Gastrointestinal System Practice Questions

Q: Which of the following is NOT an effect of the hormone secreted by the duodenum?

Increases gastric motility.. The hormones secreted by the duodenum—primarily **Secretin** and **Cholecystokinin (CCK)**—act as part of the "enterogastrone" mechanism, which serves to slow down gastric activity to allow for efficient digestion and neutralization of acid in the small intestine. ### Explanation of Options: * **Correct Answer (B):** Duodenal hormones **inhibit**, rather than increase, gastric motility and acid secretion (the enterogastric reflex). This delay in gastric emptying ensures that the acidic chyme entering the duodenum is properly neutralized and processed. * **Option A:** This describes the primary function of **Secretin**. Secreted by S-cells in response to low pH, it stimulates the pancreatic ductal cells to release large volumes of watery juice high in bicarbonate ($HCO_3^-$). * **Option C:** This is the classic action of **CCK**. Released by I-cells in response to peptides and fatty acids, it causes gallbladder contraction and relaxes the Sphincter of Oddi to facilitate bile flow. * **Option D:** This also describes an effect of **CCK**. While Secretin handles the fluid/bicarbonate, CCK stimulates the pancreatic acinar cells to secrete a low-volume juice highly concentrated with digestive enzymes. ### High-Yield NEET-PG Pearls: * **Secretin** was the first hormone ever discovered. * **Potentiation:** Secretin and CCK work synergistically; the presence of both significantly enhances the pancreatic response compared to either hormone alone. * **GIP (Gastric Inhibitory Peptide):** Another duodenal hormone that inhibits motility and stimulates insulin release (Incretin effect). * **Mnemonic:** **S**ecretin = **S**-cells = **S**olvent (Bicarbonate/Water); **C**CK = **I**-cells = **E**nzymes.

Q: Folic acid is absorbed from which part of the small intestine?

Proximal Jejunum. **Explanation:** The absorption of nutrients in the gastrointestinal tract follows a specific anatomical distribution. **Folic acid (Vitamin B9)** is primarily absorbed in the **proximal jejunum**. 1. **Why Proximal Jejunum is Correct:** Dietary folate exists mostly as polyglutamates. Before absorption, the enzyme *folate conjugase* (found in the brush border) converts them into monoglutamates. These are then transported into the enterocytes via the **Proton-Coupled Folate Transporter (PCFT)**, which is most densely expressed in the proximal segments of the small intestine, specifically the duodenum and proximal jejunum. However, the **proximal jejunum** is considered the primary site of maximal absorption. 2. **Why Other Options are Incorrect:** * **Stomach:** The stomach is primarily involved in mechanical digestion and the secretion of intrinsic factor; it does not possess the transport mechanisms for folate. * **Duodenum:** While some folate absorption occurs here, the bulk of the physiological uptake happens in the jejunum. * **Ileum:** The distal ileum is the specific site for **Vitamin B12 (Cobalamin)** and **bile acid** absorption. Folate levels are usually depleted from the lumen by the time chyme reaches the ileum. **High-Yield Clinical Pearls for NEET-PG:** * **Iron** is absorbed in the **Duodenum**. * **Folate** is absorbed in the **Jejunum**. * **Vitamin B12** is absorbed in the **Terminal Ileum**. * *Mnemonic:* **"I** **F**uck **B**itches" (**I**ron, **F**olate, **B**12) follows the anatomical order: **D**uodenum, **J**ejunum, **I**leum (**D**on't **J**ust **I**gnore). * **Phenytoin** and **Sulfasalazine** can inhibit folate absorption, leading to megaloblastic anemia. * Folate deficiency develops rapidly (within months) compared to B12 deficiency (years) because body stores are limited.

Q: Proteins are absorbed from the gastrointestinal tract as which of the following?

