The Lymphatic and Immune Systems
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| The Lymphatic System | The lymphatic system is composed of a network of vessels that penetrate nearly every tissue of the body and a collection of tissues/organs that produce immune cells.
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| Three functions of the lymphatic system | a)Fluid Recovery b)Immunity c)Lipid Absorption
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| The main components of the lymphatic system are | Lymph, Lymphatic vessels, Lymphtatic tissue, Lymphatic organs
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| Lymph | Clear, colorless fluid, low in protein. It originates at tissue fluid that has been taken up by the lymphatic vessels.When leaving a lymph node, lymph contains large numbers of lymphocytes.After a meal, lymph draining from the small intestine has a milky
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| Lymph | Lymph may also contain macrophages, hormones, cellular debris, bacteria, viruses and cancer cells.
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| Lymphatic Vessels | Lymph flows through a system of lymphatic vessels similar to blood vessels.
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| Lymphatic Vessels | The route from tissue fluid back to the blood is: lymphatic capillaries -
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| Lymphatic Vessels | are absent from the CNS, cartilage, cornea, bone and bone marrow. They are closely associated with blood capillaries, but unlike them, are closed at one end
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| Lymphatic Vessels | The lymphatic capillaries converge to form collecting vessels
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| six main lymphatic trunks,whose names indicate their locations and parts of the body they drain: | the jugular, subclavian, bronchomediastinal, intercostals, intestinal and lumbar trunks
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| Right Lymphatic Duct | This duct if formed by the convergence of the right jugular, subclavian and bronchomediastianal trunks in the right thoracic cavity.
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| Right Lymphatic Duct | It receives lymphatic drainage from the right arm, right side of thorax and head.
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| Right Lymphatic Duct | Empties into the right subclavian vein.
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| Thoracic Duct | Found on the left side, this duct is larger and longer. It begins just below the diaphragm anterior to the vertebral column. Here the two lumbar trunks and intestinal trunk join and form a prominent sac called the cisterna chili – named for the large amou
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| Thoracic Duct | It empties into the left subclavian vein.
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| Flow of Lymph | lymphatic system has no pump like the heart and it flows at even lower pressure/speed than venous blood.
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| Flow of Lymph | The primary mechanism of flow is rhythmic contractions of the lymphatic vessels, which contract when the flowing lymph stretches them.
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| Flow of Lymph | The valves of the lymphatic vessels, like those of veins, prevent the fluid from flowing backward.
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| Flow of Lymph | Lymph flow is also produced by skeletal muscles squeezing the lymphatic vessels.
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| Lymphatic Cells Include the Following Types | B Lymphocytes, T Lymphocyte, Macrophages, Natural Killer (NK) cells, Dendritic cells, Reticular cells
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| B Lymphocytes | These are lymphocytes that differentiate into plasma cells – CT cells that produce the antibodies of the immune system.
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| T Lymphocytes | These lymphocytes mature in the thymus gland The “T” stands for thymus dependant.
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| Macrophages | These are large, highly phagocytic cells of CT. They develop from monocytes that have emigrated from the blood.
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| Macrophages | They phagocytize bacteria, tissue debris, dead neutrophils.
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| Macrophages | They process foreign antigen and display antigenic fragments to T cells – thereby alerting the immune system to the presence of foreign antigen. Such marcrphages are called antigen presenting cells (APCs).
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| Natural Killer (NK) cells | These are large lymphocytes that attack/destroy bacteria, host cells that have become infected with viruses or have become cancerous, and transplanted tissue cells.
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| Natural Killer (NK) cells | They are responsible for a means of defense called immune surveillance.
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| Dendritic cells | These are branched, mobile APCs found in the epidermis, mucous membranes and lymphatic organs. In the skin, they are often called Langerhan’s cells.
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| Reticular cells | These are branched stationary cells that contribute to the stroma of the lymphatic organs and act as APCs in the thymus.
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| Lymphatic Tissues | Lymphatic (lymphoid) tissues are aggregations of lymphocytes in the CTs of mucous membranes and various organs.
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| Lymphatic Organs | Lymphatic (lymphoid) organs have well defined anatomical sites and at least partial CT capsules that separate the lymphatic tissues from neighboring tissues.
