Chapter 24 Lymphatic System

Function of Lymphatic System Transport excess interstitial fluid, called lymph in lymphatic system interstitial fluid is fluid around cells; extracellular fluid includes interstitial fluid and blood plasma Maintain fluid homeostasis Check lymph for foreign material Initiate immune response

Structure of Lymphatic System Fig. 24.2 Structure of Lymphatic System (a) Capillary bed and lymphatic capillaries Arteriole Tissue cells Lymphatic capillaries Interstitial fluid Capillary bed Venule Lymph vessels absorb excess fluid around capillary beds arterial end of capillary bed forces fluid into interstitial space around cells venous end of capillary bed reabsorbs most but not all fluid Lymph vessels transport lipids and lipid- soluble vitamins from gastrointestinal tract around body

Structure of Lymphatic System Fig. 24.2 Interstitial fluid Capillary bed Venule Structure of Lymphatic System Anchoring filament Lymphatic capillaries Lymph Tissue cells Opening Arteriole Interstitial fluid Endothelium of lymphatic capillary (a) Capillary bed and lymphatic capillaries (b) Lymphatic capillary Lymphatic capillaries are closed-end vessels interspersed through capillary beds (except in red bone marrow and CNS) Larger diameter than blood capillaries; similar structure Held in place by anchoring filaments

Structure of Lymphatic System Fig. 24.3 (b) Lymphatic vessel, cross section (a) Lymphatic vessel, longitudinal section Overlapping endothelial cells Structure of Lymphatic System Valve open (lymph flows forward) Lymph Direction of lymph flow Valve closed (backflow of lymph is prevented) LM 100x Valve Lymphatic vessel Lymphatic capillaries merge into lymphatic vessels Vessels have valves (like veins); prevents pooling of lymph Lymph from GI tract is white because of fats, called chyle b: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser

Structure of Lymphatic System Fig. 24.1 Structure of Lymphatic System Tonsils Afferent lymphatic vessels bring lymph to lymph node for filtering Efferent lymphatic vessels take filtered lymph from lymph nodes Lymph may pass through several lymph nodes in a cluster Cervical lymph nodes Right lymphatic duct Axillary lymph nodes Thymus Thoracic duct Spleen Cisterna chyli Mucosa-associated lymphatic tissue (MALT) (in small intestine) Inguinal lymph nodes Red bone marrow Lymph vessels

Lymphatic trunks Drain lymph from major body regions Fig. 24.4 Right jugular trunk Left internal jugular vein Right subclavian trunk Left subclavian vein Right lymphatic duct Lymphatic trunks Right bronchomediastinal trunk Left bronchomediastinal trunk Drain lymph from major body regions Formed from merging vessels Superior vena cava Thoracic duct Lymph nodes Azygos vein Hemiazygos vein Parietal pleura (cut) Diaphragm Cisterna chyli Inferior vena cava Left lumbar trunk Intestinal trunk Right lumbar trunk (a) Posterior thoracic wall, anterior view

Lymphatic trunk drainage Right jugular trunk Left internal jugular vein Right subclavian trunk Left subclavian vein Right lymphatic duct Right bronchomediastinal trunk Left bronchomediastinal trunk Jugular trunk; head and neck Subclavian trunk; upper limbs, breasts, superficial thoracic wall Bronchomediastinal trunks; deep thoracic structures Intestinal trunks; most abdominal structures Lumbar trunks; lower limbs, abdominopelvic wall, pelvic organs Superior vena cava Thoracic duct Lymph nodes Azygos vein Hemiazygos vein Parietal pleura (cut) Diaphragm Cisterna chyli Inferior vena cava Left lumbar trunk Intestinal trunk Right lumbar trunk (a) Posterior thoracic wall, anterior view Fig. 24.4

