Gastrointestinal Circulation — MCQs
CT scan of abdomen showing a structure branching within the liver. Identify the structure.
Which of the following is the mechanism for a decrease in splanchnic blood flow during exercise?
The stomach derives its blood supply from all these arteries directly or indirectly, except for which one?
Inhibition of myenteric plexus results in
From which part of the gastrointestinal tract is glucose absorbed?
Which of the following is true about polyaeritis nodosa?
Small intestinal peristalsis is controlled by :
Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
Which of the following inhibits gastrin secretion?
Slow wave potentials originate in which cells of the intestine?
Gastrointestinal Circulation Indian Medical PG Practice Questions and MCQs
Question 1: CT scan of abdomen showing a structure branching within the liver. Identify the structure.
- A. Portal vein (Correct Answer)
- B. Superior vena cava
- C. Inferior vena cava
- D. Splenic vein
Explanation: ***Portal vein*** - The image shows a **branching vessel within the liver parenchyma**. The **portal vein** enters the liver at the porta hepatis and branches extensively to supply the liver with nutrient-rich, deoxygenated blood from the gastrointestinal tract. - On a CT scan, the portal vein and its branches appear as prominent, contrast-filled structures centrally located within the liver, consistent with the identified structure. *Superior Vena Cava* - The **superior vena cava** is located in the **chest**, superior to the diaphragm, and drains blood from the upper body into the right atrium; it does not branch within the liver. - This vessel would not be visible in an abdominal CT slice at this level and does not show intrahepatic branching. *Inferior Vena Cava* - The **inferior vena cava (IVC)** is a large vessel located **posterior to the liver**, collecting deoxygenated blood from the lower body and liver (via hepatic veins) before emptying into the right atrium. - While it is in the abdomen, it does not branch within the liver parenchyma in the same manner as the portal vein; rather, **hepatic veins** drain into it from the liver. *Splenic Vein* - The **splenic vein** runs along the **posterior aspect of the pancreas** and eventually joins with the superior mesenteric vein to form the portal vein outside the liver. - It does not enter or branch within the liver itself; its location is too far posterior and outside the liver to match the structure indicated.
Question 2: Which of the following is the mechanism for a decrease in splanchnic blood flow during exercise?
- A. Increased splanchnic metabolic demand
- B. Arteriolar vasoconstriction due to sympathetic stimulation (Correct Answer)
- C. Arteriolar vasodilation due to parasympathetic stimulation
- D. Decreased cardiac output to splanchnic organs
Explanation: ***Arteriolar vasoconstriction due to sympathetic stimulation*** - During **exercise**, the **sympathetic nervous system** is activated, leading to a release of **norepinephrine** and **epinephrine**. These neurotransmitters bind to **alpha-1 adrenergic receptors** on **splanchnic arterioles**, causing **vasoconstriction**. - This **vasoconstriction** shunts blood away from the gastrointestinal tract, liver, and spleen, redirecting it towards the **skeletal muscles** and heart, which have a higher metabolic demand during exercise. *Increased splanchnic metabolic demand* - The **splanchnic organs** (gut, liver, spleen) actually experience a *decrease* in activity and metabolic demand during strenuous exercise, as their primary functions are temporarily reduced. - An increase in splanchnic metabolic demand would typically lead to **vasodilation** to meet those demands, not a decrease in blood flow. *Arteriolar vasodilation due to parasympathetic stimulation* - **Parasympathetic stimulation** generally causes **vasodilation** in the gut and is primarily active during rest and digestion. - During exercise, **parasympathetic activity** is *reduced*, and **sympathetic activity** predominates, leading to **vasoconstriction**, not vasodilation. *Decreased cardiac output to splanchnic organs* - While the *proportion* of **cardiac output** directed to splanchnic organs decreases during exercise, the overall **cardiac output** *increases* significantly. - The reduction in splanchnic blood flow is a result of **active vasoconstriction** and blood redistribution, not a direct decrease in total cardiac output itself, which is actually elevated.
Question 3: The stomach derives its blood supply from all these arteries directly or indirectly, except for which one?
