Lymphatic System Flashcards
Lymphatic system
■ Network of:
■ Ducts
■ Vessels
■ Organs
■ Produces, screens and moves fluid called lymph from tissues to the bloodstream
4 parts of lymphatic system
- Lymph:
■ a fluid similar to plasma, identical to interstitial fluid
■ does not have plasma proteins - Lymphatic vessels (lymphatics):
■ network that carries lymph from peripheral tissues to the venous system - Lymphoid tissues and lymphoid organs:
■ found throughout the body - Lymphocytes, phagocytes, and other immune system cells
Functions of lymphatic system
■ Is to produce, maintain, and distribute lymphocytes
■ Drain excess interstitial fluid
■ Transports dietary lipids
Lymphocyte production
■ Lymphocytes are produced:
■ in lymphoid tissues (e.g., tonsils)
■ lymphoid organs (e.g., spleen, thymus)
■ and in red bone marrow
Lymphocyte distribution
■ Lymphocytes:
■ detect and respond to antigens
■ travel into site of injury or infection
Lymphocyte circulation
■ From blood to interstitial fluid (lymph) through capillaries
■ Returns to venous blood through lymphatic vessels
Circulation of fluids
■ From blood plasma to lymph and back to the venous system
■ Also transports hormones, nutrients, and waste
Lymphatic vessels
■ Are vessels that carry lymph
■ Lymphatic system begins with smallest vessels:
■ lymphatic capillaries (terminal lymphatics)
Lymphatic capillaries differ from blood capillaries in 4 ways
■ start as pockets rather than tubes
■ have larger diameters
■ have thinner walls (this as one cell)
■ flat or irregular in section
Lymphatic capillaries
■ Absent from bones, teeth, bone marrow, and CNS
■ Very permeable (take up proteins, cell debris, pathogens, and cancer cells)
■ Endothelial cells loosely bound together with overlap
■ Overlap acts as one-way valve:
■ allows fluids, solutes, viruses, and bacteria to enter lymphatic system
■ prevents return to intercellular space
Lacteals
■ Are special lymphatic capillaries in small intestine
■ Transport lipids from digestive tract
Lymphatic vessels and valves: lymph flow
■ From lymphatic capillaries to larger lymphatic vessels containing one-way valves (more numerous than veins)
■ Lymphatic vessels travel with lymph
■ Is due to:
■ peristaltic contractions (?) of smooth muscle in lymphatic vessel walls
■ Skeletal muscular contractions (like veins)
■ important for lymph flow
■ Immobilizing a limb will slow lymph drainage
■ Arterial pulsations
■ The respiratory pump
■ There is no lymph heart
■ Rate of lymph return is slow - approximately 120 ml/hr
Lymphatic ducts and venous system: lymphatic system
■ Is similar to the circulatory system
■ Is divided into:
■ superficial lymphatics
■ deep lymphatics
Superficial lymphatics are located in:
■ skin
■ mucus membranes
■ serous membranes lining body cavities
Deep lymphatics
■ Are larger vessels that accompany deep arteries and veins
■ They have smooth muscle in their walls
■ are capable of peristalsis
Superficial and deep lymphatics
■ Join to form large lymphatic trunks
■ Trunks empty into 2 major collecting vessels:
■ thoracic duct
■ right lymphatic duct
Base of thoracic duct
■ Expands into cisterna chyli
■ Cisterna chyli receives lymph from:
■ right and left lumbar trunks
■ intestinal trunk
Thoracic duct
■ Collects lymph from (3/4 of the body):
■ left bronchiomediastinal trunk
■ left subclavian trunk
■ left jugular trunk
■ Empties into left subclavian vein
Right lymphatic duct
■ Collects lymph from (1/4 of the body):
■ right jugular trunk
■ right subclavian trunk
■ right bronchiomediastinal trunk
■ Empties into right subclavian vein
Lymphedema
Lymphedema is a chronic swelling that occurs when the lymphatic system is blocked, preventing lymph fluid from draining properly.
