Gastrointestinal System — MCQs

Gastrointestinal System Indian Medical PG Practice Questions and MCQs

Question 231: Which of the following is NOT exclusively produced by the liver?

A. Factor VII
B. Prothrombin
C. Globulin (Correct Answer)
D. Albumin

Explanation: **Explanation:** The liver is the primary metabolic factory of the body, responsible for synthesizing the majority of plasma proteins. However, the production of **Globulins** is the exception to this rule of exclusivity. 1. **Why Globulin is the correct answer:** Plasma globulins are divided into alpha ($\alpha$), beta ($\beta$), and gamma ($\gamma$) fractions. While $\alpha$ and $\beta$ globulins are synthesized by the liver, **Gamma-globulins (Immunoglobulins)** are produced by **plasma cells** (derived from B-lymphocytes) in the lymphoid tissue. Since a significant portion of the globulin fraction is produced extra-hepatically, it is not "exclusively" a liver product. 2. **Why the other options are incorrect:** * **Albumin:** This is the most abundant plasma protein and is synthesized **exclusively** by hepatocytes. It is a key marker of the liver's synthetic function. * **Factor VII & Prothrombin (Factor II):** These are Vitamin K-dependent clotting factors synthesized **exclusively** by the liver. In severe liver disease, their levels drop rapidly due to their short half-lives (especially Factor VII). **High-Yield Clinical Pearls for NEET-PG:** * **Albumin-Globulin (A:G) Ratio:** In chronic liver disease (like Cirrhosis), the A:G ratio is **reversed**. Albumin decreases (due to liver failure) and Globulins increase (due to compensatory immune activation), dropping the ratio below the normal 1.7:1. * **Shortest Half-life:** Factor VII has the shortest half-life of all clotting factors (~4–6 hours), making **Prothrombin Time (PT)** the earliest indicator of acute liver damage. * **Exceptions:** All clotting factors are produced in the liver **except** Factor VIII (produced by vascular endothelium) and von Willebrand Factor.

Question 232: Which of the following statements is true regarding Basal Metabolic Rate (BMR)?

A. BMR is not influenced by energy intake.
B. BMR increases in response to starvation.
C. BMR may decrease up to 50% during periods of starvation. (Correct Answer)
D. BMR is not responsive to changes in hormonal levels.

Explanation: ### Explanation **Correct Answer: C. BMR may decrease up to 50% during periods of starvation.** **1. Why the Correct Answer is Right:** Basal Metabolic Rate (BMR) represents the minimum energy expenditure required to maintain vital functions at rest. During prolonged starvation or malnutrition, the body initiates a compensatory mechanism to conserve energy. This involves a reduction in sympathetic nervous system activity and a decrease in the levels of metabolic hormones (primarily Thyroid hormones and Leptin). Consequently, the BMR can drop significantly—by as much as **10% to 50%**—to ensure survival by slowing down the depletion of energy stores. **2. Why the Incorrect Options are Wrong:** * **Option A:** BMR is heavily influenced by energy intake. Chronic overeating can increase BMR (via diet-induced thermogenesis), while calorie restriction decreases it. * **Option B:** BMR **decreases**, not increases, during starvation. An increase would lead to rapid depletion of fat and muscle mass, which is maladaptive. * **Option D:** BMR is highly sensitive to hormones. **Thyroxine (T4)** is the primary determinant of BMR; hyperthyroidism increases BMR, while hypothyroidism decreases it. Other hormones like epinephrine, testosterone, and growth hormone also increase BMR. **3. NEET-PG High-Yield Pearls:** * **Standard Conditions for BMR:** Measured 12 hours after the last meal (post-absorptive state), at physical and mental rest, in a thermoneutral environment. * **Surface Area Rule:** BMR is more closely related to **surface area** than to body weight. * **Gender & Age:** BMR is generally **higher in males** (due to higher muscle mass) and **decreases with age** (approx. 2% per decade after age 20). * **Specific Dynamic Action (SDA):** Also known as the thermic effect of food; it is highest for **proteins (30%)**, followed by carbohydrates (6%) and fats (4%).

