The Anatomy and Function of Your Pet’s Lymph NodesLymph nodes are a very important part of the immune system in dogs and cats. It’s important to know where they are located and what to do if you notice an enlarged or painful lymph node while petting your furry friend. Read on to learn more about lymph nodes in dogs and cats.FirstVet is the #1 online video veterinary service.FirstVet offers video calls with experienced veterinarians for just $35. You can get a consultation within minutes by downloading the FirstVet app for free from the Apple App Store or Google Play Store. Over 500,000 users trust FirstVet to care for their animals. Rating: 4.9 - more than 1600 reviewsRating: 4.9 - more than 1300 reviewsRating: 4.9 - more than 1600 reviews Download app What are lymph nodes and what do they do?Lymph nodes in dogs and cats are located in the body and pretty much have the same functions as they do in humans. They can often be the first indication that something is wrong, such as inflammation or infection as the nearby or “regional” lymph nodes may become enlarged, tender to the touch, or even reddened or warm to the touch.An enlarged lymph node due to inflammation or infection is also known as a “reactive” lymph node. The swelling or enlargement of a lymph node is a result of an increase in white blood cells and plasma cells (antibody secretion cells).The lymphatic system is a poorly understood system of very thin-walled vessels that carry and circulate “lymph.” Lymph is a fluid composed of water, lymphocytes (a type of white blood cell), and proteins/antibodies. Lymph nodes act as filters for the blood and lymph. They store additional white blood cells needed to fight infection.What causes enlarged lymph nodes?The lymphatic system doesn’t have a “pump” like the circulatory or blood system has. Rather, it relies on valves within the lymph vessels and the movement of muscles, particularly in a dog or cat’s legs. Swelling of a limb can occur if the lymph isn’t circulating normally. Lymph nodes are strategically located along the lymphatic system throughout the body and become active in producing antibodies from any organ or tissue from which it receives lymph.Unfortunately, an enlarged lymph node doesn’t always mean that a nearby infection is present. Cancer may also be present. Lymphoma is a primary cancer of the lymph node, specifically the lymphocytes within that lymph node. A secondary form of cancer within a lymph node is when cancer from one part of the body spreads or “metastasizes” to a specific lymph node.How are lymph node diseases diagnosed?After a thorough exam and lymph node palpation, your vet may recommend a simple procedure called a “fine needle aspirate” or FNA. An FNA may be performed to help determine why a particular lymph node is enlarged. A tiny needle is inserted into the lymph node and cells are withdrawn with a syringe and sent to a pathologist to be identified.Lymph Node LocationsIf we think of the front legs of dogs and cats as being the arms in humans, the lymph nodes are all located in similar places. There are many inside the trunk or main abdominal or chest cavities, however, the most commonly aspirated or peripheral lymph nodes that are easiest to find include:Submandibular nodes - are found under the jaw or literally, “under the mandible”Cervical nodes - are along the front of the neck on either side of the trachea or “windpipe.”Pre-scapular - or “pre-shoulder” nodes are found in the front of the body where the arm meets up with the collarboneAxillary nodes - are found in the “armpit” areaInguinal nodes - are found in the groin area or on the inside of where the rear limb meets the hipPopliteal nodes - are found behind the kneesWhat should I do if I think my pet’s lymph nodes are enlarged?If you’re worried about your dog’s or cat’s lymph node(s,) a physical exam by their vet and quite possibly an FNA is a really good idea. An enlarged lymph node may just be “hyperplastic” or revved up due to a nearby or regional infection or sadly, it could also reveal a primary or secondary (metastatic) cancer.Read more:Lymphoma in DogsLymphoma in CatsHow to Examine Your Pet at Home: A Step-By-Step GuideHave more questions about your pet’s lymph nodes?Schedule a video consult to speak with one of our vets.