Iron Absorption and Transport — MCQs
All of the following decrease in iron deficiency anemia except:
Distal ileum was removed in a 20-year-old girl. Which absorption deficiency will be seen?
What does hepcidin inhibit?
Which porphyrin forms the organic component of heme?
What is the primary metal ion found in myoglobin?
Which vitamin increases the absorption of iron?
Glucose is primarily absorbed from which part of the small intestine?
Which of these is true about SGLT1?
Through which of the following means of transport is folic acid absorbed in the proximal jejunum?
Method of transport of glucose in the intestine is:
Iron Absorption and Transport Indian Medical PG Practice Questions and MCQs
Question 1: All of the following decrease in iron deficiency anemia except:
- A. Serum iron
- B. Ferritin
- C. TIBC (Correct Answer)
- D. Transferrin saturation
Explanation: ***TIBC*** - In **iron deficiency anemia**, the body attempts to maximize iron absorption and transport, leading to an **increase** in **Total Iron Binding Capacity (TIBC)** [1]. - TIBC reflects the amount of **transferrin** available to bind iron; more transferrin is produced when iron stores are low [1]. *Serum iron* - **Serum iron** measures the iron circulating in the blood bound to transferrin. - In **iron deficiency anemia**, the overall amount of circulating iron is **decreased** due to insufficient iron stores [1]. *Ferritin* - **Ferritin** is a storage protein for iron, reflecting the body's iron stores [2]. - In **iron deficiency anemia**, iron stores are depleted, resulting in a **decreased** serum ferritin level [1]. *Transferrin saturation* - **Transferrin saturation** is the percentage of transferrin binding sites occupied by iron. - In **iron deficiency anemia**, with low serum iron and increased TIBC, the percentage of binding sites occupied by iron is **lowered** [1].
Question 2: Distal ileum was removed in a 20-year-old girl. Which absorption deficiency will be seen?
- A. Bile salts (Correct Answer)
- B. Iron
- C. Copper
- D. Zinc
Explanation: ***Bile salts*** - The **distal ileum** is the primary site for the active reabsorption of **bile salts** back into the enterohepatic circulation. - Their malabsorption leads to **fat malabsorption** and steatorrhea, and can lead to gallstones due to changes in bile composition. *Iron* - The majority of **iron absorption** primarily occurs in the **duodenum** and proximal jejunum, not the distal ileum. - Iron deficiency would typically result from issues higher up in the small intestine or from chronic blood loss. *Copper* - **Copper absorption** mainly occurs in the **stomach** and **duodenum**. - Deficiency typically arises from dietary inadequacy or specific genetic disorders, not distal ileal resection. *Zinc* - **Zinc absorption** occurs throughout the **small intestine**, with significant absorption in the **jejunum**. - While some zinc is absorbed in the ileum, its primary absorption site is not limited to or predominantly in the distal ileum, making malabsorption less likely with isolated distal ileum removal.
Question 3: What does hepcidin inhibit?
- A. Absorption of cobalamine
- B. Transfer of iron from enterocytes to blood (Correct Answer)
- C. Folic acid synthesis
- D. Respiratory oxidase
Explanation: ***Transfer of iron from enterocytes to blood*** - **Hepcidin** is a key regulator of iron homeostasis, primarily functioning to **reduce iron availability**. - It binds to and induces the degradation of **ferroportin**, the only known iron efflux channel found on enterocytes, macrophages, and hepatocytes. - By degrading ferroportin, hepcidin **prevents iron export from enterocytes into the bloodstream**, thereby trapping iron inside cells and reducing circulating iron levels. *Absorption of cobalamine* - **Cobalamin (Vitamin B12)** absorption is a complex process primarily involving **intrinsic factor** produced by gastric parietal cells, and subsequent absorption in the terminal ileum. - Hepcidin has **no direct role** in the absorption or metabolism of cobalamin. *Folic acid synthesis* - **Folic acid** (Vitamin B9) is absorbed primarily in the **jejunum** and its absorption is not regulated by hepcidin. - Hepcidin's role is specifically tied to **iron metabolism**, not the synthesis or absorption of other vitamins. *Respiratory oxidase* - **Respiratory oxidases** are enzymes involved in the electron transport chain, such as **cytochrome c oxidase**. - While iron is a component of some enzymes in the respiratory chain, hepcidin directly regulates **iron transport via ferroportin**, not the activity or synthesis of specific respiratory enzymes.
Question 4: Which porphyrin forms the organic component of heme?
