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Lymphatic Vessels: Definition & Function

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  • 0:01 Companions to Blood Vessels
  • 1:30 Function of Lymphatic System
  • 3:14 Lymph Nodes
  • 4:29 Lymphatic Vessels
  • 5:30 Lesson Summary
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Lesson Transcript
Instructor: Stephen Christensen
In this lesson, you will learn what lymphatic vessels are and why they are important for fluid management, immune function, and fat absorption. You'll then take a short quiz to test your knowledge.

Companions to Your Blood Vessels

Lymphatic vessels are among several structures belonging to your lymphatic system. In order to understand how lymphatic vessels work, you'll first need a rudimentary knowledge of how your circulatory system functions because many of these two systems' tasks are intertwined. In fact, the vessels of your lymphatic system tend to run right alongside the vessels of your circulatory system.

Your circulatory system consists of a pump (your heart) and a network of tubes that conduct blood throughout your body (your blood vessels). With each heartbeat, blood is forced into your arteries, which carry blood away from your heart and toward all of your tissues and organs. As your arteries travel farther from your heart, they divide into progressively smaller vessels called arterioles, which themselves divide into tiny, thin-walled, somewhat leaky vessels called capillaries.

As blood travels through your capillaries, oxygen, nutrients, and fluid are pushed into the surrounding tissues, and carbon dioxide and cellular wastes are retrieved. The blood then proceeds on its way, coursing into progressively larger vessels called venules and then into even larger veins, which finally return the blood to your heart. If the fluid that leaked into your tissues from your bloodstream remained there, your cells would soon drown in the excess. That's where your lymphatic system picks up the ball.

Function of the Lymphatic System

Mingled among the blood capillaries throughout your body is another network of tiny, thin-walled vessels called lymphatic capillaries. Lymphatic capillaries are designed to pick up the fluid that leaks into your tissues from your bloodstream and return it to your circulatory system.

Nature has ingeniously devised your lymphatic and circulatory systems so the pressure in your blood capillaries is slightly higher than the pressure in your lymphatic capillaries. This pressure gradient from blood capillary to tissue to lymphatic capillary gradually moves fluid from your circulatory system to your lymphatic system, much like water in a river flows downhill.

Just like their neighboring blood capillaries, your lymphatic capillaries join into progressively larger tubes called lymphatic vessels, which transport the fluid from your tissues (this fluid is now called lymph) toward the center of your body. Eventually, the lymph is returned to your bloodstream through two large ducts in the upper central portion of your chest.

The largest of these lymphatic ducts, the thoracic duct, originates in your abdomen, where it collects lymph from your legs, intestine, and other internal organs. As it proceeds upward into your chest, the thoracic duct collects lymph from your thoracic organs, your left arm, and the left side of your head and neck.

The right lymphatic duct, which is much shorter than the thoracic duct, begins high in the right side of your chest. It collects lymph from the right side of your chest wall, your right arm, and the right side of your head and neck. The thoracic duct and the right lymphatic duct reintroduce lymph to your bloodstream through the large veins returning to your heart from your arms: the left and right subclavian veins.

Lymph Nodes - Immune Sentries

Rather than being mere hoses that conduct lymph from your tissues to your circulatory system, lymphatic vessels serve as conduits between your lymphatic system and your immune system. Scattered strategically throughout your body are approximately 600 small, bean-shaped organs called lymph nodes. These rather drab-looking little lumps serve as checkpoints for your immune system; each lymph node is connected to its neighbors by lymphatic vessels, and each serves as a sentry to protect you from infections. All of the lymph moving through your body is filtered through at least one lymph node before it is returned to your circulatory system.

As the lymph enters a lymph node from a lymphatic vessel, it is filtered through a network of fibers, where a team of immune cells screen the lymph for debris, bacteria, cancer cells, and other potentially harmful agents. If a bad agent is detected within the lymph, the lymph node begins churning out more immune cells, antibodies, and inflammatory chemicals to destroy the invader. If you've ever had strep throat or mono, you've probably felt the enlarged glands in your neck beneath the angle of your jaw. These are simply your lymph nodes reacting to the infection in your throat.

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