Chapter 8 - The Lymphatic System

Abstract

This chapter focuses on the lymphatic system, which is composed of lymphatic vessels, lymphoid tissues and organs, lymph, and lymphocytes. Lymphatic vessels function to transport lymph away from microvascular beds and into the cardiovascular system. The first vessel within the lymphatic system is the lymphatic capillary, which is composed of loosely bound endothelial cells to facilitate the movement of water into the lymphatic system. Lymphatic capillaries converge into larger lymphatic vessels, which are similar in structure and function to venules. Lymph is formed as a filtrate of interstitial fluid, except that there is typically a higher protein concentration in lymph than the interstitial fluid. The regulation of lymph formation is governed by the formation of interstitial fluid. Lymph flows through the lymphatic system at a rate of approximately 125 mL/hour for a total of approximately 3 L of lymph formed per day, which is approximately 60% of the average blood volume. The principal regulator of lymph flow is the interstitial hydrostatic pressure, because the lymphatic system is also under a very low pressure throughout the entire system. Small changes in the interstitial pressure can have a significant effect on lymph flow through lymphatic vessels. Lymph is also propelled through the lymphatic vessels by compression of surrounding tissue. Two diseases that are associated with the lymphatic system are cancer and edema. Cancerous cells can easily enter the lymphatic system and then move to other locations within the body. Lymphedema is similar to edema and can potentially cause a large inflammatory response.