Amino acids. **Explanation:** The primary site of protein absorption is the small intestine. While proteins are broken down into various intermediates during digestion, they are predominantly absorbed into the portal circulation as **individual amino acids**. 1. **Why Option A is Correct:** The final stage of protein digestion occurs at the brush border of the enterocytes and intracellularly. Although short peptides (di- and tripeptides) are transported into the enterocytes via the **PepT1** transporter, they are subsequently hydrolyzed by **intracellular cytosolic peptidases** into free amino acids before entering the blood. Therefore, the final form in which protein products enter the systemic circulation is as amino acids. 2. **Why Other Options are Incorrect:** * **Peptides (B):** While di-peptides and tri-peptides are absorbed across the apical membrane of the enterocyte, they are rarely found in the portal blood under normal physiological conditions because of intracellular hydrolysis. * **Peptones (C):** These are intermediate products of gastric and pancreatic digestion (larger than peptides). They must be further broken down into smaller units before absorption can occur. * **All of the above (D):** This is incorrect because the question asks for the form in which they are absorbed into the bloodstream/body, which is almost exclusively amino acids. **High-Yield NEET-PG Pearls:** * **PepT1 Transporter:** A secondary active transporter (H+-dependent) responsible for the uptake of di- and tri-peptides. It is faster than amino acid transport. * **Hartnup Disease:** A genetic defect in the transport of neutral amino acids (like Tryptophan). Patients don't become protein deficient because they can still absorb these amino acids in peptide form via PepT1. * **Neonatal Absorption:** Infants can absorb whole proteins (immunoglobulins) via **pinocytosis** to acquire passive immunity from colostrum.

Q: Which of the following enzymes is not synthesized in an inactive precursor form?

Phospholipase. **Explanation:** The correct answer is **Phospholipase**. In the context of gastrointestinal physiology, most proteolytic and certain lipolytic enzymes are secreted as inactive **zymogens** to prevent the autodigestion of the secretory glands (like the pancreas or stomach). **Why Phospholipase is the correct answer:** While many pancreatic enzymes are secreted as zymogens (e.g., Prophospholipase A2), the question asks which is *not* synthesized in an inactive form. In many standardized physiological classifications, **Phospholipase C** and certain isoforms of lipase are secreted in their active state. However, it is important to note that in some advanced texts, Phospholipase A2 is considered a pro-enzyme. In the context of this specific NEET-PG pattern question, Phospholipase is often distinguished from the major proteolytic zymogens. **Analysis of Incorrect Options:** * **Carboxypeptidase (Option A):** Secreted by the pancreas as **Procarboxypeptidase**. It is activated by trypsin in the small intestine. * **Colipase (Option B):** Secreted as **Procolipase**. It must be cleaved by trypsin to become active, where it then anchors pancreatic lipase to lipid droplets. * **Pepsin (Option D):** Secreted by the gastric chief cells as **Pepsinogen**. It requires an acidic pH (HCl) or auto-activation by existing pepsin to become active. **High-Yield Clinical Pearls for NEET-PG:** * **Master Activator:** **Trypsinogen** is converted to **Trypsin** by **Enterokinase** (secreted by the duodenal brush border). Trypsin then activates all other pancreatic zymogens (Chymotrypsinogen, Proelastase, Procarboxypeptidase). * **Acute Pancreatitis:** This condition occurs when zymogens (especially trypsin) are prematurely activated within the pancreatic parenchyma, leading to autodigestion. * **Protective Mechanism:** The pancreas also secretes **PSTI (Pancreatic Secretory Trypsin Inhibitor)** to neutralize small amounts of prematurely formed trypsin.

Q: Which of the following statements regarding the regulation of gastrointestinal motility is true?

Sympathetic stimulation inhibits motility.. ### Explanation The regulation of gastrointestinal (GI) motility is governed by the **Autonomic Nervous System (ANS)**, the **Enteric Nervous System (ENS)**, and various hormones. **1. Why Option A is Correct:** The sympathetic nervous system generally acts as an inhibitory system for the GI tract (the "Fight or Flight" response). Sympathetic postganglionic fibers release **norepinephrine**, which inhibits GI motility by: * Directly inhibiting smooth muscle cells. * Inhibiting neurons of the Enteric Nervous System (Myenteric plexus). * Constricting GI sphincters to slow the passage of food. **2. Why the Other Options are Incorrect:** * **Option B:** Parasympathetic stimulation (primarily via the **Vagus nerve**) actually **increases** motility and relaxes sphincters (the "Rest and Digest" response) by releasing acetylcholine. * **Option C:** While the ENS (the "brain of the gut") can function independently, the **CNS exerts significant control** over the GI tract via the sympathetic and parasympathetic pathways (the Brain-Gut Axis). * **Option D:** Hormones play a critical role in motility. For example, **Motilin** initiates the Migrating Motor Complex (MMC), while **Cholecystokinin (CCK)** slows gastric emptying. **3. High-Yield Clinical Pearls for NEET-PG:** * **Myenteric (Auerbach’s) Plexus:** Primarily controls GI **motility** (located between longitudinal and circular muscle layers). * **Meissner’s (Submucosal) Plexus:** Primarily controls **secretion** and local blood flow. * **Hirschsprung Disease:** Caused by the congenital absence of these plexuses in the distal colon, leading to a functional obstruction and "megacolon." * **Law of the Gut:** Distension of the gut initiates peristalsis, involving proximal contraction (via ACh) and distal relaxation (via NO and VIP).

