1. Lymphatic System Chapter 20

2. An Overview • One way system flowing towards heart • Functions • Return fluid and proteins to venous blood • House phagocytic cells and lymphocytes • Carry absorbed fats from intestines to blood • Components • Lymphatic vessels • Lymph • Lymph nodes

3. Lymphatic Vessels • Capillaries • Endothelial cells form minivalves • Inflammation increases permeability • Lacteals carry fat from intestines as chyle • Collecting Vessels • Similar to veins • Varies between individuals • Trunks • Lumbar • Bronchomediastinal • Subclavian • Jugular • Intestinal • Ducts • Right lymphatic • Thoracic • Cisterna chyli • Dump to venous blood

4. Lymph Transport • Low pressure system w/o a pump • Similar return as veins • Arterial pulsations • Tunica media smooth muscle contraction • Balances with blood fluid loss • Hydrostatic and colloid pressures (Chpt. 19) • ~ 3L every 24 hours • Rate increases w/activity

5. Lymphocytes • Primary fighters of immune response • Targets are antigens • T-cells – direct attack • Attack and destroy antigens • B-cells – indirect attack • Produce antibodies from plasma cells to ‘flag’ antigens

6. Other Lymphoid Cells • Macrophages • Phagocytic themselves • Activate T-cells • Dendritic cells • Capture and move antigens to lymph nodes • Activate T-cells too • Reticular cells • Fibroblast-like cells that form supportive network

7. Lymphoid Tissue • Proliferation & surveillance sites • Primarily reticular CT (except thymus) • Diffuse lymphatic tissue • Sparse scatterings in all lymph organs, • Concentrated in lamina propria of mucus membranes • Lymphoid follicles (nodules) • Spherically packed tissue w/o capsule • Larger organs and few isolated patches • Germinal centers where B cells proliferate • Enlarge w/ increased B cell division

8. Lymph Nodes • Main lymphatic organs • Located along lymph vessel path • Concentrated near large collecting vessel junctions • Inguinal region • Axillary region • Cervical region • Functions • Filtration • Macrophages prevent foreign molecule entrance to blood • Immune system activation • Monitor for antigens to fight

9. Lymph Node Structure • Dense fibrous capsularoutside • Difference b/w node and nodule • Invaginatesforming trabeculae • Regions • Medulla • Macrophages, T cells, B cells, and plasma cells • Lymph sinuses: capillaries where macrophages ‘hunt’ • Leaking antigens activate lymphocytes in tissue • Cortex • Dense nodules w/germinal centers • Transient T cells

10. Lymphatic Circulation • Enters node in afferent lymphatic vessels • Large subscapular sinus to smaller, cortical sinuses • Enter medulla • Exit at hilum via efferent lymphatic vessels • Fewer slows flow • Allows lymphocytes & macrophages to work

11. Spleen • Largest lymphatic organ • Functions • Lymphocyte proliferation and surveillance • Stores products of RBC breakdown and platelets • Cleanse blood • Remove aged/damaged blood, debris, and foreign matter • Fetal erythrocyte production (ceases after birth) • Distinct areas • White pulp w/lymphocytes act in immune functions • Red pulp w/worn out erythrocytes and pathogens

12. Thymus • Bilobed organ at base of neck • More pronounced when young • Corresponds w/importance of immune function • T lymphocyte maturation only • Lacks B cells • Doesn’t directly fight antigens • Thymocytes secrete thymosin and thymopoietin to signal T cell maturation

13. Tonsils • Lymphatic tissue ring around pharynx • Palatine: largest and most likely infected • Lingual • Pharyngeal (adenoids) • Tubal • Follicles w/germinal centers • Gather and remove pathogens from pharynx • Crypts are deep invaginations to trap and destroy • Tonsil stones • Produces ‘memory’ immune cells for future attacks

14. Mucosa-Associated Lymphatic Tissue (MALT) • Collections of lymphatic tissue to protect external environment openings • Peyer’s patches • In walls of small intestine • Destroy bacteria before it leaves intestines • Generate ‘memory’ lymphocytes • Appendix • Junction of small and large intestine • Similar function as Peyer’s patches • Lymphoidnodules • In walls of bronchi

15. Homeostatic Imbalances • Tonsillitis: inflammation of tonsils • Lymphangitis: vasa vasorum of lymph vessels congested w/blood • Lymphedema: blockage prevents return to blood • Buboes: inflamed lymph nodes • Splenectomy: removal of a ruptured spleen • Appendectomy: removal of appendix • Elephantiasis: lymph vessels clogged by worms causing increased swelling • Hodgkin’sdisease: malignant B-cells • Non-Hodgkin’slymphoma: any lymphoma, but Hodgkin’s