Lymphatic System Revision PDF

Lymphatic system  Lymphatic system consists of: Lymph Lymph vessels (capillaries, vessels, ducts) Lymph nodes Lymph organs (spleen, thymus) Diffuse lymphoid tissue (tonsils) Bone marrow Functions of lympha...

Lymphatic system  Lymphatic system consists of: Lymph Lymph vessels (capillaries, vessels, ducts) Lymph nodes Lymph organs (spleen, thymus) Diffuse lymphoid tissue (tonsils) Bone marrow Functions of lymphatic system Tissue drainage — Excess fluid that escapes from bloodstream is drained from tissue space by network of thin walled lymphatic capillaries. Prevents swelling of tissues. Maintains blood volume (CV system). Immunity — Lymphatic organs are concerned with production and maturation of lymphocytes (white blood cells). Transports lymph around the body - contains white blood cells. Absorption in the GI tract — Breakdown products of fat and fat-soluble vitamins. The villi of the small intestine contains lymphatic capillaries (lacteals) that absorb fats and fat-soluble vitamins. Lymph Clear fluid that contains lymphocytes (white blood cells) - similar to interstitial fluid but less protein. Use the lymphatic system as a transport network - allows monitoring of tissues throughout body. Lacteals (lymphatic capillaries) in the small intestine absorb fats to give lymph a ‘milky’ appearance. Transports plasma (blood) proteins that seep out of the capillaries back into bloodstream. Larger molecules are carried away to the lymph nodes - pathogens, cell products/debris).  Lymphatic capillaries Tiny blind-ended drainage tubes within interstitial Lymphatic vessels and space. capillaries form a one-way Single layer of endothelial cells. drainage system linking More permeable and allow larger molecules to enter - interstitial space and cell debris and plasma proteins. bloodstream. Merge to form larger lymphatic vessels. Lymphatic vessels Often found running alongside veins/arteries. Numerous cup-shaped valves to ensure one-way flow of lymph. 3 layers - Fibrous covering, middle layer of smooth muscle and elastic tissue, inner lining of endothelium. Become larger as they merge, eventually forming 2 ducts - thoracic duct and right lymphatic duct. Lymphatic ducts Thoracic duct Right lymphatic duct 40cm long. Empties into left subclavian vein. 1cm long. Drains: Empties into right subclavian vein. Both legs Drains: Pelvic and abdominal cavities Right half thorax Left half thorax Right arm Left arm Head and neck. Head and neck.  Transport of lymph NO PUMPS!! Muscle layer in large lymph vessel walls has intrinsic ability to contract rhythmically (the lymphatic pump). Lymph vessels are compressed by contraction of surrounding muscles and regular pulsation of large arteries. This ‘milking’ actions helps push the lymph along. Valves present to prevent back flow of lymph. Changes in thoracic pressure can also help lymph flow. Hilum = concave surface where Lymph nodes vessels and nerves enter an organ. Oval/bean shaped organ. Lie along length of lymph vessels - often in groups. Vary in size - 1-25cm in diameter. Most numerous in vessels carrying lymph from tissues vulnerable to infections - respiratory & GI tract. Lymph usually flows between 8-10 nodes before returning to venous circulation. Structure: Outer fibrous capsule that dips into node forming partitions/trabeculae. Reticular cells - produce network of reticulin fibres which provide lymph node internal structure. Lymphatic tissue - packed with immune and defence cells (lymphocytes and macrophages). 4/5 afferent lymph nodes may enter but only one efferent vessel carries lymph away from the node. Every node has a concave surface called hilum - where the artery enters and vein and efferent vessel leave. Arranged in deep and superficial groups. Lymph from head and neck passes through deep and superficial nodes. Functions: Defence Lymph is cleaned by the reticular and lymphatic tissue as it slowly flows through the nodes. Organic matter (bacteria, cells from malignant tumour, worn out/damaged tissue cells etc.) is removed and destroyed by macrophages. Material not filtered out in one lymph nodes will pass to successive nodes and usually cleaned before entering bloodstream. If phagocytosis is incomplete, and bacteria survive, they may stimulate inflammation and enlargement of lymph node. Maturation and proliferation of lymphocytes Some lymphocytes complete maturation in lymph nodes and activated T and B lymphocytes multiply. Tonsils Uncapsulated collections of lymphoid tissue. Located in the back of the mouth. Intercept swallowed or inhaled antigens. Trap bacteria which is then destroyed by T-lymphocytes and macrophages. Infection may cause pain or obstruct breathing. Three main groups: Pharyngeal tonsil - back of nasal cavity. Palatine tonsils - pharyngeal wall back of mouth. Lingual tonsils - back and sides of tongue. Trabeculae = Spleen fibrous capsule that dips into organ to Largest lymph organ. from partitions. Contains reticular and lymphoid tissue. Lies in left region of abdominal cavity - between stomach and diaphragm. Structure: Oval shaped, soft organ, with a hilum on lower medial border. Enclosed in a fibroelastic capsule that dips into the organ to form trabeculae. Covered in peritoneum - membrane of smooth tissue. 