In this chapter... The lymphatic system helps regulate our overall fluid balance. It also contains a lot of our immune cells, which help defend our bodies from internal and external intruders. We’ll learn about how the body defends itself by recognizing its own cells and foreign cells. One of the ways immune cells work is to engulf foreign cells by a process known as endocytosis. We’ll also explore viruses and the role they play in human health.

The lymphatic system recovers fluid from the spaces between cells.

Why this is important…Without a way to recover the fluids from the spaces around your cells, you would swell up like a balloon. The lymphatic system takes care of this spillover fluid.

Foundations

The lymphatic system is a series of tubes that carry fluid back to the bloodstream (Figure 12-1). Along the path of these collecting tubes (or vessels) are nodes where the fluid is cleaned.

Stop & Think #1: Where do you think the fluid comes from that the lymphatic system recovers?

Diagram of human lymphatic system as a series of tubes throughout the body.
Highlights tube structure as well as link to the circulatory system in the veins near the heart.

FIGURE 12-1 Anatomy of the lymphatic system. ("Lymphatic system" by SGUL lymres is licensed under CC BY-SA 4.0)

Details

The key functions of the lymphatic system include:

Fluid recovery – discussed further in the next section
Immunity – the abundance of immune cells in the lymphatic system play a key role in the body’s overall immunity to disease
Lipid absorption – as discussed with the digestive system, lipids exit the small intestine and travel via lymph vessels to the veins

The lymphatic system is a network of lymph vessels, which permeate every corner of the body, carrying fluid (lymph) back to the circulatory system. Within this network are organs with their own functions:

Tonsils sample the chemicals and microorganisms in the food we swallow and the air we breathe. This allows our immune system a chance to react to potentially harmful substances.
Lymph nodes are small “traps” to clean up the lymph before it returns to the bloodstream. There are several hundred spread throughout the body. Each contains a tangle of cellular mesh that snares microorganisms and debris for the immune cells to gobble up.
The spleen is the body’s graveyard for red blood cells. Old red blood cells are not flexible enough to squeeze through its network of mesh so they burst. The pieces get eaten up by immune cells which carefully recycle precious nutrients – phospholipids, proteins and iron.

Lymphatic tissue occurs throughout the body. It is in the walls of the digestive organs, lining mucous membranes, and even makes up bone marrow.

Stop & Think #2: What might happen if one of the lymph vessels or lymph nodes became clogged?

Learning objectives

Name and identify the major organs of the lymphatic system
Describe the basic functions of the lymphatic system

Stop & Think Questions Explained

The fluid is what has leaked out of blood vessels.
If a lymph vessel or lymph node got clogged, the fluid couldn’t drain properly in that area. This would cause swelling (edema) as the area filled with fluid.