Blood Capillaries of the Heart and Other Organs

TLDR

The review examines recent work on blood capillaries, detailing their electron‑microscope morphology and confirming at least three distinct types in small laboratory mammals. Tracer experiments using colloidal gold and ferritin revealed pinocytic vesicle transport across continuous endothelium and accumulation of ferritin on the luminal side of the basement membrane in glomerular capillaries. The capillary wall consists of three concentric layers, with a continuous basement membrane that functions as the main filtration barrier in glomerular capillaries and in muscle venules/venous capillaries when the endothelium is discontinuous. Authors: M.

Abstract

The article is a review of work recently carried out on blood capillaries by the author in collaboration with Drs. M. G. Farquhar, G. Majno, and S. L. Wissig. It reviews the morphology of these vessels at the electron-microscope level and confirms the existence of at least 3 distinct types of blood capillaries in small laboratory mammals. It shows that the capillary wall consists of 3 concentric layers (endothelium, basement membrane, and adventitia), and indicates that the basement membrane forms a continuous layer in all capillaries so far studied. Experiments in which colloidal gold particles were used as a tracer have shown that, in capillaries with a continuous endothelium (muscle capillaries), the particles are transported across it by "pinocytic" vesicles. At the end of this step they must still transverse the basement membrane. Experiments on glomerular capillaries, which typically have a discontinuous s endothelium, were carried out on normal and nephrotic rats using ferritin as a tracer. By its accumulation on the luminal side of the basement membrane, the ferritin has identified this layer as the main filtration barrier. A similar function of the basement membrane was demonstrated in muscle venules and venous capillaries by experiments in which the endothelium was rendered discontinuous by local treatment with histamine and serotonin.