Gastrointestinal System Practice Questions

Q: Secretion of bile out of hepatocytes occurs via?

Active transport. ***Active transport*** - Bile secretion by hepatocytes is an **energy-dependent process** against concentration gradients, requiring specific transporter proteins. - This active mechanism ensures efficient bile flow and prevents reflux, crucial for processes like **fat digestion and absorption**. *Passive diffusion* - **Passive diffusion** involves substances moving down their concentration gradient without energy expenditure. - Bile components, like bile salts, are highly concentrated within hepatocytes and need to be moved against this gradient. *Facilitated diffusion* - This type of diffusion utilizes **transmembrane proteins** to move substances down their concentration gradient, but still does not directly consume ATP. - Bile components are often transported against their concentration gradient, which is not facilitated diffusion. *Osmosis* - **Osmosis** specifically refers to the movement of water across a semipermeable membrane from a region of higher water concentration to a region of lower water concentration. - While water is a component of bile, the primary mechanism of moving bile solutes out of the hepatocyte is not osmosis.

Q: What is the primary hormonal action of cholecystokinin (CCK) in response to fat and protein in the duodenum?

Stimulates pancreatic enzyme secretion. ***Stimulates pancreatic enzyme secretion*** - **Cholecystokinin (CCK)** is released by **I cells** in the duodenum and jejunum in response to **fat and protein** in the small intestine. - CCK's primary actions include stimulating **pancreatic enzyme secretion** (amylase, lipase, proteases) and **gallbladder contraction** to release bile. - Both actions work synergistically to digest fats and proteins, making CCK essential for **enzymatic digestion and fat emulsification**. *Stimulates gallbladder contraction* - This is indeed a **major primary function** of CCK (cholecysto = gallbladder, kinin = movement). - CCK causes gallbladder contraction to release stored bile for fat emulsification. - Both pancreatic enzyme secretion and gallbladder contraction are co-equal primary functions; in exam context, pancreatic enzyme secretion is often prioritized as it reflects the broader digestive enzyme role. *Inhibits gastric emptying* - CCK does slow gastric emptying, but this is a **secondary regulatory effect** rather than a primary hormonal action. - This allows time for proper digestion of fats and proteins in the small intestine. *Increases gastric acid secretion* - **Incorrect.** CCK actually has an **inhibitory effect** on gastric acid secretion. - **Gastrin** is the primary hormone that increases gastric acid secretion from parietal cells.

Q: Small intestinal peristalsis is controlled by :

Myenteric plexus. ***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.

Q: What is the primary function of the liver in the human body?

Detoxification and metabolism of nutrients. ***Detoxification and metabolism of nutrients*** - The liver is a central organ for **detoxifying harmful substances** (e.g., alcohol, drugs, metabolic waste products) and converting them into less toxic forms for excretion. - It plays a crucial role in the **metabolism of carbohydrates, fats, and proteins**, including processes like gluconeogenesis, glycogenolysis, and synthesis of cholesterol. *Bile production* - While the liver **produces bile**, which is essential for **fat digestion and absorption**, this is one function among many and not considered its *primary* overall function. - Bile production is a specific secretory function, whereas detoxification and nutrient metabolism encompass a broader range of vital metabolic activities. *Storage of vitamins and minerals* - The liver does store certain **vitamins (e.g., A, D, B12)** and **minerals (e.g., iron, copper)**, acting as a reservoir for these essential nutrients. - However, storage is a supportive role; the primary metabolic and detoxifying functions are more critical for maintaining homeostasis. *Production of insulin* - **Insulin** is produced by the **beta cells of the pancreas**, not the liver. - The liver responds to insulin by taking up glucose, but it is not involved in its initial synthesis.

