Kupffer cell: the blood cleaner.
This scanning electron micrograph shows the internal structure of liver tissue from an adult mouse. The sinusoids (vascular channels lined with endothelial cells) can be seen as pink structures running through the parenchyma. These contain red blood cells and Kupffer cells. Hepatocytes, shown in brown, are arranged in plates surrounding the sinusoids.
Kupffer cells are specialized macrophages located in the liver lining the walls of the sinusoids and they are part of the reticuloendothelial system (RES). When a erythrocyte is not able anymore to perform their task because of various causes (aging, diseases), it undergoes changes in its plasma membrane, making it susceptible to selective recognition by macrophages (Kupffer cells too) and subsequent phagocytosis in spleen and liver, thus removing old and defective cells and continually purging the blood. Red blood cells are broken down by phagocytic action, where the haemoglobin molecule is split. The globin chains are re-utilized, while the iron-containing portion, heme, is further broken down into iron, which is re-utilized, and bilirubin, which is conjugated to glucuronic acid within hepatocytes and secreted into the bile.
(Picture by The Cell: An Image Library).