SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Heart valve and strings, coloured scanning electron micrograph (SEM). This is the mitral valve (upper right), controlling the blood flow between two of the heart's chambers, the left atrium (top) and the left ventricle (bottom). The heart strings (thread-like structures) are known as the chordae tendineae, and are controlled by the papilliary muscles (one at lower right). The structures at lower left, known as trabeculae carneae, are muscular, columnar protrusions found on the internal surface of the ventricles.
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