Gastrointestinal System Practice Questions

Q: Inhibition of myenteric plexus results in

Decreased gut motility. ***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.

Q: Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?

Monosaccharides. ***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.

Q: What triggers the cephalic phase of gastric secretion?

On seeing food. ***On seeing food*** - The **cephalic phase** of gastric secretion is initiated by sensory input such as the sight, smell, taste, or even the thought of food. - This phase is mediated by the **vagus nerve**, stimulating gastric acid and enzyme secretion in anticipation of food arrival. *On food entering stomach* - This describes the initiation of the **gastric phase** of digestion, where mechanical stretch and chemical presence of food in the stomach stimulate further secretions. - The gastric phase primarily involves local reflexes and hormonal mechanisms (like **gastrin** release), rather than purely sensory input from the head. *On food entering intestine* - This marks the beginning of the **intestinal phase** of digestion, which involves both stimulatory and inhibitory signals for gastric secretion. - The primary role of the intestinal phase is to regulate the rate at which chyme enters the small intestine and to coordinate bile and pancreatic enzyme release. *On stress* - While stress can impact digestive function, it typically affects the **autonomic nervous system** in a generalized way, often leading to inhibition of digestion or altered motility. - Stress does not specifically trigger the cephalic phase of gastric secretion, which is a physiological response linked to nutrient anticipation.

Q: Gastric secretions are essential for absorption of -

Cobalamin. ***Cobalamin*** - **Intrinsic factor**, secreted by gastric parietal cells, is crucial for the absorption of **vitamin B12 (cobalamin)** in the terminal ileum [1]. - Without sufficient intrinsic factor, **pernicious anemia** can develop due to impaired B12 absorption [2]. *Fat* - Fat digestion primarily occurs in the **small intestine** with the help of **bile salts** and **pancreatic lipases**. - While gastric lipase begins some fat digestion, it's not essential for overall fat absorption. *Thiamine* - **Thiamine (vitamin B1)** is absorbed in the jejunum and ileum, primarily via **active transport** and passive diffusion. - Gastric secretions do not play a direct, essential role in its absorption. *Folic acid* - **Folic acid** is absorbed in the **duodenum and jejunum** as monoglutamates after being deconjugated from polyglutamate forms. - This process is not directly dependent on gastric secretions [2].

Q: Which of the following statements about gastric secretion is true?

Increased by stomach distention. ***Increased by stomach distention*** - **Stomach distention** activates local reflexes and the **vagovagal reflex**, leading to the release of **acetylcholine** and **gastrin**, which stimulate gastric acid secretion during the gastric phase. - This is a physiological response that prepares the stomach for digestion of incoming food. *Inhibited by curare* - **Curare** is a **nicotinic acetylcholine receptor antagonist** that primarily affects neuromuscular junctions, causing muscle paralysis. - It does not directly inhibit the primary mechanisms of gastric acid secretion, which are largely mediated by **muscarinic acetylcholine receptors**, histamine, and gastrin. *Stimulated by nor adrenaline* - **Noradrenaline** (norepinephrine) is a neurotransmitter of the **sympathetic nervous system**, which generally **inhibits** gastric motility and secretion. - Activation of alpha-2 adrenergic receptors can decrease gastric acid secretion. *Stimulated by an increase in tonic activity* - This statement is vague; "tonic activity" can refer to various physiological processes. If it refers to **sympathetic nervous system** tonic activity, it would **inhibit** gastric secretion. - If it implies increased vagal tone (parasympathetic activity), then secretion would be stimulated, but the phrasing is not precise enough to be unequivocally true for gastric secretion in general.

Q: What is the effect of acetylcholine on the Lower Esophageal Sphincter (LES)?

