Lymphatic system
Lymph originates as blood plasma lost from the circulatory system, which leaks out into the surrounding tissues. The lymphatic system collects this fluid by diffusion into lymph capillaries, and returns it to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid.
Lymphatic circulation
The lymphatic system acts as a secondary circulatory system, except it collaborates with white blood cells in order to protect people from being infected by viruses or bacteria. Unlike the circulatory system, the lymphatic system is not closed and has no central pump; the lymph moves slowly and under low pressure due mostly to the milking action of skeletal muscles. Like veins, lymph vessels have one-way valves and depend mainly on the movement of skeletal muscles to squeeze fluid through them. Rhythmic contraction of the vessel walls may also help draw fluid into the lymphatic capillaries. This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins.
Lymph vessels are present in the lining of the gastrointestinal tract. While most other nutrients absorbed by the small intestine are passed on to the portal venous system to drain, via the portal vein, into the liver for processing, fats are passed on to the lymphatic system, to be transported to the blood circulation via the thoracic duct. The enriched lymph originating in the lymphatics of the small intestine is called chyle (not chyme). The nutrients that are released to the circulatory system are processed by the liver, having passed through the systemic circulation. The lymph system is a one-way system (interstitial fluid back to blood).
Secondary lymphoid organs
The spleen, lymph nodes, and accessory lymphoid tissue are the secondary lymphoid organs. These organs contain a scaffolding that support circulating B- and T-lymphocytes and other immune cells like macrophages and dendritic cells. When micro-organisms invade the body or the body encounters other antigens (such as pollen), the antigens are transported from the tissue to the lymph. The lymph is carried in the lymph vessels to regional lymph nodes. In the lymph nodes, the macrophages and dendritic cells phagocytose the antigens, process them, and present the antigens to lymphocytes, which can then start producing antibodies or serve as memory cells to recognize the antigens again in the future.
Lymph Node
Lymph nodes, also incorrectly called "Lymph glands" (they do not secrete anything and are therefore not glands), are components of the lymphatic system. Lymph nodes act as filters, with an internal honeycomb of connective tissue filled with lymphocytes that collect and destroy bacteria and viruses. When the body is fighting an infection, these lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes. Humans have approximately 500-600 lymph nodes. Clusters of lymph nodes are found in the underarms, groin, neck, chest, and abdomen.
The spleen and tonsils are large lymphoid organs that serve similar functions, though the spleen filters out blood cells rather than bacteria or viruses.
Lymph originates as blood plasma lost from the circulatory system, which leaks out into the surrounding tissues. The lymphatic system collects this fluid by diffusion into lymph capillaries, and returns it to the circulatory system. Once within the lymphatic system the fluid is called lymph, and has almost the same composition as the original interstitial fluid.
Lymphatic circulation
The lymphatic system acts as a secondary circulatory system, except it collaborates with white blood cells in order to protect people from being infected by viruses or bacteria. Unlike the circulatory system, the lymphatic system is not closed and has no central pump; the lymph moves slowly and under low pressure due mostly to the milking action of skeletal muscles. Like veins, lymph vessels have one-way valves and depend mainly on the movement of skeletal muscles to squeeze fluid through them. Rhythmic contraction of the vessel walls may also help draw fluid into the lymphatic capillaries. This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins.
Lymph vessels are present in the lining of the gastrointestinal tract. While most other nutrients absorbed by the small intestine are passed on to the portal venous system to drain, via the portal vein, into the liver for processing, fats are passed on to the lymphatic system, to be transported to the blood circulation via the thoracic duct. The enriched lymph originating in the lymphatics of the small intestine is called chyle (not chyme). The nutrients that are released to the circulatory system are processed by the liver, having passed through the systemic circulation. The lymph system is a one-way system (interstitial fluid back to blood).
Secondary lymphoid organs
The spleen, lymph nodes, and accessory lymphoid tissue are the secondary lymphoid organs. These organs contain a scaffolding that support circulating B- and T-lymphocytes and other immune cells like macrophages and dendritic cells. When micro-organisms invade the body or the body encounters other antigens (such as pollen), the antigens are transported from the tissue to the lymph. The lymph is carried in the lymph vessels to regional lymph nodes. In the lymph nodes, the macrophages and dendritic cells phagocytose the antigens, process them, and present the antigens to lymphocytes, which can then start producing antibodies or serve as memory cells to recognize the antigens again in the future.
Lymph Node
Lymph nodes, also incorrectly called "Lymph glands" (they do not secrete anything and are therefore not glands), are components of the lymphatic system. Lymph nodes act as filters, with an internal honeycomb of connective tissue filled with lymphocytes that collect and destroy bacteria and viruses. When the body is fighting an infection, these lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes. Humans have approximately 500-600 lymph nodes. Clusters of lymph nodes are found in the underarms, groin, neck, chest, and abdomen.
