Lymph Function

Lymphatic vessels in the small intestine play a major role in the absorption of dietary fats (chapter 17, p. 720). Lymph also returns to the bloodstream any very small proteins that may be filtered by the blood capillaries. At the same time, lymph transports foreign particles, such as bacteria or viruses, to lymph nodes.

Although these proteins and foreign particles cannot easily enter blood capillaries, the lymphatic capillaries are adapted to receive them. Specifically, the epithelial cells that form the walls of lymphatic vessels overlap each other but are not attached. This configuration, shown in figure 16.8, creates flaplike valves in the lymphatic capillary wall, which are pushed inward when the pressure is greater on the outside of the capillary but close when the pressure is greater on the inside.

The epithelial cells of the lymphatic capillary wall are also attached to surrounding connective tissue cells by thin protein filaments. As a result, the lumen of a lymphatic capillary remains open even when the outside pressure is greater than the pressure within the lymph capillary.

H What is the relationship between tissue fluid and lymph?

^9 How do proteins in tissue fluid affect lymph formation? ^9 What are the major functions of lymph?

Epithelial cell f

Flow of lymph

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