Gastrointestinal System Practice Questions

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

Ghrelin. **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.

Q: Which of the following increases HCI secretion during the gastric phase of digestion?

Gastrin. **Explanation:** The gastric phase of digestion begins when food enters the stomach, causing distension and an increase in pH. This phase accounts for approximately 60% of total acid secretion. **Why Gastrin is Correct:** Gastrin is the primary hormone responsible for stimulating HCl secretion during the gastric phase. It is secreted by **G-cells** in the antrum of the stomach in response to stomach distension, presence of amino acids/peptides, and vagal stimulation (via Gastrin-Releasing Peptide). Gastrin stimulates parietal cells directly and indirectly by triggering **Histamine** release from Enterochromaffin-like (ECL) cells, which is the most potent stimulator of HCl production. **Why Other Options are Incorrect:** * **Pepsinogen (A):** This is an inactive proenzyme (zymogen) secreted by Chief cells. It is converted to pepsin by HCl to digest proteins but does not stimulate acid secretion itself. * **Cholecystokinin (B):** CCK is secreted by I-cells of the duodenum. While it stimulates pancreatic enzyme secretion and gallbladder contraction, it actually inhibits gastric emptying and can weakly inhibit gastric acid secretion. * **Secretin (D):** Secreted by S-cells of the duodenum in response to low pH, secretin is nature’s "anti-acid." It inhibits gastrin release and HCl secretion while stimulating bicarbonate-rich pancreatic juice to neutralize chyme. **High-Yield NEET-PG Pearls:** * **The "Big Three" Stimulators:** Acetylcholine (Vagus), Gastrin, and Histamine (via H2 receptors). * **Potentiation:** The combined effect of these three stimuli is greater than the sum of their individual effects. * **Somatostatin:** The universal inhibitor of the GI tract; it inhibits the release of gastrin and HCl. * **Proton Pump:** The final common pathway for HCl secretion is the **H+/K+ ATPase pump** on the apical membrane of parietal cells.

Q: Which of the following hormones is related to appetite and satiety?

All of the above. **Explanation:** The regulation of appetite and satiety is a complex neuroendocrine process primarily coordinated by the **Arcuate Nucleus (ARC)** of the hypothalamus. This center integrates peripheral signals to balance energy intake. * **Leptin:** Produced by **adipose tissue** (white fat), it is a long-term satiety signal. It inhibits the orexigenic NPY/AgRP neurons and stimulates anorexigenic POMC/CART neurons, thereby decreasing food intake and increasing energy expenditure. * **Peptide YY (PYY):** Secreted by the **L-cells of the ileum and colon** in response to food intake (especially fats). It acts as a short-term satiety signal to reduce appetite and slow gastric emptying (the "ileal brake"). * **Ghrelin:** Known as the **"hunger hormone,"** it is secreted primarily by the **P/D1 cells of the stomach fundus**. It is the only major peripheral hormone that stimulates appetite (orexigenic) by activating NPY/AgRP neurons. Since all three hormones play critical, distinct roles in the hunger-satiety cycle, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Leptin Deficiency:** Leads to morbid obesity and hyperphagia (rare genetic cause). * **Prader-Willi Syndrome:** Characterized by extremely high levels of **Ghrelin**, leading to insatiable hunger. * **Vagus Nerve:** While hormones are chemical signals, the Vagus nerve provides the primary neural satiety signal via gastric stretch receptors. * **CCK (Cholecystokinin):** Another potent short-term satiety signal released from the duodenum.

Q: What is the primary pigment responsible for the color of stool?