The spleen and tonsils are large lymphoid organs that serve similar functions, though the spleen filters out blood cells rather than bacteria or viruses.
Lymph nodes are bean-shaped and range in size from a few millimeters to about 1-2 cm in their normal state. They may become enlarged due to a tumor or infection. In some cases, they may feel enlarged due to past infections; although one may be perfectly healthy, one may still feel residually enlarged.
The cortex contains several oval-shaped lymphoid nodules (also called follicles) which are aggregates of lymphocytes contained within a meshwork of supporting cells. Nodules that consist mainly of small lymphocytes are called primary nodules. Nodules called secondary nodules are those that contain a pale central region called a germinal center. The germinal center forms (and thus a primary nodule becomes a secondary nodule) when a B cell that has recognized an antigen undergoes proliferation, differentiates into plasma cells, and forms antibodies.
Lymph travels to the lymph node via afferent lymphatic vessels and drains into the node just beneath the capsule in a space called the subcapsular sinus. The subcapsular sinus drains into trabecular sinuses and finally into medullary sinuses. The sinus space is criss-crossed by the pseudopods of macrophages which act to trap foreign particles and filter the lymph. The medullary sinuses converge at the hilum and lymph then leaves the lymph node via the efferent lymphatic vessel.
Lymphocytes, both B cells and T cells, constantly circulate through the lymph nodes. They enter the lymph node via the bloodstream and may cross the wall of the blood vessel by the process of diapedesis. The B cells migrate to the nodular cortex and medulla, and the T cells migrate to the deep cortex.
When a lymphocyte recognizes an antigen, B cells become activated and migrate to germinal centers. When antibody-producing plasma cells are formed, they migrate to the medullary cords. Stimulation of the lymphocytes by antigens can accelerate the migration process to about 10 times normal, resulting in characteristic swelling of the lymph nodes.
Lymph nodes of the Head and Neck
Anterior cervical
These nodes, both superficial and deep, lie above and beneath the sternocleidomastoid muscles. They drain the internal structures of the throat as well as part of the posterior pharynx, tonsils, and thyroid gland.
Posterior cervical
These nodes extend in a line posterior to the sternocleidomastoids but in front of the trapezius, from the level of the mastoid bone to the clavicle. They are frequently enlarged during upper respiratory infections.
Tonsillar
These nodes are located just below the angle of the mandible. They drain the tonsillar and posterior pharyngeal regions.
Sub-mandibular
These nodes run along the underside of the jaw on either side. They drain the structures in the floor of the mouth.
Sub-mental
These nodes are just below the chin. They drain the teeth and intra-oral cavity.
Supraclavicular
These nodes are in the hollow above the clavicle, just lateral to where it joins the sternum. They drain a part of the thoracic cavity and abdomen. Virchow's node is a left supraclavicular lymph node which receives the lymph drainage from most of the body (especially the abdomen) via the thoracic duct and is thus an early site of metastasis for various malignancies.
Lymph nodes of the arm
These drain the whole of the arm, and are divided into two groups, superficial and deep. The superficial nodes are supplied by lymphatics, which are present throughout the arm, but are particularly rich on the palm and flexor aspects of the digits.
Superficial lymph glands of the arm
These comprise the
1) supratrochlear glands, situated above the medial epicondyle of the humerus, medial to the basilic vein. They drain the C7 and C8 dermatomes.
2) deltoideopectoral glands, situated between the pectoralis major and deltoid muscles inferior to the clavicle.
Deep lymph glands of the arm
These comprise the axillary glands, which are 20-30 individual glands and can be subdivided into:
Lateral glands
Anterior or pectoral glands
Posterior or subscapular glands
Central or intermediate glands
Medial or subclavicular glands
Anterior or pectoral glands
Posterior or subscapular glands
Central or intermediate glands
Medial or subclavicular glands
Lymphocyte
A lymphocyte is a type of white blood cell involved in the human body's immune system. There are two broad categories of lymphocytes, namely T cells and B cells. Lymphocytes play an important and integral part of the body's defenses.
T cells are chiefly responsible for cell-mediated immunity whereas B cells are primarily responsible for humoral immunity (relating to antibodies). T cells are named such because these lymphocytes mature in the thymus; B cells, named for the bursa of Fabricius in which they mature in bird species, are thought to mature in the bone marrow in humans.
In the presence of an antigen, B cells can become much more metabolically active and differentiate into plasma cells, which secrete large quantities of antibodies.