Causes contraction. ***Correct Option: Causes contraction*** - Acetylcholine acts on **M3 muscarinic receptors** on LES smooth muscle cells to cause **contraction** - This is part of the **excitatory cholinergic pathway** that maintains LES tone and prevents gastroesophageal reflux - Acetylcholine is released from **excitatory motor neurons** in the myenteric plexus *Incorrect: Causes relaxation* - LES relaxation during swallowing is mediated by **nitric oxide (NO)** and **vasoactive intestinal peptide (VIP)**, NOT acetylcholine - These inhibitory neurotransmitters are released from separate **inhibitory motor neurons** - The relaxation response during swallowing is due to activation of the inhibitory pathway, which suppresses cholinergic tone *Incorrect: No effect on LES* - Acetylcholine has a significant effect on the LES - It is one of the key neurotransmitters maintaining basal LES tone - Loss of cholinergic input can lead to decreased LES pressure *Incorrect: Contraction followed by relaxation* - Acetylcholine itself causes only contraction - The swallowing reflex involves coordinated activation of inhibitory (NO/VIP) and suppression of excitatory (acetylcholine) pathways - The sequence of events is neural, not a biphasic response to acetylcholine alone

Q: Which of the following statements regarding the lower esophageal sphincter is TRUE?

It relaxes in response to swallowing.. ***It relaxes in response to swallowing.*** - The **lower esophageal sphincter (LES)** normally maintains high resting tone to prevent gastroesophageal reflux but **relaxes completely during swallowing** to allow passage of food into the stomach. - This relaxation (called **receptive relaxation**) is mediated by **vagal nerve stimulation** through release of nitric oxide (NO) and vasoactive intestinal peptide (VIP). - The relaxation occurs **before the peristaltic wave arrives**, allowing coordinated transit of the bolus. *It remains contracted during swallowing to prevent regurgitation.* - This is **incorrect** - the LES must **relax during swallowing** to allow food passage into the stomach. - Failure of LES relaxation during swallowing is the pathophysiology of **achalasia**, leading to dysphagia. - The LES only maintains contraction between swallows to prevent reflux. *Its tone is primarily influenced by the myogenic properties of the smooth muscle.* - While the LES contains smooth muscle with intrinsic myogenic properties, its tone is **predominantly regulated by neural and hormonal factors**. - **Neural control:** Vagal cholinergic pathways (increase tone), non-adrenergic non-cholinergic (NANC) pathways with NO and VIP (decrease tone). - **Hormonal factors:** Gastrin increases tone, while progesterone, CCK, and secretin decrease tone. *It contracts in response to gastric distension.* - This is **incorrect** - gastric distension actually triggers **transient LES relaxations (TLESRs)**, which are the primary mechanism of physiological reflux. - TLESRs are vagally mediated reflex responses that allow venting of gastric air. - Increased LES contraction in response to gastric distension would be counterproductive.

Q: Ptyalin is secreted by?

Salivary gland. ***Salivary gland*** - **Ptyalin**, also known as **salivary amylase**, is an enzyme produced by the salivary glands. - Its primary role is to initiate the **digestion of carbohydrates** (starches) in the mouth. *Gastric gland* - Gastric glands primarily secrete **hydrochloric acid** and **pepsinogen**, involved in protein digestion. - They do not produce ptyalin or enzymes for carbohydrate digestion. *Duodenal gland* - Duodenal glands (Brunner's glands) secrete alkaline mucus to protect the duodenum from acidic chyme. - They are not involved in the production of carbohydrate-digesting enzymes like ptyalin. *Pancreatic gland* - The pancreas produces **pancreatic amylase**, which continues starch digestion in the small intestine. - While it secretes an amylase, it is distinct from salivary amylase (ptyalin) and released into the duodenum, not the mouth.

Q: Motilin secretion is decreased in which of the following states?