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| Primary Lymphatic Organs | Red bone marrow
Thymus
They are called primary lymphatic organs because they are the sites where B and T lymphocytes, respectively, become immunocompetent – meaning able to recognize and respond to antigen.
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| Secondary Lymphatic Organs | Lymph Nodes, Tonsils, Spleen
Secondary lymphatic organs because they are populated with immunocompetent lymphocytes
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| Anatomy of red bone marrow | Its a soft, highly vascular material, Its red color comes from the abundance of RBCs.
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| Anatomy of red bone marrow | Numerous small arteries enter nutrient foramina on the bone surface, penetrate the bone and empty into large sinusoids in the marrow.
As blood cells mature, they push their way through the reticular and endothelial cells to enter the sinus and flow awa
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| Function Red Bone Marrow | Hemopoiesis (blood formation) & Immunity
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| Hemopoiesis (blood formation) | It produces all classes of formed elements of the blood
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| Thymus | The thymus is a member of the lymphatic and endocrine systems – since it houses developing lymphocytes and produces hormones that regulate their later activity.
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| Thymus Location | Between the sternum and aortic arch in the superior mediastinum.
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| Anatomy and physiology of the Thymus | The fibrous capsule of the thymus gives off trabeculae that divide the gland into several angular lobules. Each lobule has a dark staining cortex and a lighter medulla populated by T lymphocytes.
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| Reticular epithelial cells | Form a blood thymus barrier
They produce signaling molecules that promote the development and function of T cells including: Thymosin, thymopoietin, thymulin, interleukins and interferon.
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| Lymph Nodes | These are the most numerous lymphatic organs.
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| Anatomy of the lymph nodes | They are elongated or bean shaped structures, usually less than three cm long, with an indentation called the hilum on one side.
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| Anatomy of the lymph nodes | ii)Its enclosed in a fibrous capsule with trabeculae that partially divide the interior of the node into compartments.
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| Anatomy of the lymph nodes | Between the capsule and parenchyma is a narrow, clear space called the subcapsular sinus, which contains reticular fibers, macrophages and dendritic cells.
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| Anatomy of the lymph nodes | Deep to this, the organ consists mainly of a stroma of reticular connective tissue (reticular fibers and reticular cells) and a parenchyma of lymphocytes and antigen presenting cells. The parenchyma is divided into the following
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| Cortex | This is an outer are that encircles about four-fifths of the organ.
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| Medulla | This is the inner area that extends to the surface at the hilum.
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| Vascular supply of the lymph node | Several afferent lymphatic vessels lead into the node along its convex surface. Lymph flows from these vessels into the subcapsular sinus, moves slowly through the sinuses of the cortex and medulla and leaves the node through an efferent lymphatic vessel
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| Functions of the lymph nodes | Cleanse the lymph & Provide a site for B and T cell activation.
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| Stroma | The CT framework of a gland, organ, etc that mainly provide structural support..
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| Parenchyma | The tissue the performs the main physiological functions of an organ.
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| 3 main sets of tonsils | Pharyngeal Tonsil, Palatine Tonsils, Lingual Tonsils
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| Pharyngeal Tonsil | This is one tonsil located on the wall of pharynx just behind the nasal cavity.
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| Palatine Tonsils | a. There are a pair of these tonsils located at the posterior margin of the oral cavity. b. These are the largest and most often to be infected.
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| Lingual Tonsils | There are many of these concentrated in a patch on each side of the root of the tongue.
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| Spleen | This is the body’s largest lymphatic organ.
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| Spleen | Located in the posterior abdominal cavity, just inferior to the diaphragm and dorsolateral to the stomach.
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| The parenchyma has two types of tissue | Red Pulp and White Pulp
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| Red Pulp | This consists of sinusoids filled with lymphocytes.
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| White Pulp | Consists of lymphocytes and macrophages aggregated along small branches of the splenic artery.
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| Functions of the spleen | Produces blood cells in the fetus and may resume this role in adults upon extreme anemia.
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| Functions of the spleen | Produces blood cells in the fetus and may resume this role in adults upon extreme anemia.
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| Functions of the spleen | The lymphocytes/macrophages of the white pulp monitor blood for foreign antigens.
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| Functions of the spleen | Old RBCc accumulate in the sinuses of the red pulp, where they rupture and are phagocytized by macrophages.
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| Functions of the spleen | Helps to stablize blood volume by transferring excess plasma from the blood into the lymphatic system.
