Structure and Function of the Lymphatic System in Dogs (2023)

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diseases conditions of dogs

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Below is information about the structure and function of the canine lymphatic system. We will tell you what the lymphatic system is, where it is located, how the lymphatic system works in dog as well as common diseases that affect the lymphatic system in dogs. The lymphatic system is commonly referred to as the “lymph” system.

What Is the Lymphatic System?

A dog’s lymphatic system is a complex and vital system primarily responsible for the transportation of lymph and for participating in many immune functions of the body. The lymphatic system occurs throughout the body and is made up of small glands called lymph nodes, which are connected to each other by a series of vessels called lymphatics. Other important organs in this system include the bone marrow, spleen, thymus and gut-associated lymphoid tissue (GALT), which is the lymphatic tissue associated with the gastrointestinal (GI) tract.

Where Is the Canine Lymphatic System?

The lymphatic system is located throughout the body and has many components:

  • Lymph nodes or glands are small round, oval or bean-shaped structures that are located at various locations throughout the body. The lymph nodes are connected to each other by a series of vessels called lymphatics, which carry lymph from place to place. Some lymph nodes lie along the surface of the body (along the neck, under the arms, in the groin, behind the knees), while others lie deep within the body (chest and abdomen).
  • The bone marrow lies within the central shaft of bones, primarily the long bones of the body.
  • The spleen is located near the stomach in the left forward part of the abdomen.
  • The thymus is located in the front part of the chest cavity, between the trachea (windpipe) and the ribs.
  • The GALT is made up of lymph tissue scattered throughout the GI tract including the tonsils and intestines.
  • What Is the General Structure of the Lymphatic System in Dogs?

    The lymphatic system is composed of a network of lymph vessels referred to as lymphatics, as well as certain organs and tissues, including the lymph nodes, bone marrow, spleen, thymus and GALT.

    Lymph is a milky fluid that flows throughout the system. It contains proteins, fats and a type of white blood cell called lymphocytes. Lymph is collected from the fluid of various tissues and eventually is returned to the blood circulatory system. The lymphatic system provides another route by which fluid can flow from distant tissues back into the blood stream, one that is separate from capillaries and veins. It also carries proteins and other substances away from tissues that cannot be removed or transported directly into the blood system.

    Similar to the blood circulatory system, the lymphatic system is comprised of fine channels that lie adjacent to the blood vessels. These lymphatic vessels eventually merge into a rather large vessel called the thoracic duct. As the lymph is carried from distant parts of the body, it is collected into larger and larger vessels until the vessels all converge in the chest and deposit the lymph in the large vein (cranial vena cava) leading to the right atrium of the heart.

    The lymph moves through the lymphatic vessels toward the lymph nodes. The lymph nodes lie at varying points along the course of the lymphatic chain and can form clusters in some areas of the body. Lymph nodes have a dense fibrous outer coating, called a capsule and are filled with white blood cells and spaces containing lymph fluid. Several types of white blood cells predominate in the lymph nodes, particularly lymphocytes, plasma cells, and macrophages.

    The bone marrow consists of connective tissue, the cells of which form a delicate meshwork within the marrow cavity. The marrow cavity is permeated by numerous thin-walled blood vessels. Within the spaces of this tissue, the immature and adult stages of different blood cells exist.

    The spleen is the largest body of lymphatic system. It is a dark red organ that is supplied with numerous blood vessels. A tough capsule of fibrous tissue covers the spleen. The splenic “pedicle” is located along one surface and serves as the entry and exit point for blood vessels. The internal structure of the spleen consists of:

    (Video) Blood and the Lymphatic System (VETERINARY TECHNICIAN EDUCATION)

  • Red pulp – areas for red blood cell storage and for the trapping of immune proteins called antigens
  • White pulp – areas of special immune response cells called lymphocytes and reticuloendothelial cells
  • Marginal zone – an area that separates the white and red pulp and helps to filter the blood

    The thymus is an organ that varies in size depending on the age of the individual. It is largest in young animals and shrinks to a very small size in the adult.

    GALT is present throughout the gastrointestinal tract. Peyer’s Patches are aggregates of lymphoid tissue found in the small intestine and are a type of GALT.

  • What Are the Functions of the Lymphatic System in Dogs?

    The lymphatic system has several very important functions: absorbing excess fluid from tissues and returning it to the bloodstream, absorbing fat from the gastrointestinal tract, transporting white blood cells and certain proteins, and playing an important role in the immune system, particularly in the production of antibodies (immunoglobulins).

