Lymphatic System

• Lymphatic System is a network of vessels and organs that moves lymph from the tissues to the blood.
• Functions of Lymphatic System is Fluid recovery, Immunity, and Lipid absorption.
• Fluid recovery return excess tissue fluid that is not reabsorbed by the capillaries to the blood.
• Lymph nodes contain immune cells that activate an immune response to any foreign material picked up in the tissues.
• Special lymphatic vessels (Lacteals) in the small intestine absorbs dietary lipids that is not absorbed by the capillaries.
• Lymphatic vessels are similar to blood vessels.
• Lymphatic capillaries (terminal lymphatics) are closely associated with blood capillaries, unlike them they are closed on one end.
• Anatomy of Lymphatic vessels:

  • Has a sac of thin endothelial tissue that overlap each other.
  • Are not joined by tight junctions like blood capillaries.
  • Has gaps between that allows bacteria, lymphocytes, and other cell to enter along with the tissue fluid.
  • Has overlapping edges of endothelial cells that acts as valves to open and close; High tissue fluid pressure opens the flaps inward while high pressure in the capillary presses flaps outward.
• Anatomy of Lymphatic vessels pt.2:

  • Has three layers like veins but the walls are thinner and valves are closer together.
  • Tunica Intima: Endothelium with valves
  • Tunica Media: Elastic fibers and smooth muscle
  • Tunica Externa: Thin outer layer.
• Lymphatic capillaries converge to form collecting vessels, they travel alongside arteries and veins and empty into lymph nodes at irregular intervals.
• Lymph nodes contain immune cells such as lymphocytes and macrophages; Monitor lymph as it passes through for bacteria and other foreign substances, leaving through another collecting vessel.
• Lymphatic Duct (Right Side):

  • Convergence of right jugular, subclavian, bronchomediastinal in right thoracic cavity.
  • Drains right arm, right side of thorax and head
  • Empties into the right subclavian vein.
• Thoracic Duct (Left side):

  • Larger and longer than lymphatic duct
  • Begins in abdomen with two lumbar trunks and intestinal trunk joining to form a sac called cisterna chyli
  • Passes through the diaphragm with the aorta; It receives fluid from left bronchomediastinal, subclavian, and jugular trunks in thorax.
  • Drains abdomen, left arm, left side of thorax and head.
  • Empties into left subclavian vein
• Lymph is a clear, colorless fluid similar to plasma but low in protein, it flows at a lower pressure and speed than venous blood.
• Natural Killer (NK) Cells:

  • Large lymphocytes that attack and destroy bacteria, cancerous cells, and viral infected cells
• T Lymphocytes (T cells):

  • Lymphocytes that mature in the thymus
• B Lymphocytes (B cells):

  • Lymphocytes that mature in bone marrow
  • Differentiate into plasma cells that secrete antibodies
• Macrophages:

  • Large tissue phagocytic cells that develop from monocytes
  • Clean up debris, dead cells, and bacteria
  • Display antigenic fragments to certain T cells to produce antibodies against it
  • Called antigen-presenting cells (APCs)
• Dendritic cells:

  • Branched, mobile antigen-presenting cells found in the epidermis, mucous membranes, and lymph organs
  • Alert the immune system to foreign substances that breach body surfaces
  • Engulf substances by endocytosis
• Reticular cells:

  • Branched, stationary antigen-presenting cells that contribute to the framework of lymphatic organs
• Lymphatic (Lymphoid) Tissues:

  • Aggregations "collection" of lymphocytes in CT of mucous membranes
  • Diffuse lymphatic tissue lymphocytes are scattered around passages open to the outside (Respiratory, digestive, urinary, and reproductive tracts).
• Lymphatic Organs:

  • Primary: Thymus and bone marrow because T and B cells mature there.
  • Secondary: Lymph nodes, tonsils and spleen because mature lymphocytes migrate there.
• Thymus is bilobed gland that is divided into lobules; central medulla is populated with T cells, lymphocytes develop in cortex then migrate to medulla and they enter the blood or lymphatics from medulla. Produces molecules that promotes the development of T cells (thymosin, thymopoietin, thymulin, interleukins, and interferon).
• Lymph nodes are widespread but concentrated in:

  • Cervical: the neck (monitor head & neck).
  • Axillary: in the armpit (upper limbs and breast).
  • Thoracic: in thoracic cavity (mediastinum, lungs andairway).
  • Abdominal: in posterior abdominal wall (urinary andreproductive).
  • Intestinal: in mesenteries near intestines (digestive tract).
  • Inguinal: in the groin (lower limbs).
  • Popliteal: back of the knee (leg).
• Tonsils is guarded against ingested and inhaled pathogens which has deep pits called tonsillar crypts lined with lymphatic nodules.

  Three sets:

  • One median pharyngeal tonsil on pharnyx wall
  • Two palatine tonsils at opening of the oral cavity
  • Numerous lingual tonsils in patches on either side of the root of tongue
• Lymph nodes are bean shaped with indentation on one side (Hilum) and outer capsule, Lymph flows into node through afferent lymphatic vessels and filter through sinuses of cortex and medulla then leaves through efferent lymphatic vessels. It cleans the lymph before it goes back to the blood and is a site to activate T and B cells.
• Spleen has red pulp which is sinuses of erythrocytes and white pulp for lymphocytes and macrophages.

  Porous capillaries which RBCs leave bloodstream and accumulate in the red pul to reenter bloodstream; a site where worn RBCs are broken down; Lymphocytes in white pulp monitor for foreign substances while a reservoir of monocytes responds to emergencies and also destroying pathogens while repairing damaged tissues.