Second line defense I.A microbe's penetration of the first line defense encourages production of phagocytes, inflammation, fever, and antimicrobial substances. II.Formed elements in blood A.Blood consists of plasma and formed elements (cell and cell fragments). B.Leukocytes are divided into granulocytes (neutrophils, eosinophils, basophile, and dentritic cells) and agranulocytes (monocytes, lymphocytes, and NK cell). C.During many infections, the number of leukocytes increases (leukocytosis); some infections are characterized by leucopenia (decrease leukocytes).

Second line defense III.The lymphatic system (Parts of the Lymphatic System) 1.Lymph and lymph vessels. 2.Lymphatic tissue: i. lymph nodes ii. nodules iii. spleen iv.thymus v.lymphocytes mature and proliferate.

Second line defense A.Lymph 1.The tissue fluid that enters lymph capillaries similar to plasma, but more WBCs are present, and has less protein. 2.Must be returned to the blood to maintain blood volume and blood pressure.

Second line defense B.Lymph Vessels 1.Dead-end lymph capillaries are found in most tissue spaces; collect tissue fluid and proteins 2.The structure of larger lymph vessels is like that of veins; valves prevent the backflow of lymph. 3.Lymph is kept moving in lymph vessels by: i.constriction of the lymph vessels ii.the skeletal muscle pump iii.the respiratory pump

Second line defense B.Lymph Vessels 4.Lymph from the lower body and upper left quadrant enters the thoracic duct and is returned to the blood in the left subclavian vein. 5. Lymph from the upper right quadrant enters the right lymphatic duct and is returned to the blood in the right subclavian vein.

Second line defense C.Lymph Nodes—encapsulated masses of lymphatic tissue 1. Found in groups along the pathways of lymph vessels. 2.As lymph flows through the nodes: foreign material is phagocytized by fixed macrophages 3.lymphocytes are activated and fixed plasma cells produce antibodies to foreign antigens 4.The major groups of lymph nodes are the cervical, axillary, and inguinal groups. These are at the junctions of the head and extremities with the trunk; remove pathogens from the lymph from the extremities before the lymph is returned to the blood.

Second line defense D.Lymph Nodules—small unencapsulated masses of lymphatic tissue 1.Found beneath the epithelium of all mucous membranes, that is, the tracts that have natural openings to the environment. 2.Destroy pathogens that penetrate the epithelium of the respiratory, digestive, urinary, or reproductive tracts. 3.Tonsils are the lymph nodules of the pharynx; Peyer’s patches are those of the small intestine.

Second line defense E.Spleen—located in the upper left abdominal quadrant behind the stomach 1.The fetal spleen produces RBCs. 2. Functions after birth: i.contains lymphocytes to be activated and fixed plasma cells that produce antibodies ii.contains fixed macrophages (RE cells) that iii.phagocytize pathogens and old RBCs; bilirubin is formed and sent to the liver for excretion in bile iv.stores platelets and destroys damaged platelets

Second line defense F.Thymus—inferior to the thyroid gland; in the fetus and infant the thymus is large, with age the thymus shrinks 1.Produces T lymphocytes (T cells). 2. Produces thymic hormones that make T cells immunologically competent, that is, able to recognize foreign antigens and provide immunity.

Second line defense IV.Phagocytosis 1.Phagocytosis is the internalization of particulate matter by cells. Usually, the phagocytic cells or phagocytes are macrophages or neutrophils, and the particles are bacteria that are taken up and destroyed. 2.The ingested material is contained in a vesicle called a phagosome, which then fuses with one or more lysosomes to form a phagolysosome. The lysosomal enzymes are important in pathogen destruction and degradation to small molecules.

Second line defense A.Phagocytic cells 1.Polymorph nuclear PMNs present in blood and Mononuclear phagocytic cells are present in blood, lymphoid tissue, liver, spleen, lung, and other tissues that are efficient in uptake and removal of antigens.

Second line defense A.Phagocytic cells 2.Particular macrophage in the lung (alveolar macrophages), liver (Kupffer cells), and lining of spleen sinusoids and lymph node medullary sinuses, where they are strategically placed to filter off foreign material. Other examples are cells in the kidney glomerulus, brain microglia and osteoclasts in bone.

Second line defense B.The mechanism of phagocytosis 1.Pathogens can interact with macrophages and neutrophils through receptors for complement borne on these cells and IgG and other protein that opsonize the surface of pathogens as they enter the tissues 2.Phagocytosis is an active process, in which the bound pathogen is first surrounded by the phagocyte membrane and then internalized in a membrane-bounded vesicle known as a phagosome, which becomes acidified.

Second line defense B.The mechanism of phagocytosis 3.In addition to being phagocytic, macrophages and neutrophils have granules, called lysosomes, that contain enzymes, proteins, and peptides that can mediate an intracellular antimicrobial response. The phagosome fuses with one or more lysosomes to generate a phagolysosome in which the lysosomal contents are released to destroy the pathogen. Several killing mechanism.

Second line defense B.The mechanism of phagocytosis 4.The presentation of antigens is occur by bound the particle of pathogen to set of proteins known as major histocompatibility complex (MHC)which fails into two types: MHC class I synthesized free in cytoplasm of nucleated cells present antigen for CD8 T-cell and MHC class II which present within vesicles fuse with phagolysosome of macrophage, dendritic cells and B lymphocytes in a group known as antigen presenting cells APC present antigen for CD4 T- cell

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