Glucose Transporters — MCQs

10 questions

Which glucose transporter is primarily responsible for insulin-stimulated glucose transport?

All of the following substances have decreased concentration on the luminal side of the proximal convoluted tubule except:

Mutation in GLUT-2 causes which syndrome?

An 8-month-old infant is brought in with poor feeding, lethargy, hypotonia, and hepatomegaly. Labs reveal hypoglycemia and metabolic acidosis. Which condition is most likely?

A child presented with dehydration and was supplemented with ORS solution for management. Which of the following transporters help in the absorption of glucose from GIT?

Final common pathway of metabolism of carbohydrate, lipids, and protein metabolism is?

Insulin dependent glucose uptake occurs in:

Which of these is true about SGLT1?

Glucose is primarily absorbed from which part of the small intestine?

Q10

Method of transport of glucose in the intestine is:

Glucose Transporters Indian Medical PG Practice Questions and MCQs

Question 1: Which glucose transporter is primarily responsible for insulin-stimulated glucose transport?

A. GLUT1
B. GLUT2
C. GLUT3
D. GLUT4 (Correct Answer)

Explanation: ***GLUT4*** - **GLUT4** is the only glucose transporter that is **insulin-sensitive**, meaning its translocation to the cell membrane is stimulated by insulin. - It is primarily found in **adipose tissue** and **striated muscle (skeletal and cardiac muscle)**, key tissues for glucose uptake and storage. *GLUT1* - **GLUT1** is a **ubiquitous glucose transporter** found in most cell types, including red blood cells and the brain. - It provides **basal glucose uptake** regardless of insulin levels, ensuring a steady supply to vital organs. *GLUT2* - **GLUT2** is primarily located in the **liver, pancreatic beta cells, kidney, and small intestine**. - It has a **high Km** (low affinity for glucose) and is important for **glucose sensing** in the pancreas and **glucose release** from the liver. *GLUT3* - **GLUT3** is the **primary glucose transporter in neurons** and is also found in the placenta and testes. - It has a **high affinity for glucose** (low Km), ensuring a constant supply of glucose to the brain even at low blood glucose concentrations.

Question 2: All of the following substances have decreased concentration on the luminal side of the proximal convoluted tubule except:

A. Glucose
B. Amino acids
C. Bicarbonate
D. Chloride (Correct Answer)

Explanation: ***Chloride*** - As **water and other solutes** are reabsorbed from the proximal tubule, the concentration of **chloride** actually increases in the remaining luminal fluid due to continued water reabsorption. - This increased luminal **chloride concentration** then drives passive reabsorption of chloride later in the tubule. *Glucose* - **Glucose** is almost completely reabsorbed from the tubular lumen by **secondary active transport** in the early part of the proximal tubule. - Therefore, its concentration in the remaining luminal fluid rapidly decreases. *Amino acids* - Similar to glucose, **amino acids** are extensively reabsorbed by **secondary active transport** mechanisms in the proximal tubule. - Consequently, their luminal concentration significantly decreases. *Bicarbonate* - Most **bicarbonate** is reabsorbed in the proximal tubule through a process involving **carbonic anhydrase**, converting it to CO2 and water, which then diffuse into the cell. - This efficient reabsorption results in a substantial decrease in luminal bicarbonate concentration.

Question 3: Mutation in GLUT-2 causes which syndrome?

A. Dandy walker syndrome
B. Beckwith-Wiedemann syndrome
C. Menke's disease
D. Fanconi-Bickel syndrome (Correct Answer)

Explanation: ***Fanconi-Bickel syndrome*** - This syndrome is caused by a **mutation in the GLUT-2 gene**, leading to dysfunctional glucose transport in the liver, kidneys, and intestines. - Key features include **hepatorenal glycogen accumulation**, **renal tubulopathy** (Fanconi syndrome), and **impaired glucose and galactose utilization**. *Dandy-Walker syndrome* - This is a **congenital brain malformation** involving the cerebellum and fourth ventricle. - It is often associated with hydrocephalus, but not directly linked to glucose transporter defects. *Beckwith-Wiedemann syndrome* - This is an **overgrowth disorder** characterized by a high risk of childhood cancer and congenital anomalies. - It is primarily caused by genetic abnormalities on **chromosome 11p15.5** and is unrelated to GLUT-2 mutations. *Menke's disease* - This is a rare X-linked recessive disorder of **copper metabolism**, leading to severe neurological degeneration. - It results from mutations in the **ATP7A gene**, which encodes a copper-transporting ATPase.

Question 4: An 8-month-old infant is brought in with poor feeding, lethargy, hypotonia, and hepatomegaly. Labs reveal hypoglycemia and metabolic acidosis. Which condition is most likely?