- A. Splenic artery
- B. Celiac axis
- C. Hepatic artery
- D. Superior mesenteric artery (Correct Answer)
Explanation: ***Superior mesenteric artery*** - The **superior mesenteric artery (SMA)** primarily supplies the **midgut** derivatives (from the distal duodenum to the proximal two-thirds of the transverse colon), and does not directly or indirectly supply the stomach [2], [3]. - While it may communicate with branches of the celiac axis, it does not contribute to the stomach's vascularization. *Splenic artery* - The **splenic artery** is a direct branch of the celiac trunk and gives rise to the **short gastric arteries** and the **left gastroepiploic artery**, both of which supply the stomach. - The **short gastric arteries** supply the fundus of the stomach, and the **left gastroepiploic artery** supplies the greater curvature. *Hepatic artery* - The **common hepatic artery**, a branch of the celiac trunk, gives rise to the **gastroduodenal artery**, which then gives off the **right gastroepiploic artery** to the stomach’s greater curvature. - The proper hepatic artery then branches into the **right gastric artery**, which supplies the lesser curvature of the stomach. *Celiac axis* - The **celiac axis (celiac trunk)** is the main artery supplying the **foregut** and is the origin of the splenic artery, common hepatic artery, and left gastric artery, all of which directly or indirectly supply the stomach [1], [3]. - It is the primary arterial source for the stomach, spleen, liver, gallbladder, and part of the duodenum [3].
Question 4: Inhibition of myenteric plexus results in
- A. Hyperacidity
- B. Diarrhea
- C. Decreased gut motility (Correct Answer)
- D. Increased secretions
Explanation: ***Decreased gut motility*** - The **myenteric plexus** (Auerbach's plexus) is primarily responsible for regulating **gastrointestinal motility**, including peristalsis and muscle contraction. - Its inhibition would therefore lead to **reduced peristaltic movements** and **decreased gut motility**. *Hyperacidity* - **Gastric acid secretion** is mainly regulated by the vagus nerve (via acetylcholine), gastrin, and histamine, not directly by the myenteric plexus. - While gut motility can indirectly affect acid exposure, a primary and direct consequence of myenteric plexus inhibition is not hyperacidity. *Diarrhea* - **Diarrhea** is typically caused by increased gut motility, increased secretion, or decreased absorption. - Inhibition of the myenteric plexus would lead to **decreased motility**, making diarrhea an unlikely outcome. *Increased secretions* - **Gastrointestinal secretions** are largely controlled by the submucosal plexus (Meissner's plexus) and hormonal factors. - While the myenteric plexus has some indirect influence, its primary role is motility, and its inhibition would not directly lead to increased secretions.
Question 5: From which part of the gastrointestinal tract is glucose absorbed?
- A. Stomach
- B. Colon
- C. Duodenum and jejunum (Correct Answer)
- D. Ileum
Explanation: ***Duodenum and jejunum*** - The **duodenum** and **jejunum** are the primary sites for nutrient absorption in the small intestine, including the majority of **glucose**. - Their large surface area, due to **villi** and **microvilli**, and abundant transport mechanisms facilitate efficient glucose uptake. *Stomach* - The stomach's primary role is **digestion**, particularly of proteins, with very little absorption of nutrients. - While some small, lipid-soluble substances like alcohol can be absorbed, significant **glucose absorption does not occur** here. *Ileum* - The **ileum** is mainly responsible for the absorption of **vitamin B12** and **bile salts**. - Although some remaining nutrients might be absorbed, the bulk of **glucose absorption** is completed in the upstream **duodenum and jejunum**. *Colon* - The **colon's** main functions are **water and electrolyte absorption** and the formation of feces. - It does not play a significant role in the absorption of **glucose** or other macro-nutrients.
Question 6: Which of the following is true about polyaeritis nodosa?
- A. It shows fibrinoid necrosis in large blood vessels
- B. HBsAg is positive in 30% patients (Correct Answer)
- C. It has ANCA positivity
- D. Affected individuals have involvement of pulmonary circulation.
Explanation: ### HBsAg is positive in 30% patients - **Polyarteritis nodosa (PAN)** is strongly associated with **hepatitis B virus (HBV)** infection; about 30% of patients with PAN have evidence of current or past HBV infection, particularly **HBsAg positivity**. - This association suggests that HBV infection can trigger the immune complex vasculitis characteristic of PAN. ### It shows fibrinoid necrosis in large blood vessels - PAN primarily affects **medium-sized muscular arteries**, not typically large blood vessels [1]. - The inflammation causes **fibrinoid necrosis** and aneurysmal dilations in these medium-sized arteries [1]. ### It has ANCA positivity - **Polyarteritis nodosa (PAN)** is generally considered an **ANCA-negative vasculitis**. - **ANCA positivity** (especially c-ANCA/PR3-ANCA or p-ANCA/MPO-ANCA) is characteristic of other small-vessel vasculitides like **Granulomatosis with polyangiitis** or **Microscopic polyangiitis**. ### Affected individuals have involvement of pulmonary circulation. - A defining characteristic of **Polyarteritis nodosa (PAN)** is that it generally **spares the pulmonary circulation** [1]. - Pulmonary involvement is more commonly seen in other vasculitides, such as **Granulomatosis with polyangiitis (Wegener's)** or **Eosinophilic granulomatosis with polyangiitis (Churg-Strauss)**.
