lymphatic system

• Lymphatic system


  Carries fluid (lymph) from tissues to the circulatory system
• Components of the lymphatic system

  • Lymph (fluid)
  • Lymphocytes
  • Lymphatic vessels
  • Tonsils
  • Spleen
  • Thymus

  
• Lymphatic capillaries

  • Tiny, closed-ended vessels with simple squamous epithelium
  • More permeable than blood capillaries as they lack basement membranes
• Lymph flow

  1. Compression of lymphatic vessels by skeletal muscle contraction

  2. Contraction of smooth muscle in lymphatic vessel walls

  3. Pressure changes during breathing
• Lymph from uncolored areas flows through the thoracic duct before entering the blood
• Lymphatic vessels from the right upper limb, head, neck and chest empty into the right lymphatic duct which enters the right subclavian vein
• Tonsils

  • Form a protective ring of lymphatic tissue around the opening between nasal/oral cavities and pharynx
  • Protect against pathogens and harmful materials entering nose and mouth

  
• Types of tonsils

  • Palatine tonsils
  • Pharyngeal tonsils (adenoids)
  • Lingual tonsils

  
• Lymph nodes

  • Round structures distributed along lymphatic vessels
  • Most lymph passes through at least one lymph node before entering blood
  • Contain lymphatic tissue and lymphatic sinuses

  
• Spleen

  • Filters blood
  • Detects and responds to foreign substances
  • Destroys old red blood cells
• Thymus

  • Produces and matures lymphocytes
  • Site for maturation of T cells

  
• Innate immunity


  Non-specific resistance where the body recognizes and destroys certain foreign substances with the same response each time

  
• Adaptive/Specific immunity


  Immunity where the body recognizes and destroys foreign substances, and the response improves each time the foreign substance is encountered

  
• Specificity


  Ability of adaptive immunity to recognize a particular substance

  
• Memory


  Ability of adaptive immunity to "remember" previous encounters with a particular substance, resulting in faster, stronger and longer-lasting future responses
• Components of innate immunity

  • Physical barriers (skin, mucous membranes)
  • Chemical mediators (e.g. lysozyme)
  • Complement system

  
• Physical barriers must be healthy to prevent pathogens from entering the body
• Chemical mediators like lysozyme kill certain bacteria and mucus prevents entry of some pathogens
• Complement system is a group of inactive proteins in the blood that become activated to destroy pathogens
• Bodily secretions

  • Vaginal secretion
  • Defecation
  • Vomiting
• Pathogens cannot cause disease if they cannot get inside the body
• Physical barriers must be healthy
• Chemical mediators


  Molecules responsible for many aspects of innate immunity
• Chemical mediators

  • Lysozyme in tears and saliva
  • Mucus on mucous membranes
• Complement

  A group of more than 20 proteins that circulate in the blood in their inactive form
• Plasma is in the blood
• Chemical mediators that promote inflammation

  • Histamine
  • Complement
  • Prostaglandins
  • Leukotrienes
• Interferons


  Proteins that protect the body against viral infections
• How interferons protect cells against viral infections

  1. Infected cell produces viral nucleic acids and proteins

  2. New viruses are released to infect other cells

  3. Interferons bind to surface of neighboring cells

  4. Antiviral proteins inhibit viral reproduction
• White blood cells


  The most important cellular components of immunity
• Chemotaxis


  The movement of white blood cells towards chemicals released from pathogens or damaged tissues
• Phagocytosis


  The ingestion and destruction of particles by cells called phagocytes
• Important phagocytes

  • Neutrophils
  • Macrophages
• Neutrophils

  Small phagocytic cells that are usually the first to enter infected tissues from the blood in large numbers
• Pus


  An accumulation of fluid, dead neutrophils, and other cells at a site of infection
• Macrophages

  Monocytes that leave the blood, enter tissues, and enlarge about fivefold
• Mononuclear phagocytic system

  Monocytes and macrophages that are phagocytes with a single, unlobed nucleus
• Macrophages

  • Can ingest more and larger items than neutrophils
  • Appear in infected tissues after neutrophils and are responsible for most phagocytic activity in late stages of infection
  • May phagocytize microorganisms before they can replicate or cause damage
  • Protect lymph in lymph nodes and blood in spleen and liver
• Basophils


  Derived from red bone marrow, motile white blood cells that can leave the blood and enter infected tissues
• Mast cells


  Nonmotile cells in connective tissue, especially near capillaries