Gastrointestinal System Practice Questions

Q: Which secretion is directly stimulated by histamine?

Secretion of HCl in the stomach. **Secretion of HCl in the stomach** - **Histamine**, released from enterochromaffin-like (ECL) cells, acts on **H2 receptors** on **parietal cells** in the stomach. - This binding directly stimulates the parietal cells to secrete **hydrochloric acid (HCl)** into the gastric lumen. *Gastrin secretion in the stomach* - **Gastrin** is a hormone that stimulates **histamine release** from ECL cells and acts directly on parietal cells to stimulate HCl secretion. - Histamine is a downstream mediator of gastrin's action on parietal cells, not a direct stimulus for gastrin secretion itself. *Secretion of amylase by salivary glands* - **Amylase secretion** from salivary glands is primarily regulated by the **autonomic nervous system**, particularly **parasympathetic stimulation**. - Histamine does not play a direct role in the regulation of salivary amylase secretion. *Secretion of pancreatic enzymes* - **Pancreatic enzyme secretion** is primarily regulated by **cholecystokinin (CCK)** and **secretin**, hormones released in response to chyme in the duodenum. - While histamine can stimulate some pancreatic fluid and bicarbonate secretion indirectly, it is not a direct or primary stimulator of pancreatic enzyme secretion.

Q: Which of the following hormones primarily inhibits gastric emptying?

Cholecystokinin. ***Cholecystokinin (CCK)*** - **CCK** is released in response to **fat and protein** in the duodenum. - It slows gastric emptying to allow sufficient time for digestion and absorption of nutrients in the small intestine. *Gastrin* - **Gastrin** is primarily involved in **stimulating gastric acid secretion** and promoting gastric motility. - Its main effect is to increase, rather than inhibit, gastric emptying. *Secretin* - **Secretin** is released in response to **acid in the duodenum**. - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** and inhibit gastric acid secretion, but its effect on gastric emptying is less pronounced compared to CCK. *Vasoactive intestinal peptide (VIP)* - **VIP** functions as a **neurotransmitter** and hormone that causes **vasodilation**, relaxes smooth muscle, and inhibits gastric acid secretion. - While it can affect gut motility, its primary role is not the direct and significant inhibition of gastric emptying to the extent of CCK.

Q: Gastric acid secretion is stimulated during several phases associated with the ingestion and digestion of a meal. Which phase is primarily responsible for the majority of acid secretion?

Gastric. ***Gastric*** - The **gastric phase** is initiated by the presence of food in the stomach, leading to stomach distension and the presence of digested proteins and amino acids. - This phase accounts for approximately **60-70%** of total acid secretion, driven by local reflexes, vagovagal reflexes, and the release of gastrin. *Cephalic* - The **cephalic phase** is triggered by the **sight, smell, thought, or taste of food**, and accounts for about 20-30% of acid secretion. - It is mediated primarily by the **vagus nerve**, leading to the release of acetylcholine and gastrin. *Interdigestive* - The **interdigestive phase** refers to the period between meals when the stomach is empty. - During this phase, **basal acid secretion** is low and follows a circadian rhythm, primarily regulated by vagal tone and circulating gastrin. *Intestinal* - The **intestinal phase** begins once the chyme enters the small intestine and primarily functions to **inhibit** further gastric acid secretion. - While some stimulation can occur, inhibitory mechanisms, such as those from secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP), dominate to regulate gastric emptying and acid production.

Q: What factor delays gastric emptying?

Acid in duodenum. ***Acid in duodenum*** - The presence of **acid in the duodenum** stimulates the release of hormones like **secretin** and **cholecystokinin (CCK)**, which overall inhibit gastric motility and emptying to allow for neutralization and digestion. - This is a crucial feedback mechanism to protect the **duodenal mucosa** from acid damage and optimize nutrient absorption. *Distension of stomach* - **Stomach distension** generally *promotes* gastric emptying by activating stretch receptors that stimulate both local reflexes and vagal afferents, leading to increased gastric motility. - This reflex helps move food into the duodenum once the stomach has been filled sufficiently. *Gastrin* - **Gastrin** is a hormone primarily secreted in response to protein in the stomach and vagal stimulation; its main role is to *increase* gastric acid secretion and *stimulate* gastric motility, thus generally promoting rather than delaying emptying. - While high concentrations of gastrin can inhibit emptying in some contexts, its primary physiological effect on motility is typically stimulatory. *Vagal stimulation* - **Vagal stimulation** (parasympathetic innervation) generally *enhances* gastric motility and secretions, thereby promoting gastric emptying. - The **vagus nerve** plays a significant role in the cephalic and gastric phases of digestion, preparing the stomach for food and facilitating its processing.

