Lymphatic System
Lymphatics: collection of cells/ organs that destroy and neutralize pathogens that will cause disease or death
Immunity: Diverse processes that protect the body from both cellular injury, disease causing cells, and molecules known ass pathogens
-Lymphatic system works with immune system to transport and house lymphocytes and other immune cells
-Returns excess fluid in body tissues to blood to maintain blood volume
-Consists of 2 main components
- Lymph vessels, lymphoid issues and organs
- Lymph is the fluid transported within lymph vessels
-Lymph vessels begin in tissues with tiny capillaries
-Some fluid leaves blood capillaries wand is not reabsorbed by them
-This interstitial fluid moves into lymphatic capillaries where it is then called lymph
Components of lymph
-Wate, dissolved solutes and small amounts of protein
-Sometimes cell debris, pathogens, or cancer cells
-Blind ended: lymph vascular it’s is a 1 way system that only moves lymph away from tissues
-Pathogens such as bacteria and cancer cells in interstitial fluid have an easier time entering lymphatic capillaries
-Lymph nodes limit spread of pathogens through body by acting as filters
-Trapping pathogens and preventing them from traveling elsewhere
-Lymphatic vessels are a low pressure system
—No main pump to drive lymph through vessels
—Most are transporting lymph against gravity
Valves prevent backflow
-Found lodged between muscles
-Contracting muscles push lymph up towards heart
-Smooth muscle is found in walls of lymph collecting vessel
-Lymph flow is driven in part by the contractions of that smooth muscle
Clinical Corelate: Metastasis
-Wandering cancerous cells establishing secondary tumors
-Cancerous cells break free from primary tumor
-Transported in the lymph
-Develop in other locations in the body (metastasis)
Ex. Breast cancer may metastasize to the lung
Lymphatic vessels and lymph circulation
-Located adjacent to arteries and veins
-Lymph collecting vessels: lymph collected in vessels which merge to form larger vessels, lymph trunks
-Lymph trunks: 9 lymph trunks, drain from lymph specific body regions
-2 lumbar trunks: receive lymph from lower limbs and pelvic area
-2 jugular trunks: recieve lymph from head and neck
-1 intestinal trunk: recieves fat containing lymph from small lymph vessels
-2 bronchi mediastinal trunks: recieve lymph from thoracic cavity
-2 subclavian trunks: recieve lymph from upper limbs
-Intestinal trunk and lumbar trunks all drain into a large, swollen vessel called cisterna chili
-Cisterna chili and pother lymph trunks drain into one of two lymph ducts
Lymphatic ducts are fed by lymphatic trunks
-Larges lymphatic vessels
-Bring lymph to venous blood circulation
-There are two: right lymphatic ducts and thoracic duct
- Thoracic duct: drain from cisterna chili and trunks from lower body and left side of upper body
-Largest lymphatic duct, runs along anterior vertebral column and drains into junction of left internal jugular and left subclavian veins
- Right lymphatic duct: remaining trunks drain into tiny duct in junction of right internal jugular ad right subclavian veins
-Drain upper right side of the body
Primary lymphoid structures
-Involved in formation and maturation of lymphocytes
-Red bone marrow and thymus
Secondary lymphoid structures
-Don’t form lymphocytes, but house them and other immune cells
-Sites of immune response initiation
-Include lymph nodes, spleen, tonsils, and lymphatic nodules
-Include MALT (mucosa- associated lymphoid tissue)
Red bone marrow
-Located between trabeculae of spongy bone
-In flat bones of skull, ribs and sternum vertebrae, pelvis and heads of humerus ad femur
-Site of hematopoiesis: productions of bloods formed elements
-Folrmed elements include T lymphocytes and B lymphocytes
-T lymphocytes migrate to the thymus to complete maturation
Thymus-Small organ in superior mediastinum
-Primary function; generation of functional T cells capable of protecting body from pathogens
-Large and active in infants and children
-Starts to atrophy in size after age 13
-The adult thymus consists of subunits called thymus lobules- externally visible ass lumps on surface
-By age 65, rate of T cell production falls to about 2% of the rate at which an infant produces T cells
