LYMPHATIC SYSTEM

Lymphatic system has to main parts: A network of delicate lymphatic vessels with lymph fluid, and lymphoid tissues and organs scattered throughout the body (Fig. 1). The immune system and lymphatic system have complementary roles in protecting the body against harmful agents or organism like bacteria and viruses. Lymphoid organs are responsible for producing and maturing specific immune cells called lymphocytes (Fig. 2). Lymphocytes are activated during immune response. Studying these cells and their interactions with immunity process is called immunology. In addition, lymphatic system is part of the circulatory system. 

1. Maintaining fluid balance in body by absorbing excessive interstitial fluid between tissues; by this role, it helps in delivering nutrients and oxygen to tissues and in eliminating wastes, pathogens, malignant cells, and toxins from all over body tissues and it carries it to the appropriate destinations like respiratory, urinary, digestive system or skin. 

2. Lymphatic system works on breaking down harmful wastes before they reach main vessels. 

3. It absorbs fats from digestive system and carries it into circulation via lymph. 

Any foreign body, that human’s immune system cannot recognize it, is called antigen (Fig. 3), like bacteria, viruses, toxins, malignant cells, and mismatched RBCs. Those antigens are broken down mainly by lymphocytes. There are two major types of lymphocytes: T cells and B cells (Fig. 4). They have both roles in acquired immune response. T cells are type of white blood cells, acts by attacking antigens directly, while B cells transfer into plasma cells which secrete antibodies. Antibodies act to immobilize antigens.

T-cells originate from bone marrow and mature in the thymus. When foreign body enters the body, T-cells secrete signals to initiate immune response called inflammation which stimulate production of phagocytes which dissolve the infective agent (Fig. 5). B-cells are also formed in bone marrow and circulate in blood until immune response is activated (Fig. 6). They differentiate into memory cells and plasma cells. Memory cells retain a memory of the foreign body, which lead to specify immune response against it. Plasma cells produce antibodies called immunoglobulins, that interact with pathogens, producing an infective response.

Lymph is pale transudative fluid derived from plasma. It is formed by leaking of interstitial fluid into lymphatics due to hydrostatic pressure (Fig. 7). An adult produces 3-4 liters of lymphatic fluid daily, and it forms approximately 10% of blood volume. Lymph consists mostly of water (95%), other components include proteins, minerals, fats, nutrients, damaged cells, cancer cells and pathogens, in addition to lymphocytes. This structure is not steady, lymph contents can vary according to different systems, for example, in the gastrointestinal system, the lymphatic fluid has a milk-like appearance because of the presence of cholesterol and other fat products.

Lymph nodes is a site of defense against infectious and malignant conditions. When an inflammation is initiated in a lymph node, it receives additional support from other lymphatic centers, that is why it becomes swollen and tendered. Anyway, in this case the enlargement is temporary and resolves. On the other hand, enlarged lymphatic nodes due to malignant activity would be permanent, especially if it is a cancer site due to lymph spreading cancer. 

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Lymph nodes are bean-shaped capsulated structures (Fig. 8), scattered all over the body. It is estimated that an adult will have approximately 800 nodes. The most common sites of lymph nodes are in the neck, axilla, thorax, abdomen, and groin. They are part of the primary lymphoid organs and serves as filters stations against microorganisms and debris. The lymph enters a lymphatic node via multiple afferent vessels, leaves via one or two efferent vessels. Lymph nodes is involved in infectious and malignant actions in the body because they contain T and B lymphocytes and other immune cells like macrophages. Lymphocytes work on destroying pathogens and macrophages filter foreign particles from lymph. Various noxious substances are exposed to immune cells in lymphatic nodes during circulation, which activate the nodes in order to initiate the function of immune cells and also get more perfusion thus more immune cells from other parts of the immune system. That is why a swollen lymphatic node is a sign of infection. In conclusion, lymphatic nodes have two major functions: Filtration – macrophages destroy microorganisms and debris and immune system activation – monitor for antigens and mount an attack against them.

They are part of lymphoid tissue, which represents the first defense against pathogens. Tonsils are small masses located in the wall of the pharynx. Four pairs of tonsils form Waldeyer's tonsillar ring. The most common are Palatine tonsils, they located on each side of the oral pharynx. Another pair of tonsils are Pharyngeal tonsils located on the top wall of the nasal pharynx. Lingual tonsils are on the surface tissue at the base of the tongue. Finally, tubal tonsils – surround the openings of the auditory tubes into the pharynx (Fig. 9).

it is located in the upper part of chest behind the sternum, in a space called mediastinum. This organ is degenerated in adults. It is most activated during immune maturity phase in puberty, where it would be larger in size. During infancy, thymus is located in the inferior neck and extends into the mediastinum where it partially overlies the heart. In adulthood, in eventually shrinks and atrophies. As we mentioned above, thymus is the center for T (for thymus) cells to mature. It secretes special hormones to achieve this function. T-cells is responsible for adapting immune response against different pathogens (Fig. 10). 

