Lymphatic/Immune System PDF

LYMPHATIC/IMMUNE SYSTEM BY Dr. Youssef MD, RDCS 1 2  Functions of Lymphatic System 1- Return the excess interstitial fluid to the blood: at the arterial end of capillary, fluid leaves into the interstitial fluid but 90% returns into the venous...

LYMPHATIC/IMMUNE SYSTEM BY Dr. Youssef MD, RDCS 1 2  Functions of Lymphatic System 1- Return the excess interstitial fluid to the blood: at the arterial end of capillary, fluid leaves into the interstitial fluid but 90% returns into the venous end and the remaining 10% enters the lymphatic vessels {lymph} and finally enters the venous blood 2- Defense against pathogenic organisms 3- Absorption of fat and fat-soluble 3 vitamins 4  Components of Lymphatic System 1- lymph:*Fluid derived from blood plasma {similar composition} 2- lymph vessels:*Carry lymph away from tissues {unlike blood vessels} *Smallest lymph vessels are called lymph capillaries & begin in tissue spaces then merge to form lymphatic vessels that merge to form lymph trunks that merge to form two lymphatic ducts: * Right Lymphatic Duct: Receives lymph from right upper ¼ of body * Left Lymphatic Duct “Thoracic Duct”: Receives lymph from the rest of the body 5 Right lymphatic duct empties into right subclavian vein Left lymphatic duct empties into left subclavian vein Lymph capillaries in the villi of small intestine are called lacteals ( absorb fat & fat-soluble vitamins) 6 8 3- Lymphatic Organs: All lymphatic organs produce lymphocytes I- Lymph nodes: * Small bean-shaped structures * Widely distributed along the lymphatic vessels except in the brain * Filter lymph before it enters the blood * Lymph node is surrounded by connective tissue capsule and is divided into compartments {lymph nodules} 9 10 * Lymph nodules are separated by lymph sinuses * The lymph enters the LN through many afferent lymphatic vessels (on the convex side) * After filtering, lymph exits through efferent lymphatic vessels on the indented region of LN {the hilum} * There are more afferent vessels than efferent vessels 11 II- Tonsils: {masses of lymphoid tissue} a- Pharyngeal tonsils {adenoids}: located near the opening of nasal cavity into the pharynx b- Palatine tonsils {the tonsils}: located near the opening of the oral cavity into the pharynx c- Lingual tonsils: located on the posterior surface of the tongue 12 15 III-Spleen { largest lymphatic organ}: * Located in the upper left quadrant of abdominal cavity under the diaphragm, posterior & lateral to the stomach * Functions of spleen: a- Filters & stores blood b- Removes old RBCs from blood {like liver} c- Produces lymphocytes (like all lymphatic organs) 16 IV- Thymus gland: * Located anterior to the ascending aorta, and posterior to the sternum * Large in infants and children but its size decreases in adults ( involution) * Functions: a- Production and maturation of special lymphocytes {T-Lymphocytes/T-cells} b- Production of hormone thymosin that stimulates maturation of lymphocytes so, thymus gland plays important role in immunity 18  Defense Mechanism Against Infection Nonspecific mechanisms act against all harmful agents, so provide nonspecific resistance Specific mechanisms act against certain agents, so provide specific resistance {immunity} Lack of resistance is called susceptibility Nonspecific Defense Mechanisms 1- Intact skin and mucous membranes 2- Fluids like tears, saliva and urine flush pathogens out of the body 19 3- Complements: group of proteins normally found in plasma in an inactive form, upon contact with foreign bodies, each protein activates the next in an orderly manner, so that all complements become active and induce: *phagocytosis *inflammation 4- Interferons: chemical substances produced by infected cells and protect uninfected cells against viral infection 20  5- Phagocytosis: Two types of phagocytes: a- Neutrophils: small granular leukocytes b- Monocytes {macrophages}: large agranular leukocytes (macrophages in between liver cells are called Kupffer cells) 6- Inflammation {non specific defense mechanism in response to tissue damage} - Signs: redness, hotness, swelling, pain 21 and may be loss of function Inflammation may be: A- Localized:*contained in a specific area B- Systemic {generalized}:*widespread *characterized by 3 additional features: 1- Leukocytosis: due to stimulation of bone marrow to produce more WBCs 2- Fever: due to production of pyrogens that affect the hypothalamus to increase body temperature 3- Hypotension: due to generalized vasodilation & increased capillary permeability  Specific defense mechanisms {Immunity} During fetal growth, bone marrow releases immature & undifferentiated {unspecialized} lymphocytes into blood Some lymphocytes go to thymus to continue maturation to become T-cells {T- lymphocytes} then leave thymus into blood to other lymphatic organs Lymphocytes that do not go to thymus, go to fetal liver & continue maturation & differentiation to become B-cells {B- lymphocytes} then they enter blood to go to other lymphatic organs 23 A-Cell-mediated Immunity: Produced by T- cells Four types of activated T-cells: 1- Killer T-cells (destroy the antigen) 2- Helper T-cells: stimulate B-cells 3- Suppressor T-cells: inhibit B-cells 4- Memory T-cells: remember the antigen so that the second encounter produces a faster and more intense response than the first one 24 B-Antibody-mediated Immunity {humoral}: Produced by B-cells B-cells do not destroy antigen Two types of activated B-cells: 1- Plasma cells: produce antibodies (proteins) that react with antigens or their products 2- Memory B-cells: recognize the same antigen on second encounter to produce “the secondary response” 25 Acquired Immunity: 4 types 1- Active natural: acquired when the person contracts the disease {produces memory cells} 2- Active artificial: acquired when the person receives vaccination {produces memory cells} 3- Passive natural: acquired when the baby receives maternal antibodies through the placenta or breast milk {no memory cells} 4- Passive artificial: acquired when the person receives antiserum containing antibodies {no memory cells}