Lymphatic System Chapter 20

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

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

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

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

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

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

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

Lymph Node Structure Dense fibrous capsular outside – Difference b/w node and nodule – Invaginates forming 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

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

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

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

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

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 Lymphoid nodules – In walls of bronchi

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’s disease: malignant B-cells Non-Hodgkin’s lymphoma: any lymphoma, but Hodgkin’s