Lymph Vessels
Lymph vessels are thin walled, valved structures that carry lymph away from the tissues, through the lymph nodes and thoracic duct back to the general circulation. They are, therefore, highly analogous to veins and venules. They are related to the topics of Arteries, Veins, and Capillaries as well. They also are extremely necessary for life. Without lymph vessels, lymph fluid would not be able to be transported.
Thoracic duct
The thoracic duct, is an important part of the lymphatic system—it is the largest lymphatic vessel in the body. It collects most of the lymph in the body (except that from the right arm and the right side of the chest, neck and head, which is collected by the right lymphatic duct) and drains into the systemic (blood) circulation.
It is also known under various other names including the ductus thoracicus, alimentary duct, chyliferous duct, duct of Pecquet, the left lymphatic duct and Van Hoorne's canal.
Immune system
The immune system is the system of specialized cells and organs that protect an organism from outside biological influences. (Though in a broad sense, almost every organ has a protective function — for example, the tight seal of the skin or the acidic environment of the stomach.) When the immune system is functioning properly, it protects the body against bacteria and viral infections, destroying cancer cells and foreign substances. If the immune system weakens, its ability to defend the body also weakens, allowing pathogens, including viruses that cause common colds and flu, to grow and flourish in the body. The immune system also performs surveillance of tumor cells, and immune suppression has been reported to increase the risk of certain types of cancer.
The immune system is often divided into four sections:
- Natural passive immunity: Hereditary immunity, acquired from the mother, and lasting the first six months of a child's life.
- Acquired passive immunity: Non-permanent immunity gained from vaccines, such as Rabies or Tetanus.
- Natural active immunity: Having suffered a disease and its symptoms, one has natural active immunity, also known as a secondary response, where B-Cells fire off antibodies to combat a recognized antigen.
- Acquired active immunity: Permanent immunity as a result of vaccine.
Many disorders of the human immune system fall into two broad categories that are characterized by:
- Weakened immune response: There are 'congenital' (inborn) and 'acquired' forms of immunodeficiency, characterized by an attenuated response. Chronic granulomatous disease, in which phagocytes have trouble destroying pathogens, is an example of the former, while AIDS ("Acquired Immune Deficiency Syndrome"), an infectious disease caused by the HIV virus that destroys CD4+ T cells, is an example of the latter. Immunosuppressive medication intentionally induces an immunodeficiency in order to prevent rejection of transplanted organs.
- Overzealous immune response: On the other end of the scale, an overactive immune system figures in a number of other disorders, particularly autoimmune disorders such as lupus erythematosus, type I diabetes (sometimes called "juvenile onset diabetes"), multiple sclerosis, psoriasis, and rheumatoid arthritis. In these, the immune system fails to properly distinguish between self and non-self, and attacks a part of the patient's own body. Other examples of overzealous immune responses in disease include hypersensitivities, such as allergies and asthma.
Many factors can also contribute to the general weakening of the immune system:
- Malnutrition (unbalanced diet / poor eating habits that cause a lack of vitamins, minerals and Polyphenol antioxidants).
- Alcohol abuse.
- Drug abuse either intravenous or other. (Appears related to associated factors i.e. poor diet, use of infected/dirty needles, poor exercise, stress/depression).
- Medications (particularly the use of anti-cancer drugs, corticosteroids, and antibiotics).
- Radiation.
Exposure to certain environmental toxins, whether naturally occurring or from pollution. These include:
- Cigarette smoke
- Stress/Depression - Research shows that psychological stress can greatly increase your susceptibility to colds and other viral diseases, namely through an increase in serum corticosteroid levels.
- Age - Ability of the immune system to respond is decreased at early and old age.
- Decrease ability to heal due to disease or medications (i.e. Diabetes, corticosteroids, immune suppressant drugs), causing constant exposure to infectious agents without natural defense (intact skin).
- Inadequate sleep at the Delta brain wave level. According to a sleep study, we need 4 hours of Delta sleep every night.
- Lack of exercise as well as excessive exercise resulting in physiological stress.
- Long-term weightlessness.
Humoral Immunity
Humoral immunity (HIR) is the aspect of immunity that is mediated by secreted antibodies, produced in the cells of the B lymphocyte lineage (B cell). Secreted antibodies bind to antigens on the surfaces of invading microbes (such as viruses or bacteria), which flags them for destruction.
Humoral immunity refers to antibody production, and all the accessory processes that accompany it: Th2 activation and cytokine production, germinal center formation and isotype switching, affinity maturation and memory cell generation. It also refers to the effector functions of antibody, which include pathogen and toxin neutralization, classical complement activation, and opsonin promotion of phagocytosis and pathogen elimination.
