric acid secretion.

Question 586: Which causes antral gastrin release?

A. Antral distension (Correct Answer)
B. Acid
C. Secretin
D. Calcitonin

Explanation: **Antral distension** - **Antral distension** after a meal stimulates mechanoreceptors, which trigger the release of **gastrin** from G cells in the gastric antrum via a vagovagal reflex. - This gastrin release is crucial for promoting gastric acid secretion and motility to aid digestion. *Acid* - **Gastric acid** in the antrum actually **inhibits** gastrin release through a negative feedback loop mediated by somatostatin. - This mechanism prevents excessive acid production when the stomach pH drops too low. *Secretin* - **Secretin** is released from the duodenum in response to acid and functions primarily to **inhibit gastrin release** and stimulate bicarbonate and fluid secretion. - Its main role is to protect the duodenal mucosa from gastric acid. *Calcitonin* - **Calcitonin** is a hormone primarily involved in **calcium metabolism** and is secreted by the thyroid gland. - It has no direct physiological role in regulating antral gastrin release.

Question 587: If the ileum is excised, which substance will increase in the stool?

A. Iron
B. Unabsorbed fats
C. Calcium
D. Bile salts (Correct Answer)

Explanation: ***Bile salts*** - The **terminal ileum** is the **only site** for **active reabsorption of bile salts** from the enterohepatic circulation. - Excision of the ileum leads to **direct loss** of bile salt reabsorption, causing bile salts to enter the colon, resulting in **cholorrhoeic diarrhea** and malabsorption. - This is the **primary and most specific** consequence of ileal resection. - Bile salts in the colon also stimulate water and electrolyte secretion, worsening diarrhea. *Unabsorbed fats* - While **fats do increase in stool** after ileal resection (steatorrhea), this is a **secondary effect** due to bile salt deficiency. - Bile salts are essential for **fat emulsification and micelle formation**, so their loss impairs fat absorption. - However, the **direct substance lost** from ileal excision is bile salts, not fats themselves - making bile salts the more specific answer. *Calcium* - **Calcium absorption** primarily occurs in the **duodenum and proximal jejunum** (vitamin D-dependent active transport). - Ileal resection does not directly affect calcium absorption. - Calcium in stool would not significantly increase from ileal excision alone. *Iron* - **Iron absorption** mainly takes place in the **duodenum and proximal jejunum**. - Ileal excision would not affect iron absorption or increase iron in stool.

Question 588: Intrinsic factor is required for the absorption of which vitamin?

A. Vitamin B12 (Correct Answer)
B. Vitamin B2
C. Vitamin B6
D. Folic acid

Explanation: ***Vitamin B12*** - **Intrinsic factor**, a glycoprotein secreted by gastric parietal cells, binds to **vitamin B12 (cobalamin)** in the stomach. - This complex then travels to the **terminal ileum**, where it is specifically absorbed. *Vitamin B2* - **Vitamin B2 (riboflavin)** is absorbed in the **proximal small intestine** via a carrier-mediated transport system that does not involve intrinsic factor. - Deficiency can lead to **cheilosis** and **angular stomatitis**. *Vitamin B6* - **Vitamin B6 (pyridoxine)** is primarily absorbed in the **jejunum and ileum** through a non-specific, passive diffusion process and does not require intrinsic factor. - It plays a crucial role as a coenzyme in amino acid metabolism. *Folic acid* - **Folic acid (vitamin B9)** is absorbed mainly in the **jejunum** and does not depend on intrinsic factor for its absorption. - It is essential for **DNA synthesis** and red blood cell maturation, and deficiency can cause **megaloblastic anemia**.

Question 589: Gastric secretion is increased by all except which one?

A. Histamine
B. Acetylcholine
C. Gastrin
D. HCl (Correct Answer)

Explanation: ***HCl (Correct Answer - Does NOT Increase Gastric Secretion)*** - While **HCl** is a major component of gastric acid, its presence in the stomach lumen acts as a **negative feedback mechanism** to *inhibit* further gastric secretion, particularly gastrin release. - High acidity (low pH) directly **inhibits gastrin-producing G cells** and stimulates **somatostatin release**, which in turn inhibits acid secretion. - This negative feedback prevents excessive acid production and maintains pH homeostasis. *Histamine (Increases Gastric Secretion)* - **Histamine** is a powerful stimulant of gastric acid secretion, acting primarily through **H2 receptors** on parietal cells to increase cAMP levels. - It potentiates the effects of both acetylcholine and gastrin, significantly enhancing acid production. *Acetylcholine (Increases Gastric Secretion)* - **Acetylcholine**, released from vagal nerve endings, directly stimulates **parietal cells** (M3 receptors), **G cells** (gastrin release), and **ECL cells** (histamine release), all contributing to increased gastric secretion. - It plays a crucial role in the **cephalic and gastric phases** of digestion. *Gastrin (Increases Gastric Secretion)* - **Gastrin**, a hormone released from G cells in the gastric antrum, primarily stimulates **parietal cells** to secrete acid and also promotes the growth of the gastric mucosa. - It also stimulates **ECL cells** to release histamine, further augmenting acid secretion.

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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