  • The lymphatic system filters and removes debris from the tissues of the body. Cells produce proteins and waste products. The lymph absorbs these products and carries them away from the tissues because they are often too large to be effectively absorbed and removed by the bloodstream.
  • The lymphatic system, functioning along with the circulatory system, absorbs nutrients from the small intestines. A large portion of digested fats is absorbed via the lymphatic capillaries. Fat absorbed from the small intestinal lymphatic capillaries or lacteals is termed chyle.
  • The lymph nodes filter out cellular waste products and foreign material in the lymph fluid, including potentially dangerous infectious particles like bacteria and viruses. They trap material received from the lymphatic vessels and provide a site for white blood cells to mount an immune response. They act as a barrier against the entrance of these foreign substances into the bloodstream.
  • The chief function of the bone marrow is the production of various red and white blood cells.
  • The spleen is an integral part of the immune system and it filters abnormal cells from the blood. It also helps make and store blood cells.
  • The thymus is a very important part of the immune system in the newborn. It is the site where the earliest immune cells are made and where immune functions take place in the young animal.
  • GALT’s main function is to provide immunologic defenses at the surface of certain areas of the body, such as the tonsil and the lining of the intestinal tract. These are areas where the body is often exposed to foreign materials and infectious agents.
  • What Are Common Diseases of the Canine Lymphatic System?

    Due to the distribution and complexity of the lymphatic system, many disorders may affect all or some part of it. The most common disorders seen in dogs include the following:

  • Lymphoma or lymphosarcoma is a tumor of white blood cells. It is a malignant cancer, and it may affect one or more parts of the lymphatic system. Lymphoma may occur as a solid tumor associated with the lymph nodes, the intestines, kidneys, liver, spleen, thymus or other parts of the body. It may also develop as a circulating form that is confined largely to the bone marrow and blood stream. Lymphoma is one of the most common cancers seen in dogs, and has been treated with chemotherapy protocols for a number of years.
  • Lymphadenopathy is enlargement of the lymph nodes. It may represent lymphosarcoma, but may also develop for other reasons. Lymph nodes may enlarge when they are reacting to foreign substances or infection. They become larger as white blood cells proliferate within the nodes. Such reactions may also occur following vaccination or with any chronic inflammation within the body.
  • Lymphadenitis is inflammation of the lymph nodes. It may involve one or several lymph nodes, depending upon the cause. Common causes include wounds, skin infections, infections within the soft tissues of the body, nonlymphatic tumors, and areas of active healing.
  • Chylothorax is the accumulation of chyle in the chest cavity from rupture, obstruction, or abnormal development of the thoracic duct. It may develop secondary to heart disease, tumors of the thorax, diaphragmatic hernias, trauma, fungal infections, heartworm disease, and for unknown reasons. It is more common in Afghan hounds and Shiba Inu dogs than in other breeds.
  • Lymphangitis is an inflammation of the lymph vessel. It often arises from trauma, foreign bodies, and infections. It may occur at the same time as lymphadenitis.
  • Lymphangiectasia is an obstructive (blockage) disorder that causes dilation of the lymph vessels, particularly in the intestinal tract.
  • Lymphedema is an accumulation of lymph in the soft tissues of one or more of the limbs. Congenital forms occur in some dogs (e.g. poodles, Labrador retriever, Great Dane) due to deformities in either the lymphatic channels or the lymph nodes themselves. Acquired forms may occur with blockage or destruction of lymph vessels from trauma, surgery, inflammation, infection, tumors, or radiation therapy. In some cases the soft tissue swells so much that the limb may be painful or dysfunctional.
  • What Types of Diagnostic Tests Are Used to Evaluate the Lymphatic System in Dogs?

    Several tests are particularly helpful in evaluating the lymphatic system. Depending on the part or parts of the lymphatic system involved, a combination of tests may be recommended by your veterinarian.

  • A complete blood count (CBC), biochemical profile, and urinalysis are recommended to help evaluate organ functions, to detect evidence of infection or inflammation throughout the body, and to assess the types of white blood cells present in the circulation.
  • Blood tests that screen for infectious diseases such as the systemic fungal infections, the tick borne diseases and certain bacterial infections (e.g. brucellosis) may be of benefit in cases with lymphadenopathy or abnormal circulating numbers of white blood cells.
  • Chest and abdominal X-rays and ultrasonography are useful to evaluate abdominal organs including the spleen, intestines, liver, kidney and abdominal lymph nodes. They also detect the presence of fluid in the chest, such as in the case of chylothorax.
  • A bone marrow aspirate or biopsy is performed for diseases involving the bone marrow.
  • Fine-needle aspiration of enlarged lymph nodes or other abnormal tissues, followed by cytology (microscopic analysis of the cells) may be diagnostic for lymphoma, reactive lymphadenopathy or lymphadenitis. In some cases an actual biopsy (piece of tissue) is needed for diagnosis.
  • Analysis of fluid retrieved from the chest can confirm the presence of chylothorax.
  • Bacterial cultures may be submitted if bacterial infections are suspected.
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    What is the function of the lymphatic system in a dog? ›

    The lymphatic system filters and removes debris from the tissues of the body. Cells produce proteins and waste products. The lymph absorbs these products and carries them away from the tissues because they are often too large to be effectively absorbed and removed by the bloodstream.