2 types of pulp: red pulp: stores large numbers of red blood cells, white pulp: consists of lymphatic  Functions: Phagocytosis Old and abnormal erythrocytes (red blood cells) and other cellular material (leukocytes, bacteria, platelets) are destroyed mainly in red pulp of spleen. Breakdown products (bilirubin and iron) are transported to the liver via splenic and portal veins. No afferent lymphatics - not exposed to diseased spread by lymph. Storage of blood Contains up to 350ml of blood within red pulp. Can rapidly return most of this volume to circulation (in a haemorrhage). Immune response Splenomegaly = White pulp contains T and B lymphocytes - important role in immunity. Enlargement of the Activated by the presence of antigens - during infection. spleen. Lymphocyte proliferation during serious infection can cause splenomegaly. Erythropoiesis Importance for fetal blood cell production and also fulfils this function in adults. Thymus gland Lies in the behind the sternum and extends upwards. Grows until puberty and Structure: 2 lobes joined by areolar tissue. Lobes are enclosed in a fibrous capsule, that dips into their substance, dividing them into lobules. Lobules consist of irregular branching network of epithelial cells and lymphocytes Functions: Lymphocytes that enter the thymus develop into T-lymphocytes. Produces mature T-cells that can distinguish self tissue from foreign tissue. T-cell production most prolific in youth - due to shrinking of the gland after puberty and decrease in T- cell effectiveness. Stimulated by thymosin hormone. Thymus Mucosa-associated lymphoid tissue Strategically placed. Not enclosed within capsule. No afferent lymphatic vessels associated - do not filter lymph, therefore not exposed to diseases spread by lymph. Found throughout, gastrointestinal tract, respiratory tract, genitourinary tract - all body systems exposed to the environment. Main groups: Tonsils Aggregated lymphoid follicles (Peyer’s patches) - large collection of lymphoid tissue in small intestine. Lymphangitis = Lymphadenitis = Lymphadenopathy = Inflammation of the Infection of the Enlargement of the lymph vessels. lymph nodes. lymph nodes. Lymphoedema = Splenomegaly = Swelling in tissues whose Enlargement of the lymphatic draining has spleen. been obstructed. Lymphatic obstruction If a lymph vessel becomes obstructed, the lymph accumulates behind - swelling. Usually leads to low-grade inflammation and fibrosis of the lymph vessel - further obstructs the lymph flow. Main causes: Tumours Compress lymph vessels - blocking lymph flow and drainage. May grow and block a lymph vessel or node. Surgery Lymph nodes are removed in some surgical procedures - due to cancer/malignant cells spreading. Aim is to prevent; growth of secondary tumours and further spread of disease. (For example; the axillary nodes may be removed during mastectomy which can lead to obstruct lymph drainage and cause lymphoedema of affected arm). Lymphadenitis Acute lymphadenitis (acute infection of the lymph nodes) - secondary to a number of conditions. Usually caused by microbes transported in the lymph from infected tissues. Infected nodes become; inflammed, enlarged and congested with blood. Chemotaxis = Chemotaxis attracts large numbers of phagocytes. Directed movement of If defences are overwhelmed, an abscess can form inside node. defensive cells into infected Adjacent tissues may also become involved. or damaged tissue. Infected materials may be transported through other nodes and into blood. Minor lymphadenitis accompanies many infections and indicates normal proliferation of defence cells. Chronic lymphadenitis occurs following unresolved acute lymphadenitis, TB, syphilis, some low-grade infections. Infectious mononucleosis (glandular fever) Highly contagious viral infection - spread by direct contact and caused by Epstein-Barr virus (EBV). 7-10 day incubation period the viruses multiply in epithelial cells and spread to cervical lymph nodes and lymphoid tissue throughout body. Clinical features; fatigue, malaise ,tonsillitis, lymphadenopathy and splenomegaly.