Lymph Nodes

Home Up

What do lymph nodes do?

    Lymph nodes are like tiny organs all over our bodies, smack dab in the middle of lymphatic vessels.  These nodes perform these following functions

bulletfilter the lymph
bulletassist bone marrow and the thymus in the production and maturation of lymphocytes
bulletassist in getting an immune response going

The first two functions are pretty easy to understand.  The last one will take reading through all the rest of the web pages to understand... but don't worry... it's not that hard!

    As I describe the anatomy of a lymph node, I will be sure to explain how it is able to carry out each of these functions.

Lymph node anatomy

    I took the following diagram node.jpg (34701 bytes)from a Dartmouth web page on the pathology of lymph nodes (at least, it used to be there).  This diagram had a bit more detail than you need in its original form, so I edited it a bit for you.

    The first thing I want you to notice is that the direction of lymph flow is from left to right.  The lymph enters the node in the afferent lymphatic vessels, and leaves the node in the efferent lymphatic vessel.   The next important thing to see is that there are many more afferent lymphatic vessels than efferent lymphatic vessels.  Why is this important?  Because this is how the lymph node is able to filter out material... since the amount of exiting lymph is limited, the only lymph that makes it through and continues readily is that lymph that is unencumbered by large material... so the larger stuff gets trapped in the node.   That makes this larger stuff available to the cells in the node, and those cells include lymphocytes and macrophages.  How handy, right?  The junk gets trapped and the macrophages are there to clean it away!  Nice.

    To see a real section through a lymph node, go to the LUMEN histology site and choose slide 48.  If you look at slide 50 also, you'll see the reticular connective tissue that you learned about in A&P1 making up a lot of the lymph node.

    Every lymph node has one point at which the efferent lymphatic vessels leave, called the hilum of the node.  The lymph collects within the node on its way toward the hilum in channels called lymph sinuses. The central portion of the node is called the medulla, and it contains a larger sinus to collect the lymph (innermost area).  In the outer rind of the lymph node (called the cortex, but that's not given in your book), there are nodules, regions of mainly B lymphocytes.  Even the nodules can have an inner and an outer part to them, the inner part is where the lymphocytes divide, and the outer part is where the lymphocytes await stimulation by foreign material.

    There are two main categories of lymphocytes, as you will see in another web page from this week.  These two categories are T lymphocytes (T cells) and B lymphocytes (B cells).  B cells can divide within the nodules, and T cells can mature within the cortex of the node.  These things (B cell division and T cell maturation), as well as the exposure that macrophages and lymphocytes get to foreign material and the contact that T cells and B cells can make with one another in the cramped environment of the lymph node all help to get our immune response going.  This may seem confusing at the moment, but after you finish the pages for this unit, it should seem quite handy.

    If you look back through my description of the anatomy of the lymph node, you should see that I have explained all of the functions I listed for the lymph node at the top of this page.

Where are lymph nodes found?

    The short answer is:  just about everywhere.  The longer answer is that they tend to lie in clusters within the body, and there are 7 major regions containing these clusters.  The seven regions are:  cervical, axillary, inguinal, pelvic, abdominal, thoracic, and supratrochlear.  You can read up on these areas in your book for a little bit of clarification as to exactly where they are.

    The main reasons for knowing about these areas is that when lymph nodes need to be removed, you know where to look.  And also if a swelling is seen in the body, you would know if that swelling were likely to be due to a swollen lymph node.   Because lymph nodes filter lymph, cancer cells can get stuck in the nodes for a while, divide while there, and continue (eventually) on their way around the body.   And during infections, the excess of foreign material in our bodies can clog up the lymph nodes a bit so that they swell under the pressure of returning the lymph to the blood.

2011 STCC Foundation Press
written by Dawn A. Tamarkin, Ph.D.