Gastrointestinal System Practice Questions

Q: Enterochromaffin cells in the gastrointestinal tract secrete which of the following?

Both serotonin and histamine. **Explanation:** The correct answer is **C (Both serotonin and histamine)**. **Medical Concept:** Enterochromaffin (EC) cells and Enterochromaffin-like (ECL) cells are types of enteroendocrine cells found in the gastrointestinal mucosa. 1. **Enterochromaffin (EC) cells:** These are the primary source of **Serotonin (5-HT)** in the body (containing ~90% of total body serotonin). They respond to mechanical stimulation or luminal irritants to increase gut motility and secretion. 2. **Enterochromaffin-like (ECL) cells:** These are found primarily in the gastric corpus and are responsible for secreting **Histamine**. Histamine acts on H2 receptors of parietal cells to stimulate gastric acid secretion. In many medical entrance exams, including NEET-PG, the term "Enterochromaffin cells" is often used as a broad category encompassing both EC and ECL cells, making "Both" the most accurate choice. **Analysis of Options:** * **Option A & B:** While EC cells primarily secrete serotonin and ECL cells secrete histamine, selecting only one would be incomplete as both are derived from the same lineage of argentaffin/argyrophil cells in the GI tract. * **Option D:** Incorrect, as these cells are the major neuroendocrine regulators of the gut. **High-Yield Clinical Pearls for NEET-PG:** * **Carcinoid Syndrome:** Arises from tumors of EC cells (usually in the ileum), leading to excessive serotonin. Symptoms include flushing, diarrhea, and right-sided heart failure. * **Gastrin Connection:** Gastrin (from G cells) stimulates ECL cells to release histamine, which is the most potent physiological stimulus for HCl secretion. * **Markers:** These cells are identified using **Chromogranin A** (a universal marker for neuroendocrine tumors).

Q: Duodenum and Jejunum secrete ALL EXCEPT?

VIP. ### Explanation The gastrointestinal tract produces various hormones and neurotransmitters. The distinction between **hormones** (secreted into the bloodstream by endocrine cells) and **neurocrines** (secreted by neurons) is a high-yield concept for NEET-PG. **Why VIP is the Correct Answer:** **Vasoactive Intestinal Peptide (VIP)** is not a hormone secreted by the mucosal cells of the duodenum or jejunum. Instead, it is a **neurotransmitter (neurocrine)** found in the neurons of the enteric nervous system (Meissner’s and Auerbach’s plexuses). While it is present throughout the GI tract, it is released by nerve endings in response to distension and vagal stimulation, rather than being secreted by the intestinal mucosa into the portal circulation. **Analysis of Incorrect Options:** * **A. CCK (Cholecystokinin):** Secreted by **'I' cells** located primarily in the duodenum and jejunum in response to fatty acids and amino acids. * **B. Secretin:** Secreted by **'S' cells** in the duodenum and jejunum. It is released in response to acidic chyme (pH < 4.5) entering the duodenum. * **C. GIP (Glucose-dependent Insulinotropic Peptide):** Secreted by **'K' cells** in the duodenum and jejunum. It stimulates insulin release and inhibits gastric acid secretion. **High-Yield Clinical Pearls for NEET-PG:** * **VIPoma (WDHA Syndrome):** A pancreatic tumor secreting excess VIP leads to **W**atery **D**iarrhea, **H**ypokalemia, and **A**chlorhydria (also known as Verner-Morrison syndrome). * **VIP Function:** It relaxes GI smooth muscle (including the LES) and stimulates the secretion of water and electrolytes into the intestinal lumen. * **Mnemonic for Locations:** Most major GI hormones (CCK, Secretin, GIP) are concentrated in the **Duodenum and Jejunum**, whereas **Gastrin** is primarily in the Antrum and **Motilin** is throughout the upper GI tract.

Q: Which of the following nerves provides the efferent impulses necessary for the esophageal actions that occur during swallowing?