    What is the structure and function of the lymphatic system? ›

    The lymphatic system is a network of delicate tubes throughout the body. It drains fluid (called lymph) that has leaked from the blood vessels into the tissues and empties it back into the bloodstream via the lymph nodes. The main roles of the lymphatic system include: managing the fluid levels in the body.

    What is the function of the lymphatic system in animals? ›

    The main function of the lymphatic system is to collect and transport tissue fluids from the intercellular spaces in all the tissues of the body, back to the veins in the blood system. Lymph plays an important role in returning plasma proteins to the bloodstream.

    What is the structure of the lymphatic? ›

    Lymph (or lymphatic ) vessels are thin-walled valved structures that carry lymph. Lymph vessels are lined by endothelial cells and have a thin layer of smooth muscles and adventitia that bind the lymph vessels to the surrounding tissue.

    Do dogs have lymphatic system? ›

    The lymph system performs several important functions in your dog's body, including transporting white blood cells, removing waste products from tissues and cells, and helping to produce disease-fighting antibodies. Lymph nodes are small, bean-shaped organs that contain immune cells.

    Where are lymph nodes located on a dog? ›

    The lymph nodes located in the neck, chest, armpits, groin, and behind the knees are often the most visible and easy to observe. Swelling of these lymph nodes may be noted by the dog's owner, or first noted by the veterinarian on a routine physical exam.

    What are the 4 main functions of the lymphatic system? ›

    Functions of the Lymphatic System
    • The removal of excess fluids from body tissues. ...
    • Absorption of fatty acids and subsequent transport of fat, chyle, to the circulatory system.
    • Production of immune cells (such as lymphocytes, monocytes, and antibody producing cells called plasma cells).

    What are three functions of the lymphatic system? ›

    The three vital functions of the lymphatic system are to remove excess fluid from the body tissues, transport lipids or large molecules, and exhibit immune surveillance.

    What are the 7 main parts of the lymphatic system? ›

    What Does the Lymphatic System Do?
    • bone marrow.
    • spleen.
    • thymus gland.
    • lymph nodes.
    • tonsils.

    Do animals have a lymphatic system? ›

    Abstract. All vertebrate animals share in common the production of lymph through net capillary filtration from their closed circulatory system into their tissues.

    Where are lymph nodes located in animals? ›

    The common locations for the peripheral lymph nodes are the cervical nodes under the back of the jaw, the pre-scapular which are between the shoulder and the neck. The axillary lymph nodes are under the front legs and the inguinal lymph nodes are in the inguinal region of the back legs.

    Which of the following is the function of lymph? ›

    Its key functions include: Maintains fluid levels in your body: As just described, the lymphatic system collects excess fluid that drains from cells and tissue throughout your body and returns it to your bloodstream, which is then recirculated through your body.

    What are the main structures of the lymphatic system quizlet? ›

    What is the structure of the lymphatic system? The lymphatic system consists of lymphatic cappillaries, lymphatic vessals, lymph nods and lymphatic ducts. The fluid in lymphatic capillaries and vessels is called lymph.

    What are the organ of lymphatic system? ›

    The tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. This system includes the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels (a network of thin tubes that carry lymph and white blood cells).

    What are the 6 lymphatic organs? ›

    The bone marrow, spleen, thymus, lymph nodes, and lymphatic veins are all part of this system (a network of thin tubes that carry lymph and white blood cells). The lymphatic system can be broadly classified into: Primary lymphoid organs, which generate special immune system cells known as B or T lymphocytes.

    What is lymphatic drainage dogs? ›

    Lymphatic drainage is a therapeutic massage treatment. The goal of lymphatic drainage in the massage is to increase the flow of lymph and reduce toxins in the body. The lymph system is part of the dog's body's immune system and helps fight infection. Lymph itself is a clear, slightly yellow fluid.

    Where do lymph nodes drain to in dogs? ›

    The dorsal area of the pericardium drains directly into cranial mediastinal lymph nodes; the cranial and lateral areas drain into lymph vessels that pass cranially and caudally along the phrenic nerves. Those that pass cranially drain into cranial mediastinal lymph nodes.

    How can I help my dogs lymphatic system? ›

    Adequate exercise is essential to a healthy functioning lymphatic system. Movement increases the flow of lymph. Also, as your dog exercises, he draws in oxygen. Oxygen serves as a sort of pump to the lymphatic system, assisting in the removal of toxins from organs and tissue.

