Gastrointestinal System — MCQs
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What is the primary mechanism for iron absorption in the duodenum?
A patient demonstrates decreased gastric acid secretion after vagotomy. Which cell type is directly affected by vagal denervation?
During digestion of a high-fat meal, which of the following gastrointestinal hormones primarily stimulates gallbladder contraction?
Which of these is true about SGLT1?
Histamine is secreted by:
Enteropeptidase enzyme is secreted by:
Which of the following can be absorbed without being broken down, especially in infants?
Somatostatin causes all except:
Maximum potassium ion secretion is seen in:
Secretin -
Gastrointestinal System Indian Medical PG Practice Questions and MCQs
Question 481: What is the primary mechanism for iron absorption in the duodenum?
- A. Simple diffusion
- B. Passive paracellular transport
- C. Endocytosis
- D. DMT1 transporter (Correct Answer)
Explanation: ***DMT1 transporter*** - The **divalent metal transporter 1 (DMT1)** is the primary mechanism for absorbing **non-heme iron (ferrous iron, Fe2+)** into duodenal enterocytes. - This active transport process is pH-dependent and drives iron uptake against a concentration gradient. *Simple diffusion* - Applies to the movement of substances down their concentration gradient without the aid of membrane proteins, which is not the main mechanism for iron due to its ionic nature. - While some highly lipid-soluble substances can cross membranes this way, metal ions like iron require specific transporters. *Passive paracellular transport* - Involves substances moving *between* cells, rather than *through* them, often occurring in leaky epithelia. - While some fluid and electrolytes may use this route, it is not the primary or regulated pathway for iron absorption. *Endocytosis* - A process where cells engulf substances by forming vesicles from the plasma membrane. - While some macromolecules are absorbed via endocytosis, it is not the major mechanism for absorbing dietary iron in the duodenum.
Question 482: A patient demonstrates decreased gastric acid secretion after vagotomy. Which cell type is directly affected by vagal denervation?
- A. Parietal cells (Correct Answer)
- B. ECL cells
- C. Chief cells
- D. G cells
Explanation: ***Parietal cells*** - **Parietal cells** are responsible for secreting **hydrochloric acid (HCl)** in the stomach. - They receive **direct vagal innervation** and vagal stimulation directly promotes acid secretion through the neurotransmitter **acetylcholine (ACh)** acting on M3 muscarinic receptors. - After vagotomy, parietal cells lose this direct cholinergic stimulation, resulting in **decreased gastric acid secretion**. *ECL cells* - **Enterochromaffin-like (ECL) cells** produce and release **histamine**, which then acts on parietal cells via H2 receptors to stimulate acid secretion. - ECL cells are also **directly innervated by vagal efferents** and release histamine in response to acetylcholine. - However, ECL cells do not themselves secrete acid; they stimulate parietal cells to do so, making them indirectly involved in acid production. *Chief cells* - **Chief cells** primarily secrete **pepsinogen**, the inactive precursor of pepsin, and **gastric lipase**. - While vagal stimulation does promote pepsinogen secretion, these cells are not responsible for gastric acid production. *G cells* - **G cells** secrete **gastrin**, a hormone that stimulates both parietal cells (directly) and ECL cells (indirectly) to increase acid secretion. - Vagal stimulation enhances gastrin release, so vagotomy would reduce gastrin levels, but G cells themselves do not produce acid.
Question 483: During digestion of a high-fat meal, which of the following gastrointestinal hormones primarily stimulates gallbladder contraction?
- A. Secretin
- B. GIP
- C. Gastrin
- D. Cholecystokinin (Correct Answer)
Explanation: ***Cholecystokinin*** - **Cholecystokinin (CCK)** is released by I-cells in the duodenum and jejunum in response to fats and proteins in the chyme. - Its primary function related to digestion of fats is to stimulate **gallbladder contraction**, leading to the release of bile for fat emulsification. *Secretin* - **Secretin** is released by S-cells in the duodenum in response to acidic chyme from the stomach. - Its main roles include stimulating the pancreas to release **bicarbonate-rich fluid** to neutralize stomach acid and inhibiting gastric acid secretion. *GIP* - **Gastric inhibitory peptide (GIP)**, also known as glucose-dependent insulinotropic polypeptide, is released by K-cells in the duodenum and jejunum. - It stimulates **insulin secretion** from pancreatic beta cells in response to glucose and fat, and inhibits gastric acid secretion and motility. *Gastrin* - **Gastrin** is secreted by G-cells in the stomach antrum and duodenum in response to proteins and vagal stimulation. - Its main function is to stimulate **gastric acid secretion** by parietal cells and promote gastric motility.