Question 233: Zollinger-Ellison syndrome is due to increased secretion of

A. Gastrin (Correct Answer)
B. Secretin
C. VIP
D. Cholecystokinin

Explanation: **Explanation:** **Zollinger-Ellison Syndrome (ZES)** is caused by a gastrin-secreting neuroendocrine tumor, known as a **Gastrinoma**, typically located in the "gastrinoma triangle" (duodenum, pancreas, or porta hepatis). 1. **Why Gastrin is correct:** Gastrin is the primary hormone secreted in excess in ZES. It acts on the parietal cells of the stomach (via CCK-B receptors) and stimulates the release of histamine from ECL cells, leading to massive **hypersecretion of gastric acid**. This results in severe, recurrent, and often refractory peptic ulcers and diarrhea. 2. **Why other options are incorrect:** * **Secretin:** Secreted by S-cells of the duodenum; its primary role is to stimulate bicarbonate secretion from the pancreas. In ZES, a "Secretin Stimulation Test" is actually used for diagnosis, as secretin paradoxically *increases* gastrin levels in gastrinoma cells. * **VIP (Vasoactive Intestinal Peptide):** Excess VIP leads to **WDHA Syndrome** (Watery Diarrhea, Hypokalemia, Achlorhydria), also known as Verner-Morrison syndrome, not ZES. * **Cholecystokinin (CCK):** Responsible for gallbladder contraction and pancreatic enzyme secretion; it is not associated with a specific hypersecretory tumor syndrome like ZES. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Most gastrinomas are found in the **duodenum** (more common) or pancreas. * **Clinical Triad:** Hypergastrinemia, severe peptic ulcer disease, and non-beta islet cell tumor. * **Association:** Approximately 25% of ZES cases are associated with **Multiple Endocrine Neoplasia Type 1 (MEN-1)**. * **Diagnosis:** Best initial test is fasting serum gastrin levels (>1000 pg/mL is diagnostic). The most specific provocative test is the **Secretin Stimulation Test**.

Question 234: What is the most important hormone that increases gallbladder contraction after a fatty meal?

A. Gastrin
B. Secretin
C. Cholecystokinin (CCK) (Correct Answer)
D. Gastric inhibitory peptide (GIP)

Explanation: **Explanation:** The correct answer is **Cholecystokinin (CCK)**. CCK is the primary physiological mediator of gallbladder contraction and pancreatic enzyme secretion in response to a meal. **Why CCK is the correct answer:** CCK is synthesized and secreted by the **I-cells** of the duodenum and proximal jejunum. The most potent stimulus for its release is the presence of **fatty acids** and amino acids in the intestinal lumen. Once released into the bloodstream, CCK acts via two mechanisms: 1. It causes forceful **contraction of the gallbladder** smooth muscle. 2. It induces **relaxation of the Sphincter of Oddi**, allowing bile to flow into the duodenum to emulsify fats. **Why the other options are incorrect:** * **Gastrin:** Produced by G-cells, its primary role is stimulating gastric acid (HCl) secretion and mucosal growth. It has minimal effect on the gallbladder. * **Secretin:** Produced by S-cells in response to low pH (acid), it primarily stimulates the secretion of **bicarbonate-rich** pancreatic juice. It is often called "Nature's Antacid." * **Gastric Inhibitory Peptide (GIP):** Now known as Glucose-dependent Insulinotropic Peptide, it is released by K-cells. Its main functions are stimulating insulin release and inhibiting gastric acid secretion. **NEET-PG High-Yield Pearls:** * **CCK Family:** CCK is structurally related to Gastrin (both share the same C-terminal pentapeptide sequence). * **Diagnostic Use:** A "CCK-HIDA scan" is used clinically to assess gallbladder ejection fraction in suspected biliary dyskinesia. * **Vagal Influence:** While CCK is the *most important* hormonal stimulus, the **Vagus nerve** (ACh) provides the neural stimulus for gallbladder contraction during the cephalic phase of digestion.