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| Nonspecific Resistance | This includes the body’s defenses that respond to infection and trauma, regardless of the type of infectious disease agent or trauma – eg, it could be a bacterium, virus, burn or cut.
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| Specific Resistance | This involves the responses of our immune system as a third line of defense. More specifically, this involves the responses of specialized WBCs, namely B/T Cells
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| B cells - Humoral | that produce antibody that is specialized to fight infections outside the cell.
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| T cells - Cell Mediated | that are designed to fight intracellular infections, viruses and cancer.
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| Nonspecific Resistance-> First Line of Defense > | 1. Skin, 2. Mucous Membranes and mucus, 3. Epiglottis, 4. Lacrimal Apparatus and tears, 5. Urinary Tract and urine, 6. Vagina and vaginal secretions
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| Skin | This is the largest organ of the body and it has two layers, epidermis and dermis
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| Epidermis | Outer layer of the skin. Its composed of layers of epithelial cells & more specialized cells called Langerhans cells that participate in the immune response. Top layer is made up of dead epidermal cells and a tough protective protein called keratin
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| Dermis | This is in the inner and thicker layer of the skin that is made up of connective tissue.
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| Epiglottis | This is structure made of cartilage that covers the larynx and prevents microbes from entering the lower respiratory tract.
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| Lacrimal Apparatus and tears | This is composed of the lacrimal glands in the upper eye. These glands produce tears that are spread over the surface of the eye by blinking. This continual washing action prevents microbes and other foreign particles from settling into the eye.
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| Urinary Tract and urine | The flushing effect of urine and its low pH tends to inhibit microbial growth in the GU tract.
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| Vagina and vaginal secretions | The low pH produced by the normal microbiota of the female vagina helps prevent colonization by pathogens.
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| Chemical (Anti-Microbial) Factors | 1. Saliva 2. Sebum 3. Perspiration 4. Lysozyme 5. Gastric Acid 6. Transferrins
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| Saliva | Saliva helps to dilute the numbers of microbes and washes them from the surfaces of the teeth and the mucous membrane of the mouth.
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| Sebum | An oily substance produced by our oil glands that acts as a protective film over our skin. Its composed of unsaturated fatty acids that have a low pH and thereby prevent the growth of many microbes.
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| Sebum | Some microbes on the skin can metabolize the sebum which leads to an inflammatory response and acne.
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| Perspiration | This is produced by our sweat glands to help regulate body temperature. It also flushes microbes out.
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| Lysozyme | An enzyme found in many of our bodily fluids like tears and saliva. It has antimicrobial activity in that it can destroy peptidoglycan and so its highly active against gram positive bacteria.
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| Gastric Acid | This is a mixture of HCL, enzymes and mucus at a pH of 1.2 – 3.0.
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| Gastric Acid | It creates a hostile environment for most microbes, primarily due to the low pH. The acidity destroys most bacterial toxins, except those of C. botulinum and S. aureus. One organism, H.pylori can neutralize stomach acid. As a result it can grow in the sto
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| Transferrins | Our blood has iron binding proteins called transferrins. By binding to iron, they reduce the amount of iron available to microbes. As a result, microbes can’t grow.
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| Normal Microbiota | Many of the normal microbiota benefit the host by preventing the growth of pathogens in a process previously discussed called microbial antagonism.
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| Normal Microbiota | Here the normal microbiota compete with pathogens for nutrients, produce substances that are harmful to pathogens and set up an environment that is favorable for their growth in terms of oxygen supply, pH, etc.
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| Second Line of Defense -> Phagocytosis | Phagocytosis is important in our second line of defenses of our innate defense system. Its a means to fight infection and eliminate microbes with the help of specialized WBCs called phagocytes.
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| There are Two main classes of Leukocytes: | Granulocytes & Agranulocytes
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| Granulocytes | Neutrophils, Basophils, Eosinophils
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| Agranulocytes | Monoctyes, Lymphocytes
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| Neutrophils | They are important in the acute or early phase of infection and are highly phagocytic.
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| Basophils | They produce histamine, which plays a role in the inflammatory response and in allergic reactions. Not Phagocytic
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| Eosinophils | They are phagocytic and have a main role in parasitic infections.
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| Monoctyes | These WBCs circulate freely in the blood and are not phagocytic.
