CASTING METHODS OF SCANNING ELECTRON MICRO SCOPY APPLIED TO HEMAL LYMPH NODES IN RATS

Abstract

Hemal lymph nodes of the para-aortic group in rats were examined by scanning electronmicroscopy (SEM) using the corrosion cast technique. The vasoarchitecture of hemal lymphnodes was described in cast specimens filled from the abdominal aorta. A dense system ofcapillaries arranged in the mode of a meshwork could be represented in the nodal cortex. Thepostcapillary venule (PCV) with wide vascular lumina provided the prevailing vessel type ofthe deep cortex. Sphincter-like narrowings of the capillary lumen appeared at the sites wherecapillaries merged with the PCV. These vascular segments were interpreted as structurescontrolling the hemodynamics of the joining PCV thereby providing appropriate conditionsfor homing lymphocytes. No evidence was obtained from the casts for an open circulation inhemal lymph nodes. The intranodal lymphatic pathways were studied in specimensinterstitially injected with resin. The fine lymphoid tissue spaces were characterized by specialcast patterns reflecting the structural differentiation of certain nodal compartments. Afferentlymphatics could be clearly identified in casts with a retrograde filling from the subcapsularsinus. Very spacious intermediary sinuses and wide-meshed medullary sinuses could berepresented in those casts as well, thus allowing ample space for the encounter of largemacrophages with red blood cells.