Anatomy and Physiology: Major Components of the Lymphatic System

You've undoubtedly gone to the doctor for a physical exam. You've sat on a sterilized paper cover in a johnny while cold hands reeking of Purell move to the underside of your jaw and palpate. If you've ever asked your doctor what he or she was doing, they would have told you they were checking your palatine tonsils. Or, if you're like me, you said nothing, assumed they knew what they were doing, and instead spent the rest of your physical dreading blood work, or worse—peeing in a cup.

Checking your tonsils, however, is incredibly important, as is the system of which they are part. Swollen tonsils are a sign of infection. The lymphatic system is a series of nodes, ducts, and vessels that works closely with the circulatory system. If you've ever cut yourself and missed a blood vessel, you may have noticed that a clear fluid oozed out. That fluid is lymph. It flows through the vessels and nodes, helping the body fight foreign pathogens. There is twice as much lymph in your body than blood at any given moment; think of it as extra precautions that your blood sets up.

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The lymphatic system is comprised of 5 major components:

1. Vessels

Lymphatic vessels highlighted in blue. Image from Human Anatomy Atlas.

Like arteries and veins, lymphatic vessels sprawl in a connected system to collect the lymph that leaks from the blood capillaries and conduct it to the large veins of the neck at the junction of the internal jugular vein and the subclavian vein. The network functions to return lymph to the general circulation. 

2. Nodes

Image from Human Anatomy Atlas.

Lymph nodes, like the ones your doctor feels during your physical exams, are important for two reasons:

1. They filter the lymph that passes through the vessels and add lymphocytes to it. Lymphocytes are a type of white blood cell. There are two types, small lymphocytes and large lymphocytes, and they defend the host from disease and infection.

2. Lymph nodes are little meters for doctors. Overly-large lymph nodes may indicate an infection of some kind. Doctors also use them to gauge the stage a cancer patient is in.

3. The Tonsils

Image from Human Anatomy Atlas.

While "tonsils" usually refer to your palatine tonsils, which are located in the back of your throat, you in fact have 4 sets of tonsils altogether. Tonsils are lymphoepithelial tissues located in your mouth and throat. When a doctor palpates your palatine tonsils during a physical, he or she is feeling their size. Inflamed tonsils can be an indicator of such ailments as tonsillitis, strep throat, or mononucleosis. Repeated infections can result in tonsillectomy, or the removal of the palatine tonsils (shown in blue).

4. The Thymus

Image from Human Anatomy Atlas.

The thymus is a little organ that sits right above your heart. It is in the thymus that T-cells—which target pathogens and infections—mature and become specialized. The thymus (shown in blue) is that of an average adult. An infant's thymus is quite large; as you age the thymus atrophies and is replaced by adipose (fat) tissue.

5. The Spleen

Image from Human Anatomy Atlas.

The spleen (shown in blue), the largest organ of the lymphatic system, processes blood and removes dead or defective red blood cells, and keeps a reserve of blood in case  of hemorrhaging. It also produces new red blood cells in a developing fetus. The spleen also serves as a site where lymphocyte populations increase. Did you know that you can live without a spleen? Your liver will take over some of the spleen's work!

So, the next time you're sitting on an examination table while your doctor palpates your tonsils, you can ask how your lymphatic system is doing, and then wow him or her with your new-found knowledge. Trust me: doctors love that. 

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