1. 20
The Lymphatic System and Lymphoid Organs and Tissues

2. Returns fluids that leaked from blood vessels back to blood
Lymphatic System
Returns fluids that leaked from blood vessels back to blood
Consists of three parts
Network of lymphatic vessels (lymphatics)
Lymph – fluid in vessels
Lymph nodes – cleanse lymph
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3. Lymphoid Organs and Tissues
Provide structural basis of immune system
House phagocytic cells and lymphocytes
Structures include spleen, thymus, tonsils, lymph nodes, other lymphoid tissues
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4. General distribution of collecting lymphatic
Figure 20.2a The lymphatic system.
Regional
lymph
nodes:
Internal
jugular vein
Entrance of
right lymphatic
duct into vein
Cervical
nodes
Entrance of
thoracic duct
into vein
Axillary
nodes
Thoracic
duct
Cisterna
chyli
Aorta
Inguinal
nodes
Collecting
lymphatic
vessels
Drained by the right lymphatic duct
Drained by the thoracic duct
General distribution of collecting lymphatic
vessels and regional lymph nodes.
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5. Lymphocytes main warriors of immune system
Lymphoid Cells
Lymphocytes main warriors of immune system
Arise in red bone marrow
Mature into one of two main varieties
T cells (T lymphocytes)
B cells (B lymphocytes)
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6. T cells and B cells protect against antigens
Lymphocytes
T cells and B cells protect against antigens
Anything body perceives as foreign
Bacteria and bacterial toxins, viruses, mismatched RBCs, cancer cells
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7. Lymphocytes T cells B cells Manage immune response
Attack and destroy infected cells
B cells
Produce plasma cells, which secrete antibodies
Antibodies mark antigens for destruction by phagocytosis or other means
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8. Tonsils (in pharyngeal region)
Figure Lymphoid organs.
Tonsils (in pharyngeal
region)
Thymus (in thorax; most
active during youth)
Spleen (curves around
left side of stomach)
Peyer’s patches
(aggregated lymphoid
nodules in small
intestine)
Appendix
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9. Lymph Nodes
Functions
Filter lymph—macrophages destroy microorganisms and debris
Immune system activation—lymphocytes activated and mount attack against antigens
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10. Largest lymphoid organ
Spleen
Largest lymphoid organ
Served by splenic artery and vein, which enter and exit at the hilum
Functions
Site of lymphocyte proliferation and immune surveillance and response
Cleanses blood of aged cells and platelets, macrophages remove debris
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11. Photograph of the spleen in its normal position in
Figure 20.6c The spleen.
Diaphragm
Spleen
Adrenal
gland
Left
kidney
Splenic
artery
Pancreas
Photograph of the spleen in its normal position in
the abdominal cavity, anterior view.
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12. Important functions early in life
Thymus
Important functions early in life
Found in inferior neck; extends into mediastinum; partially overlies heart
Increases in size and most active during childhood
Stops growing during adolescence, then gradually atrophies
Still produces immunocompetent cells, though slowly
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13. Capsule Cortex Medulla Thymic corpuscles Figure 20.7 The thymus.
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14. Aggregates of Lymphoid Follicles
Peyer's patches
Clusters of lymphoid follicles
In wall of distal portion of small intestine
Similar structures are also found in the appendix
Peyer's patches and appendix
Destroy bacteria, preventing them from breaching intestinal wall
Generate "memory" lymphocytes
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