What are the vitamin A cells in the liver?

November 24, 2025 •

4 min read

The liver is the body's primary storage site for vitamin A, with approximately 80% of the body's total supply stored within it. The specialized cells responsible for this vital function are known as hepatic stellate cells, or Ito cells. These quiescent, star-shaped cells sequester vitamin A within cytoplasmic lipid droplets, playing a critical role in maintaining systemic vitamin A homeostasis.

Quick Summary

Hepatic stellate cells, also known as Ito cells, are the primary site for vitamin A storage in the liver. They maintain the body's retinoid homeostasis by storing vitamin A as retinyl esters in lipid droplets. In cases of liver injury or disease, these quiescent cells activate into myofibroblasts, leading to the loss of their vitamin A stores and contributing to liver fibrosis.

Key Points

Identity: The vitamin A cells in the liver are hepatic stellate cells, also known as Ito cells or lipocytes.
Location: These star-shaped cells reside in the perisinusoidal space, or Space of Disse, located between hepatocytes and the sinusoidal blood vessels.
Storage Form: Stellate cells store vitamin A primarily as retinyl esters within specialized cytoplasmic lipid droplets.
Storage Capacity: They hold the majority, approximately 80%, of the body's total vitamin A reserves.
Activation and Fibrosis: In response to liver injury, stellate cells activate into myofibroblasts, lose their vitamin A droplets, and produce excessive scar tissue, a process called liver fibrosis.
Homeostasis: Through the release and uptake of vitamin A, stellate cells regulate the vitamin's concentration in the bloodstream to maintain systemic balance.
Clinical Relevance: The activation of hepatic stellate cells is a critical event in the progression of chronic liver diseases toward cirrhosis.

The Identity and Location of Hepatic Stellate Cells

In the healthy liver, the cells responsible for vitamin A storage are known by several names, most commonly hepatic stellate cells (HSCs) or Ito cells. These non-parenchymal cells make up a small but crucial fraction of the liver's cellular population, typically residing in the perisinusoidal space, also called the Space of Disse. This anatomical location places them between the liver's primary cells, the hepatocytes, and the sinusoidal endothelial cells that line the blood vessels.

The Anatomy of the Liver and Stellate Cells

The liver is organized into lobules, which are microscopic functional units. Blood flows from the portal triad, composed of branches of the portal vein, hepatic artery, and bile duct, towards the central vein at the center of the lobule. The blood flows through liver sinusoids, which are small capillaries. The stellate cells are positioned in the space surrounding these sinusoids, allowing them to regulate blood flow and interact with multiple cell types. This strategic position is essential for their role in vitamin A storage, as it allows them to efficiently absorb vitamin A carried by chylomicron remnants in the blood.

Quiescent vs. Activated Stellate Cells

Stellate cells exist in two primary states: quiescent and activated. In a healthy, uninjured liver, they are in a quiescent state, characterized by a star-like shape and the presence of numerous cytoplasmic lipid droplets. These droplets are the storage sites for vitamin A, mostly in the form of retinyl esters. However, in response to liver injury from causes like viral hepatitis, metabolic disease, or excessive alcohol consumption, these cells undergo a transformation process. They become activated and lose their stored vitamin A, transitioning into a myofibroblast-like phenotype.

The Function of Stellate Cells in Vitamin A Metabolism

The primary function of quiescent hepatic stellate cells is to store and regulate the body's vitamin A reserves. This process is crucial for maintaining vitamin A homeostasis, ensuring a steady supply of this fat-soluble vitamin to other tissues and organs that require it.

The Storage and Release Process

After digestion, dietary vitamin A is absorbed and transported to the liver via chylomicron remnants. Hepatocytes initially process this vitamin A and then transfer it to hepatic stellate cells for long-term storage within their lipid droplets as retinyl esters. When the body requires vitamin A, the stellate cells release it back into the circulation as retinol, bound to retinol-binding protein (RBP). This dynamic process allows for daily fluctuations in vitamin A release, while the overall liver store acts as a reservoir to prevent depletion.

Impact on Liver Health and Disease

The activation of stellate cells marks a critical turning point in the development of liver diseases, particularly liver fibrosis. When activated, these cells lose their vitamin A-laden lipid droplets and begin to proliferate vigorously, migrating towards areas of injury. In this activated state, they become the main producers of extracellular matrix proteins, such as collagen, leading to the formation of scar tissue. If the chronic injury persists, this scarring can lead to cirrhosis, a severe condition characterized by distorted liver architecture and impaired function.

Comparison Table: Quiescent vs. Activated Hepatic Stellate Cells


Feature	Quiescent (Healthy Liver)	Activated (Injured Liver)
Appearance	Star-shaped, contains numerous lipid droplets	Spindle-shaped (myofibroblast-like), loses lipid droplets
Function	Vitamin A storage, regulation of liver blood flow	Extracellular matrix production, fibrogenesis, proliferation
Vitamin A	Rich in stored retinyl esters	Depleted of vitamin A stores
Extracellular Matrix	Maintains normal, delicate matrix	Produces excessive, fibrous matrix (scar tissue)
Proliferation	Low or non-proliferative	High rate of proliferation
Role in Disease	Contributes to liver health	Central driver of liver fibrosis and cirrhosis

Future Implications and Therapeutic Approaches

Understanding the dual role of hepatic stellate cells in both maintaining vitamin A homeostasis and driving liver fibrosis has opened new avenues for research and treatment. Targeting the activation process of these cells holds promise for combating chronic liver disease and reversing fibrosis. For instance, certain retinoid-based therapies show potential in inhibiting the activation of stellate cells, which could slow or reverse fibrosis. Further research into the complex signaling pathways involving stellate cells and retinoids is ongoing, with new findings constantly emerging that may lead to improved therapeutic strategies.

Conclusion

In summary, the hepatic stellate cells are the key players in the liver's storage of vitamin A. These specialized cells perform the vital function of sequestering the majority of the body's vitamin A reserves, safeguarding against deficiency and regulating its release. However, their contribution to health shifts dramatically in response to liver injury. In diseased states, they activate, release their vitamin A, and initiate a fibrogenic cascade that can culminate in serious conditions like cirrhosis. The dynamic balance between their quiescent, nutrient-storing role and their activated, fibrotic-promoting state makes them a central focus in liver physiology and pathology.

Visit PMC for more detailed information on the function of hepatic stellate cells in physiology and pathology.

Frequently Asked Questions

The primary function of hepatic stellate cells in a healthy liver is to store and manage the body's reserve of vitamin A, holding the majority of it as retinyl esters within lipid droplets.

Hepatic stellate cells are situated in the perisinusoidal space, also known as the Space of Disse, which is the area between the sinusoidal endothelial cells and the hepatocytes.

During liver injury, quiescent stellate cells become activated and transform into myofibroblasts. In this process, they lose their vitamin A stores, proliferate, and produce large amounts of extracellular matrix, leading to fibrosis.

Stellate cells release vitamin A in its retinol form to maintain normal blood levels, ensuring that other organs and tissues have access to this essential nutrient.

Yes, Ito cells are another name for hepatic stellate cells, sometimes also referred to as lipocytes or fat-storing cells, based on their function of storing fat-soluble substances like vitamin A.

Retinoids, or vitamin A and its metabolites, play a crucial role in regulating stellate cell function. Normal levels help maintain their quiescent state, while their depletion during injury contributes to the cells' activation and fibrotic activity.

Emerging evidence suggests that targeting the activation pathways of stellate cells could lead to the reversal of liver fibrosis, primarily by promoting the apoptosis or reversion of activated cells back to an inactivated state.