Q: Daily salivary secretion is

1000-1500 ml. ***1000-1500 ml*** - The average daily salivary secretion in healthy adults ranges from **1000 to 1500 ml**, with variations depending on individual factors and stimulation. - This volume is crucial for various functions, including **digestion**, oral hygiene, and speech. *1500-2000 ml* - This range is generally considered to be on the **higher side** of normal daily salivary output, exceeding the typical average. - While individual variations exist, consistent secretion at this level might suggest **hypersecretion** or ptyalism in some cases. *More than 2000 ml* - Daily salivary secretion **rarely exceeds 2000 ml** in healthy individuals. - Such high volumes could indicate a pathological condition leading to **sialorrhea** or excessive salivation. *Less than 1000 ml* - A daily salivary secretion of **less than 1000 ml** is often indicative of **hyposalivation** or dry mouth (xerostomia). - This reduced volume can lead to problems with chewing, swallowing, speaking, and an increased risk of dental caries.

Q: Which hormone is secreted by the "Delta cells" of the stomach?

Somatostatin. ***Somatostatin*** - **Delta cells (D cells)** in the stomach and pancreas secrete **somatostatin**, a potent inhibitory hormone. - Somatostatin **inhibits the release of gastrin**, histamine, secretin, cholecystokinin, and gastric acid secretion, acting as a "universal off switch." *Cholecystokinin* - **Cholecystokinin (CCK)** is primarily secreted by **I cells** in the duodenum and jejunum. - Its main functions include stimulating gallbladder contraction and pancreatic enzyme secretion. *Gastrin-releasing peptide* - **Gastrin-releasing peptide (GRP)**, also known as **bombesin**, is a neuropeptide released from **enteric neurons**. - It stimulates the release of **gastrin** from G cells. *Secretin* - **Secretin** is secreted by **S cells** in the duodenum in response to acidic chyme entering the small intestine. - Its primary role is to stimulate the pancreas to release **bicarbonate-rich fluid** to neutralize gastric acid.

Q: Lowest pH is seen in which of the gastrointestinal secretions?

Gastric juice. ***Gastric juice*** - Gastric juice contains **hydrochloric acid (HCl)**, secreted by parietal cells, which gives it a very **low pH (1.5-3.5)**. - This acidic environment is crucial for protein digestion by **pepsin** and for killing ingested microorganisms. *Bile juice* - Bile juice is typically **alkaline**, with a pH ranging from **7.6 to 8.6**. - Its primary role is to **emulsify fats** in the small intestine, and it does not contain significant acidic components. *Saliva* - Saliva has a relatively neutral pH, typically ranging from **6.2 to 7.6**. - It contains enzymes like **amylase** and **lipase** for initial carbohydrate and lipid digestion, but no strong acids. *Pancreatic juice* - Pancreatic juice is highly **alkaline**, with a pH usually between **8.0 and 8.3**, due to its high concentration of bicarbonate. - This alkalinity neutralizes the acidic chyme entering the duodenum from the stomach, creating an optimal environment for pancreatic enzymes.

Q: Sugars are primarily absorbed in?

Jejunum. ***Jejunum*** - The **jejunum** is the primary site for the absorption of most digested nutrients, including the vast majority of **monosaccharides** (simple sugars like glucose, fructose, and galactose). - Its structure, with numerous **plicae circulares**, villi, and microvilli, provides a large surface area optimized for efficient nutrient uptake. *Duodenum* - The **duodenum** is mainly involved in the **chemical digestion** of food, receiving chyme from the stomach and mixing it with digestive enzymes from the pancreas and bile from the liver. - While some minimal absorption can occur, it is not the primary site for extensive sugar absorption. *Ileum* - The **ileum** is mainly responsible for the absorption of **vitamin B12** and **bile salts**. - Although some residual nutrient absorption can happen here if the jejunum is compromised, it is not the primary physiological site for sugar absorption. *Ascending colon* - The **ascending colon** is primarily involved in the absorption of **water and electrolytes**, forming solid stool. - It does not significantly absorb sugars; undigested carbohydrates reaching the colon are typically fermented by gut bacteria.

Q: Mechanism of action of cholecystokinin?