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| Monoctyes | Upon infection, they leave the blood and enter the tissue space and mature into macrophages. Macrophages are highly phagocytic and predominate in the latter stages of infection. They take up any remaining bacteria and dead cells. Since they are derived fr
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| Monoctyes | Some macrophages are located in specific tissues and are referred to as fixed macrophages. They may be found in the liver (Kupfer cells), lungs (alveolar macrophages), spleen, lymph nodes, etc. As blood and lymph carrying microbes passes through these and
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| Lymphocytes | These include the B and T cells that are involved in our specific immune response.
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| There are four primary stages of phagocytosis | a)Chemotaxis b)Adherence c)Ingestion d)Digestion
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| Adherence | Microorganisms can be more readily phagocytized if they are opsonized – that is if they are coated with antibody or components of complement, namely C3b. This enchances their uptake by phagocytes.
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| Ingestion | Here the plasma membrane uses projections called pseudopods that surround the microbes, fuse and bring it into the cell within an enclosed vesicle called a phagosome.
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| Digestion | Now the phagosome is inside the cell. It fuses with a lysosome to form a structure called a phagolysome. In doing so, the lysosome releases its digestive enzymes into the phagosome, which kill the microbe.
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| Inflammation | The inflammatory response is activated anytime there is local (not systemic)damage to the body’s tissues.
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| The damage can be caused by a number of factors | 1. Microbial infection 2.Physical agents – like sharp objects, heat, electricity 3. Chemicals agents – acids, bases, etc.
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| There are generally four signs and symptoms of inflammation: | Redness, swelling, pain, heat & Sometimes there is loss of function.
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| The inflammatory response plays several roles: | 1. It destroys and attempts to remove the agent that has caused the damage. 2. If the agent cant be destroyed, it attempts to wall it off and limit its harmful affects. 3. Repair damaged tissue.
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| Three Stages of Inflammation: | a)Vasodilation and Increased Vascular Permeability b)Phagocyte Migration and Phagocytosis and c)Tissue Repair
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| Vasodilation | this is an increase in the diameter of blood vessels, which increases blood flow to the damaged area. This also results in redness at the site of inflammation.
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| Increased vascular permeability- | this permits substances that are normally in the blood to pass through blood vessel walls and into the tissue space. This causes swelling (edema).
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| Phagocyte Migration and Phagocytosis | 1hr after inflammatory resp. started, the flow of blood slows & phagocytes appear. They have been attracted to this area by the acute phase proteins. They stick to the inner lining of the blood vessel wall in process called margination or pavementing.
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| Phagocyte Migration and Phagocytosis | After the phagocytes have completed their function, they die. Pus will often form, which will either come to the surface or eventually be destroyed internally.
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| Tissue Repair | replacement of dead or damaged cells in the injured tissue.
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| Parenchyma | this is the functioning part of the tissue. If only parenchymal cell are involved in repair, a nearly perfect repair of the tissue occurs. eg, damage to the epidermis, which is the parenchymal layer of the skin.
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| Stroma | this is supporting and nonfunctional connective tissue. When repair cells of the stroma are involved, scar tissue is formed. eg, the capsule around the liver.
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| Fever | abnormally high body temp, generally in response to invasion by an infectious agent.In response to a bacterial infection – his causes the hypothalamus in the brain to raise the body’s temperature.
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| The Complement System | The complement system consists of a group of 20 serum proteins that participate in our nonspecific defense. (Serum is plasma without the clotting proteins).The proteins act in an ordered sequence or cascade, with each protein activating the next one to ul
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| Classical Pathway | This pathway is activated by antibody binding to antigen.
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| Alternative Pathway | Activated by the interaction of microbial polysaccharides with proteins of the Alternative Pathway, namely Factors B, D and P.
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| Consequences of Activation | CIA
Cytolysis, Inflammation, Opsonization
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| Cytolysis | Main function of complement system. C3b initiates the assembly of proteins C5– C9, which is called the membrane attack complex. Once assembled, this complex forms a transmembrane channel in the membrane of the microbe resulting loss of of ions and lysis.
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| Inflammation | Here proteins C3a and C5a bind to mast cells, basophils and platelets, causing them to release histamine, resulting in increased vascular permeability-thereby contributing to inflammation.C5a also functions as a chemotactic factor by attracting phagocytes
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| Opsonization | Here complement component C3b binds to the surface of microbes and serves as an opsonin, because it enhances attachment and ingestion by phagocytic cells.