Lymphatic ducts Larger than trunks Right jugular trunk Left internal jugular vein Right subclavian trunk Left subclavian vein Right lymphatic duct Right bronchomediastinal trunk Left bronchomediastinal trunk Larger than trunks Lymphatic trunks drain into lymphatic ducts Lymphatic ducts drain lymph into venous circulation Cisterna chyli located at base of thoracic duct receives lymph from left and right intestinal and lumbar trunks Superior vena cava Thoracic duct Lymph nodes Azygos vein Hemiazygos vein Parietal pleura (cut) Diaphragm Cisterna chyli Inferior vena cava Left lumbar trunk Intestinal trunk Right lumbar trunk Fig. 24.4 (a) Posterior thoracic wall, anterior view

Fig. 24.4 Lymphatic ducts (b) Lymph drainage pattern Area drained by right lymphatic duct Area drained by thoracic duct Right lymphatic duct drains into junction of right subclavian vein and right jugular vein Thoracic duct drains into junction of left subclavian vein and left jugular vein receives lymph from left side of head and neck, left arm, left thorax, everything inferior to diaphragm

© Andy Crumo, TDR, WHO/Science Source Edema Edema = swelling Lymphedema = swelling caused by blockage of lymph system Usually caused by obstruction Surgical removal of lymph nodes Spread of malignant tumors Scarring from radiation therapy Trauma or infection Elephantiasis = extreme lymphedema In Southeast Asia and Africa, may be caused by filarial worms infecting lymphatic system Elephantiasis (lymphatic filariasis) of the lower limb. © Andy Crumo, TDR, WHO/Science Source

“Elephant Man,” Joseph Merrick Condition NOT from edema Probably caused by neurofibromatosis type I or Proteus syndrome both pathologies of unchecked tumor growth

Lymphatic Structures – Lymph Nodules Clusters of lymphatic cells with some extracellular connective tissue Not lymph nodes (nodes have a connective tissue capsule) Germinal center creates new immune cells Sometimes many nodules together form larger structures MALT tonsils

Simple columnar epithelium Lymphatic Structures – MALT Fig. 24.8 (a) MALT in small intestine Mucosa-associated lymphatic tissue Located in mucosa of GI, respiratory, genital, urinary tracts Detect antigens and start immune response Very prominent in small intestine Peyer patches are large groups of lymphatic nodules in small intestine LM 140x Simple columnar epithelium of small intestine MALT (Peyer patches)

© Dr. P. Marazzi/Science Source Lymphatic Structures – Tonsils Lymph nodules Protect pharynx from infection Frequently inflamed and infected (acute tonsillitis) Tonsils redden and enlarge Chronic tonsillitis may require tonsillectomy © Dr. P. Marazzi/Science Source Tonsillitis. LM 40x Lymphatic nodules (c) Histology of tonsil

Lymphatic Structures – Tonsils Fig. 24.8 Lymphatic Structures – Tonsils Pharyngeal tonsil Opening of auditory tube Palate Palatine tonsil 3 groups pharyngeal tonsils (AKA adenoids) in posterior wall of nasopharynx palatine tonsils in posterolateral region of oral cavity lingual tonsils along posterior 1/3 of tongue Lingual tonsil (b) Tonsils

Lymphatic Organs – Thymus gland Large in infants and young Fig. 24.9 (a) Child’s thorax, anterior view Lymphatic Organs – Thymus gland Thyroid gland Right lung Left lung Thymus Large in infants and young Almost nonfunctional in adults Site where immune cells mature 2 thymic lobes surrounded by connective tissue Heart Diaphragm

Lymphatic Organs – Thymus gland Fig. 24.9 Lymphatic Organs – Thymus gland Trabecula Capsule Cortex Lobule trabeculae (AKA septa) are fibrous extensions of capsule around thymus divide thymus into lobules; each lobule has outer cortex; immature T-cells inner medulla; mature T-cells Medulla contains thymic corpuscles (aged, degenerated cells) Medulla LM 20x (b) Child’s thymus Lymphocytes Thymic corpuscle Epithelial cells LM 320x (c) Thymic corpuscle

