Page 151 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Circulatory system (systema cardiovasculare et Iymphovasculare) 133

Following erection, the lymph heart pumps lymph the naked eye and can be considered as a modified and
VetBooks.ir from the phallus and directs it to the venous system. As smaller version of the avian lymph node. They occur
a secondary function, the lymph heart contributes to the as both internal variants within the intima (interna) of
regulation of blood pressure in the vertebral sinus durae the lymphatic vessel (formatio lymphoreticularis muralis
matris and in the renal portal system. interna), and as external variants in the thickened adven-
titia (formatio lymphoreticularis muralis externa). Lymph
Lymphoreticular formations of birds sinuses, originating from the lymphatic vessel, are only
The term formationes lymphoreticulares parenchymato- found in external formations (Figure 6.25).
sae describes diffuse, poorly demarcated lymphoreticular Lymphoreticular cords within mural formations con-
formations that may or may not have germinal centres. tain areas of T and B lymphocytes as well as postcapillary
These occur mainly in parenchymatous organs such as venules for lymphocyte recirculation. Mural formations
endocrine glands, the liver and spleen. are stimulated by the presence of antigens within their
Mural lymphoreticular formations are spindle-shaped drainage area, potentially becoming so enlarged that they
thickenings of the walls of lymph vessels (Figures 6.25 and are distinguishable from lymph nodes only by the presence
6.26). They occur in all larger lymph vessels in the chicken of the media in the lymph vessel wall. Collectively, mural
and have yet to be found lacking in bird species studied to formations have considerable immune potential and fulfil
date. Mural lymphoreticular formations are just visible to the role of lymph nodes.

Formatio lymphoreticularis muralis externa

Sinus lymphaticus intramuralis
6.25 Wall of the initial segment of an avian lymphatic 6.26 Wall of the terminal segment of an avian lym-
collector vessel (vas lymphaticum myotypicum) with phatic collector vessel (vas lymphaticum myotypicum)
external lymphoreticular formations (schematic; left – with internal mural reticular formations (schematic;
longitudinal section, right – transverse section). left – longitudinal section, right – transverse section).

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