Lymphatic system

• lymphatic system is composed mainly of the following

  • lymphatic vessels
  • lymphoid tissues & organs
• functions of the lymphatic system

  1. Return excess tissue fluid to blood vascular system
  2. Scans for pathogens and initiates immune response
  3. Absorption in the small intestines
• Lymphocytes are white blood cells produced by bone marrow, which circulate throughout the body via the bloodstream or lymphatic vessels
• Lymphatic vessels

  • AKA lymphatics
  • forms a drainage system that picks up excess interstitial fluid (lymph) and returns it to the blood
  • porous - permeable
  • forms a one-way system towards only the heart
• lymph

  • is a clear, watery fluid that contains lymphocytes
  • carries away larger particles, e.g. bacteria and cell debris from damaged tissues, which can then be filtered out and destroyed by the lymph nodes
• lymph capillaries

  • smallest lymph vessels
  • first to receive lymph
  • Receives tissue fluid from connective tissues
  • High permeability allows entrance of tissue fluid and protein molecules, bacteria, viruses, and cancer cells
• order of lymphatic vessels

  1. lymph capillaries
  2. lymphatic collecting vessels
  3. lymph nodes
  4. lymph trunks
  5. lymph ducts
  6. thoracic duct & R lymphatic duct
  7. R & L subclavian artery
• lymphatic collecting vessels

  • collect from lymph capillaries
  • composed of the same three tunics as blood vessels
  • contain more valves than veins do
• lymphatic ducts

  • Empty into veins of the neck
  • thoracic & R lymphatic
• thoracic duct

  • AKA “left lymphatic duct”
  • begins at the cisterna chyli
  • about 40 cm long and opens into the left subclavian vein
  • It drains lymph from both legs, the pelvic and abdominal cavities, the left half of the thorax, head and neck, and the left arm
• R lymphatic duct

  • dilated lymph vessel about 1 cm long
  • opens into the right subclavian vein
  • It drains lymph from the right half of the thorax, head and neck and the right arm
• lymph trunks

  • Vessels of the lymphatic system that form from the convergence or joining of smaller lymphatic collecting vessels
  • Towards the thoracic duct or right lymphatic duct
• 5 major lymph trunks

  1. lumbar trunks
  2. intestinal trunk
  3. Bronchomediastinal trunks
  4. subclavian trunks
  5. jugular trunks
• red bone marrow

  • A soft tissue located in the center of bones
  • It is the source of all white blood cells
  • Site of maturation for B cells
• thymus

  • Bilobed organ that lies behind the breastbone
  • Extends upwards into the root of the neck
  • Site of maturation for T-Cells
• lymph node

  • Oval or bean-shaped organs that lie, often in groups, along the length of lymph vessels
  • vary in size, from size of a pinhead to size of an almond
  • Filtering and phagocytosis
  • Proliferation of lymphocytes
• lymph node - cortex

  • contains lymphocytes
• lymph node - central medulla

  • contains phagocytes
• lymph node - germinal center

  • a key site in the differentiation of B cells into plasma cells
• 4-5 Afferent lymphatic vessels in a lymph node
• 8-10 lymph nodes filter the lymph before entering the venous circulation
• spleen

  • Largest lymphoid organ
  • has white pulp & red pulp
  • Phagocytosis
  • Storage of blood
  • Immune response
  • Hematopoiesis - fetus
• Mucosa-Associated Lymphoid Tissue (MALT)

  • Collection of small lymphoid tissues
  • includes tonsils, Peyer's patches, appendix
• tonsils

  • Traps and removes bacteria or other foreign pathogens entering the throat
• peyer's patches

  • lining of small intestines
  • AKA aggregated lymphoid nodules/follicles
• appendix

  • Capture and destroy harmful bacteria = thereby preventing them from penetrating the intestinal wall
• immune system

  • a functional system rather than an organ system
  • macrophages, lymphocytes, dendritic cells
  • innate defense mechanism & adaptive defense mechanism
• innate defense mechanism (nonspecific) - first line of defense

  • skin
  • mucous membranes
  • secretions of skin and mucous membranes
• innate defense mechanism (nonspecific) - second line of defense

  • phagocytic cells
  • natural killer cells
  • antimicrobial proteins
  • inflammatory response
• adaptive defense mechanism (specific) - third line of defense

  • lymphocytes
  • antibodies
  • macrophages and other antigen-presenting cells
• common indicators of inflammation

  1. redness
  2. heat
  3. pain
  4. swelling
  5. temporary limitation of movement (for joints)
• Lacteals


  • Specialized lymphatic capillaries located in the villi of the small intestines, absorb dietary fats and fat-soluble vitamins into the lymphatic system
• antigen

  • foreign molecules/pathogens (bacteria, virus, etc.) that triggers immune response
  • self
  • nonself
• antibodies

  • proteins produced by the body’s immune system after exposure to an antigen
• Hapten/incomplete antigen

  • small molecules that are not antigenic but when binds to a larger carrier molecule, may be recognized by the immune system as foreign
  • ex. poison ivy, animal dander
• 3 important aspects of adaptive defense

  1. antigen specific
  2. systematic
  3. has memory
• basic antibody structure

  • Made up of four Polypeptide chains
  • Linked by disulfide bonds
  • Two identical heavy chains
  • Two identical light chains, but half as long as the heavy chains
  • Variable regions combine their effort to form antigen binding site
• IgG

  • enhances phagocytosis, neutralizes toxins, and triggers the complement system
  • it is the only class of antibody that can cross the placenta and therefore passed on to the fetus during pregnancy
• IgA

  • concentrates in the body fluids (tears, saliva, the secretions of the respiratory tract, and the digestive tract
  • provides localized protection of mucous membranes against bacteria and viruses
  • known as the secretory antibody
• IgM

  • the first antibody class to be secreted by the plasma cells after initial exposure to antigen
  • referred as to a macro antibody due to its large molecular size