Lymphatic Organs – Lymph Nodes Fig. 24.10 Lymphatic Organs – Lymph Nodes Medullary sinus Medulla T-lymphocytes Medullary cord B-lymphocytes Germinal center Dendritic cells Small, round or oval structures located on lymph vessels usually in clusters Surrounded by tough capsule Internal projections of capsule called trabeculae Pathway for blood vessels and nerves Lymphatic nodule Trabeculae Afferent lymphatic vessels Capsule Lymphatic nodule Cortex Germinal center Cortical sinus Hilum Valve Efferent lymphatic vessel Medullary cords Medullary sinus Trabecula Macrophage (a) Lymph node and its components Lymphocytes Medulla

Lymphatic Organs – Lymph Nodes Outer cortex Inner medulla Fig. 24.10 Lymphatic Organs – Lymph Nodes Medullary sinus Medulla T-lymphocytes Medullary cord B-lymphocytes Germinal center Dendritic cells Outer cortex lymphatic nodules lymphatic sinuses called cortical sinuses Inner medulla supported by medullary cords sinuses called medullary sinuses Hilum = indented portion of node; origin of efferent vessels Lymphatic nodule Trabeculae Afferent lymphatic vessels Capsule Lymphatic nodule Cortex Germinal center Cortical sinus Hilum Valve Efferent lymphatic vessel Medullary cords Medullary sinus Trabecula Macrophage (a) Lymph node and its components Lymphocytes Medulla

Fig. 24.10 Trabecula Capsule Germinal center within lymphatic nodule Lymphatic vessels Lymphatic nodule Medullary sinuses Lymph node Cortex Medullary cords Blood vessels Medulla Muscle LM 20x (b) Lymph node section (c) Lymph node and lymphatic vessels

Lymphatic Organs – Lymph Nodes Swelling of lymph nodes indicates immune response (infection) immune cells replicating and fighting off infection Swollen, tender lymph nodes in cervical region + sore throat = cold Swollen, tender lymph nodes all over body + sore throat + fever = mononucleosis Firm , swollen lymph node (not tender) may = metastatic cancer Cancer cells from cancer elsewhere in body travel through lymph system, lodge in lymph node and proliferate

Lymphatic Organs – Lymph Nodes Lymphoma = cancer of lymph nodes Page 737 Lymphatic Organs – Lymph Nodes LM 1000x Reed-Sternberg cell, a characteristic of Hodgkin lymphoma. Lymphoma = cancer of lymph nodes Hodgkin lymphoma usually affects young adults, people >60 double-nucleated Reed-Sternberg cell Non-Hodgkin lymphoma more common some kinds very aggressive and usually fatal some kinds very slow-growing and responsive to treatment

Lymphatic Organs – Spleen Fig. 24.11 Lymphatic Organs – Spleen (a) Anterior view of spleen Largest lymphatic organ Located between stomach and diaphragm Diaphragmatic surface convex and rounded Anteromedial border concave contains hilum, blood vessels and nerves enter and leave Surrounded by capsule with trabeculae branches of splenic artery in trabeculae called trabecular vessels Diaphragmatic surface Diaphragm Visceral surface Hilum Splenic artery Splenic vein

Lymphatic Organs – Spleen Fig. 24.11 Lymphatic Organs – Spleen Central artery White pulp Red pulp Splenic sinusoids Trabecula No cortex or medulla Cells around trabeculae divided into white pulp associated with arterial supply central artery surrounded by lymphatic cells red pulp associated with venous supply splenic cords store extra red blood cells; released when more needed by body, ex. during exercise splenic sinusoids act like enlarged capillaries; immune cells in lumen destroy old red blood cells Splenic cords Capsule (b) Red and white pulp of spleen Trabeculae Red pulp Central artery White pulp Capsule LM 40x (c) Histology of spleen