Gastrointestinal System Practice Questions

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.

Q: What is the primary function of hepatic stellate cells?

Vitamin A storage. ***Vit-A storage*** - **Hepatic stellate cells** (also known as Ito cells) are primarily responsible for storing **vitamin A** in the form of retinyl palmitate droplets. - In their quiescent state, these cells contain abundant lipid droplets that house the body's largest reserve of **vitamin A**. *Regulation of liver fibrosis* - While **hepatic stellate cells** play a critical role in **liver fibrosis**, this is a function of their activated state in response to injury, not their primary function in a healthy liver. - Upon activation, they transform into myofibroblast-like cells that produce **extracellular matrix**, contributing to fibrosis. *Secretion of cytokines* - **Hepatic stellate cells** do secrete cytokines, particularly upon activation, but this is a secondary response to injury or inflammation. - Their most well-known and constantly active role in a healthy liver is **vitamin A storage**. *Formation of extracellular matrix* - The formation of **extracellular matrix** (ECM) is a characteristic of activated **hepatic stellate cells** during liver injury and fibrosis. - In their quiescent state, these cells maintain a different role, and excessive ECM production is pathological.

Q: From which part of the gastrointestinal tract is glucose absorbed?

Duodenum and jejunum. ***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.

Q: Which of the following hormones stimulates HCl secretion in the stomach?

Gastrin. ***Gastrin*** - **Gastrin** is a hormone produced by **G cells** in the stomach antrum in response to food, particularly proteins. - It directly stimulates parietal cells to secrete **hydrochloric acid (HCl)** and indirectly increases HCl secretion by promoting histamine release. *Secretin* - **Secretin** is released from the duodenum in response to acidic chyme entering the small intestine. - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** and to inhibit gastric acid secretion, counteracting gastrin's effect. *Histamine* - While **histamine** is a potent stimulator of HCl secretion, it is a **paracrine** substance produced by enterochromaffin-like (ECL) cells, not a hormone that circulates in the blood to exert its effect. - It acts locally on parietal cells via **H2 receptors** to increase acid production. *Somatostatin* - **Somatostatin** is a hormone released by **D cells** in the stomach and duodenum. - It acts as an inhibitory hormone, **decreasing** or stopping the secretion of gastrin, secretin, and histamine, thereby reducing gastric acid secretion.

Q: Which causes antral gastrin release?

Antral distension. **Antral distension** - **Antral distension** after a meal stimulates mechanoreceptors, which trigger the release of **gastrin** from G cells in the gastric antrum via a vagovagal reflex. - This gastrin release is crucial for promoting gastric acid secretion and motility to aid digestion. *Acid* - **Gastric acid** in the antrum actually **inhibits** gastrin release through a negative feedback loop mediated by somatostatin. - This mechanism prevents excessive acid production when the stomach pH drops too low. *Secretin* - **Secretin** is released from the duodenum in response to acid and functions primarily to **inhibit gastrin release** and stimulate bicarbonate and fluid secretion. - Its main role is to protect the duodenal mucosa from gastric acid. *Calcitonin* - **Calcitonin** is a hormone primarily involved in **calcium metabolism** and is secreted by the thyroid gland. - It has no direct physiological role in regulating antral gastrin release.

Q: If the ileum is excised, which substance will increase in the stool?

Bile salts. ***Bile salts*** - The **terminal ileum** is the **only site** for **active reabsorption of bile salts** from the enterohepatic circulation. - Excision of the ileum leads to **direct loss** of bile salt reabsorption, causing bile salts to enter the colon, resulting in **cholorrhoeic diarrhea** and malabsorption. - This is the **primary and most specific** consequence of ileal resection. - Bile salts in the colon also stimulate water and electrolyte secretion, worsening diarrhea. *Unabsorbed fats* - While **fats do increase in stool** after ileal resection (steatorrhea), this is a **secondary effect** due to bile salt deficiency. - Bile salts are essential for **fat emulsification and micelle formation**, so their loss impairs fat absorption. - However, the **direct substance lost** from ileal excision is bile salts, not fats themselves - making bile salts the more specific answer. *Calcium* - **Calcium absorption** primarily occurs in the **duodenum and proximal jejunum** (vitamin D-dependent active transport). - Ileal resection does not directly affect calcium absorption. - Calcium in stool would not significantly increase from ileal excision alone. *Iron* - **Iron absorption** mainly takes place in the **duodenum and proximal jejunum**. - Ileal excision would not affect iron absorption or increase iron in stool.

