Gastrointestinal System Practice Questions

Q: All of the following increases gastric acid secretion except?

Serotonin. ***Serotonin*** - **Serotonin** (5-HT) is primarily known for its roles in gastrointestinal motility and CNS function, but it does not directly stimulate **gastric acid secretion**. - While it can influence gastric function indirectly, it is not a direct secretagogue for **parietal cells**. *Acetylcholine* - **Acetylcholine** (ACh), released from parasympathetic nerve endings, directly stimulates **parietal cells** to secrete hydrochloric acid. - It also enhances the release of **histamine** and **gastrin**, both of which promote acid secretion. *Histamine* - **Histamine**, released from enterochromaffin-like (ECL) cells in the gastric mucosa, is a potent stimulator of **gastric acid secretion**. - It acts on **H2 receptors** on parietal cells, leading to increased acid production. *Gastrin* - **Gastrin**, a hormone produced by G cells in the pyloric antrum, is a powerful stimulator of **gastric acid secretion**. - It acts directly on **parietal cells** and also promotes **histamine release** from ECL cells.

Q: The relaxation of the intestinal segment distal to the segment with the bolus of food during peristalsis is because of?

Nitric oxide (NO). ***Nitric oxide (NO)*** - **Nitric oxide (NO)** is a key **inhibitory neurotransmitter** that causes relaxation of the smooth muscle distal to the bolus during peristalsis, allowing the food to move forward. - Along with **Vasoactive Intestinal Peptide (VIP)**, NO mediates the **descending relaxation reflex** in the gut, which is essential for effective propulsion. *Substance P* - **Substance P** is an **excitatory neurotransmitter** that primarily mediates contraction of the smooth muscle proximal to the bolus during peristalsis. - It works synergistically with **acetylcholine** to initiate the muscular squeeze that propels food. *Norepinephrine from adrenergic fibers* - **Norepinephrine** is the primary neurotransmitter released by **sympathetic adrenergic fibers** in the gastrointestinal tract. - While sympathetic stimulation generally **inhibits gastrointestinal motility**, this is a systemic effect that reduces overall gut activity rather than causing the specific segmental relaxation distal to a bolus during peristalsis. - The descending relaxation during peristalsis is mediated by **intrinsic enteric neurons** (releasing NO and VIP), not by extrinsic sympathetic innervation. *VIP* - **Vasoactive Intestinal Peptide (VIP)** is an **inhibitory neurotransmitter** that causes relaxation of smooth muscle in the gut. - While VIP does contribute to descending relaxation, **nitric oxide (NO)** is considered a more significant and primary mediator of this specific relaxation during peristalsis.

Q: Which neurotransmitter primarily mediates slow synaptic transmission in the enteric nervous system?

Nitric oxide. **Nitric oxide** - **Nitric oxide (NO)** is a key **non-classical neurotransmitter** in the **enteric nervous system (ENS)**, mediating **slow synaptic transmission** due to its gaseous nature allowing for diffusion and longer-lasting effects. - It is involved in **smooth muscle relaxation**, **vasodilation**, and diverse gastrointestinal functions, including **peristalsis** and **sphincter relaxation**. *Substance P* - **Substance P** is a **neuropeptide** that acts as an **excitatory neurotransmitter** in the ENS, primarily mediating **fast synaptic transmission** and smooth muscle contraction. - It is involved in pain perception, inflammation, and is released by sensory neurons and some enteric neurons. *Serotonin* - **Serotonin (5-HT)** is a major neurotransmitter in the ENS, largely mediating **fast excitatory or inhibitory synaptic transmission** depending on the receptor subtype. - It plays a crucial role in regulating gut motility, secretion, and visceral sensation, and is involved in both rapid signaling and neuromodulation. *Acetylcholine* - **Acetylcholine (ACh)** is the primary **excitatory neurotransmitter** of the **parasympathetic nervous system** within the ENS, mediating **fast synaptic transmission** by binding to nicotinic and muscarinic receptors. - It is crucial for stimulating **smooth muscle contraction** (promoting peristalsis), increasing glandular secretions, and generally enhancing gut motility.

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: Distal ileum was removed in a 20-year-old girl. Which absorption deficiency will be seen?

Bile salts. ***Bile salts*** - The **distal ileum** is the primary site for the active reabsorption of **bile salts** back into the enterohepatic circulation. - Their malabsorption leads to **fat malabsorption** and steatorrhea, and can lead to gallstones due to changes in bile composition. *Iron* - The majority of **iron absorption** primarily occurs in the **duodenum** and proximal jejunum, not the distal ileum. - Iron deficiency would typically result from issues higher up in the small intestine or from chronic blood loss. *Copper* - **Copper absorption** mainly occurs in the **stomach** and **duodenum**. - Deficiency typically arises from dietary inadequacy or specific genetic disorders, not distal ileal resection. *Zinc* - **Zinc absorption** occurs throughout the **small intestine**, with significant absorption in the **jejunum**. - While some zinc is absorbed in the ileum, its primary absorption site is not limited to or predominantly in the distal ileum, making malabsorption less likely with isolated distal ileum removal.

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.

Question 1

All of the following increases gastric acid secretion except?

Accepted Answer

Serotonin

Answer

Acetylcholine

Answer

Histamine

Answer

Gastrin

Question 2

The relaxation of the intestinal segment distal to the segment with the bolus of food during peristalsis is because of?

Accepted Answer

Nitric oxide (NO)

Answer

Substance P

Answer

Norepinephrine from adrenergic fibers

Answer

VIP

Question 3

Which neurotransmitter primarily mediates slow synaptic transmission in the enteric nervous system?

Accepted Answer

Nitric oxide

Answer

Substance P

Answer

Serotonin

Answer

Acetylcholine

Question 4

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 5

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 6

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 7

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 8

Distal ileum was removed in a 20-year-old girl. Which absorption deficiency will be seen?

Accepted Answer

Bile salts

Answer

Iron

Answer

Copper

Answer

Zinc

Question 9

Histamine is secreted by:

Accepted Answer

Enterochromaffin-like cell (ECL cell)

Answer

Chief cell

Answer

Oxyntic cell

Answer

Parietal cell

Question 10

Enteropeptidase enzyme is secreted by:

Accepted Answer

Duodenum

Answer

Ileum

Answer

Stomach

Answer

Jejunum

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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