- Appearance- thin (not to be confused with arteries and veins)

- Function- to transport lymph fluid

- Appearance- Clear fluid, less protein than plasma

- Function- delivers the nutrients, oxygen, and hormones required by the cells

- E.g.- tonsils, thymus, spleen

- Function- immune responses

- Complex network of capillaries, thin vessels, valves, ducts, nodes, and organs

- Function: to return lymph to the systemic venous system, to maintain blood volume and fluid levels

- Lymph=excess interstitial fluid

- Interstitial fluid delivers the nutrients, oxygen, and hormones required by cells

- Lymph must be filtered to check for foreign or pathological materials (e.g. cancers, bacteria)

- System contains lymphocytes- these cells are essential to the immune response

- Blind ended capillaries present in most tissues- drain interstitial fluid from the surrounding extracellular matrix

- Capillaries run together to form larger vessels which deliver lymph into local ducts

- Walls act as one-way valves- when interstitial pressure rises, lymph is forced into vessels

- Pressure traps fluid in vessels and cannot escape

- The small intestine contains special types of lymphatic capillaries called lacteals

- Lacteals pick up not only interstitial fluid, but also dietary lipids and lipid-soluble vitamins

- The lymph of htis area has a milky color due to the lipid content- also called chyle

- Some vessels connect directly to lymphatic organs, called lymph nodes

- Small, encapsulated lymphatic organs that contain T and B cells

- Once filtered, the lymph exits the lymph node through these

- Lymph nodes can occur singularly or in groups

Receives lymph from upper left quadrant and from below diaphragm

Cisterna Chyli is the expanded inferior end of the thoracic duct located in the abdomen

- Located in both the lymphatic and cardiovascular systems

- Cells work together to elicit an immune response

- Search and destroy antigens

Any substances that are perceived as abnormal in the body (virus, cancers, bacteria)

- Retain memory of past encounters with a particular antigen; elicit a heightened response during subsequent encounters

- Allergies worsen with the increased frequency of exposures

-"Natural Killer Cells"; mature in bone marrow

- Comprise the small fraction (~2%) of the lymphcytes circulating in the blood that are neither T-cells or B-cells

- Called natural killer (NK) cells because they are already specialized to kill certain types of target cells, especially host cells that have become infected with a virus or have become cancerous

- Cells migrate through the lymphatic tissues and monitor them for the presence of antigens (proteins on cell surfaces)

- Foreign antigens stimulate the production of antibodies

- Some cells produce antibodies bind to and immobilize the foreign or abnormal agent- by binding/immobilizing, identifies it to other elements of the immune system

- Some cells attact and destroy the antigen directly

- Other cells become 'memory cells' that remember past antigen encounters- can initiate an even faster and more powerful response should the same antigen appear again

- 70-85% of body lymphocytes

- Plasma membrane contains a co-receptor that can recognize a particular antigen

- Several types of T-lymphocytes, each with a particular kind of co-receptor: 

- Helper T-lymphocytes

- Cytotoxic T-lymphocytes

- 15-30% of body lymphocytes

- Contain antigen receptors that respond to one particular antigen and cause the production of immunoglobulins (Ig), or antibodies, that respond to that particular antigen

- Five man classes of immunoglobulins are called IgG, IgA, IgD, IgM, and IgE

- These immunoglobulins are released by the specific B-lymphocytes to immobilize or neutralize specific antigens

- Also yield memory B-lymphocytes

- Some vaccines introduce mild or dead forms of an antigen

- Allows the body to fight and eliminate the illness before any symptoms ever develop; allow for the development of memory B-lymphocytes

- Depending upon the life span of the particular memory B-lymphocytes, the vaccine may provide temporary or lifelong immunity

- Large clusters of lymphatic cells and extracellular matrix that are not completely surrounded by a connective tissue capsule

- Multiple germinal centers with invaginated outer edges called crypts- crypts help trap material and facilitate its identificaiton by lymphocytes

- Pharyngeal tonsils (or adenoids) are in the posterior wall of the nasopharynx

- Palatine tonsils are in the posterolateral region of the oral cavity

- Lingual tonsils are along the posterior one-third of the tongue

- A bilobed organ located in the anterior mediastinum

- Maturation site for T-lymphocytes (T-cells)

- In infants and young children, it is quite large and extens into the superior mediastinum as well

- Continues to grow until puberty, when it reaches a maximum weight of 30-50 grams

- Cells of the thymus regress after puberty, and it is eventually replaced by adipose connective tissue

- In adults, it atrophies and becomes almost nonfuncitonal

- immune cell producer

- Largest lymphatic organ located in upper left quadrent of abdomen

- White pulp: initiates immune response when antigens detected in blood (antigen reseroir); phagocytizes bacteria and foreign materials

- Red pulp: reservoir for erythrocytes and platelets, phagocytizes old, defective erythrocytes and platelets

- Thymus loses ability to mature and differentiate T-lymphocytes

- New T-lymphocytes can be produced only by replication (mitosis)

- Helper T-lymphocytes do not respond to antigens as well, and do not always reproduce rapidly

- Fewer B-lymphocytes and other kinds of T-lymphocytes

- Overall result: ability to provide immunity and fight disease decreases; elderly are more suseptible to illness, sickness, and cancers