The Lymphatic Systemppt.ppt

The Lymphatic System Chapter 20 Objectives • Review the exchange at capillary bed • Describe the structure of the lymphatic system—lymphatic vessels, lymph, lymph nodes. • Describe the functions of the lymphatic vessels, lymph, and nodes. • Describe the functions of the lymphoid organs • Describe...

The Lymphatic System Chapter 20 Objectives • Review the exchange at capillary bed • Describe the structure of the lymphatic system—lymphatic vessels, lymph, lymph nodes. • Describe the functions of the lymphatic vessels, lymph, and nodes. • Describe the functions of the lymphoid organs • Describe the source of lymph and the mechanism of transportation Overview of lymphatic system • Consists of two semi-independent parts – A meandering network of lymphatic vessels – Lymphoid tissues and organs scattered throughout the body • Returns interstitial fluid and leaked plasma proteins back to the blood • Lymph – interstitial fluid once it has entered lymphatic vessels Lymphatic system Lymphatic system Discuss with a partner! • What is interstitial fluid and how is it formed? • How is blood, interstitial fluid, and lymph differ? Lymphatic vessels • A one-way system in which lymph flows toward the heart • Lymph vessels include: – Microscopic, permeable, blind-ended capillaries – Lymphatic collecting vessels – Trunks and ducts Lymphatic capillaries • Similar to blood capillaries, with modifications – Remarkably permeable – Loosely joined endothelial minivalves – Withstand interstitial pressure and remain open • The minivalves function as one-way gates that: – Allow interstitial fluid to enter lymph capillaries – Do not allow lymph to escape from the capillaries Lymph capillaries Function of lymph capillaries • During inflammation, lymph capillaries can absorb: – Cell debris – Pathogens – Cancer cells • Cells in the lymph nodes: – Cleanse and “examine” this debris • Lacteals – specialized lymph capillaries present in intestinal mucosa – Absorb digested fat and deliver chyle to the blood Lymphatic collecting vessels • Have the same three tunics as veins • Have thinner walls, with more internal valves • Anastomose more frequently • Collecting vessels in the skin travel with superficial veins • Deep vessels travel with arteries Lymphatic trunks • Formed by union of largest collecting vessels • Drain large areas of the body • Major trunks named for regions they collect lymph ( eg. Right and left lumbar, right and left jugular trunk) Lymphatic trunks • Lymph is delivered into one of two large trunks – Right lymphatic duct – drains the right upper arm and the right side of the head and thorax – Thoracic duct – receives from rest of body Lymphatic trunks Transportation of lymph • The lymphatic system lacks an organ that acts as a pump • Vessels are low-pressure conduits • Uses the same methods as veins to propel lymph – Active skeletal muscles – Valves to prevent backflow – Pressure changes in thorax during breathing – Pulsation of nearby arteries Transportation of lymph • Sporadic and slow • About 3 L enters bloodstream every 24 hours • Physical activity allows rapid movement of lymph Lymphoid organs Include: • Lymph nodes • Spleen • Thymus • Tonsils • Peyer’s patch * Where in the body can you find the spleen, thymus, tonsils, and Peyer’s patch? Lymphoid organs Made of: Lymphoid cells Lymphoid tissue Lymphoid cells • Lymphocytes are the main cells involved in the immune response • The two main varieties are T cells and B cells • Other lymphoid cells include macrophages (phagocytize foreign substances and help activate T cells) Lymphocytes • T cells and B cells protect the body against antigens • Antigen – anything the body perceives as foreign – Bacteria and their toxins; viruses – Mismatched RBCs or cancer cells Lymphocytes • T cells – Manage the immune response – Attack and destroy foreign cells • B cells – Produce plasma cells, which secrete antibodies – Antibodies immobilize antigens Lymphoid tissue • Important component of immune system • Houses lymphocytes and allow them to proliferate • Make up part of larger lymphoid organs Lymph nodes • Lymph nodes are the principal lymphoid organs of the body • Nodes are imbedded in connective tissue and clustered along lymphatic vessels • Aggregations of these nodes occur near the body surface in inguinal, axillary, and cervical regions of the body Functions of lymph nodes • Their two basic functions are: – Filtration – macrophages destroy microorganisms and debris – Immune system activation – monitor for antigens and mount an attack against them Structure of lymph node Spleen (Lymphoid organ) • Largest lymphoid organ, located on the left side of the abdominal cavity beneath the diaphragm • It extends to curl around the anterior aspect of the stomach • It is served by the splenic artery and vein, which enter and exit at the hilus • Functions – Site of lymphocyte proliferation – Immune surveillance and response – Cleanses the blood Other functions of the spleen • Stores breakdown products of RBCs for later reuse – Spleen salvages and store iron for later use by bone marrow • Site of fetal erythrocyte production (normally ceases after birth) • Stores blood platelets Thymus • A bilobed organ that secrets hormones (thymosin and thymopoietin) that cause T lymphocytes to become mature (immunocompetent) • The size of the thymus varies with age – In infants, it is found in the inferior neck and extends into the mediastinum where it partially overlies the heart – It increases in size and is most active during childhood – It stops growing during adolescence and then gradually atrophies Thymus • The thymus differs from other lymphoid organs in important ways – It functions strictly in T lymphocyte maturation – It does not directly fight antigens Tonsils • Simplest lymphoid organs; form a ring of lymphatic tissue around the pharynx • Location of the tonsils – Palatine tonsils – either side of the posterior end of the oral cavity – Lingual tonsils – lie at the base of the tongue – Pharyngeal tonsil – posterior wall of the nasopharynx – Tubal tonsils – surround the openings of the auditory tubes into the pharynx Peyer’s patches • Peyer’s patches – isolated clusters of lymphoid tissue, similar to tonsils – Found in the wall of the distal portion of the small intestine – Similar structures are found in the appendix • Peyer’s patches and the appendix: – Destroy bacteria, preventing them from breaching the intestinal wall – Generate “memory” lymphocytes for long-term immunity Lets review! • What is the general function of the lymphatic system? • Distinguish between the thoracic duct and right lymphatic duct. • What aids the flow of lymph? • Why is it desirable for the flow of lymph through a lymph node to be slow? • What are the major functions of the thymus and the spleen?