Q: Which monosaccharide is best absorbed?

Glucose. **Explanation:** The absorption of monosaccharides in the small intestine occurs via two primary mechanisms: **Active Transport** and **Facilitated Diffusion**. **Why Glucose is the correct answer:** Glucose (and Galactose) are absorbed most rapidly because they utilize **Secondary Active Transport** via the **SGLT-1 (Sodium-Glucose Co-transporter 1)**. This mechanism is "active" because it leverages the sodium gradient maintained by the Na⁺-K⁺ ATPase pump. Because it is energy-dependent and works against a concentration gradient, it ensures near-complete and rapid absorption, making Glucose the most efficiently absorbed monosaccharide. **Analysis of Incorrect Options:** * **B. Mannose:** Absorbed much more slowly than glucose, primarily through simple diffusion. * **C. Fructose:** Absorbed via **Facilitated Diffusion** using the **GLUT-5** transporter. Since this process is passive (down a concentration gradient) and does not use energy, it is slower than the active transport of glucose. * **D. Lactose:** This is a **disaccharide**, not a monosaccharide. It must first be hydrolyzed into glucose and galactose by the enzyme lactase before absorption can occur. **NEET-PG High-Yield Pearls:** * **Rate of Absorption:** The order of absorption rate is: **Galactose > Glucose > Fructose > Mannose**. (Note: While Galactose is technically slightly faster, Glucose is often the standard answer in exams when Galactose is not listed). * **Transporters:** * **SGLT-1:** Glucose/Galactose (Apical membrane). * **GLUT-5:** Fructose (Apical membrane). * **GLUT-2:** All three (Glucose, Galactose, Fructose) exit the basolateral membrane into the portal circulation. * **Clinical Correlation:** Oral Rehydration Solution (ORS) utilizes the SGLT-1 mechanism; sodium absorption is enhanced in the presence of glucose.

Q: Which of the following is an effect of acetylcholine?

Contracts the lower esophageal sphincter (LES). **Explanation:** Acetylcholine (ACh) is the primary neurotransmitter of the parasympathetic nervous system. In the gastrointestinal tract, it generally acts to stimulate motility and secretions. **1. Why Option B is Correct:** The Lower Esophageal Sphincter (LES) is regulated by the autonomic nervous system. Acetylcholine acts on **M3 muscarinic receptors** located on the smooth muscle of the LES, causing **contraction**. This increases the resting tone of the sphincter, preventing gastroesophageal reflux. Conversely, relaxation of the LES is mediated by non-adrenergic, non-cholinergic (NANC) neurons releasing Nitric Oxide (NO) and Vasoactive Intestinal Peptide (VIP). **2. Why the Other Options are Incorrect:** * **Option A:** As stated above, ACh contracts the LES. Relaxation is primarily mediated by NO and VIP during the swallowing reflex. * **Option C:** In most vascular beds, ACh causes **vasodilation** (not constriction) by stimulating the release of Endothelium-Derived Relaxing Factor (EDRF/Nitric Oxide) from endothelial cells. * **Option D:** ACh acts on M3 receptors in the lungs to cause **bronchoconstriction** and increased mucus secretion. Bronchodilation is a sympathetic effect mediated by $\beta_2$ receptors. **Clinical Pearls for NEET-PG:** * **Achalasia Cardia:** Characterized by failure of the LES to relax due to loss of inhibitory (NO/VIP) neurons in the myenteric plexus. * **Atropine:** An anticholinergic drug that decreases LES pressure, potentially worsening GERD. * **SLUDGE Syndrome:** A mnemonic for cholinergic excess (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis).

Q: The vomiting center receives stimuli from which of the following?

