Gastrointestinal System Practice Questions

Q: Which gastric enzyme is present in the stomach of infants but absent from the stomach of adults?

Rennin. **Explanation:** The correct answer is **Rennin** (also known as Chymosin). **1. Why Rennin is correct:** Rennin is a proteolytic enzyme secreted by the gastric glands (chief cells) in **infants**. Its primary function is the **curdling of milk**. It converts the soluble milk protein, casein, into insoluble calcium paracaseinate in the presence of calcium ions. This process slows down the passage of milk through the digestive tract, allowing more time for gastric proteases to act on it. Rennin is absent in the adult human stomach, where the function of milk curdling is taken over by Pepsin and Hydrochloric acid (HCl). **2. Why other options are incorrect:** * **Pepsin:** This is the primary proteolytic enzyme in the stomach of **both** infants and adults. It is secreted as the proenzyme pepsinogen. * **Trypsin:** This is a pancreatic enzyme, not a gastric one. It acts in the **small intestine** (duodenum) to digest proteins. * **Lipase:** Gastric lipase is present in both infants and adults. In fact, it plays a more significant role in infants for the digestion of milk fats (tributyrin) because pancreatic lipase is not yet fully developed. **3. Clinical Pearls & High-Yield Facts:** * **Spelling Tip:** Do not confuse **Rennin** (digestive enzyme) with **Renin** (hormone secreted by the juxtaglomerular cells of the kidney involved in blood pressure regulation). * **Chief Cells (Peptic Cells):** These cells secrete both Pepsinogen and Prorennin. * **pH Requirement:** Rennin works best at a pH of around 4.0, which is the typical gastric pH of a milk-fed infant, whereas Pepsin requires a more acidic pH (1.8–2.0) found in adults.

Q: During a fast, a brief phase of intense sequential contractions begins in the stomach and gradually migrates to the ileum. Release of which of the following intestinal hormones is most likely responsible for this observed effect?

Motilin. ### Explanation The phenomenon described is the **Migrating Motor Complex (MMC)**, often referred to as the "housekeeper of the gut." **Why Motilin is Correct:** The MMC is a pattern of intense electrical and mechanical activity that occurs during the **inter-digestive state** (fasting). It consists of four phases, with Phase III being the period of maximal contraction. These contractions begin in the stomach and migrate down to the terminal ileum every 90–120 minutes to clear the gut of undigested food and bacteria. **Motilin**, a 22-amino acid peptide secreted by **M cells** in the duodenum and jejunum, is the primary hormonal mediator of these contractions. Plasma motilin levels fluctuate cyclically, peaking just before the onset of Phase III. **Why the Other Options are Incorrect:** * **Cholecystokinin (CCK):** Secreted by I cells in response to fatty acids and amino acids. It stimulates gallbladder contraction and pancreatic enzyme secretion but **inhibits** gastric emptying. * **Gastrin:** Secreted by G cells in the antrum. Its primary role is to stimulate gastric acid secretion and mucosal growth, typically during the fed state. * **Gastrin-releasing peptide (GRP):** A neurotransmitter released from vagal nerve endings that stimulates G cells to release gastrin; it does not coordinate inter-digestive motility. **High-Yield NEET-PG Pearls:** * **Erythromycin Connection:** Erythromycin acts as a **motilin agonist** by binding to motilin receptors. It is clinically used as a prokinetic agent in patients with gastroparesis. * **Feeding Effect:** The MMC is immediately abolished upon **ingestion of food**, replaced by the "fed pattern" of segmentation and peristalsis. * **Site of Origin:** Unlike most GI motility, the MMC starts in the stomach (not the esophagus) and ends at the ileum.

Q: What is the approximate total daily fluid secretion by the salivary glands, stomach, and intestine in a human?

5000 ml. ### Explanation The correct answer is **5000 ml**. This value represents the cumulative volume of secretions produced by the proximal segments of the gastrointestinal tract (GIT) before reaching the small intestine. **1. Why 5000 ml is correct:** The total daily fluid input into the GIT is approximately **9000 ml (9L)**. This is composed of 2000 ml of oral intake and **7000 ml** of endogenous secretions. The question specifically asks for the sum of secretions from the salivary glands, stomach, and intestine (small intestine): * **Saliva:** ~1500 ml * **Gastric Juice:** ~2000 ml * **Small Intestine (Succus Entericus):** ~1500 ml * **Total:** 1500 + 2000 + 1500 = **5000 ml**. **2. Why other options are incorrect:** * **A (3000 ml) & B (4000 ml):** These values are too low as they likely omit either the gastric or the intestinal component. * **D (6000 ml):** This value overestimates these three specific sources. If you were to add **Bile (500 ml)** and **Pancreatic juice (1500 ml)** to the 5000 ml, the total endogenous secretion would reach 7000 ml. **3. High-Yield Clinical Pearls for NEET-PG:** * **Absorption Efficiency:** Out of the 9L total fluid load, the **small intestine** absorbs the majority (~7-7.5L), while the colon absorbs about 1.4L. Only ~100-200 ml is excreted in feces. * **Maximum Colonic Capacity:** The colon can absorb a maximum of about 5-8 liters per day; exceeding this leads to diarrhea. * **Secretory Source:** Most intestinal secretion (Succus entericus) comes from the **Crypts of Lieberkühn**, while the **Brunner’s glands** specifically secrete alkaline mucus in the duodenum.