It is considered as the biggest lymphoid organ, and it is located in the left side of the abdominal cavity under the diaphragm and lateral to the stomach. It has reddish color and oval shape and fist size, and it is surrounded by thick connective tissue capsule. It receives a good amount of blood. Spleen is the primary filtering organ for blood. It detects abnormal or old cells and remove them in addition to initiate an immune reaction. The human spleen also probably works as blood reservoir, so it provides the body of blood in case of hemorrhage for example. Spleen functions include filtering blood, recycling damaged erythrocytes, supporting blood products by storing platelets and producing red blood cells during fatal life. Of course, as part of the lymphatic system, spleen stimulates the maturation and activation of lymphocytes and monitor immune response (Fig. 11). 

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While Blood is circulating in body, a portion of plasma leaks between tissue spaces, this is called interstitial fluid. This fluid combined with other molecules like proteins should be returned to the vascular system in order not to waste blood volume; this function is done by lymphatic vessels. lymphatic vessels are thin-walled structures that carry lymph (lymph Latin, lympha, meaning "water") all over the body. Lymph was formerly the interstitial fluid; hence, not draining extra fluids from tissues will accumulate them and cause edema. Edema could lead to compression of vessels and organs and finally cause serious medical conditions like infarctions. 

Anatomically, lymphatic vessels are divided into Superficial vessels and Deep vessels. These vessels pump lymph in one direction only towards bloodstream due to presence of valves that prevent backwards flow. Lymphatic capillaries which have permeable walls and are blind ended, gather and form lymphatic vessels. After that, vessels form lymphatic ducts, which in turn drain in two major lymphatics, right lymphatic duct and the thoracic duct. Right lymphatic duct drains most of the right upper quadrant whereas thoracic duct drains the lower body including abdomen.  

Lymph capillaries are similar to blood capillaries, but they are larger in diameter and have closed ends. They have remarkable ability to drain fluids, with minivalves formed by the overlapping endothelial cells. Minivalves act as one-way gates that permits fluids to enter capillaries but not leaking from them. During medical or malignant conditions like infections or cancers, capillaries carry pathogens and cancer cells, letting lymph nodes to eliminate them. 

There are two major lymphatics in body, right lymphatic duct and the thoracic duct. Right lymphatic duct drains most of the right upper quadrant whereas thoracic duct drains the lower body including abdomen. 

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Lymphomas are any malignant activity of the lymphatic system, usually in the lymph nodes, and it could be in other lymphoid organs. They appear as solid masses, involving both T and B lymphocytes. Diffuse lymphomas or extranodal lymphomas are aggressive form which invade other tissues such as brain, lungs, or kidneys. Lymphomas are generally divided into Hodgkin’s and non-Hodgkin’s lymphoma. Common signs and symptoms include painless swelling of lymph nodes, night sweating, unexplained weight loss, tiredness. The definite diagnosis is reached by examining the suspected specimen microscopically or applying other immunoassays. Many treatment options are available such as chemotherapy, radiation therapy, stem cell/bone marrow transplantation or immunotherapy.

Uncontrolled amplification of B lymphocytes causes Hodgkin’s Lymphoma. It is characterized by lymphadenopathy, splenomegaly and enlargement of other lymphatic organs. 

Non-Hodgkin’s Lymphoma or NHL is similar to Hodgkin’s Lymphoma and could be only distinguished by microscopic examination. NHL also is named after the involved lymphocyte, either B-cell lymphoma or T-cell lymphoma. 

Lymphadenitis is the inflammation of lymph node. It could be either localized that effects only the regional lymph nodes like in case of tonsillitis; or generalized due to a disease involves the whole body such as sepsis or upper respiratory tract infection. When a lymph node is inflamed, it enlarges and filled with pus. The overlying skin becomes red or streaky too. 

When fluids are not drained from tissues, this leads to accumulating them and cause lymphoedema. This condition happens sometimes temporarily. In the case of damaging lymphatic system, lymphoedema becomes chronic and long-lasting. It is more common in extremities because they are more prone to injuries. Primary lymphoedema refers to a dysfunction in the lymphatic system while secondary lymphatic system happens due to traumas or iatrogenic injuries. 

An enlarged spleen is also known as splenomegaly. Splenomegaly could happen due to malignancy and infectious diseases. 

It is the absence of normal spleen functions either anatomically or physiologically. 

The suffix (- ectomy) refers to surgical removal operation. Thus, Lymphadenectomy is he surgical procedure in which lymphatic node is removes and sent to examined pathologically. It is usually done as part of managing cancer. 

It describes the procedure in which proteins being separated and characterized, based on their reaction with antibodies. The test is used to detect an abnormal level of antibodies.

ELISA is stand for enzyme-linked immunoassay. It is an assay used to detect antibodies in the blood. Because antibodies are produced by immune system, this test helps in detecting immune response in body. For example, it could be used in analyzing antibodies to HIV antigens. Other substances detected are hormones and antigens. It works depending on the specific molecular weight of each substance. 

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  a. Thoracic duct

  b. Lymph duct

  c. Thoracic lymph duct

  d. Lymph capillary duct

  a. Spleen

  b. Thymus

  c. Bone marrow

  d. Lymph nodes

  a. Left subclavian vein 

  b. Right subclavian vein

  c. Inferior vena cava

  d. Primary lacteal 

  a. Axilla

  b. Neck

  c. Abdomen

  d. All the above

  a. Lymphomas

  b. Lymphadenitis 

  c. Lymphedema

  d. Lymphocytes