Lymphatic system

Lymphatic System• Consists of organs, ducts, and nodes. It transports a

watery clear fluid called lymph. This fluid distributes immune cells and other factors throughout the body. It also interacts with the circulatory system to drain fluid from cells and tissues. The lymphatic system contains immune cells, which defend against infection and protect the body

Main functions of lymphatic system: • to collect and return interstitial fluid, including plasma

protein to the blood, and thus help maintain fluid balance,

• to defend the body against disease by producing lymphocytes,

• to absorb lipids from the intestine and transport them to the blood.

Lymphatic System and Immunity

• Network of vessels that assist circulating body fluids• Aids in maintaining blood volume, returns fluid to

the blood• Closely associated with the circulatory system• Organs of lymphatic system defend against

infection• Removes antigens from body• Exposes antigens to immune system

Pathways• 1. Lymphatic capillaries -microscopic, closed-

ended tubes• Extend into interstitial spaces and form

complex networks that parallel blood capillary networks

• Consist of a single layer of endothelium designed to allow tissue fluid from interstitial spaces to enter

• Lymph capillaries located in the small intestine is known as lacteals

• Fluid inside the capillary is called lymph

Pathways continued

• 2. Lymphatic vessels-similar to vein walls but thinner

• Consist of an endothelial lining, a middle layer of smooth muscle and elastic fibers, and an outer layer of connective tissue

• Also have semilunar valves that prevent backup of fluids (just like veins)

• Larger lymphatic vessels lead to lymph nodes

Pathways continued

• 3. Lymphatic trunks and collecting ducts• Trunks drain lymph from lymphatic vessels

and are named for the area they serve• Lumbar trunk drains the lymph from lower

limbs, lower abdominal wall, and pelvic organs

• Subclavian trunk drains the upper limbs• Lymphatic trunks joint one of two collecting

ducts

4. Collecting ducts• Thoracic duct is larger and longer

• Begins at abdomen and passes through diaphragm• It empties into the left subclavian vein and drains

lymph from intestinal, lumbar, and intercostal trunks, left subclavian trunk, left jugular trunk, and left bronchomediastinal trunks

• Right lymphatic duct is smaller and originates in right thorax at union of right jugular, right subclavian and right bronchomediastinal trunks • It empties into the right subclavian vein

• Cisterna Chyli – receives lymph from digestive organs

What’s next?

• After leaving the two collecting ducts, lymph enters blood stream and becomes part of the plasma

• Lymph from lower body regions, left upper limb, and left side of head and neck enters thoracic duct

• Lymph from right side of head and neck, right upper limb, and right thorax enters right lymphatic duct.

• p. 354, Figure 12.2

Lymph is returned to venous system through:•Right Lymphatic duct – drains lymph from right arm and right side of head and thorax•Thoracic duct – receives lymph from rest of body•Both ducts empty into the subclavian vein on their side of the body

Tissue fluid formation

• Lymph has the same composition as plasma except it doesn’t have plasma proteins

• Filtration from plasma exceeds reabsorption leading to net formation of tissue fluid

• This increases hydrostatic pressure of tissue fluid, and favors the movement of this fluid into the lymphatic capillaries, forming lymph.

Lymph function

• Lymphatic vessels in small intestine play a major role in absorption of dietary fats

• Lymph returns to the blood stream most of the small proteins that the blood capillaries filtered

• Lymphatic capillaries are specially designed to receive proteins and foreign particles

Lymph movement• Movement of lymph throughout the body assisted

by:• “Skeletal muscle pump” – contraction of skeletal

muscles against the lymphatic vessels• Smooth muscle contraction• Valves in lymphatic vessels• “Respiratory pump” – pressure changes when

breathing• Obstruction of system leads to edema (abnormal

accumulation of fluid in body tissues/parts)

Lymph nodes

• Contain large numbers of macrophages and lymphocytes that fight invading pathogens

• Nodes are surrounded by a capsule, which extends inside and partially subdivides the node into nodules which are the structural units of the node

• Function of nodes is to filter potentially harmful particles from lymph and to monitor body fluids, “immune surveillance”

• Nodes and red bone marrow are the centers for lymphocytes production

• Various shapes and sizes, often kidney shaped

• Lymph passes through several nodes in filtering process

central area

-indented region

-fewer efferent vessel than afferent vessel which slows lymph flow allowing more time to filter

-divide nodes into compartments

“in transit” – circulate continuously

Cortex – outer region of node, contains the germinal cells

Locations of lymph nodes

• Cervical region• Axillary region• Supratrochlear region-medial side of the

elbow• Inguinal region• Pelvic cavity• Abdominal cavity• Thoracic cavity

Lymphatic tissue• Clusters of lymphocytes in the connective tissue

of mucous membranes and various organs

• Diffuse lymphatic tissue is scattered in body passages that open to the exterior and is called mucosa-associated lymphatic tissue or MALT• In respiratory it may be called BALT (brochus

associated)• In digestive it may be called GALT (gut

associated)