Vagus. **Explanation:** The process of swallowing (deglutition) is coordinated by the swallowing center in the medulla and pons. The **Vagus nerve (CN X)** is the primary nerve responsible for the **efferent (motor) limb** of the esophageal phase of swallowing. 1. **Why Vagus is Correct:** The Vagus nerve provides motor innervation to the striated muscle of the upper third of the esophagus (via the recurrent laryngeal nerve) and the smooth muscle of the lower two-thirds (via the esophageal plexus). It coordinates the primary peristaltic wave and the relaxation of the Lower Esophageal Sphincter (LES) through the release of VIP and Nitric Oxide. 2. **Why Other Options are Incorrect:** * **Glossopharyngeal (CN IX):** While it carries sensory (afferent) impulses from the pharynx to initiate the swallow reflex and provides motor supply to the stylopharyngeus, it does not control esophageal actions. * **Hypoglossal (CN XII):** This nerve provides motor supply to the intrinsic and extrinsic muscles of the tongue, primarily involved in the oral (voluntary) phase of swallowing. * **Spinal Accessory (CN XI):** This nerve supplies the sternocleidomastoid and trapezius muscles; it has no direct role in esophageal peristalsis. **High-Yield Clinical Pearls for NEET-PG:** * **Swallowing Center:** Located in the Nucleus Tractus Solitarius (NTS) and Nucleus Ambiguus. * **Achalasia Cardia:** Failure of the Vagus-mediated relaxation of the LES due to loss of myenteric (Auerbach’s) plexus. * **Phases of Swallowing:** Oral (voluntary), Pharyngeal (involuntary), and Esophageal (involuntary). The Vagus nerve dominates the latter two.

Q: Which of the following is the last site of fat loss during starvation?

Pericardial. **Explanation:** The distribution and mobilization of adipose tissue during starvation follow a specific physiological hierarchy. Fat is categorized into **subcutaneous fat** (easily mobilized) and **visceral/structural fat** (preserved for organ protection). **Why Pericardial is Correct:** Pericardial fat is considered **structural fat**. During prolonged starvation or malnutrition (like Marasmus), the body first mobilizes storage fat from subcutaneous sites to meet energy demands. Structural fat, which provides mechanical cushioning and support to vital organs, is the last to be depleted. The pericardial fat, along with fat in the palms, soles, and retro-orbital space, is highly resistant to mobilization because its primary function is protective rather than caloric storage. **Analysis of Incorrect Options:** * **Buttocks (Option C):** This is a primary site of subcutaneous storage fat. It is one of the earliest areas to show wasting in protein-energy malnutrition. * **Omental (Option D):** This is visceral storage fat. While more metabolically active than subcutaneous fat, it is mobilized relatively early to provide free fatty acids to the liver via portal circulation. * **Periorbital (Option A):** While orbital fat is also structural, clinical studies and forensic pathology indicate that epicardial/pericardial fat remains the most resilient "last resort" fat depot in the body. **NEET-PG High-Yield Pearls:** * **Order of Fat Loss:** Subcutaneous (Face/Limbs) → Visceral (Omental/Mesenteric) → Structural (Pericardial/Retro-orbital). * **Bichat’s Fat Pad:** The buccal pad of fat in the cheeks is also a form of structural fat, which is why the face often retains a "rounded" look until advanced stages of starvation. * **Clinical Sign:** The "Monkey facies" seen in Marasmus is due to the eventual loss of even the buccal and periorbital fat pads.

Q: The MOST abundant source of ghrelin is:

