Page 149 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Circulatory system (systema cardiovasculare et Iymphovasculare) 131

cholesterol and cholesterol esters to form droplets called fibres of the surrounding connective tissue. These appear
VetBooks.ir chylomicrons. High fat diets cause the lymph to take on to regulate the movement of fluid into the lymph capil-
a milky appearance. Lymph also contains ions, hormones, laries (Figures 6.23 and 6.24). A subepithelial network of
lymph capillaries is found in the connective tissue of the
enzymes, antibodies and metabolites.
inner and outer surfaces of the body, and in the interstitial
Lymph capillaries (vas lymphocapillare) connective tissue of many organs. Lymph capillaries are
Lymph capillaries consist of an irregularly expanded absent from the central nervous system, bone marrow, red
endothelial tube. Their diameter (10–50 μm) is markedly pulp of the spleen and hyaline cartilage.
greater than that of blood capillaries. Lymph capillaries are Leading away from the lymph capillary network is
blind-ended channels that take up fluid from the intersti- a system of small, then medium and eventually large,
tium. The cells of the thin endothelium are connected by lymph vessels. Their basic structure comprises a tubu-
interdigitations and overlapping areas, occasionally only lar endothelium and a sleeve of loose connective tissue.
by zonulae occludentes. Spaces are often present between Depending upon species and body region, fibromus-
cells, and the basal lamina is usually absent or interrupted cular reinforcement of the vessel wall may be present.
by large gaps. The exterior of the endothelium is con- Like lymph capillaries, these vessels are located within
nected by delicate anchoring filaments to the collagen connective tissue.

6.20 Transverse section of the wall of a collecting duct (thoracic duct; sheep). The flattened endothelium is
surrounded by a broad subendothelial layer and a tunica media with longitudinally oriented smooth muscle
cells. Haematoxylin and eosin stain (x300).

6.21 Partial section of the wall of a lymph vessel in the medulla of a lymph node (pig). Haematoxylin and eosin
stain (x300).

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