A. Hereditary fructose intolerance
B. Galactosemia
C. Pompe disease
D. Von Gierke disease (Correct Answer)
E. Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency

Explanation: ***Von Gierke disease*** - **Type I glycogen storage disease** (GSD I) typically presents in infancy with **hypoglycemia** (due to impaired glucose release from glycogen), **hepatomegaly** (due to glycogen accumulation), and **lactic acidosis**. - Other common findings include **hyperlipidemia** and **hyperuricemia**, while **hypotonia** and **poor feeding** are generalized symptoms stemming from metabolic derangements. *Hereditary fructose intolerance* - This condition presents when **fructose** is introduced into the diet, typically after 4-6 months of age, with symptoms like **nausea, vomiting, abdominal pain**, and **hepatomegaly**. - While it can cause **hypoglycemia** and **metabolic acidosis**, the profound **hypotonia** and general metabolic collapse described in an 8-month-old on a typical diet makes GSD I more likely initially. *Galactosemia* - Symptoms usually appear within days or weeks of birth upon the initiation of **milk feeding**, including **vomiting, lethargy, poor feeding, jaundice, hepatomegaly**, and **cataracts**. - While it causes **hypoglycemia** and can lead to acidosis and hypotonia, the age of presentation and lack of specific mention of jaundice or cataracts makes it a less precise fit. *Pompe disease* - Also known as **glycogen storage disease type II**, it is characterized by the accumulation of glycogen in **lysosomes**, primarily affecting muscles. - The infantile form presents with severe **cardiomyopathy**, **muscle weakness**, and **hypotonia**, but **hypoglycemia** and **hepatomegaly** are not its primary or most prominent features. *Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency* - A **fatty acid oxidation disorder** that presents with episodic **hypoglycemia** (particularly during fasting or illness), **lethargy**, and **hepatomegaly**. - Key distinguishing features include **hypoketotic hypoglycemia** and elevated **dicarboxylic acids** on urine organic acids, but the **lactic acidosis** and overall metabolic profile are more consistent with GSD I.

Question 5: A child presented with dehydration and was supplemented with ORS solution for management. Which of the following transporters help in the absorption of glucose from GIT?

A. GLUT 2
B. SGLT 1 (Correct Answer)
C. SGLT 2
D. GLUT 1

Explanation: ***SGLT 1*** - **SGLT1 (Sodium-Glucose Co-transporter 1)** is responsible for the **active transport of glucose and galactose** from the intestinal lumen into the enterocytes, coupled with sodium. - The principle of **oral rehydration solutions (ORS)** relies on this co-transport mechanism, as glucose (or other carbohydrates like sucrose, which is broken down into glucose and fructose) facilitates the absorption of sodium and water across the intestinal wall. *GLUT 2* - **GLUT2** is primarily located on the **basolateral membrane of enterocytes** and facilitates glucose transport out of the cell into the bloodstream. It also plays a role in glucose uptake in the liver and pancreatic beta cells. - While involved in glucose handling, **GLUT2 does not absorb glucose from the intestinal lumen** into the enterocytes; rather, it transports glucose out of them. *SGLT 2* - **SGLT2 (Sodium-Glucose Co-transporter 2)** is predominantly found in the **proximal tubules of the kidneys**, where it is responsible for the reabsorption of the vast majority of filtered glucose back into the bloodstream. - It is not involved in **intestinal glucose absorption**. Selective SGLT2 inhibitors are used as antidiabetic drugs to promote glucose excretion via the kidneys. *GLUT 1* - **GLUT1 (Glucose Transporter 1)** is a ubiquitous glucose transporter found in nearly all cell types, particularly important for basal glucose uptake by tissues like the **brain** and **red blood cells**. - While essential for glucose transport in many tissues, **GLUT1 plays a negligible role in glucose absorption from the gastrointestinal tract**.

Question 6: Final common pathway of metabolism of carbohydrate, lipids, and protein metabolism is?

A. Gluconeogenesis
B. TCA (Correct Answer)
C. HMP pathway
D. Glycolysis

Explanation: ***TCA (Tricarboxylic Acid Cycle)*** - The **TCA cycle** (also called Krebs cycle or citric acid cycle) is the **final common oxidative pathway** where all three macronutrients converge - **Carbohydrates** → Pyruvate → **Acetyl-CoA** (via pyruvate dehydrogenase) - **Lipids** → Fatty acids → **Acetyl-CoA** (via beta-oxidation) - **Proteins** → Amino acids → **Acetyl-CoA or TCA intermediates** (via deamination/transamination) - Complete oxidation of acetyl-CoA occurs in the TCA cycle, producing **NADH, FADH2, and GTP** for energy production *Gluconeogenesis* - This is a **biosynthetic pathway** that synthesizes glucose from non-carbohydrate precursors (lactate, glycerol, amino acids) - It is an **anabolic process**, not the catabolic final common pathway for energy production from all macronutrients *Glycolysis* - **Carbohydrate-specific pathway** that converts glucose to pyruvate - It is only the initial breakdown pathway for carbohydrates, not the common pathway where lipids and proteins also converge - Pyruvate from glycolysis must enter TCA cycle for complete oxidation *HMP pathway (Pentose Phosphate Pathway)* - Parallel pathway to glycolysis that generates **NADPH** (for biosynthesis and antioxidant defense) and **ribose-5-phosphate** (for nucleotide synthesis) - Processes only **glucose-6-phosphate** from carbohydrate metabolism - Not involved in lipid or protein metabolism integration

