The Anatomy and Physiology of Lymphatic System

Introduction

Lymphatic system comprises an extensive and complex vessel network (channels), and lymphoid tissues as well as organs in the vertebrate body. Inside the vessels is a fluid called lymph, which circulate throughout the body in connection to the normal circulatory system. However, unlike the circulatory system, it is a one-way (the lymph does not circulate in a loop like blood). The lymphatic system has a number of functions, but majorly useful in body's fluid balance, fat and fat-soluble nutrients' absorption, and protection from pathogens (immunity) (Marianne 1).

The body needs the lymph system because as blood circulates throughout the body, plasma fluid leaks into body tissues via thin-walled capillaries. These escaping blood plasma is known as extracellular fluids, and it contains glucose, oxygen, amino acids as well as other nutrients very crucial to the tissues (Marianne 1). The lymphatic system helps to remove this fluid from the tissues, and returns them via the lymphatic network to bloodstream, hence preventing a fluid imbalance that may lead to the death of organism.

The Anatomy of Lymphatic System

The lymphatic system consists of a network of lymphatic vessels, and lymphoid tissues and organs spread throughout the body.

Lymphatic Vessels

Consists of lymphatic capillaries and lymphatic vessels. The capillaries are tiny blind-ended sacs that originate from tissues and lie parallel to the blood capillaries (Marianne 2). They have a one-layered endothelial cells just comparative to blood capillaries, but more permeable to solvent as well as large solutes.

On the other hand, larger lymphatic vessel forms when the capillaries merge. They are like veins in structure; three layers (thinner), one-way valves, and lymph nodes at certain intervals along its path. Lymphatic system forms an elaborate network of drainage system that carries lymph (the excess tissue fluid) back into the general circulation. It reaches most of the body tissues.

Lymph resembles blood plasma but has fewer proteins, contains white blood cells (monocytes and lymphocytes), and its composition vary depending on the tissues and organs it drains. Unlike blood plasma that is pumped through the vessels, lymph is squeezed through the same during the use of muscles. The lymphatic vessel has walls and valves to control the lymph movement. The valves also help in preventing fluid from going towards a wrong direction (Marianne 3). Lymph is progressively drained towards larger vessels till it reaches the lymphatic ducts, from where the filtered fluid returns to blood circulatory system.

Lymphoid Tissues and Organs

The lymphatic tissues and organs include the lymph nodes, tonsils, thymus gland, and spleen.

The lymph nodes/lymph glands: They small, oval to bean-shaped bumps scattered along the lymphatic vessels. They can be found either in groups or individually. The grouped lymph nodes are majorly found in the groin (inguinal nodes), armpit (axillary nodes), and neck (cervical nodes) whereas the individual ones are scattered in the entire body.

The structure of a lymph node is such that it has a reticular connective tissue within it, which consists of reticular fibers (a netlike, thin collagen fibers), microphages, and lymphocytes (B cells and T cells). The lymph nodes helps in filtering the lymph of debris (microorganisms and dead cells), alerts immune system to fight pathogens, and forms white blood cells (Marianne 5).

Tonsils: They are small masses of lymphatic tissues embedded in the mucosa membranes of pharynx (throat) and the oral cavity. The tonsils are covered by crypts (epithelium with deep pits), which are often exposed to dead white blood cells, bacteria, and food debris (MacGill 2).

There are three key kinds of tonsils. They are:

• Pharyngeal tonsils or the adenoids - unpaired and located on the wall of nasal pharynx.
• Palatine tonsils - paired and located at the posterior margin of oral cavity. Prone to infection and can be treated using antibiotics or may have to be removed through tonsillectomy.
• Lingual tonsils - they are paired and located on both sides of the base of the tongue.

Tonsils are structured in a way that they contain reticular connective tissues with fibers, lymphocytes, and macrophages. Its major function is to trap and destroy any bacteria and other pathogens that enter the pharynx and throat from inhaled air or ingested substances. Tonsils have external structures/folds called crypts, which trap pathogens in air, liquid, or food that come in contact with tonsils. The pathogens that, by any chance, move deeper into the reticular tissue within tonsils, are destroyed by the macrophages and lymphocytes (MacGill 3).

Spleen: The largest among the lymphatic organs, and is located just beneath the diaphragm on the left side of the body. Spleen filters blood, and, therefore, it is a soft organ and rich in blood.

Spleen filters blood of pathogens and bacteria following the same process lymph nodes go through to filter lymph. Blood gets into spleen through splenic artery, and moves into reticular connective tissues forming white and red pulps. During this movement, the lymphocytes and macrophages destroy any bacteria and pathogen that get caught in the reticular fibers. Finally, the filtered blood from the white and red pulp into the splenic vein drawing it away from the spleen.