Question 7: Small intestinal peristalsis is controlled by :
- A. Meissner's plexus
- B. Vagus nerve
- C. Parasympathetic system
- D. Myenteric plexus (Correct Answer)
Explanation: ***Myenteric plexus*** - The **myenteric (Auerbach's) plexus** is located between the longitudinal and circular muscle layers of the muscularis propria and is primarily responsible for **controlling gastrointestinal motility**, including peristalsis. - Its neurons coordinate the contractions and relaxations of these muscle layers to propel contents through the alimentary canal. *Meissners plexus* - The **Meissner's (submucosal) plexus** is located in the submucosa and mainly controls **glandular secretion**, local blood flow, and absorption, rather than muscle motility. - While it subtly influences motility through local reflexes, it is not the primary controller of peristalsis. *Vagus nerve* - The **vagus nerve (cranial nerve X)** provides parasympathetic innervation to the small intestine, modulating activity but not directly initiating or solely controlling peristalsis. - It influences the activity of the enteric nervous system (including the myenteric plexus) but does not itself generate the complex, coordinated patterns of muscle contraction. *Parasympathetic system* - The **parasympathetic nervous system**, through nerves like the vagus, generally **stimulates gastrointestinal motility**, but it acts by modulating the intrinsic enteric nervous system. - The local control and generation of specific peristaltic movements are primarily mediated by the enteric nervous system, especially the myenteric plexus.
Question 8: 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 9: Which of the following inhibits gastrin secretion?
- A. Intrinsic factor
- B. Histamine
- C. Gastrin
- D. Somatostatin (Correct Answer)
Explanation: ***Somatostatin*** - **Somatostatin** is a potent **inhibitor** of gastrin secretion, acting directly on **G cells** in the stomach via paracrine mechanisms. - It also reduces the secretion of other gastrointestinal hormones and **gastric acid**. - Somatostatin release is stimulated by **low gastric pH**, forming part of the negative feedback mechanism that regulates gastrin secretion. *Intrinsic factor* - **Intrinsic factor** is a glycoprotein essential for the absorption of **vitamin B12** in the small intestine. - It does not have a direct role in regulating the secretion of **gastrin**. *Histamine* - **Histamine** stimulates gastric acid secretion from **parietal cells** by binding to H2 receptors. - It does **not inhibit** gastrin secretion; histamine acts downstream of gastrin in the acid secretion pathway. - Histamine is released from **ECL cells** in response to gastrin stimulation. *Gastrin* - **Gastrin** is a hormone that **stimulates gastric acid secretion** from parietal cells. - Gastrin does not inhibit its own secretion; instead, it undergoes **negative feedback** regulation when the gastric pH drops below 3. - Low pH stimulates **somatostatin** release, which then inhibits further gastrin secretion.
Question 10: Slow wave potentials originate in which cells of the intestine?
- A. Myenteric plexus
- B. Parasympathetic neurons
- C. Smooth muscle cells
- D. Interstitial cells of Cajal (Correct Answer)
Explanation: ***Interstitial cells of Cajal*** - The **interstitial cells of Cajal (ICC)** are specialized mesenchymal cells that act as **pacemaker cells** for the gastrointestinal tract. - They generate **slow wave potentials** (basic electrical rhythm), which are oscillating depolarizations and repolarizations of the smooth muscle cell membrane potential. *Myenteric plexus* - The **myenteric plexus (Auerbach's plexus)** primarily controls **gastrointestinal motility** through neural pathways. - It modulates the frequency and strength of contractions but does not directly generate the slow wave potentials. *Parasympathetic neurons* - **Parasympathetic neurons** release neurotransmitters (e.g., acetylcholine) that **modulate the activity** of smooth muscle and ICC, enhancing or inhibiting slow wave activity. - They do not, however, originate the slow wave potential itself. *Smooth muscle cells* - **Smooth muscle cells** are the effector cells that contract in response to the slow waves and action potentials. - While they undergo the depolarization and repolarization of slow waves, the **initiating pacemaker activity** comes from the ICC.
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