A&P: CH. 20 [Lymphatic System]

• Lymphatic system vs. circulatory system


  Lymphatic system isn’t a closed loop as fluid and proteins make their way into the microscopic lymphatic capillaries and all collected lymph is dumped into the veins
• Lymphatic trunks

  • Two lumbar trunks
  • Two bronchomediastinal trunks
  • Two subclavian trunks
  • Two jugular trunks
  • One intestinal trunk
• Lymph movement through lymphatic vessels

  1. Travel through bigger and thicker-walled vessels, then trunks, and then ducts

  2. Smooth muscle in the lymph vessels reacts to nearby arteries pulsing and skeletal muscle contractions to keep the lymph moving along

  3. Valves in lymphatic vessels prevent backward flow
• Lymphatic capillaries


  • Smallest lymphatic vessels located throughout the interstitial space
  • Extremely permeable due to loosely overlapping endothelial cells forming one-way minivalves
  • Anchored to structures in the interstitial space by collagen filaments, allowing flexibility while retaining shape
• Lymph

  The fluid that flows through the lymphatic vessels and lymph nodes which make up the lymphatic system
• Pressure in lymph dumping junction

  Very low pressure, making it easier for lymph to flow in
• Fluid seepage from capillaries

  1. Every day 20 liters of fluid water and protein seep out of the capillaries and become part of the interstitial fluid between cells

  2. About 17 liters quickly reabsorbed back into the capillaries, leaving 3 liters of fluid behind in the tissues each day

  3. This 3 liters of fluid needs to find a way back into the blood so that the body’s interstitial fluid volume and blood volume both stay constant over time
• 20 liters of fluid seep out each day, even though the blood volume is only 5 liters, due to constant motion and recycling
• Three major roles of the lymphatic system


  • Returns fluid from the tissues back to the heart
  • Helps large molecules like hormones and lipids enter the blood
  • Helps with immune surveillance to keep infections from running amok
• Right lymphatic duct vs. thoracic duct

  • Right lymphatic duct collects lymph from the right arm and right side of the head and chest, dumping into the right jugular vein and right subclavian vein junction
  • Thoracic duct collects lymph from the rest of the body, dumping into the same junction on the left side of the body
• Advantages of the lymphatic system


  • Picks up larger molecules like hormones that are too large to get into capillaries and gets them into the bloodstream
  • Helps get nutrients to the tissues, e.g., fatty acids packaged into chylomicrons by the small intestine and moved by lacteals into the bloodstream
• Lymphatic vessels


  Collect excess interstitial fluid and return it to the blood
• Lymphatic trunks to body regions

  Named after the regions of the body they drain lymph from
• Lymph


  clear water
• Role of lymphatic system in immune function

  1. Lymphoid organs remove foreign material from lymph to prevent it from entering the bloodstream

  2. Lymphoid organs act as lookout points for the body's immune defenses
• Pathogen detection in lymph nodes


  1. Pathogens or pieces of pathogens detected by dendritic cells in lymph nodes

  2. Dendritic cells present antigens to B cells

  3. B cells, a type of lymphocyte, can make antibodies in response to foreign antigens

  4. Plasma cells produced by B cells start producing antibodies that flow into the lymph exiting the lymph node
• Lymph is cleansed at lymph nodes throughout the lymphatic system, playing an important role in immune function
• Spleen


  • About the size of a fist, located on the left side of the body below the diaphragm and on top of the stomach
  • Contains white pulp for filtering bacteria and generating antibodies, and red pulp for destroying old and defective blood cells
  • Keeps red blood cells and platelets available for emergencies
• Diffuse lymphoid tissue


  • A loose arrangement of lymphoid cells and protein, typical in the lining of the gastrointestinal and respiratory tract
• T cells

  • Lymphocytes that move between lymph nodes, lymph, and blood to search for pathogens and infected or abnormal cells tagged by antibodies
• Transport of fatty acids during a meal

  1. Fatty acids get packaged into chylomicrons by the small intestine

  2. Chylomicrons move into special lymphatic vessels called lacteals

  3. Chylomicrons make their way up into the thoracic duct and get dumped into the venous blood
• Lymph nodes

  • Tightly packed balls of lymphoid cells and protein
  • Hundreds cluster along lymph vessels, each one a few millimeters to about 1–2 cm in size
  • Can be felt concentrated along lymph trunks, especially in the neck, armpit, and groin
  • Found in the intestinal wall, known as Peyer's patches
• Tonsils

  • Include adenoid, tubal tonsils, palatine tonsils, and lingual tonsils
  • Form a ring of lymphoid tissue around the throat
  • Main job is to trap pathogens from food and air
• Thymus


  • In the upper part of the chest, most active in neonatal and pre-adolescent years, involved in the development of T cells
  • Atrophies and gets replaced by fat after puberty
  • no follicles, lacks B cells
  • does not directly fight antigens
• Lymphatic system

  A one-way network of lymphatic vessels that transports lymph, a clear fluid squeezed out of the blood, to cells for nutrients and waste removal
• MALT (mucosa-associated lymphoid tissues): strategically places mucous membranes; tonsils, peyers patches, appendix
• peyer's patches: lymphoid tissue in the small intestine a.k.a. aggregated lymphoid nodules
• appendix: tubular first part of large intestine with high concentration of lymphoid follicles

  1. destroy bacteria
  2. generate memory lymphocytes
• jugular lymph sac: lymphatic duct that drains lymph from the neck and upper chest
• except for thymus, lymphoid organs derived from mesodermal mesenchymal cells
• except for spleen and tonsils, lymphoid organs are poorly developed before birth but becomes heavily populated with lymphocytes afterwards
• circulation in lymph node

  1. afferent lymphatic vessel
  2. subcapsular sinus
  3. cortex
  4. medulla
  5. 3. medullary sinuses
  6. 4. hilum via efferent lymphatic vessel
• buboes: infected lymph nodes