Stercobilinogen. **Explanation:** The color of stool is primarily derived from the breakdown products of hemoglobin. The process begins in the reticuloendothelial system, where heme is converted to **bilirubin**. This bilirubin is conjugated in the liver and secreted into the bile, eventually entering the small intestine. In the colon, intestinal bacteria act upon conjugated bilirubin to form a group of colorless compounds known as **urobilinogens**. A specific fraction of these compounds remains in the gut and is further reduced by bacteria into **stercobilinogen**. While stercobilinogen itself is colorless, it undergoes spontaneous oxidation into **stercobilin**, a brown pigment that gives feces its characteristic color. In many medical examinations, including NEET-PG, stercobilinogen is cited as the primary precursor/pigment responsible for this process. **Analysis of Options:** * **B. Urobilinogen:** While some urobilinogen is present in the gut, most of it is either reabsorbed into the enterohepatic circulation or excreted by the kidneys (where it oxidizes to **urobilin**, giving urine its yellow color). * **C. Mevobilirubin:** This is not a standard physiological term in the bilirubin degradation pathway. * **D. Bilirubin:** Conjugated bilirubin is a greenish-yellow pigment. If it is not converted by bacteria (e.g., in rapid transit diarrhea or newborn guts), the stool may appear green or clay-colored, but it is not the pigment responsible for normal brown stool. **Clinical Pearls for NEET-PG:** * **Clay-colored stools:** Occur in **obstructive jaundice** because bilirubin cannot reach the intestine to be converted into stercobilinogen. * **Steatorrhea:** Foul-smelling, bulky, oily stools seen in malabsorption syndromes (e.g., Celiac disease, Chronic pancreatitis). * **Melena:** Black, tarry stools indicating upper GI bleed (acid-altered hemoglobin).

Q: Which of the following is NOT a primary function of gut flora?

Decreased proliferation of epithelial cells. The gut microbiota plays a vital role in maintaining intestinal homeostasis. The correct answer is **B**, as gut flora actually **increases** (rather than decreases) the proliferation and differentiation of epithelial cells. ### **Explanation of Options:** * **B (Correct):** Gut bacteria produce metabolites like **Butyrate**, which serve as the primary energy source for colonocytes. This stimulates epithelial cell turnover and strengthens the mucosal barrier. A lack of gut flora (e.g., in germ-free mice) leads to a thinner mucosa and reduced villus height. * **A:** Bacteria ferment undigested dietary fibers into **Short-Chain Fatty Acids (SCFAs)** like acetate, propionate, and butyrate. These are crucial for pH regulation and energy metabolism. * **C:** Gut flora, particularly *E. coli* and *Bacteroides*, are essential for the synthesis of **Vitamin K2 (menaquinone)** and several B-complex vitamins (B12, folate, biotin). * **D:** Commensal bacteria possess enzymes to ferment host-derived **mucins** and complex glycans, which helps maintain the protective mucus layer and provides a continuous energy source for the microbiota. ### **High-Yield NEET-PG Pearls:** * **Trophic Effect:** The most significant effect of SCFAs (especially butyrate) is the stimulation of the **G-protein coupled receptor GPR41/43**, promoting gut-associated lymphoid tissue (GALT) development. * **Competitive Exclusion:** Gut flora prevents pathogen colonization through "colonization resistance." * **Clinical Link:** Broad-spectrum antibiotic use disrupts this flora, leading to *Clostridioides difficile* overgrowth or Vitamin K deficiency (prolonged PT/INR).

Q: Where is renin primarily found?

Gastric juice. **Explanation:** The correct answer is **A. Gastric juice**. The question tests the distinction between two similarly named but functionally different substances: **Renin** (with one 'n') and **Rennin** (with two 'n's, also known as Chymosin). In many medical examinations, including NEET-PG, the term "renin" is occasionally used interchangeably in older texts or specific contexts to refer to the digestive enzyme. 1. **Why Gastric Juice is correct:** **Rennin (Chymosin)** is a proteolytic enzyme synthesized by the chief cells of the stomach in infants. Its primary role is the curdling of milk by converting soluble caseinogen into insoluble calcium caseinate. This slows down the passage of milk through the digestive tract, allowing better absorption. 2. **Why other options are incorrect:** * **Kidney:** The kidney produces **Renin** (one 'n'), an enzyme/hormone secreted by the Juxtaglomerular (JG) cells. It is part of the Renin-Angiotensin-Aldosterone System (RAAS) which regulates blood pressure. * **Liver:** The liver produces Angiotensinogen, the substrate upon which renal renin acts. * **Lung:** The lungs are the primary site for Angiotensin-Converting Enzyme (ACE), which converts Angiotensin I to Angiotensin II. **NEET-PG High-Yield Pearls:** * **Spelling Trap:** Remember: **RENNIN** (2 'n's) is for **N**ursing (digestion/stomach); **RENIN** (1 'n') is for **R**enal (kidney/BP). * **Stimulus:** Renal renin is stimulated by decreased renal perfusion, sympathetic stimulation, or low chloride delivery to the macula densa. * **Infant Physiology:** Gastric rennin is absent in adults; pepsin takes over the role of protein digestion.