Question 235: What are the actions of pure gastrin?

A. Stimulation of pepsin secretion
B. Stimulation of gastric motility
C. Increased flow of hepatic bile
D. All of the above (Correct Answer)

Explanation: **Explanation:** Gastrin is a peptide hormone primarily secreted by the **G-cells** of the gastric antrum and duodenum. Its physiological actions are mediated via **CCK-B receptors**, leading to several downstream effects on the gastrointestinal tract. 1. **Stimulation of Pepsin Secretion:** While gastrin’s primary role is the stimulation of gastric acid (HCl) from parietal cells, it also acts on **Chief cells** to increase the secretion of pepsinogen (the precursor to pepsin). 2. **Stimulation of Gastric Motility:** Gastrin promotes gastric emptying and increases the contractility of the antral muscle. It also has a trophic (growth) effect on the gastric mucosa. 3. **Increased Flow of Hepatic Bile:** Gastrin stimulates the liver to increase the secretion of bile (choleresis). It also stimulates pancreatic enzyme secretion and gallbladder contraction, though it is less potent in these roles than Cholecystokinin (CCK). **Why "All of the above" is correct:** Since gastrin independently stimulates chief cells (Option A), enhances antral contractions (Option B), and promotes bile flow (Option C), all three statements are physiological actions of the hormone. **High-Yield NEET-PG Pearls:** * **Most Potent Stimulus:** Luminal peptides and amino acids (Phenylalanine and Tryptophan) are the strongest stimuli for gastrin release. * **Inhibition:** Gastrin release is inhibited by a luminal pH < 1.5 and by the hormone **Somatostatin**. * **Zollinger-Ellison Syndrome:** A gastrin-secreting tumor (gastrinoma) leading to hyperchlorhydria and multiple refractory peptic ulcers. * **Trophic Effect:** Gastrin is unique for its ability to cause hyperplasia and hypertrophy of the gastric mucosa.

Question 236: All of the following enzymes are secreted by the exocrine pancreas except?

A. Trypsin
B. Chymotrypsin
C. Carboxypeptidase
D. Pepsin (Correct Answer)

Explanation: **Explanation:** The exocrine pancreas secretes a variety of digestive enzymes into the duodenum to break down proteins, carbohydrates, and fats. The correct answer is **Pepsin** because it is not a pancreatic enzyme; rather, it is secreted by the **stomach**. **1. Why Pepsin is the Correct Answer:** Pepsin is secreted by the **Chief cells (Peptic cells)** of the gastric mucosa as an inactive precursor called **pepsinogen**. It is activated into pepsin by the acidic environment (HCl) of the stomach. Its primary role is the initial digestion of proteins into smaller peptides in the stomach, functioning optimally at a low pH (1.8–3.5). **2. Analysis of Incorrect Options (Pancreatic Proteases):** The pancreas secretes several proteolytic enzymes, all of which are released as inactive **zymogens** to prevent autodigestion of the gland: * **Trypsin (from Trypsinogen):** Activated by the brush-border enzyme *enterokinase*. It is the "master activator" that activates all other pancreatic zymogens. * **Chymotrypsin (from Chymotrypsinogen):** Activated by trypsin; it breaks down proteins into polypeptides. * **Carboxypeptidase (from Procarboxypeptidase):** An exopeptidase activated by trypsin that cleaves amino acids from the carboxyl end of peptides. **Clinical Pearls for NEET-PG:** * **Enterokinase (Enteropeptidase):** Deficiency of this duodenal enzyme leads to functional pancreatic insufficiency because trypsinogen cannot be activated. * **Steatorrhea:** Occurs when pancreatic lipase secretion falls below 10% of normal, leading to fatty, foul-smelling stools. * **Bicarbonate:** Secreted by pancreatic **ductal cells** (stimulated by Secretin), whereas enzymes are secreted by **acinar cells** (stimulated by CCK).

Question 237: Which of the following bowel movements is not seen in a normal individual?

