the lymphatic system. what is the lymphatic system? an extensive drainage network that helps keep...
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The Lymphatic System
What is the lymphatic system?
An extensive drainage network that helps keep bodily fluid levels in balance and defends the body against infections.
Together with lymphoid organs and tissues, provide the structural basis of the immune system
Lymphatic characteristics One way system to the heart
Carries clean fluids back to the blood
Drains excess fluid from tissues Lymph is a clear, watery fluid that
contains protein molecules, salts, glucose, urea, and other substances — throughout the body.
Removes antigens from the body and exposes antigens to the immune system Lymph may contain macrophages,
viruses, bacteria, cellular debris and even traveling cancer cells.
What type of vessels make up the lymphatic system?
Vessels are called lymphatics Thin walled and analogous to
veins
2 large ducts Right lymphatic duct Thoracic duct Both empty into the right and
left subclavian veins
Drained by the right lymphatic duct
Drained by thoracic duct
Lymph nodes Principal lymphoid organs of the body
Most are bean shaped organs along lymphatic collecting vessels Up to 1 inch in size
Grouped together at various parts of the body Clusters of both superficial LNs deep
Circulation in the lymph nodes
Lymph Enters via afferent
lymphatic vessels
Travels through large subcapsular sinus and smaller sinuses
Exits the node at the hilus via efferent vessels
Afferent vessels
Efferent vessels
Critical Thinking Question
Why are there more afferent lymphatic vessels carrying lymph to the lymph nodes than there are efferent lymphatic vessels?
Answer: Fewer efferent vessels, causing flow of lymph to stagnate,
allowing lymphocytes and macrophages time to carry out functions
What function do lymph nodes have?
Filter lymph macrophages destroy microorganisms and debris
Immune system—lymphocytes are activated and mount an attack against antigens
Spleen Largest lymphoid organ
Filters blood (lymph nodes filter lymph) Filters blood of bacteria, viruses, and other debris (blood-borne
antigens “white pulp” Removes and destroys worn out red blood cells (RBCs)
Stores platelets
Site of lymphocyte production and immune surveillance and response
In fetus only: RBC are made in the spleen
Susceptible to injury; splenectomy increases risk of bacterial infection
Thymus Differs from other lymphoid organs in important
ways It functions strictly in T lymphocyte maturation
T cells become Immunocompetent It does not directly fight antigens
Size with age In infants, it is found in the inferior neck and extends
into the mediastinum, where it partially overlies the heart
Increases in size and is most active during childhood
Stops growing during adolescence and then gradually atrophies
Critical Thinking Question Why does the thymus increases in size and is MOST active during
childhood, stops growing during adolescence and then starts getting smaller?
Answer: The thymus produces a large amount of T cells so by the time a
person reaches puberty, the body has a lot of lymphocytes. The thymus also produces a variety of hormones and plays an important role in the development of immunologic competence in fetus and child.
Tonsils Simplest lymphoid organs
Form a ring of lymphatic tissue around the pharynx
Crypts trap and destroy bacteria and particulate matter
Mucosa-associated lymphoid tissue (MALT)
Mucosal surfaces within the body are protected by the mucosal immune system consisting of the mucosa-associated lymphoid tissue or MALT
An extensive diffuse system of small concentrations of lymphoid tissue found in various sites of the body such as the gastrointestinal tract, thyroid, breast, lung, salivary glands, eye, and skin to protect from foreign matter.
MALT Examples:
GALT (gut-associated lymphoid tissue, such as the Peyer's patches in the lining of the small intestines, as well as the adenoids, tonsils, and appendix)
BALT (bronchial-associated lymphoid tissue in the bronchi)
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