Q: Which hormone provides trophic action on the mucosa of the large intestine?

Gastrin. **Explanation:** **Gastrin** is the primary hormone responsible for the growth and maintenance of the gastrointestinal mucosa. While its most well-known function is the stimulation of gastric acid secretion from parietal cells, it exerts a significant **trophic (growth-promoting) effect** on the mucosa of the stomach, small intestine, and **large intestine**. It stimulates RNA and protein synthesis in these tissues; clinically, this is evidenced by the mucosal hyperplasia seen in hypergastrinemia states (e.g., Zollinger-Ellison Syndrome). **Analysis of Incorrect Options:** * **Cholecystokinin (CCK):** While CCK is structurally similar to gastrin and has trophic effects on the **exocrine pancreas** and gallbladder mucosa, it does not significantly influence the growth of the colonic mucosa. * **Secretin:** Known as "Nature’s Antacid," secretin primarily stimulates bicarbonate secretion from the pancreas and inhibits gastric acid. It does not possess trophic properties for the intestinal mucosa. * **Bile Acids:** These are detergents involved in fat digestion. Rather than being trophic, excessive primary bile acids in the colon can actually be irritating or potentially cytotoxic to the mucosa if not properly regulated. **High-Yield NEET-PG Pearls:** * **Zollinger-Ellison Syndrome:** Characterized by a gastrinoma, leading to hypergastrinemia. A key diagnostic feature is the presence of thickened gastric mucosal folds due to the trophic action of gastrin. * **Somatostatin:** Acts as the "universal inhibitor" in the GIT and antagonizes the release and effects of gastrin. * **Trophic Action Site:** Gastrin’s trophic effect is seen everywhere in the GIT **except the esophagus and the antrum** of the stomach itself.

Q: 'D' cells of the stomach secrete which of the following?

Somatostatin. **Explanation:** The correct answer is **Somatostatin**. **1. Why Somatostatin is correct:** 'D' cells (Delta cells) are found in the pancreatic islets and the gastrointestinal mucosa, specifically in the antrum and corpus of the stomach. These cells secrete **Somatostatin**, a potent inhibitory peptide. In the stomach, somatostatin acts via paracrine signaling to inhibit the release of gastrin from G-cells and histamine from ECL cells. It also acts directly on parietal cells to decrease acid secretion, effectively serving as the "universal brake" of the digestive system. **2. Why the other options are incorrect:** * **A. HCl (Hydrochloric Acid):** Secreted by **Parietal (Oxyntic) cells** located primarily in the fundus and body of the stomach. * **B. Pepsinogen:** Secreted by **Chief (Zymogenic/Peptic) cells**. Pepsinogen is a proenzyme converted to active pepsin by the acidic environment created by HCl. * **C. Histamine:** Secreted by **Enterochromaffin-like (ECL) cells**. Histamine stimulates parietal cells to produce HCl via H2 receptors. **3. NEET-PG High-Yield Pearls:** * **Stimulus for D-cells:** Low intraluminal pH (high acidity) stimulates D-cells to release somatostatin, providing a negative feedback loop to prevent over-acidification. * **G-cells:** Located in the antrum; secrete **Gastrin**. * **S-cells:** Located in the duodenum; secrete **Secretin** (the "nature's antacid"). * **I-cells:** Located in the duodenum/jejunum; secrete **Cholecystokinin (CCK)**. * **Intrinsic Factor:** Also secreted by Parietal cells; essential for Vitamin B12 absorption in the terminal ileum.

