Lymphatic

• Lymphatic system


  Fluid balance: 30L of fluids pass from blood capillaries into interstitial spaces each day, 27L go back into the blood capillaries from interstitial spaces, 3L flow to lymphatic capillaries
• Lymphatic system


  Lipid absorption: Lymphatic system absorbs lipids and other substances from the gastrointestinal tract through lacteals (located on the linings of the small intestine), chyle (lymph with high lipid content) appears as white-milky fluid
• Lymphatic system


  Defense: Pathogens, microorganisms and other foreign substances are filtered from lymph by lymph nodes and from blood by the spleen
• Lymphatic system


  • Unlike the circulatory system, the lymphatic system does not circulate fluid to and from tissues. Instead, the lymphatic system carries fluid in one direction FROM TISSUES TO CIRCULATORY SYSTEM. Lymphatic vessels carry lymph away from tissues. Valves in the vessels ensure one way flow of lymph.
• Lymphatic capillaries


  • Tiny close ended vessels consisting of squamous epithelium, more permeable than blood capillaries because they lack basement membrane, withstand interstitial pressure and remain open, presence of valves ensures one-way flow
• Tissues lacking lymphatic capillaries

  • Central nervous system
  • Bone marrow
  • Tissues lacking blood vessels (epidermis and cartilages)
• Lymphatic vessels


  • Compression of lymphatic vessels causes lymph to move forward through them due to 3 factors: contraction of surrounding skeletal muscles, periodic contraction of smooth muscle in the lymphatic vessel wall, pressure changes in the thorax during breathing
• Lymphatic vessels


  Lymphatic vessels converge and eventually empty into the blood at 2 locations: Right Lymphatic Duct (right upper extremity, right half of the head, neck, chest) and Thoracic duct (other parts of the body except those drained by the Right Lymphatic Duct)
• Tonsils


  • Simplest lymphoid organs, form a protective ring of lymphatic tissue around the openings between the nasal and oral cavities and the pharynx, protect against pathogens and other potentially harmful materials entering from the nose and mouth
• Peyer's patches


  • Isolated clusters of lymphoid tissue similar to tonsils, found in the wall of the distal portion of the small intestine, destroy bacteria and prevent them from breaching the intestinal wall, generate "memory" lymphocytes for long-term immunity
• Types of tonsils


  • Palatine tonsils
  • Pharyngeal tonsils (adenoids)
  • Lingual tonsil
• Lymph nodes


  Rounded structures varying in size from a small seed to a shelled almond, principal lymphoid organs of the body, embedded in connective tissue and clustered along lymphatic vessels
• Lymph nodes


  • Two basic functions: Filtration (macrophages destroy microorganisms and debris) and Immune system activation (monitor for antigens and mount an attack against them)
• Parts of lymph nodes

  • Capsule (dense connective tissue surrounding each lymph node), Trabeculae (extensions of capsule which subdivide a lymph node into compartments containing lymphatic tissue and lymphatic sinuses)
• Lymphatic tissue in lymph nodes

  • Consists of lymphocytes and other cells that can form dense aggregations of tissue called lymphatic nodules
• Lymphatic sinuses in lymph nodes


  • Spaces between the lymphatic tissue containing macrophages on a network of fibers
• Lymph flow inside lymph nodes

  Afferent vessels -> Lymphatic tissue and sinus -> Efferent vessels
• Functions of lymph nodes


  • Activate the immune system (pathogens in the lymph stimulate lymphocytes in the lymphatic tissue to divide, forming germinal centers) and Remove pathogens from the lymph through the action of macrophages
• Spleen


  • Roughly the size of a clenched fist, located in the left superior corner of the abdominal cavity, has a capsule of dense connective tissue and small amount of smooth muscle, and trabeculae that divide the spleen into small interconnected compartments containing specialized types of lymphatic tissues: white pulp and red pulp
• White pulp of the spleen

  • Contains mostly lymphocytes suspended on reticular fibers, involved in immune functions, surrounds arteries in the spleen
• Red pulp of the spleen

  • Remaining splenic tissue concerned with disposing of worn-out red blood cells and bloodborne pathogens, surrounds veins
• Functions of the spleen

  • Filters blood instead of lymph, cells within spleen detect and respond to foreign substances in the blood and destroy old and damaged red blood cells, also functions as a blood reservoir that can contract to release blood in emergency situations
• Thymus


  • Bilobed gland roughly triangular in shape, located superior to the mediastinum, site of maturation of T cells, has a capsule of thin connective tissue and trabeculae that divide the thymus into lobules
• Cortex and medulla of the thymus

  • Cortex (dark staining areas near the capsule and trabeculae), medulla (lighter staining central portion of the lobules with fewer lymphocytes)
• Innate immunity


  Non-specific resistance, the body recognizes and destroys certain pathogens but the response to them is the same each time the body is exposed
• Adaptive immunity


  Specific immunity, the body recognizes and destroys pathogens but the response to them improves each time the pathogen is encountered, characterized by specificity and memory
• Specificity


  Ability of adaptive immunity to recognize a particular substance, e.g. innate immunity can act against bacteria in general while adaptive immunity can distinguish among various kinds of bacteria
• Memory


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


  Central portion with fewer lymphocytes
• Immunity


  The ability to resist damage from pathogens
• Types of immunity


  • Innate immunity
  • Adaptive immunity
• Non-specific resistance


  The body recognizes and destroys certain pathogens but the response is the same
• Specific immunity


  The body recognizes and destroys pathogens, and the response improves each time the pathogen is encountered
• Characteristics of adaptive immunity


  • Specificity
  • Memory
• Specificity


  The ability of adaptive immunity to recognize a particular substance
• Memory


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

  • Physical barriers
  • Chemical mediators
  • White blood cells
• Physical barriers


  Prevent pathogens and chemicals from entering the body through the skin and mucous membranes, and by washing them away with tears, saliva and urine
• Chemical mediators


  Molecules responsible for many aspects of innate immunity, including promoting inflammation
• Interferons


  Proteins that protect the body against viral infection by stimulating infected cells to produce antiviral proteins in neighbouring cells