The Lymphatic System 20

Lymphatic System: Overview The lymphatic system is: A network of lymphatic vessels and lymphoid tissues and organs scattered throughout the body Includes the lymph vessels, lymph nodes, spleen, thymus, tonsils and appendix

Lymphatic System Functions: Returns fluid and leaked plasma proteins back to the blood Lymph – interstitial fluid/plasma once it has entered lymphatic vessels Houses WBC that defend the body

Lymphatic System: Overview Figure 20.2a

Lymphatic System: Overview Figure 20.1a

the principal lymphoid organs of the body Lymph Nodes the principal lymphoid organs of the body Monitor cell debris in the lymph Their two basic functions are: Filters out debris monitor for antigens and mount an immune attack against them

Structure of a Lymph Node Figure 20.4a, b

Afferent lymphatic vessels Cortex: • Lymphoid follicle • Germinal center • Subcapsular sinus Efferent lymphatic vessels Follicles Trabecula Subcapsular sinus Hilum Medulla: Capsule • Medullary cord • Medullary sinus Medullary cords Medullary sinuses Trabeculae (a) Capsule (b)

Largest lymphoid organ, Functions Spleen Largest lymphoid organ, Functions Site of lymphocyte rapid growth White blood cells Immune surveillance and response Cleanses the blood

Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Peyer’s patches (in intestine) Appendix

Structure of the Spleen Capsule Trabecula Splenic cords Venous sinuses Red pulp White pulp Hilum Splenic artery Central artery Splenic vein Arterioles and capillaries (a) (b) Splenic artery Splenic vein Diaphragm Capsule Spleen Adrenal gland Left kidney White pulp Splenic artery Red pulp Pancreas (c) (d)

Additional Spleen Functions Stores breakdown products of RBCs for later reuse Spleen macrophages salvage and store iron for later use by bone marrow Stores blood platelets

Thymus organ that secretes hormones (thymosin) that cause T lymphocytes to mature functions strictly in the maturing of T lymphocytes does not directly fight antigens

Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Peyer’s patches (in intestine) Appendix

Thymic (Hassall’s) corpuscle Medulla Cortex

trap and destroy bacteria and particulate matter Tonsils Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx trap and destroy bacteria and particulate matter

Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Peyer’s patches (in intestine) Appendix

Aggregates of Lymphoid Follicles appendix: Destroy bacteria, preventing them from breaching the intestinal wall Generate “memory” lymphocytes for long-term immunity

Tonsils (in pharyngeal region) Thymus (in thorax; most active during youth) Spleen (curves around left side of stomach) Peyer’s patches (in intestine) Appendix