A. Peristalsis
B. Peristaltic rush (Correct Answer)
C. Segmentation contraction
D. Migrating motor complex

Explanation: **Explanation:** The correct answer is **B. Peristaltic rush**. **1. Why Peristaltic Rush is the correct answer:** Peristaltic rush (also known as *borborygmi* or power propulsion) is a powerful, rapid wave of contraction that travels long distances over the small intestine in a very short time. Unlike normal movements, it is **pathological**. It is triggered by severe mucosal irritation (e.g., infectious diarrhea, chemical irritants, or mechanical obstruction). Its physiological purpose is to rapidly sweep harmful contents into the colon to relieve the small intestine of irritants. **2. Analysis of Incorrect Options:** * **A. Peristalsis:** This is the fundamental "propulsive" movement seen in a normal individual. It involves a contraction ring moving aborally to push chyme forward. * **C. Segmentation contraction:** This is the most common movement in the small intestine during the fed state. It involves localized rhythmic contractions that mix chyme with digestive juices and increase contact with the mucosa for absorption. * **D. Migrating Motor Complex (MMC):** This is a normal "housekeeping" movement seen during the **fasting state**. It occurs every 90–120 minutes to clear the stomach and small intestine of residual undigested food and bacteria. It is mediated by the hormone **Motilin**. **Clinical Pearls for NEET-PG:** * **Law of the Gut:** Distension of the gut initiates peristalsis; the wave always moves towards the anus (Polarity of the intestine). * **MMC Phases:** Phase III is the most active phase (intense contractions). MMC is inhibited by feeding. * **Gastroileal Reflex:** Increased gastric activity causes increased motility in the ileum and relaxation of the ileocecal sphincter (mediated by Gastrin and ANS). * **Vomiting:** Often preceded by **anti-peristalsis** (reverse peristalsis), which is also not a regular feature of healthy digestion but a protective reflex.

Question 238: Gastric emptying is mainly regulated by which of the following?

A. Neural reflexes
B. Enteric reflexes (Correct Answer)
C. Local hormones in the stomach
D. Local hormones in the duodenum

Explanation: **Explanation:** Gastric emptying is a highly regulated process that ensures the duodenum receives chyme at a rate it can effectively process. The primary control mechanism is the **Enterogastric Reflex** (a type of enteric reflex). **1. Why Enteric Reflexes are Correct:** The rate of gastric emptying is primarily determined by signals from the **duodenum**. When the duodenum is distended or contains hypertonic, acidic, or fatty chyme, it triggers the enterogastric reflex. This reflex is mediated through the **Enteric Nervous System (ENS)**—specifically the myenteric plexus—which inhibits antral contractions and increases pyloric sphincter tone, thereby slowing emptying. While autonomic nerves can modulate this, the intrinsic enteric circuitry is the fundamental regulator. **2. Why Other Options are Incorrect:** * **Neural Reflexes (A):** While the Vagus nerve (parasympathetic) and sympathetic fibers influence motility, they act as modulators. The core, moment-to-moment regulation is intrinsic to the gut wall. * **Local Hormones in the Stomach (C):** Gastrin (produced in the stomach) actually *promotes* gastric emptying by increasing antral pump activity; it does not serve as the primary regulatory "brake." * **Local Hormones in the Duodenum (D):** Hormones like Cholecystokinin (CCK), Secretin, and GIP (Enterogastrones) do inhibit emptying. However, in the hierarchy of physiological control, the **rapid neural enteric reflex** is the immediate and dominant regulator compared to the slower hormonal response. **High-Yield Clinical Pearls for NEET-PG:** * **The "Ileal Brake":** Presence of undigested food in the ileum also slows gastric emptying (mediated by GLP-1 and Peptide YY). * **Most Potent Stimulus:** Fat in the duodenum is the most potent stimulus for slowing gastric emptying (via CCK). * **Liquids vs. Solids:** Isotonic liquids empty the fastest; solids must be reduced to particles <2mm (chyme) before passing the pylorus.

Question 239: Which hormone is secreted from the stomach that controls food intake?

