Modulation of lymphocyte flow in the lymphatic compartment
of the lymph node may serve, in part, to promote lymphocyte
sensitization during an antigenic challenge. This study was
undertaken to show where this might occur by examining the
structural relationships of the intranodal lymphatic pathways,
blood vessels, and connective tissue support with respect to
lymphocyte and lymph flow. Differently stained plastic resins
were injected into the blood vessels and lymphatics of the
submandibular lymph node and visualized with a confocal laser
scanning microscope. The specimens were corroded to study the
three-dimensional cast structures by scanning electron microscopy.
Alkali digestion was also used to prepare the reticular fiber
network in the lymph node for scanning electron microscopic
examination. At the hilus of the node, two to three arteries
gave off arterioles running in medullary cords towards the cortex.
The medullary cords, the periphery of the deep cortex, and the
perifollicular zones had dense capillary networks. In contrast,
the center of the follicle and the center of the deep cortex
were less highly vascularized. High-endothelial venules were
restricted to the perifollicular zone and the periphery of the
deep cortex. At the cortico-medullary boundary, they abruptly
transformed into medullary venules with a normal endothelium.
The marginal sinus of the lymph node was crossed by thick reticular
fibers that arose from the inner sheets of the capsule. The
lymph pathway went through the marginal sinus, into the trabecular
sinus, to the cortical perifollicular sinus, the dense lymphatic
sinus around the deep cortex, and finally into the medullary
sinus. At present, the exact functional significance of the
complex lymph node lymphatic architecture is not clear. However,
the highly organized structural organization may play a significant
role in regulating and directing lymphocyte flow to facilitate
antigen presentation.
Descended marginal sinus of the placenta
