Lymphatic system

• Lacteals are located in the vili of the small intestine.
• Lacteals absorb the products of fat digestion which is transported via lymph.
• the substances transported in lymph are excess tissue fluid which is carried from the interstitial spaces as well as any excess protein from this area is also transported from the intestines, in addition lymph fluid is rich in lymphocytes.
• lymph fluid will eventually end up draining back into the vena cava and rejoin the circulating blood.
• Lymph fluid. is formed when blood flows through the tissue

  At the arterial end high pressure forces fluid from the blood into the tissue spaces.

  At the venous end where the pressure is lower the presence of plasma proteins in the blood exerts osmotic pressure which draws fluid back into the circulation.

  This process process does not retrieve all of the fluid present, the fluid remaining in the interstitial space forms lymph.
• The spleen is found in the cranial abdominal cavity and lies next to the stomach.
• The thymus is located in the mediastinum which is in the cranial thorax
• peyers patches are located in the lymphoid tissue of the small intestine
• tonsils are located in the pharynx
• a function of the lymphatic system is to transport excess interstitial fluid and return it to the blood
• A function of the lymphatic system is to transport excess protein from the interstitial spaces and return it to the blood
• a function of the lymphatic system is to transport products of fat digestion via the lacteals in the vili of the small intestine.
• The lymphatic system has a role in immunity as it is rich in lymphocytes which are the cells that produce antibodies.
• a function of the lymphatic system is to filter lymph via the lymphnodes and produce antibodies.
• If an infection is present in the body the tissue of the lymph nodes becomes hyperplastic as they respond by producing additional lymphocytes to support the immune response.  They also have an important role in filtering lymph to prevent pathogens from the interstitial spaces reaching the bloodstream
• In active immunity the animal produces its own antibodies in response to challenge with an antigen. this means the animals own immune system does the work.
• In passive immunity the animal is given a ready made source of antibodies and does not manufacture its own.
• Active immunity is generally stronger and long lasting and associated with production of memory cells. Passive is only temporary with no memory cells created
• Active natural – being exposed to disease and developing antibodies.
• active artificial – being given a vaccine and developing antibodies, stronger and longer lasting response with creation of immune memory cells, can take up to 2 weeks for peak antibody production.
• •Passive natural – receiving antibodies via colostrum or placental transfer.
• Artificial natural – receiving hyperimmune serum/plasma transfer as part of treatment, immediate protection however it is temporary and no immune memory cells are created
• Humoral immunity is when specific B-lymphocytes  can  recognise specific antigens and change to become plasma cells which can then produce specific antibodies depending on the pathogen

  Some plasma cells will become memory cells – when the animal encounters the infection again they remember the antigen and produce a rapid antibody response
• Cellular immunity involves T-lymphocytes. They do not produce antibodies but they are cytotoxic meaning the assist in humoral immune response.
• the reticulo-endothelial system is a network of phagocytic cells which work along side T-cells and B-cells to complete the immune response.
• the canine lymph nodes are:

  • submandibular
  • pre-scapular
  • axillary
  • inguinal
  • popliteal
• immunity is when the body recognises an antigen and responds to it.
• lymphatic vessels are blind ended. they are small and can form larger vessles. they have valves to prevent back flow. they are highly permeable due to thin walls with a large surface area. they pass through body tissue.
• lymphatic ducts collect lymph before it goes back into the blood stream.
• Tracheal ducts drain the head and neck
• the right lymphatic duct drains the forelimbs and the thorax
• the cisterna chyli originates in the abdomen and drains the rest of the of the body and passes through the diaphragm where it becomes the thoracic duct which drains into the cranial vena cava.
• an oedema can be caused by a lymphatic blockage, leaky capillaries and inactivity.