The lymphatic vessel shown in this figure shows a region where the vessel is making a U-shaped turn in the plane of the section, thus disappearing at the top and bottom of the micro-graph. The wall of the vessel consists of an endothelial lining and a small amount of connective tissue, with one being indis tinguishable from the other. A valve (Val), which is characteristic of their nuclei are seen here as cross-sectioned profiles. The arteriole on the right is a very small arteriole, having only a single layer of smooth muscle. Again, the muscle cell nuclei are seen in longitudinal profile. The endothelial cell nuclei appear as the small round profiles at the luminal surface. A venule is seen in proximity to the larger arteriole, and a cross section of peripheral nerve (N) is seen in proximity to the smaller arteriole. Compare the wall of the venule, consisting only of endothelium and a thin layer of connective tissue, with the arterioles. Also, note the relatively large lumen of the venule.
PLATE 35 • ARTERIOLES, VENULES, AND LYMPHATIC VESSELS profile. After the arteriole makes an acute turn (segment numbered 2), the vessel wall is cut to reveal the lumen. Here, the smooth muscle nuclei appear as round profiles and the nuclei of the endothelial cells lining the lumen appear in longitudinal profile. In the segment numbered 3, the vessel wall is again only grazed. In the segment numbered 4, the cut is deeper, again showing the lumen and some of the endothelial cells in face view (arrowheads). The structure below the vessel is a Pacinian corpuscle (P).
lymphatic vessels, is seen within the vessel. It is formed of a miniscule layer of connective tissue that is covered on both sides by endothelium. The arrows indicate nuclei that are just barely visible at this magnification; most of them belong to endothelial cells. Typically, the lumen contains precipitated lymph material (L); sometimes, lymphocytes may be present. Adjacent to the vessel, on the right, is adipose tissue (AT) and on the upper left is dense irregular connective tissue (DCT).
Lymphatic vessel, fngertip, human, Mallory ×375.
The lymphatic vessel shown here is contained within dense irregular connective tissue (DCT). The lumen is irregular, appearing relatively narrow below the valve (Val). A few endothelial cell nuclei are evident (arrows). A thin layer of connective tissue that is present outside of the endothelium blends with the dense connective tissue beyond the wall of the vessel. A venule (V) is also present; it can readily be distinguished from the lymphatic vessel by the presence of red blood cells in the lumen.
KEY A, arteriole Ad, adipocyte AT, adipose tissue DCT, dense irregular connective tissue L, lymph material N, nerve P, Pacinian corpuscle V, venule Val, valve arrowheads, endothelial cells arrows, endothelial cell nuclei
PLATE 35 • ARTERIOLES, VENULES, AND LYMPHATIC VESSELS VVV NNN AAA ATATDCTDCTPP11223344AT DCT P 1 2 3 4 ValValVal DCTDCTATAT LLDCT AT L AdAdDCTDCTDCTDCTVVAALLLLAd DCT DCTV ValValVal A L L