Through IP3- DAG system. ***Through IP3- DAG system*** - Cholecystokinin (CCK) primarily acts via **Gq protein-coupled receptors**, leading to the activation of **phospholipase C**. - This activation results in the hydrolysis of **PIP2 into IP3 and DAG**, which then mediate intracellular signaling cascades, causing actions like gallbladder contraction and pancreatic enzyme secretion. *Activation of adenylyl cyclase* - This mechanism is typically associated with **Gs protein-coupled receptors**, leading to increased levels of **cyclic AMP (cAMP)**. - Hormones like **glucagon** and **epinephrine** often utilize this pathway, which is distinct from CCK's primary signaling. *Opening of ion channels* - While ion channels are crucial for many cellular processes, CCK's direct mechanism of action typically involves **intracellular second messengers** rather than direct gating of ion channels. - Neurotransmitters like **acetylcholine** can directly open ion channels, but this is not the main signaling pathway for CCK. *Transcription factors* - Transcription factors regulate **gene expression** by binding to DNA, which is a slower, more long-term cellular response. - While CCK can eventually influence gene expression, its direct and immediate effects (e.g., gallbladder contraction) are mediated by **rapid second messenger systems**, not primary transcription factor modulation.

Q: Which of the following is the primary site of gastrin production?

Gastric G cells. ***Gastric G cells*** - **G cells**, primarily located in the **antrum of the stomach**, are the main site for **gastrin production** - Gastrin is a hormone that stimulates the secretion of **gastric acid** by the parietal cells in the oxyntic glands of the stomach - G cells are specialized endocrine cells that release gastrin in response to gastric distension, amino acids, and vagal stimulation *Pancreas* - The pancreas produces hormones such as **insulin** and **glucagon**, and digestive enzymes like **amylase** and **lipase** - While the pancreas does contain some hormone-producing cells, it is not the primary site for gastrin synthesis *Pituitary gland* - The **pituitary gland** is the master endocrine gland, regulating various **hormonal axes** like thyroid, adrenal, and reproductive functions - It does not produce gastrin; its hormones include **growth hormone**, **prolactin**, **TSH**, **ACTH**, **FSH**, and **LH** *Gastric chief cells* - Chief cells (also called zymogenic cells) are located in the **gastric glands of the fundus and body** of the stomach - They produce **pepsinogen**, the inactive precursor of the proteolytic enzyme pepsin, not gastrin

Question 1

Secretion of bile out of hepatocytes occurs via?

Accepted Answer

Active transport

Answer

Passive diffusion

Answer

Facilitated diffusion

Answer

Osmosis

Question 2

What is the primary hormonal action of cholecystokinin (CCK) in response to fat and protein in the duodenum?

Accepted Answer

Stimulates pancreatic enzyme secretion

Answer

Stimulates gallbladder contraction

Answer

Inhibits gastric emptying

Answer

Increases gastric acid secretion

Question 3

Small intestinal peristalsis is controlled by :

Accepted Answer

Myenteric plexus

Answer

Meissner's plexus

Answer

Vagus nerve

Answer

Parasympathetic system

Question 4

What is the primary function of the liver in the human body?

Accepted Answer

Detoxification and metabolism of nutrients

Answer

Production of insulin

Answer

Bile production

Answer

Storage of vitamins and minerals

Question 5

Daily salivary secretion is

Accepted Answer

1000-1500 ml

Answer

1500-2000 ml

Answer

More than 2000 ml

Answer

Less than 1000 ml

Question 6

Which hormone is secreted by the "Delta cells" of the stomach?

Accepted Answer

Somatostatin

Answer

Cholecystokinin

Answer

Gastrin-releasing peptide

Answer

Secretin

Question 7

Lowest pH is seen in which of the gastrointestinal secretions?

Accepted Answer

Gastric juice

Answer

Bile juice

Answer

Saliva

Answer

Pancreatic juice

Question 8

Sugars are primarily absorbed in?

Accepted Answer

Jejunum

Answer

Duodenum

Answer

Ascending colon

Answer

Ileum

Question 9

Mechanism of action of cholecystokinin?

Accepted Answer

Through IP3- DAG system

Answer

Activation of adenylyl cyclase

Answer

Opening of ion channels

Answer

Transcription factors

Question 10

Which of the following is the primary site of gastrin production?

Accepted Answer

Gastric G cells

Answer

Gastric chief cells

Answer

Pancreas

Answer

Pituitary gland

Gastrointestinal System — MCQs

Gastrointestinal System — MCQs

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