Comparative Digestive System — MCQs
Which absorbs least water?
Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
Lower esophageal sphincter pressure is increased by all of the following substances, EXCEPT:
What does the following radiograph from a double contrast esophagram represent?
The mucosal lining of the vagina is composed of cells:
Maximum concentration of vitamin A is found in which organ?
What is the primary glycerol-containing absorption product of dietary triglycerides in the gut?
Which one of the following tests should be applied to compare mean haemoglobin level of two groups of antenatal mothers?
Which of the following muscles causes the forward movement of the condyle in the mandibular fossa?
Which nerve marked as $X$ is shown in the image given below? (Recent NEET Pattern 2016-17)
Comparative Digestive System Indian Medical PG Practice Questions and MCQs
Question 1: Which absorbs least water?
- A. Cellulose (Correct Answer)
- B. Mucilage
- C. Pectin
- D. Gums
Explanation: ***Cellulose*** - **Cellulose** is a **polysaccharide** with strong **intermolecular hydrogen bonding** between its linear chains. - These strong bonds form a highly ordered, crystalline structure that makes it **insoluble in water** and resistant to water absorption. *Mucilage* - **Mucilage** consists of **polysaccharides** that have a high capacity to absorb water, forming a slimy, gelatinous mass. - This property is due to its highly branched structure and abundance of **hydroxyl groups**, which readily form hydrogen bonds with water. *Pectin* - **Pectin** is a complex **polysaccharide** found in plant cell walls, known for its ability to absorb significant amounts of water. - It forms **gels** with water, a property widely utilized in food production. *Gums* - **Gums** are a diverse group of **polysaccharides** that are highly soluble in water and have an excellent capacity for water absorption. - They tend to form **viscous solutions** or gels when mixed with water.
Question 2: Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
- A. Disaccharides
- B. Polysaccharides
- C. Monosaccharides (Correct Answer)
- D. 5-carbon sugars
Explanation: ***Monosaccharides*** - **Monosaccharides**, like glucose and fructose, are the simplest forms of carbohydrates and do not require further digestion. - They are directly absorbed into the bloodstream from the intestinal lumen via specific **transporters** on the enterocyte membrane. *Disaccharides* - **Disaccharides**, such as sucrose and lactose, must first be broken down into their constituent monosaccharides by **brush border enzymes** (e.g., lactase, sucrase) before absorption can occur. - This additional enzymatic step makes their absorption less efficient than that of monosaccharides. *Polysaccharides* - **Polysaccharides**, including starch and glycogen, are complex carbohydrates requiring extensive digestion by enzymes like **amylase** in the mouth and small intestine. - This multi-step breakdown into monosaccharides is the least efficient process and takes the longest time. *5-carbon sugars* - While 5-carbon sugars (**pentoses**) like ribose and deoxyribose are monosaccharides and can be absorbed, they are not a primary energy source in the diet and are not absorbed as efficiently or in as large quantities as the metabolically more significant 6-carbon monosaccharides (hexoses like glucose). - The question asks which *type* of carbohydrate is most efficiently absorbed, and **monosaccharides** as a general category (including 6-carbon sugars) are the most efficient.
Question 3: Lower esophageal sphincter pressure is increased by all of the following substances, EXCEPT:
- A. Motilin
- B. Gastrin
- C. Substance P
- D. Secretin (Correct Answer)
Explanation: ***Secretin*** - **Secretin** is a gastrointestinal hormone that *decreases* lower esophageal sphincter (LES) pressure - This hormone is released from S cells in the duodenum in response to acidic chyme - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** to neutralize acidic chyme entering the duodenum - By decreasing LES pressure, it facilitates the passage of gastric contents into the duodenum during digestion *Gastrin* - **Gastrin** is a hormone that *increases* lower esophageal sphincter (LES) pressure - This helps prevent gastroesophageal reflux when the stomach is distended - It also stimulates the secretion of **gastric acid** by parietal cells in the stomach - Released from G cells in the gastric antrum in response to protein ingestion *Motilin* - **Motilin** is a peptide hormone that *increases* lower esophageal sphincter (LES) pressure - It initiates the **migrating motor complex (MMC)** during the interdigestive period - Stimulates gastric and intestinal motility - Released from M cells in the duodenum and jejunum *Substance P* - **Substance P** is a neuropeptide that *increases* lower esophageal sphincter (LES) pressure - Functions as both a neurotransmitter and neuromodulator in the enteric nervous system - Plays a role in **smooth muscle contraction** and gastrointestinal motility - Also involved in pain transmission and inflammatory responses
Question 4: What does the following radiograph from a double contrast esophagram represent?
