Gastrointestinal Hormones — MCQs
Insulin secretion is normally stimulated by -
Somatostatin is secreted by which type of cells in the pancreas?
Two normal, healthy subjects volunteer for a study on insulin secretion. In Patient 1, blood glucose is increased to 150 mg/dL by direct intravenous infusion. In Patient 2, blood glucose is increased to 150 mg/dL by ingestion of oral glucose. The peak plasma insulin concentration produced in Patient 1 is 70 uU/mL while in Patient 2, it is 95 uU/mL. Which of the following best explains the higher insulin concentration in Patient 2?
Best provocative test for diagnosis of Gastrinoma is:
What is the most important site for gastrin-producing cells?
Which of the following is NOT true about ghrelin?
What is the primary function of the myenteric plexus?
Which cells are referred to as "Pacemaker cells" with relation to "BER"?
From which part of the gastrointestinal tract is glucose absorbed?
Small intestinal peristalsis is controlled by :
Gastrointestinal Hormones Indian Medical PG Practice Questions and MCQs
Question 1: Insulin secretion is normally stimulated by -
- A. GLP-1 (Correct Answer)
- B. GLP-2
- C. α-adrenergic receptors
- D. VIP
Explanation: ***GLP-1*** - **Glucagon-like peptide-1 (GLP-1)** is an **incretin hormone** that stimulates glucose-dependent insulin secretion from pancreatic beta cells. - It also **suppresses glucagon secretion**, slows gastric emptying, and promotes satiety, all contributing to blood glucose regulation. *GLP-2* - **Glucagon-like peptide-2 (GLP-2)** primarily affects the **gastrointestinal tract**, promoting mucosal growth and nutrient absorption. - It does not directly stimulate **insulin secretion**. *α-adrenergic receptors* - Activation of **α-adrenergic receptors** on pancreatic beta cells by catecholamines like adrenaline and noradrenaline actually **inhibits insulin secretion**. - This response is part of the **stress response**, prioritizing glucose availability for vital organs. *VIP* - **Vasoactive intestinal peptide (VIP)** is a **neuropeptide** that acts as a potent vasodilator and stimulates intestinal water and electrolyte secretion. - While it has some effects on metabolism, it is not a primary or direct stimulator of **insulin secretion** under normal physiological conditions.
Question 2: Somatostatin is secreted by which type of cells in the pancreas?
- A. Gamma cells
- B. Delta cells (Correct Answer)
- C. Alpha cells
- D. Beta cells
Explanation: ***Delta cells*** - **Delta cells** (δ-cells) of the pancreatic islets are responsible for secreting **somatostatin**. - Somatostatin acts as a paracrine inhibitor, regulating the secretion of other pancreatic hormones like insulin and glucagon. *Gamma cells* - The term "gamma cells" is not a standard classification for pancreatic islet cells. - Pancreatic islet cells are typically categorized as alpha, beta, delta, and PP (pancreatic polypeptide) cells. *Alpha cells* - **Alpha cells** (α-cells) are responsible for secreting **glucagon**. - Glucagon primarily acts to raise blood glucose levels. *Beta cells* - **Beta cells** (β-cells) are the most abundant pancreatic islet cells and produce **insulin**. - Insulin is crucial for lowering blood glucose by promoting glucose uptake into cells.
Question 3: Two normal, healthy subjects volunteer for a study on insulin secretion. In Patient 1, blood glucose is increased to 150 mg/dL by direct intravenous infusion. In Patient 2, blood glucose is increased to 150 mg/dL by ingestion of oral glucose. The peak plasma insulin concentration produced in Patient 1 is 70 uU/mL while in Patient 2, it is 95 uU/mL. Which of the following best explains the higher insulin concentration in Patient 2?