-Each lobule contains 2 regions - an outer cortex and inner medulla
-Cortex contains densely packed T cells
-Medulla thought to be set of destruction of certain population of T cells
-There are no lymphoid follicles in thymus because it lacks B cells
Secondary Lymphoid Structures
-House lymphocytes ad other immune cells within a reticular tissue matrix
-Organized into lymphoid organs and lymphoid nodules
-Organs have a complete capsule of dense irregular connective tissue (spelled and lymph nodes)
-Other lymphoid structures have an incomplete capsule or lack one (tonsils, MALT,diffuse lymphoid nodules)
Lymph Nodes
-Small bean shaped clusters of lymphatic tissue that filter lymph, remove unwanted substances
-Located along lymphatic vessels throughout the body:
-Axillary- armpit
-Cervical- neck
-Inginual- groin
-Mesenteric- abdominal cavity
-Lymph nodes have an external tissue capsule that surrounds a network of reticular fibers
-Filled with macrophages, lymphocytes, and dendritic cells
-2 main regions: outer cortex and inner medulla
-Lymphatic cortex consists of lymphoid follicles divided by trabeculae (inward extensions of capsule)
-Afferent lymphatic vessels bring lymph to the node
-Efferent vessels drains the lymph node
-Located in the hilum (involuted potion of the node)
The cortex contains lymphoid nodules
•Reticular fibers support a germinal center
•Houses proliferating B lymphocytes & some macrophages
•Surrounding mantle zone contains T-lymphocytes, macrophages, and dendritic cells
•Cortical sinuses are tiny open channels lined by macrophages
Node’s medulla contains medullary cords
•Connective tissue fibers that support B-lymphocytes, T-lymphocytes, and macrophages
•Medullary sinuses are tiny open channels lined with macrophages
Malignant cells from lymphoid structures
•Nontender, enlarged lymph node
•Possible night sweats, fever, and weight loss
•Hodgkin lymphoma
•Affects young adults and people over 60
•If caught early, cured by excision, radiation, and chemotherapy
•Non-Hodgkin lymphoma
•More common
•Some kinds aggressive, others slow growing
Spleen
•Largest lymphoid organ in body
•Located in left upper quadrant of abdominopelvic cavity
•Soap-sized purplish-brown organ
•Composed of reticular fibers & surrounded by a capsule
Two distinct histological regions are found in reticular network:
1.Red pulp – contains macrophages that destroy old RBCs
2.White pulp – clusters of T- & B- lymphocytes and macrophages around central artery
Monitoring blood as it flows through the spleen:
•White pulp filters and monitors foreign bodies & bacteria in blood (not lymph)
•Macrophages in sinusoids of red pulp remove particles
•Phagocytize bacteria, debris, defective erythrocytes and platelets
•In first 5 months of fetal life, spleen makes blood cells
1.Pharyngeal tonsil (adenoids) – in nasopharynx
2.Palatine tonsils – in posterolateral oral cavity
3.Lingual tonsil - at base of tongue
Tonsillar crypts – epithelium lining tonsils is deeply indented in several locations
•Trap bacteria & debris
•Tonsil location puts them into contact with a large number of potential pathogens
Clinical Corelate: Tonsillitis
Acute tonsillitis: inflammation & infection of tonsils by viruses or bacteria
•Palatine tonsils most commonly affected
•May partially obstruct pharynx
•Symptoms: fever, chills, sore throat, and difficulty swallowing
•May be infected by viruses or bacteria
•Persistent recurrent infections chronic tonsillitis
Lymphoid nodules:
•Clusters of lymphoid cells with some extracellular matrix
•Scattered nodules termed diffuse lymphoid tissue
•Found in every organ
•Helps defend against infection
•In some areas, group together to form larger structures
•Ex: MALT
Mucosa-associated lymphatic tissue (MALT)
•Loosely organized clusters of lymphoid tissue (B & T cells) that protects mucous membrane
•Located in gastrointestinal, respiratory, genital, and urinary tracts
•Help defend against foreign substances
Specialized MALT is found in 3 locations:
1.Tonsils – located in oral & nasal cavities
2.Peyer’s patches (aggregated lymphoid nodules) – located in ilium of small intestine
3.Appendix – protrudes from large intestine
Peyer’s patches - allow defense against any bacteria that have escaped from large intestine