Introduction to the Lymphatic System PDF

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Introduction to the Lymphatic System...

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Introduction to the Lymphatic System Tissues and organs in the lymphatic system - Lymph nodes - Lymphatic vessels – large and small - Spleen - Accessory tissues – tonsils, pharyngeal tonsils, appendix and Peyer’s patches Role of the lymphatic system is … cleaning The lymphatic system, cleans in several ways… - Assists in maintaining fluid balance - Protects the body for infection - Absorbs fat Fluid balance - As blood circulates through capillaries in the tissues, water and dissolved substances are constantly exchanged between bloodstream and fluid surrounding cells - Some fluid and proteins often left behind in the tissues, following exchange - The lymphatic system removes the fluid left behind and deposits it in the venous system near the heart Protection for infection - The lymphatic system is involved in fighting infection - White blood cells (lymphocytes) live and multiply in the lymphatic system – they destroy foreign organisms - Lymphoid or specialised immune tissue is scattered throughout the body and filters harmful microbes and cellular debris Absorption of fat - Following breakdown (chemical and mechanical) of food in the digestive tract- most nutrients are absorbed through capillaries - Many digested fats are too big to enter blood capillaries, so instead they are absorbed by lymphatic capillaries and added to blood stream when lymph joins the bloodstream Lymphatic vessels and Lymph nodes - Lymphatic tissues are connected by thin walled drainage channels – lymphatic vessels - Afferent lymphatic vessels carry lymph into the lymph nodes - Lymph slowly filters through the node and is collected into lymphatic vessels - Lymphatic capillaries (wider than blood capillaries) are located throughout most of the body - Lymphatic capillaries allow drainage of extra-cellular fluid into them but will not allow it to get out

Specialised Lymphatic Capillaries- Role of Absorption - Specialised lymphatic capillaries – lacteals are located in the lining of the small intestine and absorb digestive fats - Fats taken into the lacteals are transported in the lymphatic vessles until the lymph added to blood Lymph fluid - Clear fluid- circulates around the body It contains:  Water  Proteins  Cellular waste  Lipids  Hormones  Dead cells  Bacteria Lymphatic drainage Lymphatic vessel carrying lymph away from regional nodes drain into 2 terminal vessels: - The right lymphatic duct- short - The thoracic duct - larger, drains everywhere apart from right upper quadrant - Can be damaged in chest surgery Movement of lymph - More fluid = faster contraction of vessels - Skeletal muscles- help to pump lymph - Changes in pressure within the chest during breathing help to move it through the system - One way valves- stop backflow - Lymphoedema – swelling of an arm / leg – can occur after surgery, radiation therapy - Common cause of Lymphoedema – lymph node removal – following breast / prostate surgery LYMPH NODES Structure of a lymph node - Surrounded by a thin, fibrous capsule - From the capsule bands of connective tissue Extend into the node and divide it into 3:  Superficial cortex (outside) – contains follicles mainly made of B cells  Deep cortex – consists mostly of T cells  Medulla (centre) – plasma cells which secrete immune-active proteins (immunoglobulins) - Small, oval-shaped structures situated within a network of lymph channels

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Most abundant in head, neck, under arms (axillae), abdomen, pelvis and groin. Filter lymph Lymph nodes help remove and destroy antigens (substances capable of causing an immune response) that circulate in blood and lymph Trap cancer cells. Cancer cells may still divide and reproduce and spread from node to node. If caught early can be surgically removed preventing cancerous cells from entering blood stream Nodes are found in groups that serve a particular region

Lymph node enlargement - Lymph nodes enlarge as they fill with new lymphocytes and natural killer cells in the presence of infection or cancer. - The full nodes may become visible or can be felt – a condition called lymphadenopathy - If the node is overwhelmed, bacteria can infect the node and spread along the vessel, which becomes inflamed – lymphangitis. - This shows as a red line ‘tracking’ to the next set of nodes. Thymus gland - Thymus gland is a lymphoid organ - Job – to promote the development of immature lymphocytes into mature Tlymphocytes - Peak size puberty and shrinks in older age Thymus gland – processes T-lymphocytes - Thymus divided into lobules:  Outer cortex  Inner medulla. - Lymphocytes multiply in cortex – and mature in the medulla. Leave thymus via blood vessels in medulla - Each lobule produces the hormone thymosin that promotes the development of T-cells from stem cells

Spleen - Located in left upper quadrant below diaphragm - Dark red, oval structure About the size of a fist Largest lymphatic organ - Fibrous capsule surrounding it - Bands of connective tissue from the capsule extend inwards Inside the spleen - Splenic pulp – red and white - Red pulp – system of blood-filled cavities known as sinusoids, supported by a network of fibres and various types of white blood cells - White pulp – compact masses of lymphocytes surrounding splenic artery

Jobs of the spleen Pac-man like white blood cells (phagocytes) in the spleen:  Breakdown worn-out or abnormal red blood cells (RBCs) – causing the  Release of haemoglobin which also breaks down  Filter and remove bacteria and other foreign substances  Stimulate other white blood cells to initiate immune response  Stores blood and 20-30% of platelets  Makes RBCs in foetus  If the spleen is removed due to disease or trauma, the liver and bone marrow assume its function Accessory lymphoid organs and tissues - These include tonsils, pharyngeal tonsils, appendix and Peyer’s patches, sometimes known as MALT or mucosa-associated lymphoid tissue - Remove foreign debris in much the same way as lymph nodes - Located in areas in which microbial access is more likely, such as the: - Naso-pharynx (tonsils including pharyngeal tonsils) - Abdomen (appendix and Peyer’s patches) Peyer’s patches – collections or aggregated lymphoid nodules - Usually found in the ileum - Have an important immune function – detect microbes and other antigens in the ileum, which may have entered the gut from the environment. - If necessary they initiate an immune response via the mucosa - Excessive growth of these patches can lead to intussusception (more common in children) causing a bowel obstruction...