- A. Ingested glucose increases duodenal secretion of gastric inhibitory peptide (GIP), increasing beta cell release of insulin (Correct Answer)
- B. Intravenous glucose increases islet cell secretion of somatostatin, inhibiting beta cell release of insulin
- C. Intravenous glucose increases islet cell secretion of glucagon, inhibiting beta cell release of insulin
- D. Ingested glucose activates a sympathetic reflex that increases beta cell release of insulin
Explanation: ***Ingested glucose increases duodenal secretion of gastric inhibitory peptide (GIP), increasing beta cell release of insulin*** - **Oral glucose ingestion** stimulates the release of **incretin hormones** like **GIP (glucose-dependent insulinotropic polypeptide)** and GLP-1 (glucagon-like peptide-1) from the small intestine. - These **incretins amplify glucose-stimulated insulin secretion** from pancreatic beta cells, explaining the **higher insulin response** in Patient 2 compared to Patient 1, who received intravenous glucose and thus bypassed the intestinal incretin release. *Intravenous glucose increases islet cell secretion of somatostatin, inhibiting beta cell release of insulin* - While somatostatin does inhibit insulin secretion, its release is typically stimulated by high nutrient levels or certain hormones, not directly by **intravenous glucose** in a way that would explain the difference between the two patients. - The primary physiological difference between oral and intravenous glucose administration regarding insulin response is the **incretin effect**, not differential somatostatin secretion. *Intravenous glucose increases islet cell secretion of glucagon, inhibiting beta cell release of insulin* - **Glucagon** is generally secreted in response to **low blood glucose** and works to raise it, not inhibit insulin release in this specific context. - Furthermore, **glucose stimulation typically suppresses glucagon secretion**, so an increase in glucagon with intravenous glucose is unlikely and wouldn't explain the lower insulin. *Ingested glucose activates a sympathetic reflex that increases beta cell release of insulin* - The **sympathetic nervous system** generally **inhibits insulin secretion** (via alpha-adrenergic receptors) and stimulates glucagon secretion, particularly during stress or exercise. - Therefore, an activation of a sympathetic reflex due to ingested glucose would more likely *decrease* or have a minimal effect on insulin release, rather than increasing it.
Question 4: Best provocative test for diagnosis of Gastrinoma is:
- A. Ca++ infusion test
- B. Secretin injection test (Correct Answer)
- C. ACTH stimulation test
- D. Steroid assay
Explanation: ***Secretin injection test*** - The **secretin injection test** is the most reliable provocative test for gastrinoma, leading to a paradoxical increase in gastrin levels [1]. - In normal individuals, secretin suppresses gastrin release, but in gastrinoma, it stimulates **gastrin secretion** [1]. *Ca++ infusion test* - The **calcium infusion test** can also stimulate gastrin release in gastrinoma patients, but it is less specific and potentially more risky than the secretin test due to potential side effects like cardiac arrhythmias. - It involves infusing calcium gluconate to observe any uncharacteristic rise in gastrin. *ACTH stimulation test* - The **ACTH stimulation test** is used to evaluate adrenal gland function, particularly in suspected cases of adrenal insufficiency or hypercortisolism [2]. - It does not have any direct relevance to the diagnosis of **gastrinoma**. *Steroid assay* - **Steroid assays** measure levels of various steroid hormones (e.g., cortisol, aldosterone) in the body to assess adrenal or gonadal function. - This test is not used for diagnosing **gastrinoma**.
Question 5: What is the most important site for gastrin-producing cells?
- A. Cardia
- B. Fundus
- C. Antrum (Correct Answer)
- D. Duodenum
Explanation: ***Antrum*** - The **G cells**, which produce gastrin, are most concentrated in the gastric **antrum**. - **Gastrin** plays a crucial role in stimulating parietal cells to secrete hydrochloric acid and promoting gastric motility. *Cardia* - The cardia is the entry point of the esophagus into the stomach and contains mostly **mucus-secreting cells** for protection against reflux. - It has a minimal number of gastrin-producing G cells compared to the antrum. *Fundus* - The **fundus** is primarily responsible for storing food and contains abundant parietal cells for **acid secretion** and chief cells for **pepsinogen production**. - While it does contain some endocrine cells, it is not the main site for gastrin production. *Duodenum* - The **duodenum** contains some G cells, but they are less abundant than in the gastric antrum. - Its primary role is digestion and absorption, with major secretions including **cholecystokinin** and **secretin**.
