Each day about 50% of total blood proteins leak out of the capillaries into tissue fluid and return to blood via lymphatics

Transcription

1 LYMPHATIC SYSTEM CHAPTER 20 The 2 most important functions of the lymphatic system: 1. Maintain fluid balance in the internal environment 2. Immunity 2 systems that need Lymphatic: Cardiovascular Immune Plasma filters out of the arterial end of capillaries into the space between cells (interstitial space) because of the pressure there. Most of this interstitial fluid is (1) absorbed by the cells or (2) reabsorbed by the blood before it flows out of the tissue A small percentage of it remains behind in the spaces If more remained, there would be (1) massive swelling-edema and possible death destruction (2) SHOCK because of loss of fluid in the circulatory system. The lymphatic vessels drain the excess fluid and return it to the venous blood just before it reaches the heart COMPONENTS OF THE LYMPHATIC SYSTEM 1. Lymph/Lymphatic vessels 2. Lymph nodes 3. Lymph nodules-peyer s Patches in intestinal tract 4. Specialized lymphatic organs-tonsils, spleen, and thymus Lymph and interstitial fluid are similar to blood plasma EXCEPT that they have a lower % of proteins than plasma does -The thoracic duct has a much higher % of protein because it flows from the liver and the small intestine before it reaches the Thoracic duct Since lymph doesn t clot, if damage to main lymphatic trunks occurs death can occur-because it is impossible to maintain adequate serum protein concentration by dietary means-if significant loss of lymph continues, emaciation occurs and is potentially fatal Lymphatic vessels differ from blood vessels 1. Not a closed ring/begin blindly in the intercellular spaces of soft tissues of the body 2. Originate as lymphatic capillaries or in the villi of the SI as lacteals 3. Independent of but lie side by side with blood capillary networks 4. Have lymph nodes located along their course 5. Have small openings-clefts-between cells in walls so they are very permeable 6. Most have capacity for repair or regeneration when damaged 7.Smaller than veins 8. Thinner walls than veins 9. Have more valves than veins-to keep lymph flowing in one direction-prevent backflowsemilunar valves

2 Branches merge to form trunks- RIGHT LYMPHATIC DUCT (Drains just right quadrant) empties into R. subclavian where it joins the Internal Jugular vein THORACIC DUCT (Drains all the rest of the body) empties into the L. subclavian where it joins the Internal Jugular vein Proteins that accumulate in tissue spaces can return to blood only via lymphaticsgreat clinical importance -anything blocking lymphatic return causes blood protein concentration and blood osmotic pressure to fall below normal and death will follow Lacteals in villi absorb fats and other nutrients->milky lymph CHYLE Each day about 50% of total blood proteins leak out of the capillaries into tissue fluid and return to blood via lymphatics LYMPHATIC PUMP Return 3 L/day to circulatory system No HEART TO PUMP LYMPH SO LYMPHOKINETIC ACTIONS-similar to what makes venous blood return to heart 1. Breathing movements-changes in pressure between thoracic and abdominal cavities 2. Skeletal muscle contractions Lymph pours into central veins most rapidly at the peak of inspiration-diaphragm descends and causes intraabdominal pressure to increase as intrathoracic decreases->pressure in abd portion of thoracic duct increases and decreases in thoracic portion-so pressure gradient forms causing lymph to flow upward- Rate of flow proportional to depth of inspiration Most lymph flow in body is result of contracting skeletal muscles- milk lymphatic vessels and push lymph forward-during exercise lymph flow may increase 1-15 fold **Contraction of smooth muscle plays a minor role **Also, arterial pulsations, postural changes, and massage of body soft tissues STRUCTURE OF LYMPH NODES Oval or bean shaped-small as a pinhead or large as a lima bean Enclosed by fibrous capsule Fed by several AFFERENT LYMPHATIC VESSELS (with one way valves) Drained by ONE EFFERENT VESSEL (with one way valves) So lymph percolates slowly through sinuses (spaces) TRABECULAE extend from capsule toward center CORTICAL NODULES along the edge or cortex-separated by the trabeculae