Graft rejection usually triggers CMIR. Incompatible blood transfusion triggers HIR.
Cell-mediated immunity
Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages and natural killer cells, the production of antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches; 1. Humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum), 2. Cellular immunity, for which the protective function of immunization was associated with cells. Cellular immunity protects the body by:
Humoral immunity (HIR) is the aspect of immunity that is mediated by secreted antibodies, produced in the cells of the B lymphocyte lineage (B cell). Secreted antibodies bind to antigens on the surfaces of invading microbes (such as viruses or bacteria), which flags them for destruction.
Humoral immunity refers to antibody production, and all the accessory processes that accompany it: Th2 activation and cytokine production, germinal center formation and isotype switching, affinity maturation and memory cell generation. It also refers to the effector functions of antibody, which include pathogen and toxin neutralization, classical complement activation, and opsonin promotion of phagocytosis and pathogen elimination.
Graft rejection usually triggers CMIR. Incompatible blood transfusion triggers HIR.
Cell-mediated immunity
Cell-mediated immunity is an immune response that does not involve antibodies but rather involves the activation of macrophages and natural killer cells, the production of antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches; 1. Humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum), 2. Cellular immunity, for which the protective function of immunization was associated with cells. Cellular immunity protects the body by:
- Activating antigen-specific cytotoxic T-lymphocytes that are able to lyse body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens; activating macrophages and natural killer cells, enabling them to destroy intracellular pathogens; and
- stimulating cells to secrete a variety of cytokines that influence the function of other cells involved in adaptive immune responses and innate immune responses.
Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria. It also plays a major role in transplant rejection.
Immunological tolerance
Immunological tolerance is the process by which the immune system does not attack an antigen. It occurs in two forms: natural tolerance and induced tolerance.
Natural Tolerance
Natural tolerance is the body's tolerance for its own antigens and proteins. When naturals tolerance fails, or when the body does not properly recognize itself, an autoimmune disorder results.
Induced Tolerance
Induced tolerance is the immune system's tolerance for external antigens. It is created through some form of manipulation, such as medication. One of the most important roles of induced tolerance is in organ transplantation, when the body must be forced to accept an external organ. The failure of the body to accept an organ is known as transplant rejection. To prevent rejection, a variety of medicines are used to produce induced tolerance.
Immunosuppression
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, but medically induced immuno-suppression is carried out via drugs. This is usually done to prevent the body from rejecting an organ transplant or for the treatment of auto-immune diseases such as rheumatoid arthritis or Crohn's disease.
When an organ is transplanted, the immune system of the recipient will most likely recognize it as foreign tissue and attack it. The destruction of the organ will, if untreated, end in the death of the recipient.
In the past, radiation therapy was used to decrease the strength of the immune system, but now immunosuppressant drugs are used to inhibit the reaction of the immune system. The downside is that with such a deactivated immune system, the body is very vulnerable to opportunistic infections, even those usually considered harmless. Also, prolonged use of immunosuppressants increases the risk of cancer.
Cortisone was the first immunosuppressant identified. The more effective azathioprine was identified in 1959, but it was not until the discovery of cyclosporine in 1970 that transplant surgery found a sufficiently powerful immunosuppressive.
Bone Marrow
Bone marrow (or "medulla ossea") is the tissue comprising the center of large bones. It is the place where new blood cells are produced. Bone marrow contains two types of stem cells: hematopoietic (which can produce blood cells) and stromal (which can produce fat, cartilage and bone). Stromal stem cells have the capability to differentiate into many kinds of tissues, such as nervous tissue. Hematopoietic stem cells give rise to the three classes of blood cell that are found in the circulation: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes).
The tissue of bone marrow, where pluripotential hematopoietic stem cells produce blood cells, is called "myeloid tissue".
"Long bones", like the femur are tubular in structure, and the hollow middle is filled with yellow marrow. While the majority of long bones are formed of cortical ("compact") material; at the ends are the epiphysis, which are generally composed of cancellous ("spongy") material and red marrow. Large amounts of red bone marrow can also be found in flatter bones like those of the pelvis and skull.
Spleen
The spleen is a ductless, vertebrate gland that is closely associated with the circulatory system, where it functions in the destruction of old red blood cells in holding a reservoir of blood. It is regarded as one of the centres of activity of the reticuloendothelial system. Until recently, the purpose of the spleen was not known. It is increasingly recognized that its absence leads to a predisposition to certain infections.
Anatomy
The spleen monitors, destroys and stores red blood cells. In addition to this, the spleen has two functions, the red and white pulp. The white pulp helps fight infections and the red pulp removes unwanted materials.