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| Inactivation of Complement | Once complement has performed its function its quickly inactivated so that damage to host tissue is minimized. Various regulatory proteins in the blood inactivate complement.
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| Interferons | These are antiviral proteins produced by animal cells, in response to a viral infection.
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| There are three types of human interferons: | Alpha, beta and gamma interferons.
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| Mechanism of action of alpha and beta interferons: | Oligoadenylate synthase & Protein Kinase
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| Oligoadenylate synthase | Degrades viral mRNA
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| Protein Kinase | Inhibits protein synthesis.
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| Gamma-IFN | This interferon is produced by lymphocytes and it stimulates neutrophils to destroy bacteria.
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| Limitations of interferons: | Beneficial for only a short time & Have no effect on cells that are already infected with virus.
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| We are currently producing recombinant interferons for therapeutic purposes: | Alpha-IFN (Intron A) & Beta-IFN (Betaseron)
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| Alpha-IFN (Intron A) | Approved for treating Kaposi’s sarcoma, Hepatitis B/C.
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| Beta-IFN (Betaseron) | Slows the progression of multiple sclerosis.
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| Nonspecific Resistance | This includes the body’s defenses that respond to infection and trauma, regardless of the type of infectious disease agent or trauma.Nonspecific resistance includes a first and second line of defense – as we have discussed.
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| Specific Resistance | third line of defense
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| Immunity | Immunity is a specific defensive response to an organism or foreign substance not belonging to the body.
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| B cells | These cells produce antibody that is specialized to fight infections outside the cell.
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| T cells | These cells are designed to fight intracellular infections, viruses and cancer
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| Types of Acquired Immunity | Naturally Acquired Immunity & Artificially Acquired Immunity
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| Naturally Acquired Active Immunity | Obtained when antigens enter the body naturally during daily life. In response, the body produces antibodies and specialized lymphocytes. Once acquired, this type of immunity may be lifelong for some diseases, like chicken pox and measles.
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| Naturally Acquired Passive Immunity | This involves the natural transfer of maternal antibodies from the placenta to the fetus and also from breast milk. The mother’s immunity to any infectious disease agents, like diptheria, polio, etc will be conferred to the infant. However, some infectiou
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| Artificially Acquired Active Immunity | Through vaccination; immunity doesn't happen naturally. Vaccines are prepared from parts microbes, like capsules, killed microbes or inactivated toxins. These substances can no longer cause disease but are seen by body as antigenic elicit immune resp
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| Artificially Acquired Passive Immunity | These antibodies are injected into a sick person and they confer immediate protection against the disease. Immunity is only temporary because the recipient’s system degrades the antibodies quickly.
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| Artificially Acquired Passive Immunity | Example 1: Tetanus immune globulin is can be given immediately to anyone suspected of having tetanus. It will neutralize the tetanus toxin before it causes irreversible damage to the CNS.
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| Artificially Acquired Passive Immunity | Example 2: Rabbies immune globulin
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| The Nature of Antigens | As mentioned previously, antigens are foreign substances that the body recognizes as nonself
Microbial antigens are parts of the microbe.Nonmicrobial antigens include pollen, egg white, cell surface mol. on blood cells, transplanted tissue.
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| Antibody Structure | It has four chains composed of protein.
The ends of the Y shaped molecule are called variable regions.
The lower parts of the Y’s arms and the stem are called constant regions.The stem itself is called the Fc region.
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| Antibody Structure | At its basic level, an antibody is a Y shaped molecule, sometimes called a monomer
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| There are five classes of immunoglobulins (or antibodies) | IgG,IgM, IgA, IgD, IgE
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| IgG | The most abundant antibody in our serum –accounting for 80% of all antibodies in serum. Its present in the blood, lymphatics and intestine and can readily cross the walls of blood vessels and enter the tissue space.
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| IgG | IgG provides protection against circulating bacteria, viruses and can neutralize bacterial toxins. It can also activate (fix) complement and serves as an opsonin.
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| IgG | IgG provides long term immunity to infections and is the antibody that crosses the placenta to provide passive immunity to the fetus.
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| IgM | This class make up 5-10% of antibodies found in the serum.