Lymphatic tissue• In some places lymphocytes and macrophages

congregate into masses called lymphatic nodules (come and go as you get infections.)• In distal portion of small intestine they form

clusters called Peyer’s patches.• In some places these nodules are always

present (tonsils, lymph nodes, appendix)• Tonsils – three pairs of enlarged lymph nodes in the

pharynx• Pharyngeal tonsils (adenoids) – back of the sinuses• Palatine tonsils – in palate that separates the nasal

and oral cavities• Lingual tonsils – base of tongue

Lymphatic tissue• Appendix - function appears to expose white blood

cells to a variety of antigens, or foreign substances, present in the gastrointestinal tract, helps to suppress potentially destructive antibody responses while promoting local immunity.

http://www.scientificamerican.com/article.cfm?id=what-is-the-function-of-t

Lymph organs

• Thymus gland-located above the heart in the mediastinum and produces T lymphocytes

• Thymus is largest in childhood and shrinks with age

• Spleen is the largest lymphatic organ and filters blood to protect against infections• White pulp in spleen contains many lymphocytes• Red pulp in spleen contains red blood cells and

lymphocytes and macrophages

Body Defenses• 1st Line of Defense – Non-Specific Barriers

• Prevention of pathogens entering the body• Skin and mucus membranes (includes skin, tears, saliva, gastric

juices and mucus membranes)• 2nd Line of Defense - Non-Specific -Leukocytes

• Killing the pathogen that enters body by phagocytic action• Inflammatory response – phagocytes move to infected area, due

to stimulation by chemicals released by damage cells. Phagocytes engulf pathogen and digest it

• P. 359 text• 3rd Line of Defense – Specific Immune Response

• Killing the pathogen by antibody action• Immune response system – lymphocytes release antibody in

response to presence of antigen

Nonspecific Immune Responses • 1 - Inflammation - response to tissue injury

serving to defend against foreign invader; redness, heat, swelling, pain

• 2 - Interferon - group of proteins that defend against viral infection; prevents replication of virus in other host cells

• 3 - Natural killer cells - lymphocyte-like cells that rather nonspecifically lyse & destroy virus-infected cells & cancer cells

• 4 - The complement system - inactive plasma proteins that, when activated, destroy foreign cells; “complement” the work of antibodies

Nonspecific Immune Responses: Inflammatory Response

Specific Immune Responses• Often more effective than nonspecific response• Specific response begins due to presence of an

antigen• Selective attack aimed at "target" following prior

exposure • Two classes of responses:

• Cell-mediated immunity - activated T lymphocytes

• Humoral immunity - antibodies produced by B lymphocytes

Cell Mediated vs. Humoral Immunity

Cell Mediated• The lymphocytes –

Cytotoxic T-Cells (killer T-cells) themselves defend the body by injecting or destroying infected cell

• Killer T-cells also produce T memory cells which "remember" a specific protein or antigen.

Humoral(antibody-mediated system)

• Protection provided by antibodies present in “humors” – fluids

• binding activates lymphocytes to undergo clonal selection to produce plasma cells or memory cell• plasma cells manufacture quantities of

antibodies (Immunoglobulins - Ig) that bind to the foreign invader (the antigen) and prime it for destruction.

• B memory cells retain a "memory" of the specific antigen that can be used to mobilize the immune system faster if the body encounters the antigen later in life. These cells generally persist for years.

Two separate but overlapping arms of immunity

A response to an agent against which the body has already

formed memory cells is called a secondary response. All other

responses are primary responses.

Antibodies/Immunoglobulins• Antibodies/Immunoglobulins are proteins that bind to

specific antigens. B cells, located in lymphoid tissue, release the antibodies, which then circulate in the blood plasma, lymph, or extracellular fluids.

• Some antibodies migrate to other areas of the body, such as the respiratory tract or the placenta, or enter various body secretions, such as saliva, sweat, and milk

• There are five classes of antibodies (or immunoglobulins): IgA, IgD, IgE, IgG, and IgM.

• Antibodies bind to antigens, thus forming an antigen-antibody complex. This complex attracts macrophages, which will phagocytize any foreign substance that has that specific antigen-antibody complex.