Gastric fundus. **Explanation:** **1. Why Gastric Fundus is Correct:** Ghrelin, often referred to as the "hunger hormone," is a 28-amino acid peptide primarily secreted by specialized neuroendocrine cells known as **P/D1 cells** (in humans) or **X/A-like cells** (in rats). The highest density of these cells is found in the **oxyntic mucosa of the gastric fundus**. Ghrelin acts on the hypothalamus to stimulate appetite (orexigenic effect) and promotes the secretion of Growth Hormone from the anterior pituitary. **2. Why Other Options are Incorrect:** * **Gastric Body:** While the body of the stomach contains some ghrelin-producing cells, the concentration is significantly lower than in the fundus. The fundus accounts for approximately 80% of the stomach's ghrelin production. * **Gastric Pylorus & Duodenum:** These areas contain a much smaller population of ghrelin cells. As you move distally from the fundus toward the duodenum, jejunum, and ileum, the concentration of ghrelin-producing cells decreases progressively. **3. High-Yield Clinical Pearls for NEET-PG:** * **Bariatric Surgery:** The dramatic weight loss seen after **Sleeve Gastrectomy** is partly attributed to the surgical removal of the gastric fundus, which leads to a significant drop in circulating ghrelin levels, thereby reducing hunger. * **Prader-Willi Syndrome:** This is a high-yield association where patients have fasting hyperghrelinemia, contributing to hyperphagia and obesity. * **Opposing Hormone:** Remember that **Leptin** (produced by adipose tissue) is the functional antagonist to Ghrelin; Leptin induces satiety, while Ghrelin induces hunger. * **Sleep Deprivation:** Lack of sleep increases ghrelin levels and decreases leptin levels, often leading to weight gain.

Q: Gall bladder bile is different from hepatic bile in that it has:

Less water. **Explanation:** The primary function of the gallbladder is to store and concentrate bile produced by the liver. This concentration process occurs through the active reabsorption of sodium, chloride, and bicarbonate ions across the gallbladder epithelium. Water follows these solutes osmotically, leading to a significant reduction in volume (up to 5–10 times). **1. Why "Less Water" is correct:** As the gallbladder mucosa absorbs electrolytes and water, the bile becomes highly concentrated. Consequently, gallbladder bile has a much lower water content compared to hepatic bile. This allows the gallbladder to store the daily output of hepatic bile in a small anatomical space. **2. Analysis of Incorrect Options:** * **A. Less fatty acids:** Incorrect. As water is removed, the concentration of organic constituents like bile salts, cholesterol, and fatty acids **increases** significantly. * **C. More chloride:** Incorrect. Chloride and bicarbonate are actively **reabsorbed** by the gallbladder mucosa to facilitate water movement, making their concentration lower in gallbladder bile than in hepatic bile. * **D. Less solids:** Incorrect. Because water is removed while bile salts and pigments remain, the percentage of **solids increases** (from ~3% in hepatic bile to ~10–15% in gallbladder bile). **Clinical Pearls for NEET-PG:** * **pH Change:** Gallbladder bile is more **acidic** (pH 7.0–7.4) than hepatic bile (pH 7.8–8.0) due to the reabsorption of alkaline bicarbonate. * **Bile Acid-Dependent Flow:** The most important stimulant for bile secretion is the presence of bile salts in the enterohepatic circulation. * **CCK Role:** Cholecystokinin (CCK) is the most potent stimulus for gallbladder contraction and relaxation of the Sphincter of Oddi.

Q: Intestinal flora (bacteria) digests all EXCEPT:

Lignin. **Explanation:** The human gastrointestinal tract lacks the endogenous enzymes required to break down complex dietary fibers (polysaccharides). This task is performed by the **intestinal microflora** (primarily in the colon) through a process called **fermentation**. **Why Lignin is the correct answer:** Lignin is a complex, non-carbohydrate polymer found in the secondary cell walls of plants. Unlike cellulose or pectin, lignin is highly resistant to both human digestive enzymes and bacterial fermentation. It is considered a **completely indigestible** fiber that passes through the GI tract unchanged, providing bulk to the stool but no nutritional or fermentative byproduct. **Analysis of Incorrect Options:** * **Cellulose (A):** While humans lack cellulase, colonic bacteria possess the enzymes to partially ferment cellulose into short-chain fatty acids (SCFAs). * **Pectin (C):** Pectin is a soluble fiber that is almost **completely fermented** by intestinal bacteria. It is highly fermentable compared to cellulose. * **Starch (D):** Specifically "Resistant Starch" (starch that escapes digestion in the small intestine) is a major substrate for bacterial fermentation in the large bowel. **NEET-PG High-Yield Pearls:** 1. **Short-Chain Fatty Acids (SCFAs):** The primary products of bacterial fermentation are **Acetate, Propionate, and Butyrate**. 2. **Butyrate:** This is the preferred energy source for **colonocytes** and has anti-inflammatory properties. 3. **Gas Production:** Bacterial fermentation also produces gases like $CO_2$, $H_2$, and $CH_4$ (methane). 4. **Dietary Fiber Classification:** Remember that while most fibers are polysaccharides, **Lignin is the exception** (it is a polymer of phenylpropane units).