- A. Esophageal atresia
- B. Esophageal stenosis
- C. Feline esophagus (Correct Answer)
- D. Tracheoesophageal fistula
Explanation: **Feline esophagus (Correct)** - The image displays a characteristic transverse striation pattern along the esophageal mucosa, resembling the rings seen in the esophagus of a cat (hence "feline esophagus") - This finding is often associated with gastroesophageal reflux disease (GERD) or eosinophilic esophagitis, representing mucosal edema and inflammation - Also known as "ringed esophagus" or "corrugated esophagus" *Esophageal atresia (Incorrect)* - This is a congenital condition where the esophagus ends in a blind pouch, making it impossible for food to reach the stomach - The radiograph clearly shows a patent esophagus with contrast flowing through it, which rules out atresia *Esophageal stenosis (Incorrect)* - Esophageal stenosis refers to a narrowing of the esophagus, which would appear as a constricted segment on a barium swallow - While there is some irregularity, the primary pattern seen is transverse rings, not a focal, sustained narrowing typical of stenosis *Tracheoesophageal fistula (Incorrect)* - A tracheoesophageal fistula is an abnormal connection between the esophagus and the trachea - This would typically present with aspiration of contrast into the trachea or lungs, which is not evident in the provided image
Question 5: The mucosal lining of the vagina is composed of cells:
- A. Stratified squamous non-keratinized (Correct Answer)
- B. Ciliated columnar epithelium
- C. Pseudostratified columnar epithelium
- D. Transitional epithelium
Explanation: ***Stratified squamous non-keratinized*** - The **vaginal epithelium** is composed of several layers of flattened, nucleated cells that provide **protection against friction** and resist pathogen entry during intercourse and childbirth [1]. - The **non-keratinized nature** ensures the mucosa remains moist and flexible, essential for its function. *Ciliated columnar epithelium* - This type of epithelium is found in locations like the **fallopian tubes** and parts of the **respiratory tract**, where cilia help in moving fluids or particles. - It does not provide the robust protective barrier required for the vagina. *Pseudostratified columnar epithelium* - This epithelium, characterized by nuclei at different levels giving a "pseudostratified" appearance, is typically found in the **trachea** and **bronchi**. In the uterus, however, the endometrial glands are lined by regular, tall, pseudostratified columnar cells during the proliferative phase [2]. - Its primary function is secretion and absorption, not the physical protection needed in the vagina. *Transitional epithelium* - Also known as **urothelium**, this type is specialized to accommodate stretching and is found in the **urinary bladder** and ureters. - It is not suited for the constant friction and protective role of the vaginal lining.
Question 6: Maximum concentration of vitamin A is found in which organ?
- A. Liver (Correct Answer)
- B. Kidney
- C. Lung
- D. Heart
Explanation: ***Liver*** - The **liver** is the primary organ for **storage of vitamin A** (retinyl esters), accounting for 90% of the body's total vitamin A content. - **Hepatic stellate cells** within the liver are specialized for storing the majority of this fat-soluble vitamin. *Kidney* - The **kidney** plays a role in **vitamin D metabolism** and excretion, but not significant vitamin A storage. - While it helps regulate blood levels of various substances, it does not accumulate large quantities of vitamin A. *Lung* - The **lung** does not serve as a major storage site for **vitamin A**. - Its primary functions are related to **gas exchange**, not nutrient storage. *Heart* - The **heart** is responsible for **pumping blood** throughout the body and has minimal involvement in vitamin A storage. - It utilizes certain vitamins for its metabolic processes but does not act as a primary reservoir.
Question 7: What is the primary glycerol-containing absorption product of dietary triglycerides in the gut?
- A. Fatty acids
- B. Mono acyl glycerol (Correct Answer)
- C. Diacyl glycerol
- D. Triglycerides
Explanation: ***Monoacylglycerol (2-MAG)*** - **Pancreatic lipase** hydrolyzes dietary triglycerides at positions 1 and 3, producing **2-monoacylglycerol** and **free fatty acids** as the two major products. - As the **primary glycerol-containing product**, 2-monoacylglycerol constitutes approximately **25% of digested lipid mass** and is essential for efficient **triglyceride resynthesis** in enterocytes. - Both 2-MAG and fatty acids are packaged into **mixed micelles** and co-absorbed, but 2-MAG is the predominant form containing the **intact glycerol backbone**. *Fatty acids* - **Free fatty acids** are co-absorbed with 2-monoacylglycerol in approximately a **2:1 molar ratio** (2 fatty acids per 1 monoacylglycerol). - While quantitatively significant, fatty acids do **not contain the glycerol backbone** structure. - Both products are required for efficient absorption and subsequent **triglyceride resynthesis** within enterocytes. *Diacylglycerol* - **Diacylglycerol** is a minor intermediate product during triglyceride hydrolysis. - It is rapidly hydrolyzed further by **pancreatic lipase** to yield **monoacylglycerol** and free fatty acids. - Not a significant absorption product in the intestinal lumen. *Triglycerides* - **Intact triglycerides** are too large and hydrophobic to be absorbed directly across the intestinal brush border. - They must first undergo **enzymatic hydrolysis** by pancreatic lipase into smaller absorbable units (2-MAG and fatty acids).