3 Cortical nodules are packed with lymphocytes-surrounding area called a GERMINAL CENTER When infection is present, germinal centers form and node begins to release lymphocytes B-lymphocytes-begin final stages of maturation here in the GC and then finish to become antibody producing plasma cells in the denser outer layers The center, or MEDULLA of a lymph node is composed of sinuses and medullary cords- Both Cortical and Medullary sinuses are lined with macrophages for phagocytosis NOTICE LOCATIONS OF LYMPH NODES (NOT ON TEST) 1. PREAURICULAR LYMPH NODES-just in front of the ear 2. SUBMENTAL AND SUBMAXILLARY GROUPS-floor or mouth 3. SUPERFICIAL CERVICAL LYMPH NODES-in neck along sternocleidomastoid 4. SUPERFICIAL CUBITAL, OR SUPRATROCHLEAR LYMPH NODES-above bend of elbow 5. AXILLARY LYMPH NODES-underarm and in upper chest 6. INGUINAL LYMPH NODES-in groin FUNCTIONS OF LYMPH NODES 1. Defense a. Lymph flows slowly thru them b. Gives time to remove microbes and other injurious particles (soot) and phagocytose them c. Sometimes overwhelmed and infection of the node (adenitis) results d. Cancer cells often break away from malignant tumor and travel to the lymph nodes and they become cancerous-can block lymph flow and cause edema in the area 2. Hematopoiesis a. Final stages of maturation for some types of lymphocytes and monocytes (B cells) LYMPHATIC DRAINAGE OF THE BREAST Cancer of the breast is one of the most common forms of malignancy in women Often metastasize from this primary site to rest of body thru lymphatic system Surgical procedures mastectomies-all or some of breast tissue removed Lymphedema may occur because lymph flow is interrupted by removal of lymph vesselsusually restored by growth of new lymphatic vessels in area Anastomoses (connections) occur between lymphatics from both breasts across midline Results in spread from one breast to the other TONSILS Help protect against bacteria invading nasal and oral cavities 1. PALATINE TONSILS-on each side of throat 2. PHATYNGEAL TONSILS-adenoids-near posterior opening of nasal cavity 3. LINGUAL TONSILS-near base of tongue Tonsilitis (Inflammation of tonsils) Tonsillectomy (Removal of tonsils)-controversial because of their critical immunological role

4 THYMUS PRIMARY ORGAN OF THE LYMPHATIC SYSTEM Unpaired with 2 lobes-in the mediastinum-behind the sternum and extending up into the neck Relative size largest in 2 year old Absolute size largest at puberty Gradually atrophies and may be replaced by fat as age-probably completes its essential work early in childhood INVOLUTION (shrinkage of an organ) Did not understand its role until 1961-plays a critical part in body s immune system TWO FUNCTIONS 1. Final site of lymphocyte development before birth 2. Secretes hormones called thymosin that enable lymphocytes to develop into mature T cells-t cells attack foreign or abnormal cells and regulate immune function SPLEEN Located below diaphragm above L kidney, colon and stomach HYPERTROPHIES during infectious diseases and atrophies in old age SPLENOMEGALY-abnormal spleen enlargement is observed in various disorders-scarlet fever, syphilis, and typhoid fever, also in hypertension and hemolytic anemia Surgical removal of the spleen may be required for some of these FUNCTIONS: 1. Defense-as blood passes thru, removes microbes and phagocytoses them 2. Hematopoieses-Some WBCs complete development and become activated here- Also, before birth RBCs are formed in spleen-later, only in extreme hemolytic anemia 3. RBC and Platelet destruction-remove and phagocytize worn out RBCs and imperfect platelets-breaks apart hemoglobin and salvage iron and globin and returns to bloodstream to store in bone marrow and liver 4. Reservoir for blood-has normal volume of about 350 ml of blood-can empty to 200 ml in less than a minute to help body- self-transfusion -response to stress from hemorrhage USE ILLUSTRATION FROM PAGE 639

5 DISORDERS OF THE LYMPHATIC SYSTEM 1. LYMPHEDEMA-swelling because of obstruction of the lymphatics and accumulation of lymph a. Congenital lymphedema-women 15->25-1 st soft->firm and painful-diuretics or surgery b. Fliaria-parasitic worms seen in the tropics-elephantiasis 2. LYMPHANGITIS-inflammation of lymphatic vessel-from invasion of infectious organism-red streaks extend from infected are up arm or leg->necrosis (tissue death) may occur-abscess (collection of fluid) can occur infectious agents may spread into bloodstream causing SEPTICEMIA (blood poisoning) 3 LYMPHOMA-tumor of cells of lymphoid tissue-usually malignant-usually originate in isolated lymph nodes and spread from node to node thru anastomoses of the lymphatic vessels a. Hodgkin s and non-hodgkin s lymphoma 1. Hodgkin s is malignancy with uncertain etiology-may be viral induced tumor of T cells-no evidence to support that usually begins as painless enlarged lymph nodes in neck or axilla->spreads-may cause anemia, lymphedema, leukocytosis, fever and weight loss-potentially curable with radiation therapy if it hasn t spread beyond lymphatic system-chemotherapy is used in more advanced cases-infection is common complication 2. Non-Hodgkin s-malignancy of lymphoid tissue other than Hodgkin s lymphoma-etiology uncertain-maybe virus-patients with immunodeficiencies such as AIDS often develop this-not NECESSARILY-Usually a more generalized involvement of lymph nodes-central NS also often involved- Radiation and chemotherapy are treatments of choice 4. TONSILITIS-already discussed-may extend to middle ear by way of Eustachian tubes-maybe tonsillectomy