Q: Which of the following is NOT an action of cholecystokinin?

Stimulation of gastric emptying. **Explanation:** Cholecystokinin (CCK) is a peptide hormone secreted by the **I-cells** of the duodenum and jejunum in response to the presence of peptides, amino acids, and fatty acids. Its primary physiological role is to facilitate digestion by coordinating the release of bile and enzymes while regulating the flow of chyme. **Why Option D is the Correct Answer:** CCK **inhibits** gastric emptying (it does not stimulate it). By slowing the rate at which the stomach empties into the duodenum, CCK ensures that the small intestine has adequate time to neutralize gastric acid and emulsify fats. This is known as the "enterogastric reflex." **Analysis of Incorrect Options:** * **Option A:** CCK causes **contraction of the gallbladder** and simultaneous relaxation of the **Sphincter of Oddi**, which is essential for bile release into the duodenum. * **Option B:** CCK is the most potent stimulator of the acinar cells in the pancreas, leading to the secretion of **pancreatic juice rich in enzymes** (proteases, lipases, and amylases). * **Option C:** CCK stimulates the release of **enterokinase** (enteropeptidase) from the duodenal mucosa. Enterokinase is the "master switch" that converts trypsinogen to active trypsin. **High-Yield NEET-PG Pearls:** * **Stimulus for release:** Fatty acids and amino acids (specifically Tryptophan and Phenylalanine). * **Trophic effect:** CCK promotes the growth (hypertrophy) of the exocrine pancreas. * **Satiety:** CCK acts on the hypothalamus to inhibit food intake (satiety signal). * **Diagnostic use:** The **CCK-HIDA scan** is used to evaluate gallbladder contractility and ejection fraction.

Q: Which of the following is absorbed in the proximal intestine?

Iron. **Explanation:** The absorption of nutrients in the gastrointestinal tract follows a specific anatomical gradient. The **proximal intestine (Duodenum and Jejunum)** is the primary site for the absorption of divalent metal ions and the bulk of macronutrients. **1. Why Iron is Correct:** Iron absorption occurs predominantly in the **duodenum** and upper jejunum. It requires an acidic environment to remain in the soluble ferrous ($Fe^{2+}$) state. The enterocytes in the proximal intestine express specific transporters like **DMT-1** (Divalent Metal Transporter 1) and **Ferroportin** to facilitate this process. **2. Why other options are incorrect:** * **Electrolytes:** While some electrolytes are absorbed proximally, the bulk of electrolyte and water reabsorption occurs throughout the entire length of the small intestine and significantly in the **colon**. * **Bile Salts:** These undergo enterohepatic circulation and are specifically reabsorbed via active transport in the **terminal ileum**. * **Vitamin B12:** After binding to the Intrinsic Factor (IF) in the stomach, the IF-B12 complex is absorbed exclusively in the **terminal ileum** via cubilin receptors. **High-Yield NEET-PG Pearls:** * **Mnemonic for Proximal to Distal absorption:** **"Iron** First, **Folate** Second, **B12** Last" (Duodenum $\rightarrow$ Jejunum $\rightarrow$ Ileum). * **Iron:** Absorbed in the Duodenum. * **Folate:** Absorbed in the Jejunum. * **B12 & Bile Salts:** Absorbed in the Terminal Ileum. * **Clinical Correlation:** Patients with Celiac disease (affecting the proximal bowel) often present with iron-deficiency anemia, whereas Crohn’s disease (affecting the terminal ileum) leads to B12 deficiency and megaloblastic anemia.

