inside the heart - Tissue-paper thin but tough, the valves of the human heart open and close to pump 6 quarts of blood a day through miles kilometers) of vessels. That’s equivalent to 20 treks across the United States from coast to coast.
Two interphase cells with immunofluorescence labeling of actin filaments (purple), microtubules (yellow), and nuclei (green). This image won first place in the Nikon 2003 Small World photo competition. The Cell: An Image Library - Image