Q: Maldigestion of protein and fat is manifested in chronic pancreatitis only if the damage to pancreatic tissue exceeds?

90%. ***90%*** - **Maldigestion** of protein and fat in chronic pancreatitis typically occurs when there is extensive damage to the pancreatic tissue, specifically affecting more than **90%** of its functional capacity. - This threshold is critical because the pancreas has a significant reserve capacity for enzyme production, meaning a large portion must be damaged before **exocrine insufficiency** becomes clinically apparent. *30%* - Damage to only **30%** of pancreatic tissue is generally below the threshold for significant clinical manifestations of maldigestion. - The remaining **70%** of functional tissue can still adequately produce digestive enzymes to prevent widespread nutrient malabsorption. *50%* - While **50%** damage is substantial, it usually does not lead to overt clinical symptoms of maldigestion, particularly fat malabsorption (**steatorrhea**). - The body's compensatory mechanisms and the remaining functional pancreatic mass can still maintain relatively normal digestion at this stage. *75%* - Although **75%** damage represents significant pancreatic loss, it often does not fully manifest as severe maldigestion of protein and fat. - Significant **steatorrhea** and **protein malabsorption** typically require an even greater reduction in exocrine function.

Q: The primary hormone secreted by duodenal cells in response to dietary fats and proteins is:

CCK. ***Correct Answer: CCK (Cholecystokinin)*** - **Cholecystokinin (CCK)** is primarily released from the **duodenal I-cells** in response to the presence of **fats and proteins** in the chyme entering the duodenum. - Its main functions include stimulating **gallbladder contraction** (releasing bile for fat emulsification) and **pancreatic enzyme secretion** (for nutrient digestion). *Incorrect: Secretin* - **Secretin** is primarily released in response to **acidic chyme** entering the duodenum, not directly by fats and proteins. - Its main roles are to stimulate the pancreas to release **bicarbonate-rich fluid** to neutralize gastric acid and to inhibit gastric acid secretion. *Incorrect: Gastrin* - **Gastrin** is secreted by **G-cells** in the stomach and duodenum, primarily in response to food (especially proteins) and vagal stimulation. - Its main function is to stimulate **gastric acid secretion** by parietal cells, not directly to dietary fats and proteins as a primary duodenal response. *Incorrect: Motilin* - **Motilin** is released from the small intestine during the **interdigestive period** (when fasting). - It plays a key role in initiating the **migrating motor complex (MMC)**, which sweeps undigested food and bacteria from the stomach and small intestine into the colon.

Q: What is the approximate total volume of saliva secreted daily by an adult?

1-1.5 L. ***1-1.5 L*** - The **average daily saliva production** in healthy adults typically ranges from **1000 mL to 1500 mL** (1-1.5 liters). - This is the **standard physiological range** cited in major textbooks including **Guyton & Hall** and **Ganong's Review of Medical Physiology**. - This volume is essential for **digestion** (salivary amylase initiates carbohydrate breakdown), **oral hygiene** (antibacterial properties), **lubrication**, and **speech**. *0.75-1 L* - This range represents the **lower end** of normal salivary production. - While some individuals may produce this amount, it is **below the typical average** cited in standard physiology references. - This volume might be seen during periods of **reduced stimulation** or mild **dehydration**. *2-2.5 L* - This range represents a **significant overestimation** of normal daily saliva volume. - Such excessive production would be **beyond the physiological range** and could indicate **pathological hypersalivation** (sialorrhea). *3-3.5 L* - This volume is **substantially higher** than normal salivary secretion. - Production at this level would be indicative of a **pathological condition** such as **mercury poisoning**, **organophosphate toxicity**, or **severe neurological disorders** affecting salivary control.

Q: Pentagastrin stimulation test is used to assess which organ?

Stomach. ***Stomach*** - The **pentagastrin stimulation test** is used to assess the stomach's ability to secrete acid [1]. - Pentagastrin is a synthetic analog of **gastrin**, a hormone that stimulates gastric acid secretion from **parietal cells** [1]. *Lung* - The lung is primarily involved in **gas exchange** and is assessed through tests like spirometry, chest X-rays, and arterial blood gas analysis [2]. - Pentagastrin has no direct diagnostic role in assessing lung function. *Liver* - The liver's function is evaluated by tests such as liver enzymes (ALT, AST), bilirubin levels, and imaging studies like ultrasound or MRI. - Pentagastrin is not a relevant diagnostic tool for assessing liver health or function. *Heart* - Cardiac function is assessed with electrocardiograms (ECG), echocardiography, stress tests, and measurement of cardiac biomarkers. - Pentagastrin stimulation has no application in the diagnosis or evaluation of heart conditions.