    How big should a dogs lymph nodes be? ›

    Lymph node exam

    Enlargement- most should feel the size of a marble or less (depends on the size of your pet). If one of them is larger than this, painful, or the area around it is swollen or painful, it should be examined by one of our doctors.

    Do dogs have lymph nodes under their arms? ›

    Armpit Glands

    The set of glands in the area of your dog's armpits are known as lymph nodes. These axillary lymph nodes, as they're called, are located on either side of your dog. Lymph nodes are approximately the size of a bean and swell up when your dog experiences infections, viruses or wounds.

    Which lymph nodes are palpable in dogs? ›

    The lymph nodes generally palpated in dogs and cats include the submandibular, prescapular, and popliteal lymph nodes. Popliteal and prescapular lymph nodes are preferred biopsy sites for animals with generalized lymphadenopathy.

    Do animals have lymphatic system? ›

    All vertebrate animals share in common the production of lymph through net capillary filtration from their closed circulatory system into their tissues.

    How do you give a dog a lymphatic massage? ›

    Start by rubbing your dog's feet, and then move up to the joints, kneading, and applying light, circular pressure. Continue over the body with long strokes and soft presses. Applying gentle pressure encourages lymph flow through the body.

    What are your lymph nodes for? ›

    Your lymph nodes, also called lymph glands, play a vital role in your body's ability to fight off infections. They function as filters, trapping viruses, bacteria and other causes of illnesses before they can infect other parts of your body.

    Is one of the main lymphatic duct? ›

    A lymph duct is a great lymphatic vessel that empties lymph into one of the subclavian veins. There are two lymph ducts in the body—the right lymphatic duct and the thoracic duct.
    Lymph duct
    LatinDuctus lymphaticus
    Anatomical terminology
    5 more rows

    Where are lymph nodes located in animals? ›

    The common locations for the peripheral lymph nodes are the cervical nodes under the back of the jaw, the pre-scapular which are between the shoulder and the neck. The axillary lymph nodes are under the front legs and the inguinal lymph nodes are in the inguinal region of the back legs.

    What animals have lymph nodes? ›

    General. Lymph nodes are found in mammals as rounded to bean-shaped lymphoid structures. They are surrounded by a collagenous capsule from which trabeculae enter into the node, and connected by lymph vessels. The basic anatomical features are the cortex/paracortex and medulla (1).

    What circulates the lymphatic system? ›

    Fluid that is forced out of the bloodstream during normal circulation is filtered through lymph nodes to remove bacteria, abnormal cells and other matter. This fluid is then transported back into the bloodstream via the lymph vessels. Lymph only moves in one direction, toward the heart.

    What causes a dogs lymph nodes to swell? ›

    There are several possible infectious causes of enlarged lymph nodes, including but not limited to: bacterial, tick-borne, fungal, and parasitic. Many dogs who have one of these infections will also have other symptoms such as fever, lethargy, or diarrhea.

    Can you massage a dogs lymph nodes? ›

    Improving the flow and drainage of lymph around the body is good for dogs in lots of ways. Begin by working your way up from the paws. Lymphatic drainage massage uses very light pressure, as well as long, gentle, rhythmic strokes and soft pumping movements toward, over, and away from the lymph nodes.

    What does lymphedema look like in dogs? ›

    Symptoms of Lymphedema in Dogs

    Swelling is an obvious sign of lymphedema. While other injuries may cause tissue swelling, this condition happens as a result of lymphatic fluid pooling in parts of a dog's body.

    What are the 4 main functions of the lymphatic system? ›

    Your lymphatic system, part of your immune system, has many functions. They include protecting your body from illness-causing invaders, maintaining body fluid levels, absorbing digestive tract fats and removing cellular waste.

    Where are the 4 main locations of lymph nodes in the body? ›

    Where are lymph nodes located? Lymph nodes are located throughout the body, including the neck, armpits, groin, around the gut, and between the lungs.

    What are the 2 main lymphatic vessels? ›

    The two major lymphatics of the body include the right lymphatic duct and the thoracic duct. The right duct drains most of the right upper quadrant whereas the thoracic duct drains the lower body including the extremities and abdomen.

    What are the 5 lymphatic trunks? ›

    Lymphatic trunks
    • jugular trunks: drain the neck.
    • subclavian trunks: drain the upper limbs.
    • bronchomediastinal trunks: drain the chest.
    • intercostal trunks: drain the chest wall.
    • lumbar trunks.
    • intestinal trunk: drains the gut.
    18 Apr 2022

    Where does lymph system drain? ›

    The lymphatic vessels drain into collecting ducts, which empty their contents into the two subclavian veins, located under the collarbones. These veins join to form the superior vena cava, the large vein that drains blood from the upper body into the heart.


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