It is the largest organ derived from mesenchyme and lying in the mesentery. The organ consists of masses of lymphoid tissue of granular appearance located around fine terminal branches of veins and arteries. These vessels are connected through the splenic pulp by modified capillaries called splenic sinuses. Cross sections of the spleen reveal a red soft surface which is divided into red and white pulp. Red pulp corresponds to the sinuses which are usually filled with blood. The white pulp shows white nodules, called Malpighian corpuscles. Under the microscope, these areas correspond to lymphoid follicles, rich in B-lymphocytes, and the periarteriolar lymphoid sheaths, rich in T-lymphocytes.
The human spleen is located in the upper left part of the abdomen, behind the stomach and just below the diaphragm. In normal individuals this organ measures about 125 × 75 × 50 mm (5 × 3 × 2 in) in size.
In certain animals such as dogs and horses, the spleen sequesters a large number of erythrocytes (red blood cells), which can be dumped into the bloodstream during periods of physical exertion. These animals also have large hearts in relation to their body size to accommodate the higher-viscosity blood that results. Some athletes have tried doping themselves with their own stored red blood cells to try to achieve the same effect, but the human heart is not equipped to handle the higher-viscosity blood.
Approximately 10% of people have one or more accessory spleens. They may form near the hilum of the main spleen, the junction at which the splenic vessels enter and leave the organ.
Disorders
Enlargement of the spleen is known as splenomegaly. It may be caused by malaria, bacterial endocarditis, leukemia, pernicious anaemia, leishmaniasis, Hodgkin's disease, Banti's disease, hereditary spherocytosis, cysts, glandular fever (mononucleosis), and tumors. Primary tumors of the spleen include hemangiomas and hemangiosarcomas. Marked splenomegaly may result in the spleen occupying a large portion of the left side of the abdomen.
The spleen is the largest collection of lymphoid tissue in the body. It is normally palpable in preterm infants, in 30% of normal, full-term neonates, and in 5% to 10% of infants and toddlers. A spleen easily palpable below the costal margin in any child over the age of 3-4 years should be considered abnormal until proven otherwise.
Splenomegaly can result from antigenic stimulation (Eg, infection), obstruction of blood flow (Eg, portal vein obstruction), underlying functional abnormality (Eg, hemolytic anemia), or infiltration (Eg, leukemia or storage disease, such as Gaucher's disease). The most common cause of acute splenomegaly in children is viral infection, which is transient and usually moderate. Basic work-up for acute splenomegaly includes a complete blood count with differential, platelet count, and reticulocyte and atypical lymphocyte counts to exclude hemolytic anemia and leukemia. Assessment of IgM antibodies to viral capsid antigen (a rising titer) is indicated to confirm Epstein-Barr virus or cytomegalovirus. Other infections should be excluded if these tests are negative.
Absence
The absence of a spleen predisposes to some septicemia infections. Vaccination and antibiotic measures are discussed under asplenia.
Immunological tolerance
Immunological tolerance is the process by which the immune system does not attack an antigen. It occurs in two forms: natural tolerance and induced tolerance.
Natural Tolerance
Natural tolerance is the body's tolerance for its own antigens and proteins. When naturals tolerance fails, or when the body does not properly recognize itself, an autoimmune disorder results.
Induced Tolerance
Induced tolerance is the immune system's tolerance for external antigens. It is created through some form of manipulation, such as medication. One of the most important roles of induced tolerance is in organ transplantation, when the body must be forced to accept an external organ. The failure of the body to accept an organ is known as transplant rejection. To prevent rejection, a variety of medicines are used to produce induced tolerance.
Immunosuppression
Immunosuppression involves an act that reduces the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, but medically induced immuno-suppression is carried out via drugs. This is usually done to prevent the body from rejecting an organ transplant or for the treatment of auto-immune diseases such as rheumatoid arthritis or Crohn's disease.
When an organ is transplanted, the immune system of the recipient will most likely recognize it as foreign tissue and attack it. The destruction of the organ will, if untreated, end in the death of the recipient.
In the past, radiation therapy was used to decrease the strength of the immune system, but now immunosuppressant drugs are used to inhibit the reaction of the immune system. The downside is that with such a deactivated immune system, the body is very vulnerable to opportunistic infections, even those usually considered harmless. Also, prolonged use of immunosuppressants increases the risk of cancer.
Cortisone was the first immunosuppressant identified. The more effective azathioprine was identified in 1959, but it was not until the discovery of cyclosporine in 1970 that transplant surgery found a sufficiently powerful immunosuppressive.