Immunoglobulins (Ig) (MADGE)• IgG-80% of antibody, activates complement,

crosses placenta to protect fetus, active against bacteria and viruses

• IgA-13%, found in breast milk, tears, and other fluids, most common in mucosa

• IgM-6 %, develops in plasma (anti-A and anti-B antibodies), also activates complement, reacts usually on first exposures

• IgD, found on most B cells, important in activating B cells

• IgE, associated with allergic reactions (hay fever, asthma, hives)

Lymphocytes

Types of Immunity• Natural Acquired Immunity

• Active – immunity acquired by exposure to disease (antibodies) , last for years and sometimes for life

• Passive – acquired naturally by fetus through passage of antibodies form mother through placenta or breast milk, temporary

• Artificial Acquired Immunity • Active - vaccines, immunizations, dead or weaken

pathogen injected into body to produce antibodies• Passive– injection of antibodies from another

person or animal, short term

Self vs. Nonself cells• Key to a healthy immune system is its ability to

distinguish between the body’s own cells, recognized as “self,” and foreign cells, or “nonself.” • Body’s immune defenses normally coexist

peacefully with cells that carry distinctive “self” marker molecules.

• When immune defenders encounter foreign cells or organisms carrying markers that say “nonself,” they quickly launch an attack.

Self vs. Nonself cells• Major Histocompatibility Complex (MHC) (also

called human leukocyte antigens, HLAs) is the mechanism by which the immune system is able to differentiate between self and nonself cells. MCH generates markers on the plasma membrane.

• MHC is a collection of glycoproteins (proteins with a carbohydrate) that exist on the plasma membranes of nearly all body cells

• proteins of a single individual are unique, its extremely unlikely two people will possess cells with the same set of MHC molecules (except for identical twins)

Self vs. Nonself cells • Immunocompetence – the ability of body’s

immune cells to recognize (by binding) specific antigens• Lymphocytes develop tolerance for self-antigens• Lymphocytes once immunocompetent only react to

one distinct antigen• Lymphocytes become immunocompetent before

meeting antigens they may later attack• It is our genes that determine what specific foreign

substance our immune system will be able to recognize and resist

• P. 363-364 text

Self vs. Nonself cells

• In abnormal situations, the immune system can mistake self for nonself and launch an attack against the body’s own cells or tissues. The result is called an autoimmune disease (MS, Rheumatoid arthritis, Type I Diabetes, Autoimmune thyroid disorders, Crohn’s, Lupus)

Immune System Protection• Immune system protects against infection,

but also against other antigens• Blood group antigens• Tissue antigens (i.e., graft rejection)

• For successful organ graft, immune system must be suppressed

• Transplanted tissue must be cleared of immune cells, too

• Treatment usually requires some form of immunosuppression therapy.

Four major types of grafts

• Autograft – tissue grafts transplanted from one site to another in the same person

• Isograft – tissue grafts donated be a genetically identical person, twin

• Allograft – tissue grafts are taken from an in related person

• Xenograft – tissue grafts harvested from a different animal species, such as transplanting a baboon heart into a human heart.

Summary• The lymphatic system helps maintain homeostasis of

fluids, and also helps remove antigens from the body

• The immune system consists of barriers (physical and chemical) and specific and nonspecific mechanisms to eliminate antigens

• “Immune cells” are blood cells. Some circulate in the blood and can then migrate into tissues at site of injury. These include neutrophils and macrophages.

Summary• All blood cells arise in the bone marrow. B

lymphocytes initially develop in the bone marrow and then migrate to lymphoid tissues (esp. lymph nodes and spleen) T lymphocytes develop in the thymus

• B cells produce antibodies, which interact with antigen to help eliminate it.

• Helper T cells regulate the immune response; cytotoxic T cells kill virus-infected cells and probably tumor cells. (They also are responsible for transplant rejection.)

Summary

• B and T cell response is antigen-specific and has “memory” (second response is faster and stronger than the first)

• Immune system can be overly responsive to antigens (hypersensitivity/allergy) or can mistakenly be directed against self antigen (autoimmunity)

• Immune deficiencies leave people vulnerable to infection

Review Questions:• 1. All of the following belong to the lymphatic system EXCEPT

A. lymph.B. lymphatic vessels.C. red bone marrow.D. yellow bone marrow.

• 2. Which of the following cells produce antibodies?A. T-lymphocytesB. B-lymphocytesC. monocytesD. Phagocytes

• 3. Lymph nodesA. are bean-shaped organs.B. are located along lymphatic vessels.C. are scattered throughout the body.D. All of the above.

Review Questions:• 4. Worn-out and damaged red blood cells are destroyed in the

A. thymus gland.B. tonsils.C. spleen.D. lymph nodes

• 5. The first line of defense against disease-causing organisms isA. cell-based immunity.B. production of antibodies.C. inflammation.D. the intact skin.

• 6. Complement proteinsA. are found in blood plasma.B. are present in infected cells.C. are produced by T-cells.D. are produced by B-cells

Review Questions:• 7. All of the following are symptoms of inflammation EXCEPT

A. painB. rednessC. feverD. Swelling

• 8. Which of the following can act as an antigen?A. bacteriaB. virusesC. foodD. All of the above.

