The lymphatic system

• Functions:

  • transport clean fluids back to the blood
  • Drains excess fluids from tissues
  • removes debris from cells of body
  • Transports fats from digestive system
• Lymph is fluid that contains white blood cells, proteins, fats, glucose, amino acids, hormones, vitamins, minerals, waste products, bacteria, viruses, cancerous cells.
• Lymph nodes filter out pathogens and foreign substances from the lymph.
• The lymphatic vessels are one-way valves that prevent backflow of lymph.
• Lymph organs:

  Tonsils

  Thymus

  Spleen

  Lymph nodes

  Mucosa Associated Lymphoid Tissue (MALT)

  Gut Associated Lymphoid Tissue (GALT)
• Lymphocytes are produced by bone marrow and mature in secondary lymphoid tissue such as lymph nodes, spleen, tonsils, thymus gland, Peyer's patches, appendix, and mucosal surfaces.
• Major Lymph nodes:

  Thoracic

  Axillary

  Cervical

  Inguinal

  Supratrochlear

  Abdominal

  Pelvic
• Hematopoietic stem cells can become a common myeloid progenitor or a common lymphoid progenitor.
• Common myeloid progenitor cells create erythrocytes (rbc) , mast cells, myeloblasts, and megakaryocytes.
• Megakaryocytes create thrombocytes (platelets)
• Myeloblasts create basophils, neutrophils, eosinophils, and monocytes.
• Monocytes create macrophages and dendritic cells.
• Common lymphoid progenitor cells create natural killer cells and small lymphocytes. Small lymphocytes turn into T or B lymphocytes. B lymphocytes can make plasma cells.
• Lymphatic vessels and capillaries:

  Lymphatic vessels begin as capillaries which are closed on one end. The capillaries are located between cells of many tissues and merge to form lymphatic vessels which have thin walls and many valves.
• The lymphatic system also includes lymph nodes, tonsils, adenoids, appendix, Peyer's patches, and mucosa associated lymph tissue. These structures contain immune cells and filter pathogens from the body.
• Lymph passes from the lymphatic vessels through the lymph nodes and into the lymph trunks.
• Lymph trunks include the lumbar, intestinal, bronochomediastinal, subclavian, and jugular trunks.
• Lymph trunks merge to form the thoracic duct or the right lymphatic duct.
• Routes for drainage

  A) right lymphatic

  B) thoracic

  
• Formation and flow of lymph

  Interstitial fluid -> lymph capillaries -> lymph vessels -> lymph trunks -> lymph ducts -> subclavian veins
• Primary lymphatic organs


  where immune cells become immunocompetent: red bone marrow and thymus
• Secondary lymphatic organs and tissues

  Lymph nodes

  spleen

  lymphatic nodules
• Lymphatic nodules

  Masses of lymphatic tissue that are not surrounded by a capsule. They are scattered throughout the lamina propria of the mucous membranes lining the GI, urinary, and reproductive tracts and respiratory airways.

  Lymphatic nodules are in areas referred to as MALT ( mucosa-associated-lymphatic-tissue)
• Innate immunity

  protection against invasion by a wide variety of pathogens and their toxins. The two lines of defense are the skin and mucous membranes and internal defenses.
• Mechanical defenses

  skin

  mucous membranes

  tears

  saliva

  mucus

  cilia

  epiglottis

  urine flow

  defecating

  vomitting
• Chemical defenses

  Sebum

  lysozoyme

  gastric juice
• Internal defenses

  Antimicrobial proteins

  phagocytes

  natural killer cells

  inflammation

  fever
• Interferons

  Protect uninfected host cells from viral infection
• Complement system


  Causes cytolysis of microbes; promotes phagocytosis; contributes to inflammation
• Antimicrobial proteins

  have broad-spectrum antimicrobial activities and attract dendritic cells and mast cells
• Natural killer cells

  Kill infected target cells by releasing granules that contain perforin and granzymes; phagocytes then kill released microbes.

  Ingest foreign particulate matter.
• Inflammation

  Confines and destroys microbes; initiates tissue repair
• fever

  intensifies effects of interferons;inhibits growth of some microbes; speeds up body reactions that aid repair
• Adaptive immunity

  body's ability to defend itself against specific invading agents (antigens).
• Epitopes

  certain small parts of a large antigen molecule that acts as triggers for immune responses
• B cells can recognize and bind to antigens in lymph, interstitial fluid, or blood plasma.
• T cells only recognize fragments of antigenic proteins that are processed and presented in a certain way.
• Antigen-presenting

  antigenic proteins are broken down into peptide fragments that associate with MHC molecules that is then inserted into the plasma membrane of a body cell
• Exogenous antigen processing

  1. phagocytosis of an antigen
  2. digestion of antigen into peptide fragments
  3. synthesis of MHC-II molecules
  4. packing of MHC-II molecules into a vesicle
  5. vesicles containing antigen peptide fragments and MHC-II molecules fuse
  6. antigen peptide fragments bind to MHC-II molecules
  7. Vesicle undergoes exocytosis and antigen-MHC-II complexes are insteryed into plasma membrane
• Endogenous antigen processing

  1. digestion of antigen into peptide fragments
  2. synthesis of MHC-I molecules
  3. antigen peptide fragments bind to MHC-I molecules
  4. packaging of antigen-MHC-I molecules into a vesicle
  5. vesicles undergoes exocytosis and antigen-MHC-I complexes are inserted into plasma membrane