- A. Uroporphyrin
- B. Coproporphyrin
- C. Deuteroporphyrin
- D. Protoporphyrin IX (Correct Answer)
Explanation: ***Protoporphyrin IX*** - **Heme** is formed by the insertion of an **iron atom (Fe2+)** into the center of **protoporphyrin IX**. - **Protoporphyrin IX** is the immediate precursor to heme in the **heme synthesis pathway**. *Uroporphyrin* - **Uroporphyrin** is an earlier precursor in the **heme synthesis pathway** and is much more hydrophilic than protoporphyrin. - It accumulates in diseases like **congenital erythropoietic porphyria (CEP)**, leading to photosensitivity. *Coproporphyrin* - **Coproporphyrin** is an intermediate in the **heme synthesis pathway**, formed after uroporphyrinogen. - It is also more water-soluble than protoporphyrin and its accumulation can be seen in various porphyrias. *Deuteroporphyrin* - **Deuteroporphyrin** is a synthetic porphyrin or a less common natural porphyrin that is not directly involved as the organic component of heme in mammals. - While it is structurally similar to protoporphyrin, it does not serve as the direct precursor for heme formation in the human body.
Question 5: What is the primary metal ion found in myoglobin?
- A. Iron (Correct Answer)
- B. Copper
- C. Selenium
- D. Zinc
Explanation: ***Iron*** - **Iron** is the central metal ion in the **heme group** of myoglobin. - It is responsible for **binding oxygen** reversibly, which is myoglobin's primary function in muscle tissue. *Copper* - **Copper** is a component of several enzymes, such as **cytochrome c oxidase** and **superoxide dismutase**, but not myoglobin. - It plays a role in **electron transport** and connective tissue formation. *Selenium* - **Selenium** is an essential trace element that functions as a component of **glutathione peroxidase**, an antioxidant enzyme. - It is not found in the structure of myoglobin. *Zinc* - **Zinc** is a critical component of many enzymes, including **carbonic anhydrase** and **DNA polymerase**. - It is involved in **immune function** and wound healing, but not in oxygen transport by myoglobin.
Question 6: Which vitamin increases the absorption of iron?
- A. Riboflavin
- B. Vitamin A
- C. Thiamin
- D. Vitamin C (Correct Answer)
Explanation: ***Vitamin C*** - **Ascorbic acid** (Vitamin C) acts as a reducing agent, converting ferric iron (Fe3+) in the diet to ferrous iron (Fe2+), which is more soluble and readily absorbed in the duodenum. - It also counteracts the effects of absorption inhibitors like phytates and polyphenols found in plant-based foods, further enhancing **non-heme iron absorption**. *Riboflavin* - **Riboflavin** (Vitamin B2) is crucial for various metabolic processes, including red blood cell production, but it does not directly enhance iron absorption. - Deficiency can lead to anemia, but this is due to impaired red blood cell synthesis, not altered iron uptake. *Vitamin A* - **Vitamin A** plays a role in the mobilization of iron stores and erythrocyte differentiation, and deficiency can exacerbate iron deficiency anemia. - However, it does not directly increase the absorption of dietary iron from the gut. *Thiamin* - **Thiamin** (Vitamin B1) is essential for carbohydrate metabolism and nerve function. - It has no known direct role in the absorption or metabolism of iron.
Question 7: 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 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: Through which of the following means of transport is folic acid absorbed in the proximal jejunum?
- A. Facilitated diffusion
- B. Both active and passive transport (Correct Answer)
- C. Active transport
- D. Passive transport
Explanation: ***Both active and passive transport*** - **Folic acid** absorption in the **proximal jejunum** occurs through **both active and passive mechanisms**. - At **low physiological concentrations**, an **active carrier-mediated transport** system is primarily responsible, while at **higher concentrations** (e.g., from supplements), **passive diffusion** also plays a significant role. *Facilitated diffusion* - While a type of passive transport, **facilitated diffusion** alone does not fully encompass the entirety of folic acid absorption, especially at low concentrations. - It relies on a **concentration gradient** and **carrier proteins** but does not require metabolic energy. *Active transport* - **Active transport** is crucial for absorbing folic acid when its concentration is low in the gut lumen. - This process requires **energy** and specific **carrier proteins**, like the **reduced folate carrier (RFC)**, to transport folate against a concentration gradient. *Passive transport* - **Passive transport**, specifically **simple diffusion**, contributes to folic acid absorption but primarily at **high lumen concentrations**, such as after taking large doses of supplements. - It occurs down a **concentration gradient** and does not require energy or specific carriers.
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**.
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