• 9. Vaccination is an example ofA. naturally acquired active immunity.B. naturally acquired passive immunity.C. artificially acquired active immunity.D. artificially acquired passive immunity

Review Questions:• 10. Cell-mediated immunity is provided by

A. macrophages.B. basophils.C. T-cells.D. B-cells.

• 11. One of the functions that the lymphatic system performs is to return excess __________fluid to the blood.

A. ClearB. InterstitialC. Red-coloredD. thoracic

Review Questions:• 12. Lymph nodes are widely distributed throughout the body along the lymphatic pathways

where they filter _______before it is returned to the ________.A. lymph, bloodB. lymph, heartC. blood, heartD. blood, lymph

• 13. Lymph enters a lymph node through __________, filters through ________, and leaves through ________.

A. efferent vessels, afferent vessels, sinusesB. sinuses, afferent vessels, efferent vesselsC. afferent vessels, sinuses, efferent vesselsD. afferent vessels, efferent vessels, sinuses

Review Questions:• 14. The tonsils that are located near the opening of the oral cavity that separates the nasal and

oral cavities• A. lingual

B. pharyngealC. palatineD. Oral

• 15. The thymus also produces a hormone,___________ , that stimulates the maturation of lymphocytes in other lymphatic organs.

A. oxytocinB. thymosinC. calcitonin

D. estrogen

Review Questions:• 16. The lymphatic system absorbs __________ from the digestive

system. A. lipidsB. lymphC. nutrientsD. Proteins

• 16 A. What is the name of the specialize lymph capillaries in the digestive system?

• 17. All the lymph that is collected returns to venous circulation by entering into the __________.

A. CapilliariesB. lactealsC. right and left subclavian veinsd. lymphatic ducts

Review Questions:• 18. Which is the only cell that does not mature in the bone

marrow?A. T cellsB. B cellsC. macrophagesD. neutrophils

• 19. Fluid that passes through the lymphatic vessels?A. Flows toward the lungsB. Passes from the lymphatic vessels into the arteriesC. Enters the left ventricle of the heart through the right

thoracic ductD. Moves in a single direction toward the heart

Review Questions:• 20. Peyer's patches are aggregates (collections) of lymphatic

nodules found in the area of the __________.A. tonsilsB. appendixC. ileum of the small intestineD. thymus gland

• 20A. Peyer’s patch is an example of what type of tissue and where is another location it can be found?

• 21. Which of the following would be considered a nonspecific barrier?A. skinB. feverC. NK cellsD. T cells

Review Questions:• 22. Vasodilatation is part of the second line of defense because it results in

greater flow of WBCs to the infected site. What chemical causes the vessels to dilate?A. histamineB. postaglandinC. complement proteinsD. interferons

• 23. A fever is considered to be a __________ defense. A. specificB. nonspecificC. nonspecific barrier

Review Questions:• 24. Where are the major histocompatibility complex

molecules located?A. in the plasma of bloodB. on the cell membraneC. in the interstitial fluidD. in the cell nucleolus

• 25. Which of the following types of immune responses involves antigens binding directly to the B cells causing the production of antibodies?A. APC immunityB. humoral immunityC. cell-mediated immunityD. Nonspecific immunity

Review Questions:• 26. Which of the following antibodies are involved in causing

basophils to release histamine ( as in the case of an allergic reation)?A. IgAB. IgGC. IgED. IgM

• 27. The process of transferring antibodies from mom to baby is known as __________ immunity. A. activeB. passiveC. antibioticD. immunizations

Review Questions:• 28. Vaccines work to prevent a person from getting a specific

virus during the flu season because the vaccine stimulates the __________. A. first line of the body’s defensesB. activity of T cellsC. production of memory B cellsD. Production of NK cells

• 29. The immune system’s loss of its ability to distinguish “self” from “nonself” results in :

A. Autoimmune diseasesB. Immune response diseasesC. Immunodeficiency diseasesD. Cell-mediated immune deficiency diseases

Review Questions:• 30. All the following are important functions of the lymph

nodes except:A. They serve as sites for production of antibodiesB. They remove foreign material phagocytized by macrophagesC. They are the sites where antigens stimulate the immune systemD. They function in the production of neutophils, eosinophils and basophils

• 31. Lymphocytes that develop immunocompetence in the thymus are:A. B lymphocytesB. T lymphocytesC. MacrophagesD. Plasma cells

Review Questions:

32. The movement of fluid through the lymphatic vessels is assisted by:

A. Pressure from the right ventricleB. Pressure of contracting skeletal musclesC. Movement of phagocytes such as macrophagesD. Movement of red blood cells