Question 7: Insulin dependent glucose uptake occurs in:

A. Brain
B. Epithelial cells of small intestine
C. Muscle (Correct Answer)
D. Kidney

Explanation: ***Muscle*** - **Insulin** stimulates glucose uptake in **muscle cells** by promoting the translocation of **GLUT4 transporters** to the cell surface. - This process is crucial for removing glucose from the blood and storing it as **glycogen** in muscle tissue. - Along with **adipose tissue**, muscle is one of the **primary sites of insulin-dependent glucose uptake** in the body. *Brain* - The brain primarily uses **GLUT1** and **GLUT3 transporters** for glucose uptake, which are **insulin-independent**. - These transporters are always active, ensuring a continuous supply of glucose to the brain, regardless of insulin levels. *Epithelial cells of small intestine* - Glucose absorption in the small intestine initially occurs via **SGLT1** (sodium-glucose co-transporter 1) at the apical membrane and then exits into the bloodstream via **GLUT2** at the basolateral membrane. - This process is mainly regulated by the concentration gradient of glucose and sodium, not directly by **insulin**. *Kidney* - The kidneys reabsorb glucose from the filtrate primarily via **SGLT1** and **SGLT2** transporters in the renal tubules. - This reabsorption mechanism is **insulin-independent** and aims to conserve glucose, preventing its loss in urine.

Question 8: Which of these is true about SGLT1?

A. Secondary active transport of glucose in prostate
B. Secondary active transport of glucose in brain
C. Secondary active transport of glucose in intestine (Correct Answer)
D. Secondary active transport of glucose in rods and cones

Explanation: ***Secondary active transport of glucose in intestine*** - **SGLT1** is the primary transporter responsible for **glucose and galactose absorption** from the lumen of the small intestine into the enterocytes. - It uses the electrochemical gradient of **sodium** to co-transport glucose against its concentration gradient, classifying it as **secondary active transport**. *Secondary active transport of glucose in prostate* - While glucose is vital for prostate metabolism, its transport predominantly involves **GLUTs** (e.g., GLUT1), not SGLT1. - SGLT1 is generally not found in significant amounts in the prostate. *Secondary active transport of glucose in brain* - Glucose transport across the **blood-brain barrier** and into brain cells is primarily mediated by **GLUT1** and other GLUT transporters, which are **facilitated diffusers**, not SGLT1. - SGLT1 has a very limited role, if any, in normal brain glucose uptake. *Secondary active transport of glucose in rods and cones* - Retinal photoreceptors (rods and cones) indeed rely on glucose, but its uptake is mainly via **GLUT1** and other GLUT family members. - **SGLT1** is not a significant transporter for glucose in these cells.

Question 9: Glucose is primarily absorbed from which part of the small intestine?

A. Proximal part of the small intestine (Correct Answer)
B. Distal part of the small intestine
C. Cecum
D. Colon

Explanation: ***Proximal part of the small intestine*** - The majority of nutrient absorption, including **glucose**, occurs in the **duodenum** and **jejunum**, which constitute the proximal small intestine. - Glucose absorption mechanisms, such as **SGLT1** and **GLUT2** transporters, are highly concentrated and active in this region. - This is where the surface area is maximized with villi and microvilli for optimal absorption. *Distal part of the small intestine* - The **ileum**, which is the distal part, is primarily responsible for absorbing **vitamin B12** and **bile salts**, not the bulk of glucose. - While some minimal glucose absorption might occur, it is not the primary site. *Cecum* - The cecum is the beginning of the **large intestine** and is involved in **water** and **electrolyte** absorption and microbial fermentation. - It is not involved in significant nutrient absorption like glucose. *Colon* - The colon is part of the **large intestine** and primarily absorbs **water** and **electrolytes**. - By the time contents reach the colon, virtually all glucose has already been absorbed in the small intestine.

Question 10: Method of transport of glucose in the intestine is:

A. Primary active transport
B. Counter transport
C. Simple diffusion
D. Secondary active transport (Correct Answer)

Explanation: ***Secondary active transport*** - Glucose is primarily transported into intestinal cells via the **SGLT1 transporter**, which uses the electrochemical gradient of sodium to move glucose against its concentration gradient. - This process is called **secondary active transport** because it indirectly uses energy derived from the Na+/K+-ATPase pump, which maintains the sodium gradient. *Primary active transport* - This transport mechanism directly uses **ATP hydrolysis** to move a substance against its concentration gradient, such as the Na+/K+-ATPase pump itself. - While essential for maintaining the Na+ gradient, **primary active transport** doesn't directly transport glucose into enterocytes. *Counter transport* - Also known as **antiport**, this mechanism involves the simultaneous movement of two substances across a membrane in opposite directions. - While present in some physiological processes, it is **not the primary method** for glucose uptake in the intestine. *Simple diffusion* - This is the passive movement of substances across a membrane down their concentration gradient, **without the help of transporters or energy**. - Glucose is a relatively large, polar molecule and cannot readily cross the lipid bilayer via **simple diffusion**.

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free