Q: What is the primary role of bile salts in digestion?

Emulsification of dietary lipids. **Explanation:** **1. Why Emulsification is the Correct Answer:** Bile salts are amphipathic molecules (containing both hydrophilic and hydrophobic ends) derived from cholesterol. Their primary role is the **emulsification of dietary lipids**. Large fat globules are broken down into smaller droplets, increasing the surface area for pancreatic lipase to act upon. Furthermore, bile salts are essential for the formation of **micelles**, which ferry the products of lipid digestion (monoglycerides and free fatty acids) to the intestinal brush border for absorption. **2. Why Other Options are Incorrect:** * **Option A:** Vitamin B12 absorption requires **Intrinsic Factor** (secreted by gastric parietal cells) and occurs in the terminal ileum. Bile salts are not directly involved in this process. * **Option B:** While phospholipids (like lecithin) are components of bile and cell membranes, the primary *digestive* function of bile salts is not structural membrane formation. * **Option C:** Degradation of fatty acids (Beta-oxidation) is an intracellular metabolic process occurring in the mitochondria, not a digestive process in the gut lumen. **3. NEET-PG High-Yield Pearls:** * **Enterohepatic Circulation:** 95% of bile salts are reabsorbed in the **terminal ileum** via active transport and returned to the liver. * **Choleretic Action:** Bile salts themselves are the most potent stimulators of further bile secretion. * **Steatorrhea:** Deficiency of bile salts (due to ileal resection or biliary obstruction) leads to fat malabsorption and foul-smelling, oily stools. * **Rate-limiting step:** The enzyme **7-alpha-hydroxylase** is the rate-limiting step in bile acid synthesis from cholesterol.

Question 1

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

Accepted Answer

Ghrelin

Answer

Orexin

Answer

Insulin-like growth factor

Answer

Cholecystokinin

Question 2

Which of the following increases HCI secretion during the gastric phase of digestion?

Accepted Answer

Gastrin

Answer

Pepsinogen

Answer

Cholecystokinin (CCK)

Answer

Secretin

Question 3

Which of the following hormones is related to appetite and satiety?

Accepted Answer

All of the above

Answer

Leptin

Answer

Peptide YY (PYY)

Answer

Ghrelin

Question 4

What is the primary pigment responsible for the color of stool?

Accepted Answer

Stercobilinogen

Answer

Urobilinogen

Answer

Mevobilirubin

Answer

Bilirubin

Question 5

Which of the following is NOT a primary function of gut flora?

Accepted Answer

Decreased proliferation of epithelial cells

Answer

Synthesis of short-chain fatty acids

Answer

Production of vitamin K

Answer

Fermentation of mucin

Question 6

Where is renin primarily found?

Accepted Answer

Gastric juice

Answer

Liver

Answer

Kidney

Answer

Lung

Question 7

Which hormone provides trophic action on the mucosa of the large intestine?

Accepted Answer

Gastrin

Answer

Cholecystokinin

Answer

Secretin

Answer

Bile acid

Question 8

'D' cells of the stomach secrete which of the following?

Accepted Answer

Somatostatin

Answer

HCL

Answer

Pepsinogen

Answer

Histamine

Question 9

After massive small bowel resection, how do the intestines compensate?

Accepted Answer

Lengthening of individual villi

Answer

Increasing the number of villi

Answer

Increased lifespan of absorptive cells

Answer

Increased synthesis of digestive enzymes by absorptive cells

Question 10

What is the primary role of bile salts in digestion?

Accepted Answer

Emulsification of dietary lipids

Answer

Absorption of Vitamin B12

Answer

Formation of the lipid bilayer of cell membranes

Answer

Degradation of fatty acids

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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