Q: Intrinsic factor is required for the absorption of which vitamin?

Vitamin B12. ***Vitamin B12*** - **Intrinsic factor**, a glycoprotein secreted by gastric parietal cells, binds to **vitamin B12 (cobalamin)** in the stomach. - This complex then travels to the **terminal ileum**, where it is specifically absorbed. *Vitamin B2* - **Vitamin B2 (riboflavin)** is absorbed in the **proximal small intestine** via a carrier-mediated transport system that does not involve intrinsic factor. - Deficiency can lead to **cheilosis** and **angular stomatitis**. *Vitamin B6* - **Vitamin B6 (pyridoxine)** is primarily absorbed in the **jejunum and ileum** through a non-specific, passive diffusion process and does not require intrinsic factor. - It plays a crucial role as a coenzyme in amino acid metabolism. *Folic acid* - **Folic acid (vitamin B9)** is absorbed mainly in the **jejunum** and does not depend on intrinsic factor for its absorption. - It is essential for **DNA synthesis** and red blood cell maturation, and deficiency can cause **megaloblastic anemia**.

Q: Gastric secretion is increased by all except which one?

HCl. ***HCl (Correct Answer - Does NOT Increase Gastric Secretion)*** - While **HCl** is a major component of gastric acid, its presence in the stomach lumen acts as a **negative feedback mechanism** to *inhibit* further gastric secretion, particularly gastrin release. - High acidity (low pH) directly **inhibits gastrin-producing G cells** and stimulates **somatostatin release**, which in turn inhibits acid secretion. - This negative feedback prevents excessive acid production and maintains pH homeostasis. *Histamine (Increases Gastric Secretion)* - **Histamine** is a powerful stimulant of gastric acid secretion, acting primarily through **H2 receptors** on parietal cells to increase cAMP levels. - It potentiates the effects of both acetylcholine and gastrin, significantly enhancing acid production. *Acetylcholine (Increases Gastric Secretion)* - **Acetylcholine**, released from vagal nerve endings, directly stimulates **parietal cells** (M3 receptors), **G cells** (gastrin release), and **ECL cells** (histamine release), all contributing to increased gastric secretion. - It plays a crucial role in the **cephalic and gastric phases** of digestion. *Gastrin (Increases Gastric Secretion)* - **Gastrin**, a hormone released from G cells in the gastric antrum, primarily stimulates **parietal cells** to secrete acid and also promotes the growth of the gastric mucosa. - It also stimulates **ECL cells** to release histamine, further augmenting acid secretion.

Question 1

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

Question 2

What is the primary function of hepatic stellate cells?

Accepted Answer

Vitamin A storage

Answer

Regulation of liver fibrosis

Answer

Secretion of cytokines

Answer

Formation of extracellular matrix

Question 3

From which part of the gastrointestinal tract is glucose absorbed?

Accepted Answer

Duodenum and jejunum

Answer

Stomach

Answer

Colon

Answer

Ileum

Question 4

Which of the following hormones stimulates HCl secretion in the stomach?

Accepted Answer

Gastrin

Answer

Histamine

Answer

Secretin

Answer

Somatostatin

Question 5

Which causes antral gastrin release?

Accepted Answer

Antral distension

Answer

Acid

Answer

Secretin

Answer

Calcitonin

Question 6

If the ileum is excised, which substance will increase in the stool?

Accepted Answer

Bile salts

Answer

Iron

Answer

Unabsorbed fats

Answer

Calcium

Question 7

Intrinsic factor is required for the absorption of which vitamin?

Accepted Answer

Vitamin B12

Answer

Vitamin B2

Answer

Vitamin B6

Answer

Folic acid

Question 8

Gastric secretion is increased by all except which one?

Accepted Answer

HCl

Answer

Histamine

Answer

Acetylcholine

Answer

Gastrin

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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