Question 6: Which of the following is NOT true about ghrelin?
- A. Has anorexic effect (Correct Answer)
- B. Stimulates growth hormone release
- C. Secreted by gastric fundus cells
- D. Increases gastric motility
Explanation: ***Has anorexic effect*** - Ghrelin is known as the **"hunger hormone"** because it stimulates appetite and has an **orexigenic effect**, meaning it increases food intake. - Therefore, stating that it has an **anorexic effect** (reduces appetite) is incorrect. *Stimulates growth hormone release* - Ghrelin is a **natural ligand** for the **growth hormone secretagogue receptor (GHSR)**. - This binding leads to the stimulation of **growth hormone (GH)** release from the pituitary gland. *Secreted by gastric fundus cells* - The primary source of ghrelin in the body is the **P/D1 cells** found in the mucosa of the **gastric fundus**. - Smaller amounts are also produced in the small intestine, pancreas, and hypothalamus. *Increases gastric motility* - Ghrelin is involved in regulating stomach function and can **increase gastric motility** and acid secretion. - This action helps to prepare the digestive system for incoming food.
Question 7: What is the primary function of the myenteric plexus?
- A. Regulating GI secretion
- B. Regulating local blood flow
- C. Regulating motility (Correct Answer)
- D. Regulating absorption
Explanation: ***Regulating motility*** - The myenteric plexus, also known as **Auerbach's plexus**, is primarily responsible for coordinating the **rhythmic contractions** and **relaxation of the gastrointestinal (GI) smooth muscle**. - Its strategic location between the **longitudinal and circular muscle layers** allows it to directly influence the strength and frequency of peristalsis, thus regulating the movement of food through the digestive tract. *Regulating GI secretion* - While it has some indirect influence, the **submucosal plexus** (Meissner's plexus) is the primary neural network regulating **secretory functions** of the GI tract. - The myenteric plexus's main role is more directly related to muscle contraction and relaxation rather than glandular secretion. *Regulating local blood flow* - Local blood flow in the GI tract is primarily regulated by the **sympathetic and parasympathetic nervous systems**, along with local metabolic factors and hormones. - The myenteric plexus has a minimal direct role in the control of **GI blood vessel smooth muscle**. *Regulating absorption* - Absorption is primarily a function of the **intestinal epithelial cells** and is regulated by various transport mechanisms, hormones, and local factors. - While the enteric nervous system influences mucosal function indirectly, the myenteric plexus's primary role is **motor control** rather than directly regulating nutrient absorption processes.
Question 8: Which cells are referred to as "Pacemaker cells" with relation to "BER"?
- A. SA node
- B. AV node
- C. Interstitial cells of Cajal (Correct Answer)
- D. Pyramidal cells
Explanation: ***Interstitial cells of Cajal*** - The **Interstitial cells of Cajal (ICC)** are specialized cells in the gastrointestinal tract that act as the **pacemaker cells** for the **Basic Electrical Rhythm (BER)**. - They generate slow waves of **depolarization** and **repolarization**, which determine the frequency and rhythm of smooth muscle contractions. *SA node* - The **sinoatrial (SA) node** is the natural pacemaker of the **heart**, initiating the cardiac electrical impulse. - It controls the heart rate, not the **BER** of the gastrointestinal tract. *AV node* - The **atrioventricular (AV) node** is part of the heart's electrical conduction system, responsible for delaying and transmitting impulses from the atria to the ventricles. - It does not regulate the **BER** of the gastrointestinal system. *Pyramidal cells* - **Pyramidal cells** are a type of neuron found in various parts of the brain, particularly the cerebral cortex and hippocampus. - They are involved in cognitive functions and motor control, and have no role in generating the **BER** in the gut.
Question 9: 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 10: 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.
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