Gastrointestinal System Practice Questions

Q: What is the primary mechanism for iron absorption in the duodenum?

DMT1 transporter. ***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.

Q: A patient demonstrates decreased gastric acid secretion after vagotomy. Which cell type is directly affected by vagal denervation?

Parietal cells. ***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.

Q: During digestion of a high-fat meal, which of the following gastrointestinal hormones primarily stimulates gallbladder contraction?

Cholecystokinin. ***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.

Q: Which of these is true about SGLT1?

Secondary active transport of glucose in intestine. ***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.

Q: Histamine is secreted by:

Enterochromaffin-like cell (ECL cell). ***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).

Q: Enteropeptidase enzyme is secreted by:

Duodenum. ***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.

Q: Which of the following can be absorbed without being broken down, especially in infants?

Protein. ***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.

Q: Somatostatin causes all except:

Stimulates gastrin secretion. ***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.

Q: Maximum potassium ion secretion is seen in:

Colonic secretions. ***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.

Q: Secretin -

Reduces Gastric secretion. ***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.

Question 1

What is the primary mechanism for iron absorption in the duodenum?

Accepted Answer

DMT1 transporter

Answer

Simple diffusion

Answer

Passive paracellular transport

Answer

Endocytosis

Question 2

A patient demonstrates decreased gastric acid secretion after vagotomy. Which cell type is directly affected by vagal denervation?

Accepted Answer

Parietal cells

Answer

ECL cells

Answer

Chief cells

Answer

G cells

Question 3

During digestion of a high-fat meal, which of the following gastrointestinal hormones primarily stimulates gallbladder contraction?

Accepted Answer

Cholecystokinin

Answer

Secretin

Answer

GIP

Answer

Gastrin

Question 4

Which of these is true about SGLT1?

Accepted Answer

Secondary active transport of glucose in intestine

Answer

Secondary active transport of glucose in prostate

Answer

Secondary active transport of glucose in brain

Answer

Secondary active transport of glucose in rods and cones

Question 5

Histamine is secreted by:

Accepted Answer

Enterochromaffin-like cell (ECL cell)

Answer

Chief cell

Answer

Oxyntic cell

Answer

Parietal cell

Question 6

Enteropeptidase enzyme is secreted by:

Accepted Answer

Duodenum

Answer

Ileum

Answer

Stomach

Answer

Jejunum

Question 7

Which of the following can be absorbed without being broken down, especially in infants?

Accepted Answer

Protein

Answer

a-Dextrins

Answer

Sucrose

Answer

Triglycerides

Question 8

Somatostatin causes all except:

Accepted Answer

Stimulates gastrin secretion

Answer

Reduces gastric motility

Answer

Decreases insulin secretion

Answer

Inhibits secretion of motilin

Question 9

Maximum potassium ion secretion is seen in:

Accepted Answer

Colonic secretions

Answer

Saliva

Answer

Gastric secretions

Answer

Jejunal secretions

Question 10

Secretin -

Accepted Answer

Reduces Gastric secretion

Answer

Secretion of pancreatic juice rich in enzyme

Answer

Reduces the action of CCK

Answer

Increases Gastric secretion

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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