Lipoproteins complexes are soluble aggregates of lipids and proteins that transport lipids through the blood and lymph. Despite their differences in lipid and protein composition, all lipoproteins share common structural features, notably a spherical shape that can be detected by electron microscopy. The lipoproteins help maintain in solubilized form some 500 mg of total lipid per 100 mL of human blood in the postabsorptive state, after the contents of a meal have been digested and absorbed into the bloodstream.