Immunity Dr.Talar
Immunity: is the ability of the human body to resist almost all types of offending agents that tend to damage the tissues and organs or it s a special system for combating different infectious or toxic agents. Offending agents like: 1. Infectious agents: 2. toxic agents(toxins) Micro-organisms Bacteria Viruses Parasites Fungi
Note: Human body lives in symbiotic with many of these micro-organisms normally and with varying degree as Normal Flora in: Skin, GIT, respiratory pathway, genito-urinary tract and lining membranes of the eyes. Immune system is basically composed of : 1. White blood cells (WBCs) 2. Tissue cells derived from WBCs and these work together in 2 ways to prevent disease {mechanisms}: A. By actually invading the infectious agents Phagocytosis. B. Via formation of antibodies and acquired lymphocytes acquired immunity.
1 st line defenses: 1. Skin: Tissue macrophages in skin + subcutaneous tissues(histocytes) 2. GIT: destruction of the swallowed micro-organisms: Mouth: saliva Stomach: acid HCl + Digestive enzymes Small intestine (pyere s patches which is lymphoid tissue underneath gut epithelium), Micro-organisms are absorbed into circulation(hepato-enteric/portal circulation) Liver (liver macrophages kupffer cells ) General circulation (Blood)
3. Respiratory tract: Nose: nasal hairs + mucus discharge Throat: Pharynx Adenoid + tonsils 4. Blood: Alveoli macrophages in alveoli A. Chemicals in blood. B. White blood cells stored in lymph nodes, bone marrow, spleen and thymus.
White blood cells (WBCs) Leukocytes White blood cells are mobile units of the body s defense system. They are specifically transported to areas of serious infection & inflammation, thereby providing rapid and potent defense. white blood cell count: 4,000 11,000 cell/mm 3 White blood cells (that are normally present in blood) 1. Granulocytes: 2. Agranulocytes: polymorphonuclear Lymphocytes Neutrophils Monocytes Basophils Plasma cells Eosinophils Poly: multiple Morpho: different shapes Note: when monocytes enter tissues they become macrophages.
Note: Called granulocytes owing to the presence of granules in their cytoplasm(granular appearance). Origin: 1. Granulocytes + monocytes In only Bone marrow(bm). 2. Lymphocytes + plasma cells Bone marrow + Lymphogenous tissues. Lymphoid tissues are: Lymph nodes(glands), spleen, thymus, tonsils, various pockets of lymphoid tissues, bone marrow lymphoid tissues and lymphoid tissues underneath gut epithelia peyer s patches.
Types Of Immunity 1.Innate/Generalized/Non-specific Immunity: Mechanism: phagocytosis (which is function of neutrophils + tissue macrophages), but basically phagocytosis is function of Granulocytes and monocytes. Note: Granulocytes: Neutrophils, basophils, eosinophils and since Neutrophils are the most abundant, it will cancel all functions of the small number of eosinophils and basophils. Monocytes once enter tissues become mature and called tissue macrophages. 2. Acquired/Adaptive/Specific Immunity: Initiated by antigens and it s the product of body s lymphocytes.
Lymphocytes: 1. B-lymphocytes 2. T-lymphocytes Antibody function Activated T-lymphocytes (human immunity) (cell-mediated immunity) Mechanisms of acquired immunity
Innate Immunity: Mechanism = Phagocytosis Cells responsible (function of): Neutrophils and tissue macrophages. Neutrophils: are mature cells that can attack and destroy bacteria even in the circulating blood. Tissue macrophages: begin life as monocytes immature cells while still in blood and have little ability to fight against infectious agents at that time once they enter the tissues, they swell, increase in size and they are now called tissue macrophages and they become extremely capable of combating disease agents in the tissues. Mechanism: 1. White blood cells enter the tissue spaces from circulating by diapedesis, that s squeezing through the pores of the blood capillaries, even though a pore is much smaller than a cell, a small portion of the cell slides through the pore at a time.
2. White blood cells, move though tissue spaces by Ameboid motion. They are attached to the area of infection/inflammation by chemotaxis. Chemotaxis: is the process of attracing/moving of neutrophils and tissue macrophages toward the area of infection/inflammation via different chemical substances called chemotactic agents for example: 1. Bacterial/Viral toxins 2.tissue debris Chemotaxis is effective up to 100 micrometers away from the inflamed tissue!! And as almost no tissue area is more than 50 micrometers away from a capillary, the chemotactic signal can be always effective. 3. Phagocytosis: is the cellular(neutrophils and tissue macrophages) ingestion of offending agents.
On approaching the particle to be phagocytized the white blood cell, first attaches itself to the particle. Then projects pseudopodia in all directions around the particle. The pseudopodia meet one another, fuse and creating an enclosed chamber that contains the phagocytized particle. Then the chamber invaginates to inside of the cytoplasmic cavity and breaks away from the outer cell membrane to form a free-floating phagocytic vesicle (phagosome) inside the cytoplasm. Then the phagosome fuses with the lysosomes inside the phagocyte and creates a digestive vesicle, digesting the phagocytized particle immediately. Note: Lysosome contains: digestive enzymes and bactericidal agents.
Neutrophils Tissue Macrophages They are mature cells, have the ability to phagocytose in blood and immediately upon entering tissues. They are end-stage product of monocytes weak phagocytes and immature in blood that mature after entering tissues & become extremely powerful phagocytes. They are weaker phagocytes, that can phagocytize 3-20 bacteria. They are more powerful phagocytes than neutrophils & are capable of phagocytizing up to 100 bacteria. After phagocytosis they become inactive and die. After digesting the particles, macrophages can extrude the residual product! And survives & function for many more months. They are smaller cells that can t phagocytize particles larger than bacteria. They are large cells, capable of ingesting large particles for example: Red blood cells and malarial parasite.
Osmosis Net diffusion of water Is the process of net movement of water caused by a concentration difference of water. By far, the most abundant substance that diffuses through the cell membrane is water. Enough water ordinarily diffuses in each direction through red blood cell membrane per second to equal about 100 times the volume of the cell itself. Yet, normally the amount that diffuses in the two directions is balanced so precisely that zero net movement of water occurs therefore the volume of the cell remains constant. However, under certain conditions, a concentration difference for water can develop across a membrane, just as concentration difference of other substances.
When this happens, net movement of water does occur across the cell membrane, causing the cell either to swell or shrink, depending on the direction of water movement.