Ultrastructure of atrial and ventricular endocardium and cardiac capillary endothelium of the pike.

The endocardium of the pike Esox lucius L. consists of an attenuated squamous endothelium, a sparse population of subendothelial cells, and varying amounts of collagen. Fibroblasts are not found in the endocardium, and the collagen is probably produced by the endothelium. Capillary and endocardial endothelium differ structurally in several aspects. Plasmalemmal vesicles are far more abundant in capillary endothelium, while the amount of ribosomes and endoplasmic reticulum is much smaller. Golgi complexes are well developed in endocardial cells, but not in capillary endothelia mainly have a transport function, while the endocardial endothelium is also largely concerned in protein synthesis.