Q: Under resting conditions, what is the predominant ion in saliva?

Bicarbonate. **Explanation:** Saliva is a unique hypotonic fluid produced by acinar cells and modified by ductal cells. The composition of saliva is highly dependent on the **flow rate**. **1. Why Bicarbonate is the Correct Answer:** Under **resting (low flow) conditions**, saliva travels slowly through the salivary ducts. This allows ample time for the ductal epithelium to modify the primary secretion. Specifically, the ductal cells secrete **Bicarbonate ($HCO_3^-$)** into the lumen in exchange for Chloride. While the concentrations of Sodium and Chloride decrease significantly during resting states due to reabsorption, Bicarbonate remains relatively high compared to its plasma concentration because of active secretion. Therefore, in a resting state, Bicarbonate is the predominant anion. **2. Why the Other Options are Incorrect:** * **Sodium (A) and Chloride (C):** At resting flow rates, the ductal cells have maximum time to reabsorb $Na^+$ and $Cl^-$. Consequently, their concentrations are at their **lowest** during resting conditions (making saliva most hypotonic). They only increase as the flow rate increases. * **Hydrogen (B):** Saliva is generally alkaline to neutral (pH 6.0–7.4) to protect dental enamel and neutralize gastric acid. High Hydrogen ion concentration would make saliva acidic, which is not the physiological norm. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Flow Rate Rule:** As salivary flow rate **increases**, the composition of saliva becomes more like plasma (Sodium and Chloride levels rise). * **Aldosterone Effect:** Aldosterone acts on salivary ducts just like the renal tubules—increasing $Na^+$ reabsorption and $K^+$ secretion. * **Tonicity:** Saliva is **always hypotonic**, but it is *most* hypotonic at the lowest (resting) flow rates. * **Potassium:** Saliva is the only digestive secretion where the concentration of $K^+$ is always higher than in plasma.

Question 1

Enterochromaffin cells in the gastrointestinal tract secrete which of the following?

Accepted Answer

Both serotonin and histamine

Answer

Serotonin

Answer

Histamine

Answer

Neither serotonin nor histamine

Question 2

Duodenum and Jejunum secrete ALL EXCEPT?

Accepted Answer

VIP

Answer

CCK

Answer

Secretin

Answer

GIP

Question 3

Which of the following nerves provides the efferent impulses necessary for the esophageal actions that occur during swallowing?

Accepted Answer

Vagus

Answer

Glossopharyngeal

Answer

Hypoglossal

Answer

Spinal accessory

Question 4

Which of the following is the last site of fat loss during starvation?

Accepted Answer

Pericardial

Answer

Periorbital

Answer

Buttocks

Answer

Omental

Question 5

The MOST abundant source of ghrelin is:

Accepted Answer

Gastric fundus

Answer

Gastric body

Answer

Gastric pylorus

Answer

First part of duodenum

Question 6

Gall bladder bile is different from hepatic bile in that it has:

Accepted Answer

Less water

Answer

Less fatty acids

Answer

More chloride

Answer

Less solids

Question 7

Intestinal flora (bacteria) digests all EXCEPT:

Accepted Answer

Lignin

Answer

Cellulose

Answer

Pectin

Answer

Starch

Question 8

Which of the following is NOT an action of cholecystokinin?

Accepted Answer

Stimulation of gastric emptying

Answer

Contraction of the gallbladder

Answer

Secretion of pancreatic juice rich in enzymes

Answer

Increased secretion of enterokinase

Question 9

Which of the following is absorbed in the proximal intestine?

Accepted Answer

Iron

Answer

Electrolytes

Answer

Bile salts

Answer

Vitamin B12

Question 10

Under resting conditions, what is the predominant ion in saliva?

Accepted Answer

Bicarbonate

Answer

Sodium

Answer

Hydrogen

Answer

Chloride

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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