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
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–
–
–
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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
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–
–
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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