Bone Marrow
Bone marrow (or "medulla ossea") is the tissue comprising the center of large bones. It is the place where new blood cells are produced. Bone marrow contains two types of stem cells: hematopoietic (which can produce blood cells) and stromal (which can produce fat, cartilage and bone). Stromal stem cells have the capability to differentiate into many kinds of tissues, such as nervous tissue. Hematopoietic stem cells give rise to the three classes of blood cell that are found in the circulation: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes).
The tissue of bone marrow, where pluripotential hematopoietic stem cells produce blood cells, is called "myeloid tissue".
"Long bones", like the femur are tubular in structure, and the hollow middle is filled with yellow marrow. While the majority of long bones are formed of cortical ("compact") material; at the ends are the epiphysis, which are generally composed of cancellous ("spongy") material and red marrow. Large amounts of red bone marrow can also be found in flatter bones like those of the pelvis and skull.
Spleen
The spleen is a ductless, vertebrate gland that is closely associated with the circulatory system, where it functions in the destruction of old red blood cells in holding a reservoir of blood. It is regarded as one of the centres of activity of the reticuloendothelial system. Until recently, the purpose of the spleen was not known. It is increasingly recognized that its absence leads to a predisposition to certain infections.
Anatomy
The spleen monitors, destroys and stores red blood cells. In addition to this, the spleen has two functions, the red and white pulp. The white pulp helps fight infections and the red pulp removes unwanted materials.
It is the largest organ derived from mesenchyme and lying in the mesentery. The organ consists of masses of lymphoid tissue of granular appearance located around fine terminal branches of veins and arteries. These vessels are connected through the splenic pulp by modified capillaries called splenic sinuses. Cross sections of the spleen reveal a red soft surface which is divided into red and white pulp. Red pulp corresponds to the sinuses which are usually filled with blood. The white pulp shows white nodules, called Malpighian corpuscles. Under the microscope, these areas correspond to lymphoid follicles, rich in B-lymphocytes, and the periarteriolar lymphoid sheaths, rich in T-lymphocytes.
The human spleen is located in the upper left part of the abdomen, behind the stomach and just below the diaphragm. In normal individuals this organ measures about 125 × 75 × 50 mm (5 × 3 × 2 in) in size.
In certain animals such as dogs and horses, the spleen sequesters a large number of erythrocytes (red blood cells), which can be dumped into the bloodstream during periods of physical exertion. These animals also have large hearts in relation to their body size to accommodate the higher-viscosity blood that results. Some athletes have tried doping themselves with their own stored red blood cells to try to achieve the same effect, but the human heart is not equipped to handle the higher-viscosity blood.
Approximately 10% of people have one or more accessory spleens. They may form near the hilum of the main spleen, the junction at which the splenic vessels enter and leave the organ.
Disorders
Enlargement of the spleen is known as splenomegaly. It may be caused by malaria, bacterial endocarditis, leukemia, pernicious anaemia, leishmaniasis, Hodgkin's disease, Banti's disease, hereditary spherocytosis, cysts, glandular fever (mononucleosis), and tumors. Primary tumors of the spleen include hemangiomas and hemangiosarcomas. Marked splenomegaly may result in the spleen occupying a large portion of the left side of the abdomen.
The spleen is the largest collection of lymphoid tissue in the body. It is normally palpable in preterm infants, in 30% of normal, full-term neonates, and in 5% to 10% of infants and toddlers. A spleen easily palpable below the costal margin in any child over the age of 3-4 years should be considered abnormal until proven otherwise.
Splenomegaly can result from antigenic stimulation (Eg, infection), obstruction of blood flow (Eg, portal vein obstruction), underlying functional abnormality (Eg, hemolytic anemia), or infiltration (Eg, leukemia or storage disease, such as Gaucher's disease). The most common cause of acute splenomegaly in children is viral infection, which is transient and usually moderate. Basic work-up for acute splenomegaly includes a complete blood count with differential, platelet count, and reticulocyte and atypical lymphocyte counts to exclude hemolytic anemia and leukemia. Assessment of IgM antibodies to viral capsid antigen (a rising titer) is indicated to confirm Epstein-Barr virus or cytomegalovirus. Other infections should be excluded if these tests are negative.
Absence
The absence of a spleen predisposes to some septicemia infections. Vaccination and antibiotic measures are discussed under asplenia.
- Some people congenitally completely lack a spleen, although this is rare.
- Sickle-cell disease can cause a functional asplenia (or autosplenectomy) by causing infarctions of the spleen during repeated sickle-cell crises.
