Which part of the liver stores vitamin A?

Correct Answer: B. Ito cells

Ito cells (hepatic stellate cells) are the primary storage site for vitamin A in the liver, accounting for approximately 50–80% of total body vitamin A stores. These cells are located in the space of Disse (between hepatocytes and sinusoidal endothelium) and contain lipid droplets rich in retinyl esters. When vitamin A (retinol) is absorbed from the intestine and transported to the liver bound to retinol-binding protein (RBP), it is taken up by hepatocytes and transferred to Ito cells for storage. During vitamin A deficiency, Ito cells release stored retinyl esters, which are hydrolyzed to retinol and bound to RBP for systemic distribution. This storage function is crucial in the Indian context, where vitamin A deficiency remains a significant public health concern, particularly in children. The distinction between Ito cells and hepatocytes is critical: while hepatocytes synthesize RBP and participate in vitamin A metabolism, they do not serve as the primary storage depot. Ito cells also play roles in extracellular matrix synthesis and hepatic fibrosis, but their vitamin A storage capacity is their defining metabolic feature.

Why the other options are wrong

A. Kupffer cells — Kupffer cells are resident hepatic macrophages that function in immune surveillance and phagocytosis of pathogens and debris. They do not store vitamin A in significant amounts. This is a common trap because students may confuse the storage role of Ito cells with the metabolic roles of other sinusoidal cells. Kupffer cells are involved in iron metabolism and immune function, not lipid-soluble vitamin storage. C. Endothelial cells — Sinusoidal endothelial cells form the barrier between blood and hepatocytes but lack the lipid droplet capacity required for vitamin A storage. While they are permeable to retinol-binding protein and facilitate vitamin A transport, they do not accumulate or store retinyl esters. This option may appeal to students who recognize the spatial proximity of endothelial cells to the space of Disse but confuse proximity with function. D. Hepatocytes — Although hepatocytes are the primary site of vitamin A uptake and metabolism (synthesizing RBP and participating in retinoid signaling), they are not the storage depot. Hepatocytes rapidly transfer absorbed retinol to Ito cells for long-term storage. This is a deliberate NBE trap: students may assume the metabolically active hepatocyte is the storage site, but the actual storage function is delegated to Ito cells.

High-Yield Facts

Mnemonics

ITO = I Take Omegas (and Vitamins) Ito cells store lipid-soluble vitamins (A, D, E, K) in their lipid droplets. Remember: Ito = Intracellular lipid droplets = storage. SPACE of Disse = Ito's Home Ito cells live in the space of Disse (between hepatocytes and endothelium). This spatial clue helps you recall their location and function as the liver's 'vitamin A warehouse.'

NBE Trap

NBE pairs "hepatocytes" with vitamin A metabolism to lure students who confuse the metabolically active cell (hepatocyte) with the storage cell (Ito cell). The trap exploits the assumption that the cell doing the work is also the cell doing the storage.

Clinical Pearl

In Indian children with protein-energy malnutrition and vitamin A deficiency, Ito cell depletion of retinyl esters is the rate-limiting step in maintaining serum retinol levels. This is why vitamin A supplementation programs (IAP recommends 200,000 IU every 6 months for children 6–59 months) are critical for preventing corneal scarring and blindness—they replenish both circulating and hepatic stores.

_Reference: Guyton & Hall Textbook of Medical Physiology, Ch. 71 (Liver Functions); Robbins & Cotran Pathologic Basis of Disease, Ch. 18 (Liver and Biliary Tract)_