During intra-tissue hemorrhage, erythrocytes escaping from blood vessels are taken up by macrophages and degraded by their lysosomes, causing Fe3+ from erythrocyte hemoglobin to bind with proteins into ferritin particles visible under electron microscopy, and several ferritin particles aggregate into coarser brownish-yellow refractive particles visible under light microscopy, called iron-containing heme. Ferritin is an unstable ferritin aggregate containing brown pigment of iron. Intravascular hemolysis produces excessive free hemoglobin excreted by the kidneys, producing hemoglobinuria, part of which is reabsorbed and degraded by renal tubular epithelial cells to produce ferric hemoglobin, which is deposited in the epithelial cells if it exceeds the transport capacity of renal tubular epithelial cells, and the cells are excreted in the urine, forming ferric hemoglobinuria.