■ Interferes with immune system function
Lymphocytes
■ Make up 20–30% of circulating leukocytes
■ Most are stored, not circulating
2 main classes of circulating lymphocytes
- T cells:
■ thymus-dependent - B cells:
■ bone–marrow WBCs
Other supporting cells
■ Macrophages phagocytize foreign substances; help activate T cells
■ Dendritic cells capture antigens and deliver them to lymph nodes; activate T cells
■ Reticular cells produce reticular fiber stroma that supports other cells in lymphoid organs
T Cells
■ Make up 80% of circulating lymphocytes
3 main types of T cells
• Cytotoxic T cells
• Helper T cells
• Suppressor T cells
Cytotoxic T cells
■ Attack cells infected by viruses
■ Produce cell-mediated immunity
Helper T cells
■ Stimulate function of T cells and B cells
Regulatory/Suppressor T cells
■ Inhibit function of T cells and B cells
■ Control sensitivity of immune response
B cells
■ Make up 10–15% of circulating lymphocytes
■ Differentiate into plasma cells
Plasma cells
■ Produce and secrete antibodies (immunoglobin proteins)
Antigens
■ Antibody generators
■ Act as targets which identify any pathogen or foreign compound
Antibody-mediated immunity
■ A chain of events which destroys the target compound or organism
Lymphocyte distribution
■ Tissues maintain different T cell and B cell populations
■ Lymphocytes wander through tissues:
■ enter blood vessels or lymphatics for transport
■ can survive wk- few months
Lymphocyte production involves:
■ bone marrow
■ thymus
■ peripheral lymphoid tissues
Hemocytoblasts
In bone marrow, divide into 2 types of lymphoid progenitor cells
1. Myeloid stem cells
2. Lymphoid stem cells
Lymphoid stem cells
■ Group 1:
■ remain in bone marrow
■ produce B cells and natural killer cells
■ Group 2:
■ migrate from bone marrow to peripheral tissue
■ produce T cells in environment isolated by blood-thymus barrier
T cells and B cells
■ Migrate throughout the body:
■ to defend peripheral tissues
■ Retain their ability to divide:
■ is essential to immune system function
Interleukin-7
A cytokine produced by stromal cells in bone marrow
Lymphoid tissues
■ Surveillance vantage point for lymphocytes and macrophages
■ Largely reticular connective tissue – type of loose connective tissue
2main types of lymphoid tissues
■ Diffuse lymphoid tissue of lymphoid cells and reticular fibers in ~ every body organ
■ Lymphoid follicles (nodules) are solid, spherical bodies of tightly packed lymphoid cells and reticular fibers
■ Germinal centers of proliferating B cells
■ May form part of larger lymphoid organs
Distribution of lymphoid nodules
■ Lymph nodes
■ Spleen
■ Respiratory tract (tonsils)
■ Along digestive and urinary tracts
Mucosa-associated lymphoid tissue (MALT)
■ Lymph Nodules - Large aggregations of naked (no capsule, trabeculae, or hilum) lymphoid tissue
■ found embedded in mucous membranes of systems that communicate with external environment
■ Protect against outside harmful substances in food or air
■ These include:
■ the Gastrointestinal Tract
■ the Genitourinary Tract
■ the Upper Respiratory Tract
■ Commonly referred to as the Mucosal Associated Lymphoid Tissues or the MALT
Gut-associated lymphoid tissues (GALT)
■ Are a type of MALT located specifically in the GI tract
■ Peyer’s patches – aggregated lymphoid nodules located throughout the small intestines
■ Appendix
■ Peyer’s patches and appendix:
■ Destroy bacteria, preventing them from breaching intestinal wall
■ Generate “memory” lymphocytes
The 5 tonsils (GALT)
■ In wall of pharynx:
■ left and right palatine tonsils
■ pharyngeal tonsil (adenoid)
■ 2 lingual tonsils
Lymphoid organs
■ Are separated from surrounding tissues
■ By a fibrous connective-tissue capsule
Lymph nodes
■ Range from 1–25 mm diameter
■ Act as filters for lymph fluid
■ Embedded in connective tissue, in clusters along lymphatic vessels
■ Near body surface in inguinal, axillary, and cervical regions of body
The stroma (structural portion)
■ structural latticework consisting primarily of reticular connective tissue. Containing:
■ Trabeculae are Bundles of connective tissue fibers
■ Extend from capsule into interior of lymph node
