What happens to excess iron that cannot be stored in the liver?

Excess iron that cannot be stored in the liver typically remains in the bloodstream or is transferred to the bone marrow. This occurs because the body has a limited capacity to store iron, primarily through ferritin and hemosiderin in the liver. When storage capacity is reached, circulating iron can lead to toxicity, and its regulation becomes critical.

The iron that remains in the bloodstream can be bound to transferrin, a protein responsible for transporting iron to different tissues. In particular, bone marrow can utilize this available iron for erythropoiesis, which is the production of red blood cells. Thus, rather than converting to ferritin or being excreted, the excess iron competently circulates for immediate physiological needs or is stored in other tissues, but without any more significant storage in the liver itself.

In this context, the other responses do not accurately reflect the behavior of excess iron. Although muscle tissue can store some iron, it is not a primary storage site when the liver's capacity is exceeded. Furthermore, iron is not excreted significantly through urine under normal physiological conditions, and while ferritin is an important storage form of iron in the liver, it does not address the question of what happens to excess iron when liver stores are