- It may be removed surgically (known as a splenectomy), and indeed often is. For example, it may be removed following abdominal injuries with rupture and hemorrhage of the spleen, or in the treatment of certain blood diseases (Idiopathic thrombocytopenic purpura, hereditary spherocytosis, etc.), certain forms of lymphoma or for the removal of splenic tumors or cysts.
Thymus
The thymus is an organ located in the upper anterior portion of the chest cavity. The thymus plays an important role in the development of the immune system in early life, and its cells form a part of the body's normal immune system. It is most active before puberty, after which it shrinks in size and activity in most individuals and is replaced with fat.
Tonsil
The tonsils are areas of lymphoid tissue on either side of the throat. An infection of the tonsils is called tonsillitis.
As with other organs of the lymphatic system, the tonsils act as part of the immune system to help protect against infection. In particular, they are believed to be involved in helping fight off pharyngeal and upper respiratory tract infections.
Tonsils in humans include, from superior to inferior: pharyngeal tonsils (also known as adenoids), tubal tonsils, palatine tonsils, and lingual tonsils. Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring. Tonsils tend to reach their largest size near puberty, and they gradually undergo atrophy thereafter. However, they are largest relative to the diameter of the throat in young children, and tonsillectomy (surgical removal of tonsils) may be indicated if they are obstructing the airway or interfering with swallowing.
Most commonly, the term "tonsils" refers to the palatine tonsils that can be seen in the back of the throat.
Tonsillitis is an inflammation of the tonsils and will often, but not necessarily, cause a sore throat and fever. In chronic cases tonsillectomy may be indicated.
Tonsillar crypts
The palatine tonsils include numerous pits and crevices, termed "tonsillar crypts," which often harbor large numbers of bacteria and which serve as a locus of infection. Tonsil crypts are indentations on the tonsil that resemble the pores of the skin.
Autoimmunity
Autoimmunity is the failure of an organism to recognize its own constituent parts (down to the sub-molecular levels) as "Self", which results in an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease, the prominent examples being Systemic Lupus Erythematosus (SLE), Sjögren's syndrome and Rheumatoid Arthritis (RA).
The illusory misconception that an individual's immune system is totally incapable of recognizing "self" antigens is not new. Paul Ehrlich, at the beginning of the twentieth century, proposed the concept of horror autotoxicus, wherein a 'normal' body does not mount an immune response against its own tissues. Any autoimmune response thus was perceived to be abnormal and postulated to be connected with human disease. Now, it is accepted that autoimmune responses are vital to the development and functioning of vertebrate immune system, and central to the development of immunological tolerance to self-antigens. The latter concept has been somewhat prematurely termed natural autoimmunity. Autoimmunity should not be confused with alloimmunity.
List of autoimmune diseases
Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. In other words, the body attacks its own cells. Today there are more than 40 human diseases classified as either definite or probable autoimmune diseases, and they affect 5% to 7% of the population. Almost all autoimmune diseases appear without warning or apparent cause, and most patients suffer from fatigue.
Diseases with a complete or partial autoimmune etiology:
The thymus is an organ located in the upper anterior portion of the chest cavity. The thymus plays an important role in the development of the immune system in early life, and its cells form a part of the body's normal immune system. It is most active before puberty, after which it shrinks in size and activity in most individuals and is replaced with fat.
Tonsil
The tonsils are areas of lymphoid tissue on either side of the throat. An infection of the tonsils is called tonsillitis.
As with other organs of the lymphatic system, the tonsils act as part of the immune system to help protect against infection. In particular, they are believed to be involved in helping fight off pharyngeal and upper respiratory tract infections.
Tonsils in humans include, from superior to inferior: pharyngeal tonsils (also known as adenoids), tubal tonsils, palatine tonsils, and lingual tonsils. Together this set of lymphatic tissue is called the tonsillar ring or Waldeyer's ring. Tonsils tend to reach their largest size near puberty, and they gradually undergo atrophy thereafter. However, they are largest relative to the diameter of the throat in young children, and tonsillectomy (surgical removal of tonsils) may be indicated if they are obstructing the airway or interfering with swallowing.
Most commonly, the term "tonsils" refers to the palatine tonsils that can be seen in the back of the throat.
Tonsillitis is an inflammation of the tonsils and will often, but not necessarily, cause a sore throat and fever. In chronic cases tonsillectomy may be indicated.
Tonsillar crypts
The palatine tonsils include numerous pits and crevices, termed "tonsillar crypts," which often harbor large numbers of bacteria and which serve as a locus of infection. Tonsil crypts are indentations on the tonsil that resemble the pores of the skin.
