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
Lymphatic Organs
 Lymph nodes
 Spleen
 Thymus
 Tonsils
 Peyer’s patches
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
Lymph nodes
 Superficial
 Cervical
 Axillary
 Inguinal
 Deep
 Tracheobronchial
 Aortic
 Iliac
Circulation in the lymph nodes
 Lymph
Afferent
vessels
 Enters via afferent
lymphatic vessels
Efferent
vessels
 Travels through large
subcapsular sinus and
smaller sinuses
 Exits the node at the
hilus via 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
Lymphangiogram
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
Spleen
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 mucosaassociated 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)