Module 8: Lymphatic System
Learning Objectives:
By the end of this module, students will be able to:
- Explain the structure and function of the lymphatic vessels.
- Identify the functions of the lymphatic system.
- Describe the relationship between the lymphatic system and immune function.
- Predict the consequences of the anatomy of the lymphatic system (e.g., cancer spread) and lymphatic system dysfunction.
- Describe the organs of the lymphatic system and their functions in the immune system.
Terms to Know
|
Vessels
Lymphatic System
|
Lymphatic System (continued)
|
The immune system is the complex collection of cells and organs that destroys or neutralizes pathogens that otherwise cause disease or death. For most people, the lymphatic system is associated with the immune system to such a degree that the two systems are virtually indistinguishable. The lymphatic system is the system of vessels, cells, and organs that carries excess fluids to the bloodstream and filter pathogens from the blood. The swelling of lymph nodes during an infection and the transport of lymphocytes via the lymphatic vessels are two examples of the many connections between these critical organ systems.
Lymph contains a liquid matrix and white blood cells. Lymphatic capillaries are extremely permeable, allowing larger molecules and excess fluid from interstitial spaces to enter the lymphatic vessels. Lymph drains into blood vessels, delivering molecules to the blood that could not directly enter the bloodstream. In this way, specialized lymphatic capillaries transport absorbed fats away from the intestine and deliver these molecules to the blood.
Functions of the Lymphatic System
A major function of the lymphatic system is to drain body fluids and return them to the bloodstream. Blood pressure causes leakage of fluid from the capillaries, resulting in fluid accumulation in the interstitial space—that is, spaces between individual cells in the tissues. In humans, 20 liters of plasma are released into the tissues’ interstitial space each day due to capillary filtration. Once this filtrate is out of the bloodstream and in the tissue spaces, it is referred to as interstitial fluid. Of this, 17 liters are reabsorbed directly by the blood vessels. But what happens to the remaining three liters? This is where the lymphatic system comes into play. It drains the excess fluid and empties it back into the bloodstream via a series of vessels, trunks, and ducts. Lymph is the term used to describe interstitial fluid once it has entered the lymphatic system. When the lymphatic system is damaged in some way, such as by being blocked by cancer cells or destroyed by injury, protein-rich interstitial fluid accumulates (sometimes “backs up” from the lymph vessels) in the tissue spaces. This inappropriate accumulation of fluid referred to as lymphedema may lead to serious medical consequences.
As the vertebrate immune system evolved, the network of lymphatic vessels became convenient avenues