Q: At concentrations present in the diet, which vitamin is absorbed primarily by diffusion?

Vitamin D. ***Vitamin D*** - **Fat-soluble vitamins** (A, D, E, K) like Vitamin D are absorbed from the intestine primarily through **passive diffusion** at **dietary/physiological concentrations**. - They are incorporated into **mixed micelles** in the intestinal lumen, which facilitate their transport to the enterocyte membrane. - The **lipophilic nature** of these vitamins allows them to passively diffuse across the lipid bilayer of the enterocyte membrane **without requiring specific transporters**. - Once inside enterocytes, they are packaged into **chylomicrons** for lymphatic transport. *Vitamin C* - **Water-soluble vitamin C** is absorbed via **sodium-dependent vitamin C transporters (SVCTs)** - specifically SVCT1 in the small intestine. - At high (pharmacological) concentrations, passive diffusion can contribute to its absorption, but at dietary concentrations, active transport predominates. *Folate* - Folate, a **water-soluble B vitamin**, is absorbed primarily through **active transport mechanisms**, specifically via the **reduced folate carrier (RFC)** and **proton-coupled folate transporter (PCFT)**. - These transporters are essential for efficient folate uptake even at low concentrations. *Niacin* - Niacin (**Vitamin B3**) is absorbed through **carrier-mediated transport** at physiological (dietary) concentrations. - At pharmacological doses, simple passive diffusion can dominate, but this is not the primary mechanism at normal dietary levels.

Q: Which of the following is not a function of the liver?

Production of vitamin K. ***Production of vitamin K*** - The **liver** is essential for activating **vitamin K** and producing **vitamin K-dependent clotting factors**, such as factors II, VII, IX, and X. - However, the liver itself does not *produce* vitamin K. Instead, **intestinal bacteria** synthesize vitamin K, which is then absorbed. *Production of albumin* - The liver is the primary site for the synthesis of **albumin**, a crucial plasma protein. - **Albumin** plays a vital role in maintaining **oncotic pressure**, transporting hormones, and carrying drugs in the bloodstream. *Detoxification of ammonia* - The liver is responsible for detoxifying **ammonia** by converting it into **urea** through the urea cycle. - This process is essential as **high levels of ammonia** are neurotoxic. *Metabolism of drugs* - The liver is the main organ for **drug metabolism** through various enzyme systems, including the cytochrome P450 system. - This process transforms drugs into more water-soluble compounds, facilitating their excretion from the body.

Question 1

Which secretion is directly stimulated by histamine?

Accepted Answer

Secretion of HCl in the stomach

Answer

Gastrin secretion in the stomach

Answer

Secretion of amylase by salivary glands

Answer

Secretion of pancreatic enzymes

Question 2

Which of the following hormones primarily inhibits gastric emptying?

Accepted Answer

Cholecystokinin

Answer

Gastrin

Answer

Secretin

Answer

Vasoactive intestinal peptide

Question 3

Gastric acid secretion is stimulated during several phases associated with the ingestion and digestion of a meal. Which phase is primarily responsible for the majority of acid secretion?

Accepted Answer

Gastric

Answer

Cephalic

Answer

Intestinal

Answer

Interdigestive

Question 4

What factor delays gastric emptying?

Accepted Answer

Acid in duodenum

Answer

Distension of stomach

Answer

Gastrin

Answer

Vagal stimulation

Question 5

Maldigestion of protein and fat is manifested in chronic pancreatitis only if the damage to pancreatic tissue exceeds?

Accepted Answer

90%

Answer

30%

Answer

50%

Answer

75%

Question 6

The primary hormone secreted by duodenal cells in response to dietary fats and proteins is:

Accepted Answer

CCK

Answer

Secretin

Answer

Gastrin

Answer

Motilin

Question 7

What is the approximate total volume of saliva secreted daily by an adult?

Accepted Answer

1-1.5 L

Answer

3-3.5 L

Answer

2-2.5 L

Answer

0.75-1 L

Question 8

Pentagastrin stimulation test is used to assess which organ?

Accepted Answer

Stomach

Answer

Lung

Answer

Liver

Answer

Heart

Question 9

At concentrations present in the diet, which vitamin is absorbed primarily by diffusion?

Accepted Answer

Vitamin D

Answer

Folate

Answer

Niacin

Answer

Vitamin C

Question 10

Which of the following is not a function of the liver?

Accepted Answer

Production of vitamin K

Answer

Metabolism of drugs

Answer

Detoxification of ammonia

Answer

Production of albumin

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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