Question 484: Which of these is true about SGLT1?
- A. Secondary active transport of glucose in prostate
- B. Secondary active transport of glucose in brain
- C. Secondary active transport of glucose in intestine (Correct Answer)
- D. Secondary active transport of glucose in rods and cones
Explanation: ***Secondary active transport of glucose in intestine*** - **SGLT1** is the primary transporter responsible for **glucose and galactose absorption** from the lumen of the small intestine into the enterocytes. - It uses the electrochemical gradient of **sodium** to co-transport glucose against its concentration gradient, classifying it as **secondary active transport**. *Secondary active transport of glucose in prostate* - While glucose is vital for prostate metabolism, its transport predominantly involves **GLUTs** (e.g., GLUT1), not SGLT1. - SGLT1 is generally not found in significant amounts in the prostate. *Secondary active transport of glucose in brain* - Glucose transport across the **blood-brain barrier** and into brain cells is primarily mediated by **GLUT1** and other GLUT transporters, which are **facilitated diffusers**, not SGLT1. - SGLT1 has a very limited role, if any, in normal brain glucose uptake. *Secondary active transport of glucose in rods and cones* - Retinal photoreceptors (rods and cones) indeed rely on glucose, but its uptake is mainly via **GLUT1** and other GLUT family members. - **SGLT1** is not a significant transporter for glucose in these cells.
Question 485: Histamine is secreted by:
- A. Enterochromaffin-like cell (ECL cell) (Correct Answer)
- B. Chief cell
- C. Oxyntic cell
- D. Parietal cell
Explanation: ***Enterochromaffin-like cell (ECL cell)*** - **Enterochromaffin-like (ECL) cells** are located in the gastric mucosa and are the primary source of histamine in the stomach. - Histamine released by ECL cells stimulates **parietal cells** to secrete hydrochloric acid. - Note: ECL cells are distinct from enterochromaffin (EC) cells, which primarily secrete serotonin. *Chief cell* - **Chief cells** primarily secrete pepsinogen, the inactive precursor of the digestive enzyme pepsin. - They also produce gastric lipase, which aids in fat digestion. *Oxyntic cell* - The term **oxyntic (or parietal) cell** refers to the same cell type responsible for secreting hydrochloric acid and intrinsic factor. - They do not directly secrete histamine; instead, their acid secretion is stimulated by histamine. *Parietal cell* - **Parietal cells** are responsible for secreting hydrochloric acid and intrinsic factor, crucial for vitamin B12 absorption. - Their acid secretion is stimulated by acetylcholine, gastrin, and **histamine** (released from ECL cells).
Question 486: Enteropeptidase enzyme is secreted by:
- A. Ileum
- B. Duodenum (Correct Answer)
- C. Stomach
- D. Jejunum
Explanation: ***Duodenum*** - **Enteropeptidase** (also known as enterokinase) is a key enzyme primarily secreted by the mucosal cells of the **duodenum**. - Its main function is to activate **trypsinogen** (from the pancreas) into **trypsin**, initiating a cascade of protein digestion. *Ileum* - The ileum is primarily involved in the absorption of **vitamin B12** and **bile salts**. - It does not significantly contribute to the secretion of digestive enzymes like enteropeptidase. *Stomach* - The stomach secretes **pepsin** (to digest proteins) and **hydrochloric acid**, and is involved in initial protein digestion. - It does not produce enteropeptidase, which acts much later in the digestive process. *Jejunum* - The jejunum is a major site for the absorption of **nutrients** like carbohydrates, fats, and proteins. - While it has some brush border enzymes, the primary secretion of enteropeptidase occurs in the duodenum.
Question 487: Which of the following can be absorbed without being broken down, especially in infants?
- A. a-Dextrins
- B. Protein (Correct Answer)
- C. Sucrose
- D. Triglycerides
Explanation: ***Protein*** - In infants, particularly during the neonatal period, the intestinal epithelium exhibits increased **permeability** allowing for the absorption of intact proteins. - This phenomenon is crucial for the passive transfer of **maternal antibodies** (immunoglobulins) present in breast milk, providing temporary immunity to the infant. - This mechanism of intact protein absorption is known as **pinocytosis** and is especially prominent in the first few days of life. *a-Dextrins* - These are oligosaccharides derived from starch and require further enzymatic breakdown by **maltase-glucoamylase** before they can be absorbed as monosaccharides. - They cannot be absorbed intact, as their molecular size is too large to pass through the intestinal epithelial cells directly. *Sucrose* - Sucrose is a disaccharide that must be hydrolyzed into its constituent monosaccharides, **glucose and fructose**, by the enzyme **sucrase** in the brush border before absorption. - Intact sucrose molecules are too large to be absorbed across the intestinal wall. *Triglycerides* - Triglycerides are complex lipids that are first emulsified by bile salts and then hydrolyzed into **monoglycerides and free fatty acids** by pancreatic lipase. - These smaller components are then absorbed and re-esterified within the intestinal cells, rather than being absorbed as intact triglycerides.
