Gastrointestinal System Practice Questions

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.

Q: Which GI hormone is classified as an incretin and primarily responsible for the glucose-dependent stimulation of insulin secretion?

GIP. ***GIP*** - **Glucose-dependent insulinotropic polypeptide (GIP)** is a hormone with **incretin** activity produced in the duodenum and jejunum. - Its primary role is to stimulate **insulin secretion** from pancreatic beta cells in a glucose-dependent manner, meaning insulin release is enhanced when blood glucose levels are high. *Gastrin* - **Gastrin** is a hormone primarily secreted by G cells in the stomach and duodenum. - Its main function is to stimulate the secretion of **gastric acid (HCl)** by parietal cells, playing a key role in digestion, not insulin secretion. *Secretin* - **Secretin** is released by S cells in the duodenum in response to acidic chyme entering the small intestine. - It primarily stimulates the pancreas to release **bicarbonate-rich fluid** to neutralize stomach acid, and it inhibits gastric acid secretion, with no direct role as an incretin. *CCK* - **Cholecystokinin (CCK)** is secreted by I cells in the duodenum and jejunum, mainly in response to fats and proteins. - CCK primarily stimulates the contraction of the **gallbladder** to release bile and the secretion of **pancreatic enzymes**, and it also promotes satiety.

Question 1

Which of the following hormones primarily inhibits gastric emptying?

Accepted Answer

Cholecystokinin

Answer

Gastrin

Answer

Secretin

Answer

Vasoactive intestinal peptide

Question 2

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 3

What factor delays gastric emptying?

Accepted Answer

Acid in duodenum

Answer

Distension of stomach

Answer

Gastrin

Answer

Vagal stimulation

Question 4

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 5

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 6

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 7

Pentagastrin stimulation test is used to assess which organ?

Accepted Answer

Stomach

Answer

Lung

Answer

Liver

Answer

Heart

Question 8

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 9

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

Question 10

Which GI hormone is classified as an incretin and primarily responsible for the glucose-dependent stimulation of insulin secretion?

Accepted Answer

GIP

Answer

Gastrin

Answer

Secretin

Answer

CCK

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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