week 12

• Lymphatic System


  The body's sewer system & immunity system
• Lymphatic System


  • Part of the circulatory system
  • Consists of: Thymus, Lymph nodes, Lymph vessels, Lymphocytes, Lymph, Spleen, Tonsils, MALT, Bone marrow
• Functions of the Lymphatic System

  1. Removes toxins, cellular waste & excess water

  2. Recycles interstitial fluid & maintains fluid levels

  3. Provides immune protection (fights pathogens)

  4. Assists in the absorption of digested fats in the ileum
• Interstitial Fluid


  Extracellular fluid present outside the blood vessels
• Drainage of Interstitial Fluid

  1. Lymphatic capillaries present throughout blood capillaries

  2. Excess interstitial fluid drains into lymphatic capillaries – now called lymph

  3. Lymph contains a variety of substances, including proteins, salts, glucose, fats, water, and white blood cells
• Thymus

  • Located just anterosuperior to the heart
  • Responsible for the production and maturation of T-cells
  • Most active in early pre-adolescent period, Involutes (shrinks) in early teens and activity is reduced
  • Almost absent in the elderly
• Spleen


  • Fist sized organ located under the ribcage and above the stomach
  • Functions as a kind of 'large lymph node' for the blood
  • Stores excess blood, Filters blood & cleans it, Removes cellular waste, Gets rid of old or damaged blood cells, Makes white blood cells and antibodies that help you fight infection, Maintains the levels of fluid in your body
• Tonsils


  • Lymphoid tissue aggregates situated near the entrance of the digestive and respiratory tracts
  • Help filter out germs that enter through your nose or mouth to protect the rest of your body from infection
  • Produce white blood cells and antibodies for the mouth and throat
• Lymph Nodes


  • Small, bean-shaped organs
  • Lymphatic vessels carry lymph through lymph nodes
  • Clustered at certain regions throughout the body
  • Scan/filter lymph for pathogens
  • Contain lymphocytes (immune cells) to kill pathogenic cells
  • Capture cancer cells and prevent their circulation
  • Absorbs some of the fats in our diet from the intestine
• Lymph Vessels


  • Thin-walled vessels structured like blood vessels
  • Collects and carries lymph from peripheral tissues for filtering
  • Returns lymph to the blood system once it has been filtered
  • Contain valves to prevent lymph from flowing back
  • 3 types: Capillaries, Lymph vessels, Ducts
• Lymphatic tissue is concentrated in areas exposed to the external environment, such as the gastrointestinal tract, nasopharynx, thyroid, lung, salivary glands, eye, and skin
• Mucosa-Associated Lymphatic Tissue (MALT)


  Part of the first and secondary line of defence, when the pathogens have passed the first line and before they can enter the body
• Lymph


  A clear white fluid that composed of: White blood cells, Interstitial fluid, Cell waste, toxins & destroyed pathogen fragments, Chyle
• Fluid Exchange: Blood to Lymph to Blood

  1. Interstitial fluid leaks from blood capillaries into tissues

  2. 90% re-enters capillary due to colloid osmotic pressure

  3. Lymph capillaries pick up the remaining 10% and help return it to your circulatory system
• Flow of Lymph


  1. One way drainage system

  2. Lymphatic capillaries -> lymphatic vessels & lymph nodes -> lymphatic trunks -> right lymphatic ducts & thoracic duct -> right and left subclavian veins
• Ensuring Unidirectional Flow of Lymph

  • Lymphatic capillaries are blind-ended and have flap-like mini-valves
  • All other lymphatic structures (vessels, trunks, ducts) have internal valves to prevent backflow
• Lymphocytes


  • Type of white blood cell
  • Made in the Bone marrow and Thymus
  • Two main types: B-cells and T-cells
• Red Bone Marrow


  • Specialised connective tissue
  • Contains pluripotent stem cells for the formation of blood cells (hematopoitesis)
  • Produces erythrocytes, leukocytes and thrombocytes
• The Immune System


  A series of defence systems that protect against disease-causing organisms (pathogens)
• Three Lines of Defence

  • Physical barriers
  • Innate immunity (born with it)
  • Adaptive immunity (learned)
• 1st Line of Defence: Physical Barriers

  • Skin and mucosal linings
  • Skin contains cells which secrete keratin and fatty acids
  • Mucosal linings in oral, nasal, respiratory, digestive, and genitourinary tracts
• 2nd Line of Defence: Innate Immunity

  • Lymphocytes identify generic pathogen proteins and destroy cells containing pathogens
  • Monocytes, Eosinophils, Basophils, Neutrophils, Mast cells
• 3rd Line of Defence: Adaptive Immunity


  • B and T cells identify specific pathogen antigens
  • T cells release antitoxins to destroy infected cells
  • B cells replicate to produce memory cells and plasma cells that release antibodies
• Lymphatic System Dysregulations


  • Lymphangitis
  • Lymphoma