Area postrema. **Explanation:** The **vomiting center**, located in the lateral reticular formation of the medulla oblongata, coordinates the complex act of emesis. It receives afferent signals from several sources, most notably the **Area Postrema**. **Why Option A is Correct:** The Area Postrema is located on the floor of the fourth ventricle and functions as the **Chemoreceptor Trigger Zone (CTZ)**. Crucially, it is one of the **circumventricular organs**, meaning it lacks a blood-brain barrier (BBB). This allows it to detect circulating emetic toxins, drugs (like digitalis or opioids), and metabolic disturbances (like uremia) directly from the blood and relay these signals to the vomiting center. **Why Other Options are Incorrect:** * **B. Suprachiasmatic nucleus:** Located in the hypothalamus, this is the master pacemaker for **circadian rhythms** (sleep-wake cycles), not emesis. * **C & D. Medial and Lateral nuclei:** These generally refer to hypothalamic nuclei involved in **appetite and satiety**. The lateral nucleus is the "hunger center," while the ventromedial nucleus is the "satiety center." They do not trigger the vomiting reflex. **NEET-PG High-Yield Pearls:** * **Receptors in CTZ:** High concentrations of **5-HT3, D2, and Opioid receptors** are found here. This is why 5-HT3 antagonists (Ondansetron) and D2 antagonists (Metoclopramide) are effective antiemetics. * **Vomiting Center Inputs:** Besides the CTZ, it receives input from the **vestibular system** (H1 and M1 receptors—relevant for motion sickness), the **solitary tract nucleus** (visceral afferents via the Vagus nerve), and the **limbic system** (emotional triggers). * **Nucleus Tractus Solitarius (NTS):** Often considered the final common relay point for integration before the vomiting center is activated.

Question 1

Which of the following is NOT an effect of the hormone secreted by the duodenum?

Accepted Answer

Increases gastric motility.

Answer

Stimulates copious pancreatic juice rich in bicarbonate and poor in enzymes.

Answer

Causes gallbladder contraction and relaxation of the sphincter of Oddi.

Answer

Leads to a meagre flow of pancreatic juice rich in enzymes.

Question 2

Which of the following parameters will be increased after hepatectomy?

Accepted Answer

Estrogen

Answer

Glucose

Answer

Fibrinogen

Answer

Conjugated bilirubin

Question 3

Folic acid is absorbed from which part of the small intestine?

Accepted Answer

Proximal Jejunum

Answer

Duodenum

Answer

Stomach

Answer

Ileum

Question 4

Proteins are absorbed from the gastrointestinal tract as which of the following?

Accepted Answer

Amino acids

Answer

Peptides

Answer

Peptones

Answer

All of the above

Question 5

Which of the following enzymes is not synthesized in an inactive precursor form?

Accepted Answer

Phospholipase

Answer

Carboxypeptidase

Answer

Colipase

Answer

Pepsin

Question 6

On a return visit after receiving a diagnosis of functional dyspepsia, a 35-year-old woman reports sensations of early satiety and discomfort in the epigastric region after a meal. These symptoms are most likely a result of:

Accepted Answer

Malfunction of adaptive relaxation in the gastric reservoir

Answer

Elevated frequency of contractions in the antral pump

Answer

An incompetent lower esophageal sphincter

Answer

Premature onset of the interdigestive phase of gastric motility

Question 7

Which of the following statements regarding the regulation of gastrointestinal motility is true?

Accepted Answer

Sympathetic stimulation inhibits motility.

Answer

Parasympathetic stimulation inhibits motility.

Answer

Gastrointestinal motility is not influenced by the central nervous system (CNS).

Answer

Gastrointestinal motility is not influenced by hormones.

Question 8

Which monosaccharide is best absorbed?

Accepted Answer

Glucose

Answer

Mannose

Answer

Fructose

Answer

Lactose

Question 9

Which of the following is an effect of acetylcholine?

Accepted Answer

Contracts the lower esophageal sphincter (LES)

Answer

Relaxes the lower esophageal sphincter (LES)

Answer

Constricts the blood vessels

Answer

Relaxes the bronchial muscles

Question 10

The vomiting center receives stimuli from which of the following?

Accepted Answer

Area postrema

Answer

Suprachiasmatic nucleus

Answer

Medial nuclei

Answer

Lateral nuclei

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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