Q: Which hormone causes increased food intake?

Ghrelin. **Explanation:** The regulation of food intake is controlled by the hypothalamus, specifically through the interplay of **orexigenic** (appetite-stimulating) and **anorexigenic** (appetite-suppressing) signals. **Why Ghrelin is Correct:** Ghrelin is a peptide hormone secreted primarily by the **P/D1 cells of the stomach fundus**. It is known as the "hunger hormone" because it is the only peripheral hormone that stimulates food intake (orexigenic). It acts on the **Arcuate Nucleus** of the hypothalamus to stimulate **NPY (Neuropeptide Y)** and **AgRP (Agouti-related peptide)** neurons, which increase appetite and growth hormone secretion. Ghrelin levels rise sharply before meals and fall immediately after eating. **Why Other Options are Incorrect:** * **Leptin:** Produced by adipocytes, it is a long-term satiety signal. It inhibits NPY/AgRP neurons and stimulates POMC neurons, thereby **decreasing** food intake. * **CART (Cocaine-and-Amphetamine-Regulated Transcript):** This is a potent **anorexigenic** neurotransmitter found in the hypothalamus that decreases appetite. * **Serotonin (5-HT):** In the CNS, serotonin acts as a **satiety signal**. Drugs that increase serotonin levels (like fenfluramine) were historically used to suppress appetite. **High-Yield Clinical Pearls for NEET-PG:** * **Prader-Willi Syndrome:** Characterized by hyperphagia and obesity due to pathologically **elevated Ghrelin levels**. * **Sleep Deprivation:** Increases Ghrelin and decreases Leptin, leading to weight gain. * **Vagus Nerve:** Ghrelin signals are also transmitted via the vagus nerve to the brainstem. * **Post-Gastric Bypass:** Weight loss is partly attributed to a significant **reduction in Ghrelin** levels due to the bypass of the stomach fundus.

Q: What is the migrating motility complex?

It occurs at a rate of 5 cm per minute from the stomach.. The **Migrating Motility Complex (MMC)** is a distinct pattern of electromechanical activity observed in the gastrointestinal smooth muscle during the **interdigestive state** (fasting). ### **Explanation of the Correct Option** **Option D** is correct because the MMC acts as a "housekeeper" of the small intestine. It originates in the stomach and moves aborally (downward) toward the ileum. In the small intestine, these waves propagate at a velocity of approximately **5 cm per minute**, effectively clearing residual undigested food, secretions, and bacteria into the colon. ### **Analysis of Incorrect Options** * **Option A:** The MMC occurs during **fasting**. It is immediately **abolished by the arrival of food** in the stomach, which triggers the fed-state pattern (segmentation and peristalsis). * **Option B:** It begins in the **stomach** (specifically the body/antrum) and moves down to the terminal ileum; it does not start in the lower small intestine. * **Option C:** While basic electrical rhythm is controlled by pacemaker cells (Interstitial Cells of Cajal), the MMC specifically is regulated by the hormone **Motilin** and the enteric nervous system. ### **NEET-PG High-Yield Pearls** * **Hormonal Control:** **Motilin** is the primary mediator. Erythromycin (a motilin agonist) can be used to stimulate GI motility. * **Phases:** It consists of 4 phases; **Phase III** is the most active phase with intense contractions. * **Cycle Duration:** A complete cycle repeats every **90 to 120 minutes** during fasting. * **Function:** Prevents **Small Intestinal Bacterial Overgrowth (SIBO)** by sweeping bacteria into the large intestine.

Q: Acinar cells of the Exocrine Pancreas secrete which of the following?

Proteases. **Explanation:** The pancreas is a dual-function gland consisting of endocrine and exocrine components. The **exocrine pancreas** is composed of **acinar cells** and ductal cells. Acinar cells are responsible for synthesizing, storing, and secreting digestive enzymes. These include **proteases** (such as trypsinogen, chymotrypsinogen, and procarboxypeptidase), lipases, and amylases. These enzymes are secreted as inactive proenzymes (zymogens) to prevent autodigestion of the gland and are activated in the duodenum by enterokinase. **Analysis of Incorrect Options:** * **A & C (Glucagon and Insulin):** These are hormones produced by the **endocrine pancreas** (Islets of Langerhans). Specifically, Alpha cells secrete glucagon and Beta cells secrete insulin. They are released directly into the bloodstream, not into the pancreatic ducts. * **B (Lysozyme):** While lysozyme is an antibacterial enzyme found in saliva and the secretions of **Paneth cells** in the small intestine, it is not a primary secretion of pancreatic acinar cells. **High-Yield Clinical Pearls for NEET-PG:** * **Ductal Cells:** Unlike acinar cells, ductal cells secrete a large volume of juice rich in **Bicarbonate ($HCO_3^-$)**, stimulated primarily by the hormone **Secretin**. * **CCK (Cholecystokinin):** This is the primary stimulus for **acinar cells** to release digestive enzymes. * **Trypsin Inhibitor:** Acinar cells also secrete a trypsin inhibitor to prevent the premature activation of trypsin within the pancreatic ducts, a key protective mechanism against **Acute Pancreatitis**.