Question 8: Which one of the following tests should be applied to compare mean haemoglobin level of two groups of antenatal mothers?
- A. Analysis of variance
- B. Chi-square test
- C. Unpaired t-test (Correct Answer)
- D. Paired t-test
Explanation: ***Unpaired t-Test*** - The **unpaired t-test** is used to compare the means of **two independent groups** on a continuous variable, such as hemoglobin levels. - Antenatal mothers in two distinct groups are independent, and **hemoglobin level is a continuous variable**, making this the appropriate choice. *Analysis of variance* - **ANOVA** (Analysis of Variance) is used to compare the means of **three or more independent groups**. - Since there are only **two groups** being compared, ANOVA is not the most efficient or appropriate test. *Chi-square test* - The **Chi-square test** is used to analyze the association between **two categorical variables**. - Hemoglobin level is a **continuous variable**, not categorical, so this test is not suitable for comparing means. *Paired t-test* - The **paired t-test** is used to compare the means of **two related groups** or the same group measured at two different times (e.g., before and after an intervention). - The two groups of antenatal mothers are **independent**, not paired or related.
Question 9: Which of the following muscles causes the forward movement of the condyle in the mandibular fossa?
- A. Masseter
- B. Lateral pterygoid (Correct Answer)
- C. Medial pterygoid
- D. Temporalis
Explanation: ***Lateral pterygoid*** - The **lateral pterygoid muscle** (especially its inferior head) is primarily responsible for **protrusion (forward movement)** of the mandible, causing the condyle to slide anteriorly along the articular eminence in the temporomandibular joint. - Its superior head stabilizes the **articular disc** during jaw movements, while the inferior head produces the forward translation. *Masseter* - The **masseter muscle** is a powerful muscle of mastication primarily involved in **elevation (closing)** of the mandible. - While it can assist slightly in protrusion when both sides contract, it does not produce the forward gliding movement of the condyle. *Medial pterygoid* - The **medial pterygoid muscle** primarily functions in **elevating** the mandible and assists in **protrusion** and grinding movements. - While it contributes to protrusion, the **lateral pterygoid** is the primary muscle responsible for the forward movement of the condyle. *Temporalis* - The **temporalis muscle** is a strong elevator of the mandible and its posterior fibers act as a **retractor**, pulling the mandible backward. - It opposes forward movement and is responsible for retrusion, not protrusion of the condyle.
Question 10: Which nerve marked as $X$ is shown in the image given below? (Recent NEET Pattern 2016-17)
- A. Nerve of Laterjet
- B. Criminal nerve of Grassi (Correct Answer)
- C. Crow's feet
- D. Celiac trunk
Explanation: ***Correct: Criminal nerve of Grassi*** - The image shows the **vagal innervation to the stomach**. The nerve marked 'X' is a **posterior gastric nerve** branch that innervates the **fundus** and is often referred to as the criminal nerve of Grassi due to its implication in **recurrent ulceration if not transected during vagotomy**. - This nerve is part of the **posterior vagal trunk** and specifically innervates the posterior aspect of the fundus and body of the stomach. Its omission during a vagotomy can lead to continued acid secretion. *Incorrect: Nerve of Laterjet* - The nerve of Laterjet refers to the **anterior and posterior gastric nerves** that run along the **lesser curvature** of the stomach. - These nerves primarily innervate the **body and antrum** of the stomach and control acid secretion from the parietal cells. *Incorrect: Crow's feet* - "Crow's feet" refers to the **pyloric branches** of the anterior and posterior nerves of Laterjet, which ramify around the **pylorus**. - These are distinguished from the nerve of Grassi which supplies the fundus. *Incorrect: Celiac trunk* - The celiac trunk is an **artery**, not a nerve. It is a major visceral branch of the aorta that supplies blood to the foregut structures, including the stomach, liver, and spleen. - It does not represent neural innervation as depicted in the image.
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