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| IgM | Its the first antibody that is produced in response to an infection – so the presence of IgM is diagnostic of infection with a specific pathogen. Its very effective against bacteria and in agglutinating antigens. Like IgG, it can activate complement and s
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| IgM | It’s the largest antibody. As a result of its size, it can’t readily cross blood vessel walls and enter the tissue space. It remains in the blood, lymphatics and on the surface of B cells.
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| IgA | a)Accounts for 10-15% of the antibody in our serum, where it is referred to as serum IgA.
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| IgA | b)In our mucus membranes and secretions (tears, saliva, milk, etc) IgA is highly concentrated. Here it is referred to as secretory IgA. Collectively it is the most abundant antibody in the body. Secretory IgA functions to prevent attachment of pathogens a
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| IgD | Accounts for only 0.2% of serum antibodies.
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| IgE | Makes up only 0.002% of total serum antibody.
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| IgE | b)Found tightly bound by its Fc region to the surface of mast cells and basophils where it participates in allergic reactions. When antigens, like pollen, react with IgE, the IgE stimulates the mast cells or basophil to release histamine – which is part o
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| IgE | Also involved in parasitic infections.
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| Development of B Cells, | B cells originate from the bone marrow in the adult and the liver in the fetus. Any B cells that react with themselves during fetal development, that is – they react against self antigen – are seen by the body as harmful.
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| Clonal Deletion | B Cells They are destroyed by a process called Clonal Deletion.
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| Apoptosis | Mature B cells in these lymphoid organs that do not encounter and respond to any stimulating antigen die by a mechanism called apoptosis, which is a programmed cell death.
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| Activation of Antibody-Producing B Cells by Clonal Selection | When a B cell recognizes a specific extracelluar antigen (bacteria, bacterial toxins or viruses that are circulating in body fluids), it becomes activated. More specifically the B cell divides and differentiates into two populations of cells
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| T–dependent Antigen | Requires prior interaction of an antigen presenting cell (APC) and a T helper cell.
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| T –independent Antigen | W/out prior interaction of an APC and T helper cell.
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| Agglutination | Here the antibodies bind to the antigens and cause them to aggregate into clumps. These clumps are more easily ingested by phagocytes.
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| Opsonization | Here the antigen has been covered by antibodies. Such antigen–antibody complexes are also more readily ingested by phagocytes
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| Complement Activation | Antigen-antibody complexes activate complement which eventually leads to lysis.
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| Neutralization | In this process, IgG antibodies either neutralize bacterial toxins by blocking their active sites or neutralize viruses and bacteria by blocking their attachment to the host cell.
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| Antibody Dependent Cell Mediated Cytotoxicity (ADCC) | In some cases, organisms like parasites or protozoa are too large to be phagocytized – that is, taken in by a WBC and digested.
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| Antibody Dependent Cell Mediated Cytotoxicity (ADCC) | Immune system has developed a strategy whereby these large organisms can be killed.
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| Antibody Dependent Cell Mediated Cytotoxicity (ADCC) | The parasite becomes covered with antibodies, which bind to the surface in such a way that their Fc stem regions are exposed. Now NK cells and cells of the nonspecific defense system like macrophages, neutrophils and eosinophils bind to the exposed Fc reg
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| Antibody Dependent Cell Mediated Cytotoxicity (ADCC) | Now these cells release lytic enzymes that directly destroy the parasite.
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| Immunological Memory | We can measure the intensity of our immune response by measuring our antibody titer – this is the amount of a given antibody in the serum.
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| Immunological Memory | IgM antibodies are produced first – w/in about 3 days and disappear by day 15.
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| Immunological Memory | By day 7, IgG is produced and it provides longer term immunity. Then declines by day 25.
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| Immunological Memory | The second exposure to the same antigen illicits a secondary immune response. It is often called a memory response because it stimulates memory cells that were formed during the primary exposure to the antigen. The main antibody produced is IgG and its pr
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| Development of T Cells, Activation and General Properties | Cell Mediated Immunity is primarily based on the activity of specialized lymphocytes called T cells. T cells originate from stem cells in the adult bone marrow.
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| Some important classes of cytokines | Interleukin-1 & Interleukin-2Interleukins - when these cytokines are found to be directly involved with leukocytes, they are called interleukins. A number of interleukins have been discovered that have various functions.
