Draining excess interstitial fluid

Transporting dietary lipids

Lymphatic vessels:• In spaces between cells• Closed at one end, converge to form larger vessels (like veins) to trunks to right and left duct to venous blood• Contain valves to ensure

one way movement• Flow through lymph nodes (masses of B and T cells) Lymphatic capillaries:• Anchored by elastic filaments• Open and close with pressure differences

Lymphatic Organs & Tissues

• Divided into 2 groups– Primary lymphatic organs

• Sites where stem cells divide & become immunocompetent

• Red bone marrow, thymus

– Secondary lymphatic organs• Sites where immune response occurs• Lymph nodes, spleen, lymphatic nodules, etc.

Thymus:• Located between sternum and

aorta (mediastinum)• Two lobes divided into lobules• Cortex (outer layer) of

immature cells -T cells: antigenic activity:

-dendritic cells: assist maturation-epithelial cells: “educate” pre-T cells by positive selection-macrophages: clear debris

and dead cells • Medulla (inner layer) of mature

T cells, epithelial cells, dendritic cells, and macrophages

Lymph nodes: • Lymph flows in through afferent vessels and out through efferent vessels• Made up of nodules

-Primary nodules: B cells

-Secondary nodules: plasma cell and memory B cell formation

Spleen: • Located between stomach and

diaphragm• Contains white and red pulp

-White pulp: lymphocytes and macrophages around central arteries

-Red pulp: red blood cells, macrophages, lymphocytes, plasma cells,

and granulocytes• Removes worn out or

defective RBCs

• Stores platelet• Produces blood cells in

fetus

Lymphatic nodules: no capsule• Throughout mucus

membranes (MALT= mucosa-associated lymphatic tissue)

• Tonsils

Figure 12.6

Nonspecific Resistance/ Innate Defenses: born with and offer immediate protection• First line of defense- skin and mucous membranes

• Physical and chemical barrier

Inflammation

Figure 12.7

© 2012 Pearson Education, Inc.

Adaptive Defense System: Third Line of Defense•Three aspects of adaptive defense•Antigen specific—recognizes and acts against particular foreign substances•Systemic—not restricted to the initial infection site•Memory—recognizes and mounts a stronger attack on previously encountered pathogens

© 2012 Pearson Education, Inc.

Adaptive Defense System: Third Line of Defense•Cells of the adaptive defense system•Lymphocytes respond to specific antigens•B lymphocytes (B cells)•T lymphocytes (T cells)

•Macrophages help lymphocytes

© 2012 Pearson Education, Inc.

Adaptive Defense System: Third Line of Defense• Immunocompetent—cell becomes capable of responding to a specific antigen by binding to it•Cells of the adaptive defense system •Lymphocytes•Originate from hemocytoblasts in the red bone marrow•B lymphocytes become immunocompetent in the bone marrow (remember B for Bone marrow)•T lymphocytes become immunocompetent in the thymus (remember T for Thymus)

Figure 12.11, step 1a

Red bone marrow: site of lymphocyte origin

Primary lymphoid organs: site ofdevelopment of immunocompetence asB or T cellsSecondary lymphoid organs: site ofantigen encounter, and activation tobecome effector and memory B or T cells

Immature (naive)lymphocytes

Redbone marrow

KEY:

Figure 12.11, step 1b

Red bone marrow: site of lymphocyte origin

Primary lymphoid organs: site ofdevelopment of immunocompetence asB or T cellsSecondary lymphoid organs: site ofantigen encounter, and activation tobecome effector and memory B or T cells

Lymphocytes destined to become T cellsmigrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow.

Bone marrowThymus

Immature (naive)lymphocytes

Redbone marrow

1

KEY:

Figure 12.11, step 2

Red bone marrow: site of lymphocyte origin

Primary lymphoid organs: site ofdevelopment of immunocompetence asB or T cellsSecondary lymphoid organs: site ofantigen encounter, and activation tobecome effector and memory B or T cells

Lymphocytes destined to become T cellsmigrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow.

Immunocompetent but still naive lymphocytes leave the thymus and bone marrow. They “seed” the lymph nodes, spleen, and other lymphoid tissues, where they encounter their antigen and become activated.

Lymph nodes,spleen, and otherlymphoid tissues

Bone marrowThymus

Immature (naive)lymphocytes

Redbone marrow

1

2

KEY:

Figure 12.11, step 3

Red bone marrow: site of lymphocyte origin

Primary lymphoid organs: site ofdevelopment of immunocompetence asB or T cellsSecondary lymphoid organs: site ofantigen encounter, and activation tobecome effector and memory B or T cells

Lymphocytes destined to become T cellsmigrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow.

Immunocompetent but still naive lymphocytes leave the thymus and bone marrow. They “seed” the lymph nodes, spleen, and other lymphoid tissues, where they encounter their antigen and become activated.

Antigen-activated (mature) immunocompetent lymphocytes (effector cells and memory cells) circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body.

Lymph nodes,spleen, and otherlymphoid tissues

Bone marrowThymus

Immature (naive)lymphocytes

Redbone marrow

1

2

3

KEY:

Active immunity