Lymphatic system

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Before we start revising on LS, let us recall some of important related terms on this subject

Lymphadenopathy: Disease of lymph glands

Lymphangitis: Inflammation of lymph vessels

Splenomegaly: Splenic enlargement

Lymphocyte: Lymphatic cells

Tonsillectomy: Surgical removal of lymph node

Lymphoid: Lymph

Lymphatic anatomy and physiology

LS is composed of the tonsils, spleen, thymus, numerous glands, vessels, and cells that provide the body with immunity and destroy pathogens. LS also important for the constant transport of fluid (lymph) from the interstitial spaces to the general circulating blood

Tonsils

Tonsils are made up of lymphoid tissue but are not referred as lymph node. 2 tonsils are located in the throat (each side) near the base of the tongue. They are hidden within tonsillar crypts in the throat. Therefore during physical examination of a normal patient, tonsils may not be visible (unless a disease process is present to create tonsillitis).

Normal healthy tonsil

(couldnt found animal picture though)

Spleen

Spleen is large, tongue-shaped organ located in the left craniodorsal abdominal cavity closely associated with the stomach and protected by the caudal rib cage. On the routine physical examination, the speen is not palpable unless splenomegaly exists. Spleen is very important for filtration of the blood It also serves as a very important storage area for red blood cells. During times of hemorrhage or increased need for greater oxygen transport in the body, the spleen will eject some of its stired blood back into circulation.

Thymus

Thymus is a glandular lymphoid organ located in the mediastinum of the cranioventral thoracic cavity. Thymus is extremely important for maturation of specialized lymphocytes for the production of immunoglobulins (antibodies).The thymus is quite large in young, developing animals. As the animal age, the size and function of the thymus diminish. Consequently, the immune capabilities of a very young and of geriatric animals is compromised. The very young have not yet produced sufficient amounts of immunoglobulins, and geriatric animals no longer have the capacity to maintain sufficient antibody levels. This leaves these patients very susceptible to disease.

The location of the thymus gland differs in different animals. In mammals is located around the trachea at the level of the heart. Lying beneath the sternum (breastbone) and above the treachea (windpipe) and heart which is a small the two-lobed gland; each lobe is made up of LYMPHATIC tissue just behind the breastbone, and the soft, gelatinous tissue of the marrow deep within our long bones. In these primary lymphoid organs, lymphocytes grow and develop"In addition to the heart, the space between the lungs (mediastinum) contains the trachea, esophagus, thymus, large blood vessels, lymphatic vessels, and nerves. In newborn animal, the gland is small and grows with the animal until the onset of puberty then become small again.

Position of thymus

Lymph nodes and vessels

Lymph glands (lymph nodes) are located throughout the body. The peripheral lymph nodes that are clinically important for physical examinations in small animals are axillary lymph nodes, the precapular lymph nodes, the mandibular lymph nodes, the cervical lymph nodes, the popliteal lymph nodes and superficial inguinal lymph nodes. The mandibular, prescapular and popliteal lymph nodes should alwyas be palpated during PE of small animal patient. Retropharyngeal lymph nodes cannot be palpated. Lymph nodes are small, glandular structures that are partly responsible for the production of lymphocytes. Connected by network of lymphatic vessels, the lymph nodes are responsible for filtration of lymphatic fluid. Lymphatic fluid does not flow in response to pressure within lymphatic system. Lymphatic fluid is passively absorbed from the interstitium into the lymphatic vessels. One way valves keep the fluid flowing in one direction. Most pf the lymphatic fluid of the body wil enter the bloodstream via the thoracic duct. Generally, lymphatic fluid is transparent, colorless, watery substance.

Position of lymph nodes in a dog

Significant functions of LS

Edema

Excessive accumulation of interstitial fluid is clinically referred to as edema. If the lymphatic system is diseased in some way, it may not be able to accommodate the routine production and flow of the interstitial fluid. Absorption of fluid into the lymphatic vessels may be impaired because of obstruction. Many other mechanisms may contribute to edema formation. Some of those mechanisms include lymohatic disease, changes in osmotic pressure (hypoprotaenemia) changes in hydrostatic pressure and inflammation due to tissue trauma.

Inflammation

The edematous fluid serves to dilute cytotoxic agents as well as provide some protective cushioning of the area upon inflammation due to leaking of fluid from the vessles excessively into the interstitium.

Immunity

Immunogenic responses

Source: Veterinary Medical terminology 2nd ed D.E Christenson saunders elsevier