Q: Which of the following factors increases gastric motility?

None of the above. ### Explanation The rate of gastric emptying and motility is primarily regulated by the nature of the chyme entering the duodenum. The correct answer is **None of the above** because all the listed factors actually **inhibit** or delay gastric motility rather than increase it. #### Why the options are incorrect: * **Acid in the duodenum (Option A):** When acidic chyme (pH < 3.5–4.0) enters the duodenum, it triggers the **enterogastric reflex** and the release of **Secretin**. Both mechanisms potently inhibit gastric motility to protect the duodenal mucosa and allow time for neutralization by pancreatic bicarbonate. * **Fatty food in the stomach (Option B):** Fats are the slowest macronutrients to empty. The presence of fat in the duodenum stimulates the release of **Cholecystokinin (CCK)** and **Gastric Inhibitory Peptide (GIP)**, which significantly decrease gastric emptying to ensure adequate time for emulsification and digestion. * **Carbohydrates in the stomach (Option C):** While carbohydrates empty faster than proteins and fats, they do not *increase* motility beyond the basal rate. In fact, hypertonic solutions (like concentrated sugars) in the duodenum trigger osmoreceptors that slow down gastric emptying. #### High-Yield NEET-PG Pearls: * **Order of Gastric Emptying:** Carbohydrates > Proteins > Fats (Slowest). * **Liquids vs. Solids:** Isotonic liquids empty the fastest; solids must be ground to particles < 2mm (antral mill) before passing the pylorus. * **Key Inhibitors:** CCK is the most potent inhibitor of gastric emptying triggered by fat. * **Stimulant:** The only major factor that increases gastric motility is **Gastrin** (and physical distension of the stomach via the vago-vagal reflex). * **Clinical Correlation:** **Gastroparesis** (delayed emptying) is common in Diabetes Mellitus due to autonomic neuropathy, while **Dumping Syndrome** occurs after gastric surgery due to rapid emptying of hypertonic chyme.

Question 1

Which gastric enzyme is present in the stomach of infants but absent from the stomach of adults?

Accepted Answer

Rennin

Answer

Pepsin

Answer

Trypsin

Answer

Lipase

Question 2

During a fast, a brief phase of intense sequential contractions begins in the stomach and gradually migrates to the ileum. Release of which of the following intestinal hormones is most likely responsible for this observed effect?

Accepted Answer

Motilin

Answer

Cholecystokinin

Answer

Gastrin

Answer

Gastrin-releasing peptide

Question 3

Which one of the following statements regarding the regulation of gastrointestinal function is true?

Accepted Answer

Salivary secretion is stimulated by both branches of the autonomic nervous system, although not to the same degree.

Answer

The main sympathetic nerve supply to the digestive tract is the vagus.

Answer

In general, sympathetic stimulation is excitatory to digestive activity.

Answer

Parasympathetic stimulation of the salivary glands produces a saliva rich in mucus.

Question 4

What is the approximate total daily fluid secretion by the salivary glands, stomach, and intestine in a human?

Accepted Answer

5000 ml

Answer

3000 ml

Answer

4000 ml

Answer

6000 ml

Question 5

Which hormone causes increased food intake?

Accepted Answer

Ghrelin

Answer

Leptin

Answer

Cart

Answer

Serotonin

Question 6

What is the migrating motility complex?

Accepted Answer

It occurs at a rate of 5 cm per minute from the stomach.

Answer

It occurs upon arrival of food in the stomach.

Answer

It begins in the lower part of the small intestine.

Answer

It is initiated by pacemaker cells in the intestine.

Question 7

Which of the following segments of the gastrointestinal tract exhibits slow waves/basic electrical rhythm (BER) in increasing order?

Accepted Answer

Stomach < Sigmoid colon < Jejunum

Answer

Jejunum > Sigmoid colon > Stomach

Answer

Jejunum < Sigmoid colon < Stomach

Answer

Stomach > Sigmoid colon > Jejunum

Question 8

Which ion is present in higher concentration in gastric secretions compared to blood?

Accepted Answer

Cl-

Answer

HCO3-

Answer

K+

Answer

Na+

Question 9

Acinar cells of the Exocrine Pancreas secrete which of the following?

Accepted Answer

Proteases

Answer

Glucagon

Answer

Lysozyme

Answer

Insulin

Question 10

Which of the following factors increases gastric motility?

Accepted Answer

None of the above

Answer

Acid in the duodenum

Answer

Fatty food in the stomach

Answer

Carbohydrates in the stomach

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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