Lymphatic vessels drain interstitial fluid (lymph) from lymphatic spaces, joining eventually to the thoracic ducts and right lymphatic duct which both drain into the venous system.

• Lymph is moved through the vessels primarily by the movement of surrounding organs and tissues.

Examine large and small lymphatic vessels (Figs. 11-23 and 11-24) in slides 4, 79, and 99.

• Note the appearance of lymph in the lumens, compared to that of blood in vessels. This is a distinctive, identifying feature of lymphatic vessels.

Compare and contrast the walls of lymphatics with walls of similar-sized veins.

Why do the endothelial cells of lymphatics often appear to be non-nucleated?

Now for the respiratory system.