DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Contracted heart muscle fibres (ventricle) with partial overlying pericardium and collagen fibres, coloured scanning electron micrograph (SEM). The heart muscle produces regular electrical impulses causing the muscle myofibrils to slide over one another and contract the cardiac muscle. The pericardium is a double-walled, membranous sac surrounding the heart. The pericardium has a tough outer fibrous layer (fibrous pericardium) and a delicate serous layer (serous pericardium). The inner serous pericardial layer is the wall adjacent to the heart (partially seen here). It is split into two layers, the epicardium (just above the heart) and the parietal layer. Between the two layers is the pericardial cavity, which contains serous fluid. Both layers consist of flattened squamous epithelial cells and connective tissue. The serous pericardium lubricates the heart, preventing friction. Magnification: x440 when shortest axis printed at 25 millimetres.
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