The Lymphatic System

24 de Apr de 2016

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The Lymphatic System

  1. THE LYMPHATIC SYSTEM Veterinary Physiology
  2. What is the Lymphatic System? • The lymphatic system is a network of: capillaries, vessels, ducts, nodes and tissues • It is part of the circulatory system • It carries excess tissue fluid (lymph) back to the circulating blood • It is found in all regions of the body except the central nervous system and bone marrow • It produces lymphocytes, which in turn produce antibodies – so technically, it has a role in immunity
  3. 4 Functions of the Lymphatic System 1. Return excess lymph to the circulating blood 2. Filter lymph to remove bacteria and other foreign particles.This takes places in the lymph nodes 3. Transport waste materials – the products of fat digestion and fat-soluble vitamins from the lacteals of the intestinal villi to the circulation 4. To produce lymphocytes, which in turn make antibodies
  4. How is Lymph formed? – Removing ExcessTissue Fluid The systolic force of the heart creates hydrostatic pressure and this pushes water out of the capillaries. Certain blood proteins are unable to pass through the capillary walls and this results in a water potential and the build up of these proteins results in osmosis in an attempt to reach equilibrium. However, equilibrium is never reached because blood is constantly flowing.The water that leaks out of the capillaries is known as tissue fluid. To prevent a build up of tissue fluid surrounding the cells in the tissue, some of it enters the lymph vessels where it becomes lymph. It eventually re-joins the blood. It is essential for this to happen because if the build up of fluid becomes too great, this could result in the fluid accumulating and forming an oedema, which is very painful.Therefore, the lymphatic system prevents – it is known as lymphatic drainage. Lymph mainly consists of water, sugar and electrolytes. It has less larger proteins than plasma as these were unable to pass through the capillary walls.
  5. LymphVessel Lymphatic vessels have a similar structure to veins. Lymph flow is mainly passive and relies on the contractions of surrounding muscles to move the lymph along. The valves prevent the backflow and pooling of lymph in the vessels.
  6. Lymphatic Ducts The lymphatic vessels enter the larger lymphatic ducts which drain the lymph back into the blood vessels to be returned to the heart.The main ducts are… • The right lymphatic duct – the smaller duct which empties blood from the head, neck, thorax and right forelimb into the right side of the heart via the right subclavian vein • The thoracic duct – the main lymphatic duct which collects blood from the rest of the body. It empties blood into the heart via the cranial vena cava • There is also a pair of tracheal ducts that drain the head and neck into the thoracic duct or one of the large veins near the heart
  7. Where lymph is carried to the node Where lymph is carried away from the node Where lymphocytes are produced Hilius – where the lymph vessel leave Trabeculae – support for the node
  8. Lymph Nodes The lymphocytes produced by the lymph nodes are important within the immune system as they containT and B cells. All lymph passes through at least one node before returning to circulation.This is important because each node acts as a mechanical filter by trapping foreign matter (such as bacteria particles) and destroying them using phagocytic cells. These phagocytic cells, such as macrophages, are located in the medulla of the node.This attempts to halt the spread of disease around the body. Lymph nodes are located around the body and some are superficial so can be palpitated. During times of infection or disease, lymph nodes can swell – this is known as lymphadenopathy.The swelling is a result of the active macrophage and the lymphocytes multiplying.
  9. Palatable Lymph Node’s Location
  10. LymphaticTissue Primary LymphoidTissue Secondary Lymphoid Tissue Bone Marrow Lymph Nodes Thymus Gland Mucosal-associated LymphoidTissue (MALT) Bursa of Fabricus (Birds) Peyer’s Patch Peyer’s Patch (cattle, sheep, pigs, dogs, horses) Spleen Appendix (rabbits) Tonsil
  11. Thymus Gland The thymus gland is especially important in young animals (late fetal and early postnatal life) who have immature immune sytems – the thymus gland kick starts normal development. It producesT lymphocytes which give rise to the cell mediated immune response. It lies caudal to the neck, in the cranial thoracic inlet. During puberty, the thymus gland regresses and may eventually disappear.
  12. Spleen This is the largest lymphoid organ located near the greater curvature of the stomach, within the greater omentum. It is not essential for life so can be surgically removed. It does however have a number of functions which are split into red pulp and white pulp… • Reservoir for red blood cells and platelets • Destroys worn out red blood cells – this is the job of the phagocytic cells but the iron from the RBCs is preserve for re- use in haemoglobin synthesis • Removal of particular matter from the circulation – filtering out foreign particles which are then destroyed by phagocytes • Produces lymphocytes
  13. Tonsils The tonsils form a ring of lymphoid tissue around the junction of the pharynx with the oral cavity and act as a first line of defence against microorganisms that enter via the mouth.
  14. What Can GoWrong? Equine Lymphangitis This occurs when the lymphatic flow is impaired so instead it accumulates and the result is an oedema. Causes: • Inflammation of the lymphatic system • Standing for too long • Infection • As a result of a small wound (It is essential a fracture is ruled out as the cause!!) Treatment: Antibiotics, massaging, movement, cold hosing
  15. What Can GoWrong? Lymphoma  A neoplasm originating in the lymphoid tissue (outside the bone marrow) Mean onset is 6-9 years in dogs and 8-12 years in cats and can be graded from I-V. Owner’s will usually present their animal showing symptoms such as lethargy, anorexia and upon examination, the vet will notice general lymphadenopathy. A fine needle aspirant can be used to aid diagnosis. Treatment: • Chemotherapy – can result in total remission in 69-90% cases but a median survival time of 6-12 months. If no response to this treatment, ‘back up’ drugs can be used but approximately 40-50% of dogs respond to this • Surgery to prevent advancement
  16. Lymphoma –WHO Grading • I  solitary node or lymphoid tissue in a single organ • II  multiple lymph node involvement in a single region • III  generalised lymph node involvement • IV  liver and/or spleen involvement • V  Bone marrow and/or other organs involved