Scanning electron microscopy of mouse endocardium and venae cordis minimae foramina

Summary

The fine surface morphology of the endocardium and the venae cordis minimae foramina has been examined using the scanning electron microscope. The morphology of the endocardium differed in various sites in the atria and ventricles. The endocardial appearance included: fusiform cells with fine cell extensions from their ends; villiform, cuneiform and cusp-shaped projections; beaded strands of cells; groups of cells forming ridges and bulging spheroidal nuclear projections. In areas where the endocardium is flatter and smoother the endocardial cells have only slightly bulging nuclei which give the surface a macular appearance. Structures resembling intercellular bridges were seen in some areas. Both the cell surface projections and the whole cell alignment were in the direction of systolic blood flow, thus effectively minimising the flow resistance and turbulence. The cell surfaces were pitted, suggesting pinocytotic activity, ridged or possessed microvilli.

Both unguarded and valved venae cordis minimae foramina were seen, the latter generally, being in the form of flap valves. Unguarded foramina less than 5 μ in diameter had a sphincterlike appearance while those foramina larger than 5 μ were variable in structure. In view of the presence of the complex foramina and variable endocardial cell types the endocardium is a complex and specific structural entity distinguishing it form normal vascular endothelium.