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| Interleukin-1 | a)it activates T-helper cells.
b)chemically attracts phagocytes
c)produces fever – is sometimes called endogenous pyrogen
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| Interleukin-2 | a)activates the T helper cell to form a clone of mature T helper cells.
b)causes proliferation/differentiation of B cells.
c)activates Tc and Nk cells.
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| Interferons | a class of cytokines that fiExample: alpha and beta interferonght virus infected cells .
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| Chemokines | these are cytokines that chemically attract leukocytes to an infected area.Example: Interleukin-8 – attracts phagocytes.
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| Four Types of T Cells | Helper T Cells, Cytotoxic T Cells, Delayed Hypersensitivity T Cells, Suppressor T Cells
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| Helper T Cells | The T helper cell is the central cell of the entire specific immune response. Once activated, this cell can activate T cytotoxic cells, B cells(causing them to produce antibody) and macrophages.
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| Cytotoxic T Cells | These cells destroy cells that are infected intracellularly with viruses and bacteria. Once they encounter the antigen-MHC complex on the surface of an infected cell, the Cytotoxic T cell releases a protein called perforin which lyses the infected cell.
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| Delayed Hypersensitivity T Cells | This group has been found to be associated with allergic reactions and with rejection of transplanted tissue.
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| Suppressor T Cells | This group of T cells is thought to downregulate the immune system once it has completed its function.
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| Nonspecific Cells of CMI | Macrophages & Natural Killer Cells
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| Macrophage | When macrophages become activated, their phagocytic activity is greatly increased. They can become activated by ingestion of antigen or by cytokines produced by activated T helper cells.
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| Natural Killer Cells | These cells are important in fighting virus infected cells, parasites and cancerous cells.
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| Natural Killer Cells | They are not phagocytic but can lyse their target cell.
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| The Interrelationship Between Cell Mediated and Humoral Immunity | 1. The CMI System Cooperates With B Cells to Produce Antibodies 2. The Humoral Immune System Cooperates With Cells In ADCC
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| Lymphatic Vessels | A lymphatic capillary consists of a sac of thin endothelial cells that loosely overlap each other. The overlapping edges act as valvelike flaps that can open and close. When tissue fluid pressure is high, it pushes the flaps inward (open) and fluid flows
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| Lymphatic Vessels | Lymphatic endothelial cells are not joined by tight junctions, nor do they have a continuous basement membrane – unlike the endothelial cells of blood capillaries.
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| Lymphatic Vessels | The cells are tethered to surrounding tissue by protein filaments that prevent the sac from collapsing
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| lymphadenitis | When a lymph node is under challenge from a foreign antigen, it may become swollen/painful to the touch
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| lymphadenopathy | The collective term for all lymph node diseases
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| Tonsils | The tonsils are patches of lympathic tissue located at the entrance to the pharynx – where they guard against ingested/inhaled pathogens.
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| Tonsils | Each tonsil is covered by an epithelium and has deep pits called tonsillar crypts lined by lymphatic nodules. The crypts often contain food debris, dead WBCs, bacteria and antigenic chemicals.
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| Mucous Membranes and mucus | They line our gastrointestinal, respiratory and genitourinary tracts
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| They line our gastrointestinal, respiratory and genitourinary tracts | In the lower respiratory tract the goblet cells that produce mucus are also covered by cilia. This mechanism traps microbes and foreign particles and works to move it upward. This mechanism has been called a ciliary escalator.
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| Mucous Membranes and mucus | Alcohol and cigarette smoke also destroy the ciliary barrier.
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| Chemotaxis | Several things can attract phagocytes to the site, including: damaged tissue cells, products from microbial cells and components of the complement system namely fragment C5a.
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| apoptosis | Since the body makes 100 million lymphocytes a day, there must be some biological m
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| Clonal Selection | Some of the B cells form clones of Plasma Cells which produce antibody that is specific to the stimulating antigen.
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| Clonal Selection | Other B cells form Memory Cells which function in long term immunity. Years later, if the host is stimulated by the same antigen, these memory cells become active and are the basis of the secondary immune response.
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| Consequences of Antigen-Antibody Binding | So antibodies, in themselves, do not directly destroy the antigen. Rather they tag the antigen so that its more readily recognized and destroyed through other mechanisms – eg, phagocytosis, complement, ADCC.
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