Ingested meal. ***Ingested meal*** - Motilin secretion is **decreased after a meal** due to the presence of food in the small intestine, which stimulates other gastrointestinal hormones and neuronal reflexes that inhibit motilin release. - The primary role of motilin is to stimulate **gastric and intestinal motility** during fasting, clearing residual food and preventing bacterial overgrowth, making its activity counterproductive during digestion. *Thirsty* - **Thirst** is primarily regulated by antidiuretic hormone (ADH) and the renin-angiotensin-aldosterone system, and it does not directly impact motilin secretion. - Motilin's main function is related to gut motility, largely independent of the body's hydration status. *Starving* - Motilin levels tend to be **higher during fasting or starvation**, as it plays a crucial role in initiating the **migrating motor complex (MMC)**, which sweeps undigested material through the gastrointestinal tract. - This activity prevents bacterial overgrowth and prepares the gut for the next meal; thus, its secretion is increased, not decreased. *Interdigestive state* - The **interdigestive state** refers to the period between meals, which is synonymous with a fasting or starving state. - During this period, motilin secretion is **increased** to stimulate the **migrating motor complex (MMC)**, which is essential for gut cleansing.

Q: What percentage of gastric secretion is attributed to the cephalic phase?

20%. ***20%*** - The **cephalic phase** of gastric secretion is initiated by the sight, smell, taste, or even thought of food and accounts for approximately **20-30%** of total gastric acid secretion. - This phase is mediated by the **vagus nerve**, stimulating parietal cells (via acetylcholine) and G cells (via gastrin-releasing peptide) to release acid and gastrin, respectively. *70 %* - **70%** represents the approximate contribution of the **gastric phase** to total gastric secretion, which is the largest phase. - This phase is activated by the presence of food in the stomach, distension, and the presence of amino acids and peptides. *10%* - **10%** is a value that is too low for the cephalic phase; it typically accounts for a more significant portion of initial acid secretion. - This percentage is sometimes associated with the intestinal phase, which produces a smaller amount of acid secretion after chyme enters the duodenum. *100%* - **100%** is incorrect because gastric secretion is a complex process involving multiple phases (cephalic, gastric, intestinal), each contributing a portion of the total secretion. - Each phase has distinct stimuli and regulatory mechanisms, ensuring a coordinated digestive response.

Question 1

Inhibition of myenteric plexus results in

Accepted Answer

Decreased gut motility

Answer

Hyperacidity

Answer

Diarrhea

Answer

Increased secretions

Question 2

Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?

Accepted Answer

Monosaccharides

Answer

Disaccharides

Answer

Polysaccharides

Answer

5-carbon sugars

Question 3

What triggers the cephalic phase of gastric secretion?

Accepted Answer

On seeing food

Answer

On food entering stomach

Answer

On food entering intestine

Answer

On stress

Question 4

Gastric secretions are essential for absorption of -

Accepted Answer

Cobalamin

Answer

Fat

Answer

Thiamine

Answer

Folic acid

Question 5

Which of the following statements about gastric secretion is true?

Accepted Answer

Increased by stomach distention

Answer

Inhibited by curare

Answer

Stimulated by nor adrenaline

Answer

Stimulated by an increase in tonic activity

Question 6

What is the effect of acetylcholine on the Lower Esophageal Sphincter (LES)?

Accepted Answer

Causes contraction

Answer

Causes relaxation

Answer

No effect on LES

Answer

Contraction followed by relaxation

Question 7

Which of the following statements regarding the lower esophageal sphincter is TRUE?

Accepted Answer

It relaxes in response to swallowing.

Answer

It remains contracted during swallowing to prevent regurgitation.

Answer

Its tone is primarily influenced by the myogenic properties of the smooth muscle.

Answer

It contracts in response to gastric distension.

Question 8

Ptyalin is secreted by?

Accepted Answer

Salivary gland

Answer

Gastric gland

Answer

Duodenal gland

Answer

Pancreatic gland

Question 9

Motilin secretion is decreased in which of the following states?

Accepted Answer

Ingested meal

Answer

Thirsty

Answer

Starving

Answer

Interdigestive state

Question 10

What percentage of gastric secretion is attributed to the cephalic phase?

Accepted Answer

20%

Answer

70%

Answer

10%

Answer

100%

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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