■ Hilus - shallow indentation where blood vessels and nerves reach the lymph node
Lymph node vessels
■ Many afferent vessels carry lymph from peripheral tissues to lymph node
■ Fewer vessels leave lymph nodes at hilus
■ Slows lymph flow through the node
■ allows lymphocytes and macrophages time to function
Lymph node functions
■ 2 main functions
■ Filtering and Immune System Activation (Antigen presentation)
■ filtering:
■ purifies lymph before return to venous circulation
■ Removes:
■ debris
■ pathogens
■ 99% of antigens
■ Antigen Presentation
■ First step in immune response
■ process where an antigen-presenting cell (APC) takes up a foreign antigen, processes it into smaller peptides, and then displays those peptides on its surface, bound to MHC molecules, for recognition by immune cells like T lymphocytes
■ or attached to dendritic cells to stimulate lymphocytes
Lymphoid functions
■ Lymphoid tissues and lymph nodes:
■ distributed to monitor peripheral infections
■ respond before infections reach vital organs of trunk
Lymph glands
■ Large lymph nodes at groin and base of neck
■ Swell in response to inflammation
Lymphadenopathy (Lymphadenitis)
Chronic or excessive enlargement of lymph nodes may indicate infections, endocrine disorders, or cancer
Lymphangitis
■ inflammation of the lymphatic channels
■ Pathogens invade the lymphatic vessels through a wound or as a complication of infection
■ irregular streaks on the skin extending proximally toward regional lymph nodes.
■ Treat with large does of antibiotics
■ Iimobalize the limb (Why?)
The thymus
■ Located in mediastinum
■ Deteriorates after puberty:
■ diminishing effectiveness of immune system
Division of thymus
■ Thymus is divided into 2 thymic lobes
■ Septa divide thymus parenchyma into smaller lobules
Thymic lobule
■ Contains a dense outer cortex
■ And a pale central medulla
Lymphocytes
■ Divide in the cortex
■ T cells migrate from cortex into medulla
■ Mature T cells leave thymus by medullary blood vessels
Reticular epithelial cells in the cortex
■ Dendritic cells surround lymphocytes in cortex
■ Maintain blood-thymus barrier (only in cortex)
■ Secrete thymic hormones that stimulate:
■ stem cell divisions
■ T cell differentiation
The medulla
■ Contains fewer lymphocytes
■ The medulla has no blood–thymus barrier:
■ T cells can enter or exit bloodstream
■ Keratinized Epithelial Cells form concentric layer (Hassall’s or Thymic corpuscles).
■ thymic corpuscles involved in regulatory T cell development (prevent autoimmunity)
Thymus hormones
■ Thymosins
■ Promote development of lymphocytes
DiGeorge syndrome
■ Congenital absence of thymus
■ Marked by serious combined immuno-deficiencies (SCIDS).
■ Life in a sterile bubble with death often resulting from opportunistic infection.
Functions of the spleen
- Removal of abnormal blood cells and other blood components by phagocytosis
- Storage of iron recycled from red blood cells
- Initiation of immune responses by B cells and T cells:
■ in response to antigens in circulating blood - The Stores blood platelets and monocytes
- May be site of fetal erythrocyte production (normally ceases before birth)
Structure of spleen
■ Attached to stomach by gastrosplenic ligament
■ Splenic veins, arteries, and lymphatic vessels:
■ communicate with liver at hilus
■ Inside fibrous capsule:
■ red pulp: which contains many red blood cells
■ white pulp: resembles lymphoid nodules
Red pulp
■ Contains elements of circulating blood:
■ plus fixed and free macrophages
Splenic circulation
■ Blood passes through:
■ network of reticular fibers
■ Then enters large sinusoids (lined by macrophages):
■ which empty into trabecular veins
Spleen function
■ Phagocytes and other lymphocytes in spleen:
■ identify and attack damaged and infected cells
■ in circulating blood
■ The spleen filters and cleans the blood
Splenectomy
■ Removal of the spleen, usually due to damage
■ The spleen is very difficult to repair surgically
■ Surgeons now know that the spleen will repair its self with time – less splenectomies today
■ People with out a spleen are more susceptible to infections
■ specifically blood infections