Spleen also destroys the worn out blood cells with the help of macrophages through the process of phagocytosis. Finally, spleen also acts as a blood reservoir, and is able to stabilize blood volume by transporting surplus plasma from blood circulatory system to lymphoidal system.

Thymus gland: This organ is unpaired and covers just above the heart. The T cells (that target infections and pathogens) mature and undergo specialization in this gland. Therefore, the organ play a significant role in setting up body's immune system (MacGill 3). It is the source of lymphocytes serving the nodes, vessels, and spleen before birth. However, after birth, the thymus secretes hormone that allows lymphocytes (white blood cells) to advance into plasma cells. This organ degenerates with time as it completes its essential function by the end of childhood. It is largest at youth, especially puberty, and as adulthood sets, it gets replaced with adipose tissues.

The thymus glands mainly consists of T lymphocytes. Immature T cells are produced in the red bone marrows, released into the blood, and then migrate to the thymus gland for maturity. The thymosins in the glands play the role of maturing the T cells, which then move back into the blood as well as lymphatic organs to fight pathogens.

The Physiology of Lymphatic System

The anatomy of this system is structured in a manner that enhances its normal functions of fluid balance, absorption, and body immunity.

Fluid Balance

The body is majorly composed of fluid within cavities and tissue spaces, and in the tiny spaces around cells (interstitial spaces). The lymphatic system has vessels and lymph capillaries that can reach these areas and drain any excess fluid back to the veins. Therefore, the lymphatic system helps to maintain fluid balance by returning excess proteins and fluids from tissues. The leaked fluids cannot be able to return through the blood vessels. The lymphatic system drains back approximately 10% of the plasma to blood vessels (Rizzo 357). Two to three liters of fluid is returned on a daily basis, including the large proteins that may not be transported via the blood circulatory systems. The tissues would swell, blood pressure would increase, and blood volume would reduce in the absence of lymphatic system to drain the excess fluid.

Fat Absorption

The lymphatic system enables absorption of fat from intestines to the blood via lacteals, the special lymphatic capillaries. The tiny lacteals forms part of the villi along the gastrointestinal tract. They are capable of absorbing fats-soluble vitamins and fats hence forming chyle, a milky white fluid. The chyle contains emulsified fats and lymph. The lacteals therefore delivers nutrients indirectly as it drains the chyle into the venous blood circulation. The blood capillaries, however, take up the rest of the nutrients directly (MacGill 3).

Body Immunity

Lymphatic system defends the body against bacteria and pathogens and without them the organism would perish very soon from infections. The bodies are normally exposed to hazardous micro-organisms, potential to cause infections (MacGill 3). The skin, toxic barriers, and friendly bacteria are the body's first defense. However, the pathogens that succeed in penetrating into the body are often neutralized by the help of the lymphatic system, which enables the appropriate response of the immune system.

The lymphatic system has white blood cells known as lymphocytes, which are of two types; the T lymphocyte cells and B cells. These cells travel within the lymphatic system and as they reach the lymph nodes, they get filtered and, on contact with the bacteria, viruses, and other pathogens, they get activated. The activated lymphocytes are called antigens, forming antibodies that defend the body (MacGill 3). Usually, lymph nodes are more grouped in the armpits, groin, and neck, and during a body defense in response to illness, these areas tend to develop the swollen glands. The first encounter of lymphocytes with pathogens is at the lymph nodes, where they initiate their defensive response.

The activated lymphocytes (white blood cells) then get transported up the lymphatic system before reaching the blood stream. Once in the blood circulatory system, they are able to spread the immune response throughout the body. The action of lymphocytes in the lymphatic system forms an adaptive immune response, which is specific and provides a long-lasting prevention of particular pathogens (Marianne 4).

Conclusion

In summary, body immunity entails lymphocytes differentiation and activation. The process include immunocompetence, activation, and circulation. In immunicompetence, the cells destined to be T cells move from bone marrow to thymus, mature and develop immunicompetence there, On the other hand, the B cells develop immunocompetence in the bone marrow. Second, after B cells and T cells leaving the bone marrow and thymus respectively as inactive cells, the get activated when they come in contact with the pathogens in the infected connective tissues (Rizzo 357). This process occurs as a result of the antigen challenge. Finally, the mature lymphocytes (activated) circulate continuously in the lymph and blood stream, and throughout the lymphoid tissues and organs of the body.

Works Cited

MacGill, Markus. "Lymphatic System: Definition, Anatomy, Function, and Diseases." Medical News Today, MediLexicon International, 23 Feb. 2018, www.medicalnewstoday.com/articles/303087.php.

Marianne, Belleza. "Lymphatic System Anatomy and Physiology: Study Guide for Nurses." Nurseslabs, Nurseslabs, 23 Sept. 2017, nurseslabs.com/lymphatic-system-anatomy-physiology/.

Rizzo, Donald C. Fundamentals of anatomy and physiology. Cengage Learning, 2015.