A. Orexin
B. Insulin-like growth factor
C. Cholecystokinin
D. Ghrelin (Correct Answer)

Explanation: **Explanation:** **Ghrelin** is the correct answer because it is the only known circulating hormone that acts as a potent **orexigenic** (appetite-stimulant) signal. It is primarily secreted by the **P/D1 cells** (oxyntic cells) in the fundus of the stomach. Ghrelin levels rise sharply before meals (during fasting) and fall rapidly after food intake. It acts on the arcuate nucleus of the hypothalamus to stimulate the release of Neuropeptide Y (NPY) and Agouti-related peptide (AgRP), which increase hunger. **Analysis of Incorrect Options:** * **A. Orexin:** Also known as hypocretin, these are neuropeptides produced in the **lateral hypothalamus**, not the stomach. They regulate wakefulness and food intake. * **B. Insulin-like growth factor (IGF):** Primarily produced in the **liver** in response to Growth Hormone. It is involved in cell growth and development rather than the acute control of food intake. * **C. Cholecystokinin (CCK):** Secreted by **I-cells of the duodenum and jejunum**. Unlike Ghrelin, CCK is an **anorexigenic** hormone; it promotes satiety and inhibits gastric emptying. **High-Yield Clinical Pearls for NEET-PG:** * **"The Hunger Hormone":** Ghrelin is the only peripheral hormone that increases appetite. * **Prader-Willi Syndrome:** Characterized by hyperphagia and obesity due to pathologically high levels of Ghrelin. * **Bariatric Surgery:** Gastric bypass or sleeve gastrectomy leads to a significant drop in Ghrelin levels because the fundus (the primary source) is removed or bypassed, contributing to postoperative weight loss. * **Sleep Deprivation:** Lack of sleep increases Ghrelin and decreases Leptin, leading to increased appetite and obesity risk.

Question 240: Maximum postprandial motility is seen in which part of the colon?

A. Ascending colon
B. Transverse colon
C. Descending colon (Correct Answer)
D. Sigmoid colon

Explanation: **Explanation:** The correct answer is **Descending colon**. **1. Why the Descending Colon is Correct:** Postprandial motility is primarily driven by the **gastrocolic reflex**, a physiological reflex where the distension of the stomach by food triggers increased propulsive activity in the colon. While the reflex affects the entire large intestine, physiological studies using manometry have demonstrated that the **descending colon** exhibits the highest increase in phasic and propulsive contractile activity following a meal. This is functionally significant as it facilitates the movement of fecal matter toward the rectum for eventual defecation. **2. Why the Other Options are Incorrect:** * **Ascending Colon:** This region is primarily involved in the absorption of water and electrolytes and the mixing of contents (haustral churning). While it shows increased activity post-meal, its motility is less intense compared to the distal segments. * **Transverse Colon:** This acts as a primary site for storage and further dehydration of feces. Its postprandial response is moderate but serves more as a conduit than the primary site of maximal contractile force. * **Sigmoid Colon:** Although the sigmoid colon is highly active and often the site of high pressure (relevant in diverticulosis), the peak increase in *propulsive* motility immediately following a meal is recorded in the descending colon. **3. Clinical Pearls for NEET-PG:** * **Gastrocolic Reflex:** Mediated by gastrin and the extrinsic autonomic nervous system (parasympathetic). * **Mass Movements:** These are giant migrating contractions that occur 1–3 times per day, usually after breakfast, and are the primary force moving contents into the rectum. * **Site of slowest transit:** The rectosigmoid junction generally has the slowest transit to allow for storage. * **Irritable Bowel Syndrome (IBS):** Patients often have an exaggerated gastrocolic reflex, leading to immediate postprandial urgency.

Practice by Chapter

Gastrointestinal Motility

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Gastrointestinal Secretions

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Digestion and Absorption

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Gastrointestinal Hormones

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Hepatobiliary Physiology

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Pancreatic Exocrine Function

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Gastrointestinal Circulation

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Intestinal Immune System

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Gut Microbiome

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Regulation of Food Intake

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