Question 488: Somatostatin causes all except:
- A. Reduces gastric motility
- B. Stimulates gastrin secretion (Correct Answer)
- C. Decreases insulin secretion
- D. Inhibits secretion of motilin
Explanation: ***Stimulates gastrin secretion*** - Somatostatin is a **universal inhibitor** of secretory processes and hormone release throughout the gastrointestinal tract and pancreas. It **inhibits** the secretion of gastrin, not stimulates it. - Gastrin is a hormone that stimulates **acid secretion** in the stomach; somatostatin's role is to counteract this by reducing gastrin release. *Reduces gastric motility* - Somatostatin has an **inhibitory effect on gut motility**, slowing down the movement of food through the digestive tract. - This action helps to prolong nutrient absorption and allows more time for digestive processes. *Decreases insulin secretion* - Somatostatin inhibits the secretion of both **insulin** and **glucagon** from the pancreatic islets. - This regulatory action helps in maintaining stable blood glucose levels by moderating post-prandial hormone release. *Inhibits secretion of motilin* - Somatostatin is known to **inhibit the release of motilin**, a hormone that regulates gut motility and stimulates contractions of the stomach and small intestine. - By inhibiting motilin, somatostatin contributes to its overall effect of reducing gastrointestinal motility.
Question 489: Maximum potassium ion secretion is seen in:
- A. Saliva
- B. Gastric secretions
- C. Jejunal secretions
- D. Colonic secretions (Correct Answer)
Explanation: ***Colonic secretions*** - The **colon** plays a crucial role in maintaining **potassium balance** by actively secreting it into the lumen for excretion. - This secretion is particularly high during conditions of **high dietary potassium intake** or **aldosterone stimulation**. - Potassium concentration in colonic secretions can reach **90-100 mEq/L**, which is 2-3 times higher than plasma levels. *Saliva* - While saliva contains potassium, its concentration is relatively low compared to colonic secretions, and its overall contribution to **potassium secretion** is minor. - The primary function of saliva is to initiate digestion and lubricate food, not to regulate electrolyte balance significantly. *Gastric secretions* - Gastric secretions, such as **hydrochloric acid**, are primarily involved in digestion and have a relatively low potassium concentration. - Their main role is to create an acidic environment and break down food particles. *Jejunal secretions* - The jejunum primarily absorbs nutrients and water, and while it does handle electrolytes, its net function is generally to **absorb potassium** rather than to secrete it significantly. - Significant potassium secretion in the small intestine is not a primary function.
Question 490: Secretin -
- A. Secretion of pancreatic juice rich in enzyme
- B. Reduces the action of CCK
- C. Reduces Gastric secretion (Correct Answer)
- D. Increases Gastric secretion
Explanation: ***Reduces Gastric secretion*** - **Secretin** is released in response to *acidic chyme* entering the duodenum, and one of its primary roles is to **inhibit gastric acid secretion** and gastric motility. - This inhibitory effect helps to protect the duodenal mucosa from acid damage and allows for optimal enzyme function in the small intestine. *Secretion of pancreatic juice rich in enzyme* - This function is primarily associated with **cholecystokinin (CCK)**, which stimulates the pancreas to secrete an enzyme-rich pancreatic fluid. - While secretin does stimulate pancreatic juice secretion, it primarily induces a **bicarbonate-rich fluid** to neutralize acidic chyme, not enzyme-rich fluid. *Reduces the action of CCK PZ* - **Secretin** typically *potentiates* the actions of **CCK**, particularly in stimulating pancreatic enzyme secretion and gallbladder contraction. - There is no evidence that secretin reduces the action of CCK; in fact, they often work synergistically. *Increases Gastric secretion* - **Secretin** is a member of the *gastrointestinal hormone family* that primarily **inhibits gastric acid secretion** and reduces gastric emptying. - Hormones like **gastrin** are responsible for *increasing* gastric secretion.
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