Lymphatic System

• The lymphatic system:

  • Transports lymph through the lymph capillaries and lymph vessels
  • Controls body fluids and destroys harmful microorganisms
  • Consists of lymph, lymphatics, lymph nodes, the tonsils, the spleen, the thymus gland, and Peyer's patches.
• The functions of the lymphatic system are

  • to drain interstitial fluid from tissue spaces

  • to transport fats from the digestive tract to the blood

  • to develop immunities

  • to produce lymphocytes
• Some blood plasma gets forced through the blood capillary walls into spaces between tissue cells. This is called interstitial fluid.
• Interstitial/tissue/intercellular fluid is found in the spaces between the cells. It is formed from blood plasma, water, and protein, leaking from capillaries.
• Lymph:

  Is found in lymphatic vessels and formed by interstitial fluid mixing with protein after entering the lymphatic capillaries.
• Lymph Composition:

  ➢ Water ➢ Protein ➢ Fat and other substances Both interstitial and lymph fluids resemble blood plasma in composition
• Lymph capillaries drain interstitial fluid, which is now called lymph, and pass this fluid on to lymph vessels called lymphatics.
• In the villi of the small intestine, special lymphatics called lacteals pick up fats and transport them to the blood.
• Lymph in lacteals looks milky and is called chyle.
• Lymphatic capillaries:

  • Some are lacteals (capillaries originating in the villi)
  • Closed-ended capillaries located in tissue spaces
  • Lined by endothelial cells
  • Have pores between endothelial cells
• Larger lymphatic vessels

  Formed by the merger of lymphatic capillaries and small lymphatics
• Right lymphatic duct

  Drains lymph from the right upper quadrant of the body into the right subclavian vein.
• Left lymphatic (Thoracic) duct

  Originates from the cisterna chyli in the lumbar region

  Drains lymph from the right lower quadrant of the body and the entire left side of the body into the subclavian vein
• Structure of lymphatic vessels - Resemble veins except:

  • Lymphatics have thinner walls.
  • Lymphatics contain more valves.
  • Lymphatics contain lymph nodes located at intervals. 2. Numerous semilunar valves present
• Functions of lymphatic vessels:

  1. Return fluid to blood
  2. Return proteins and large particulates to blood
  3. Fat and other nutrients from the small intestine are absorbed by lacteals
• Lymph node


  • Surrounded by a capsule
  • Capsule extends inward, dividing the node into several cortical nodules
  • Cortical nodules filled with B lymphocytes and macrophages
  • Around each cortical nodule are sinuses with the lymph
  • In the center is the medulla, composed of medullary cords and sinuses
  • Medullary sinuses filled with phagocytic reticuloendothelial cells
  • Efferent lymphatics exit the lymph node at the hilum, with a slight depression on one side
  • Blood vessels and nerves also exit and enter at the hilum
  • Afferent lymphatics enter the lymph node at various locations on the node
• Locations of lymph nodes:

  Preauricular lymph nodes

  Submental and submaxillary lymph nodes (floor of mouth)

  Superficial cervical lymph nodes (neck)

  Superficial cubital, or supratrochlear, lymph nodes (just above the bend of the elbow)

  Axillary lymph nodes (under arm & upper chest)

  Inguinal lymph nodes (groin)
• Functions of lymph nodes

  1. Defense a. Filtration b. Phagocytosis
  2. Hematopoiesis a. Maturation of some lymphocytes and monocytes that migrated from red marrow
• Lymphatic Drainage of the Breast:

  There are two sets of lymphatics draining the breast

  1. Lymphatics that originate in and drain skin over the breast
  2. Lymphatics that originate in and drain breast substance
  3. the Lymph nodes associated with the breast - the 85% of lymph from breast enters lymph nodes of axillary region.
• Tonsils (nodules):

  • Palatine tonsils (tonsils) - two on each side of the oral cavity
  • Pharyngeal tonsils (adenoids) - one in the nasopharynx
  • Lingual tonsils - two located at the base of the tongue
• Structure of the thymus

  1. Each lobe is divided into lobules, each with a cortex and medulla
• Function of the thymus

  • Immature lymphocytes formed in red marrow move to the thymus.
  • Lymphocytes mature and are distributed to the spleen, lymph nodes, and lymphoid tissue before birth.
  • After birth, the thymus secretes thymosin, which enables lymphocytes to develop into T cells.
• Location of the spleen: upper left part of the abdominal cavity.
• Structure of the spleen: it resembles large lymph node that is encapsulated
• Blood enters the white pulp (full of lymphocytes), then the red pulp, then venous sinuses, and into veins.
• Functions of the spleen

  1. Defense a. Bacteria eaten by reticuloendothelial cells lining venous sinuses
  2. Hematopoiesis a. Maturing of monocytes and lymphocytes b. RBCs formed before birth
  3. Red blood cell and platelet destruction a. Worn RBCs phagocytosed by sinusoid reticuloendothelial cells
  4. Blood reservoir a. Normal volume of 350 ml. b. Volume decreased by about 200 ml by sympathetic stimulation