Autoimmunity
Autoimmunity is the failure of an organism to recognize its own constituent parts (down to the sub-molecular levels) as "Self", which results in an immune response against its own cells and tissues. Any disease that results from such an aberrant immune response is termed an autoimmune disease, the prominent examples being Systemic Lupus Erythematosus (SLE), Sjögren's syndrome and Rheumatoid Arthritis (RA).
The illusory misconception that an individual's immune system is totally incapable of recognizing "self" antigens is not new. Paul Ehrlich, at the beginning of the twentieth century, proposed the concept of horror autotoxicus, wherein a 'normal' body does not mount an immune response against its own tissues. Any autoimmune response thus was perceived to be abnormal and postulated to be connected with human disease. Now, it is accepted that autoimmune responses are vital to the development and functioning of vertebrate immune system, and central to the development of immunological tolerance to self-antigens. The latter concept has been somewhat prematurely termed natural autoimmunity. Autoimmunity should not be confused with alloimmunity.
List of autoimmune diseases
Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. In other words, the body attacks its own cells. Today there are more than 40 human diseases classified as either definite or probable autoimmune diseases, and they affect 5% to 7% of the population. Almost all autoimmune diseases appear without warning or apparent cause, and most patients suffer from fatigue.
Diseases with a complete or partial autoimmune etiology:
- Acute disseminated encephalomyelitis (ADEM) is a form of encephalitis caused by an autoimmune reaction and typically occurring a few days or weeks after a viral infection or a vaccination.
- Addison's disease is often caused by autoimmune destruction of the adrenal cortex.
- Antiphospholipid antibody syndrome (APS) affects the blood-clotting process. It causes blood clots to form in veins and/or arteries.
- Aplastic anemia is often caused by an autoimmune attack on the bone marrow.
- Autoimmune hepatitis is a disorder wherein the liver is the target of the body's own autoimmune system.
- Coeliac disease is a disease characterized by chronic inflammation of the proximal portion of the small intestine caused by exposure to certain dietary gluten proteins.
- Crohn's disease is a form of inflammatory bowel disease characterized by chronic inflammation of the intestinal tract. Major symptoms include abdominal pain and diarrhea.
Diabetes mellitus (type 1) is the result of an autoimmune attack on the islet cells of the pancreas. - Goodpasture's syndrome is a disease characterized by rapid destruction of the kidneys and hemorrhaging of the lungs through autoimmune reaction against an antigen found in both organs.
- Graves' disease is the most common form of hyperthyroidism, and is caused by anti-thyroid antibodies that have the effect of stimulating the thyroid into overproduction of thyroid hormone.
- Guillain-Barré syndrome (GBS) is an acquired immune-mediated inflammatory disorder of the peripheral nervous system (i.e., not the brain and spinal column). It is also called acute inflammatory demyelinating polyneuropathy, acute idiopathic polyradiculoneuritis, acute idiopathic polyneuritis and Landry's ascending paralysis.
- Hashimoto's disease is a common form of hypothyroidism, characterized by initial inflammation of the thyroid, and, later, dysfunction and goiter. There are several characteristic antibodies (e.g., anti-thyroglobulin).
- Lupus erythematosus is a chronic (long-lasting) autoimmune disease wherein the immune system, for unknown reasons, becomes hyperactive and attacks normal tissue. This attack results in inflammation and brings about symptoms. This is a "Non-organ-specific" type of autoimmune disease.
- Multiple sclerosis is a disorder of the central nervous system (brain and spinal cord) characterized by decreased nerve function due to myelin loss and secondary axonal damage.
- Myasthenia gravis is a disorder of neuromuscular transmission leading to fluctuating weakness and fatigue. Weakness is caused by circulating antibodies that block acetylcholine receptors at the neuromuscular junction.
- Opsoclonus myoclonus syndrome (OMS) is a neurological disorder that appears to the result of an autoimmune attack on the nervous system. Symptoms include opsoclonus, myoclonus, ataxia, intention tremor, dysphasia, dysarthria, mutism, hypotonia, lethargy, irritability or malaise. About half of all OMS cases occur in association with neuroblastoma.
Optic neuritis is an inflammation of the optic nerve that may cause a complete or partial loss of vision. - Ord's thyroiditis is a thyroiditis similar to Hashimoto's disease, except that the thyroid is reduced in size. In Europe, this form of thyroid inflammation is more common than Hashimoto's disease.
- Pemphigus is an autoimmune disorder that causes blistering and raw sores on skin and mucous membranes.
- Polyarthritis in dogs is an immune reaction severely affecting the joints of dogs. Although rare and of unknown cause it can render a dog immobile even at a very young age. Treatment includes cortisone-type drugs.
- Primary biliary cirrhosis appears to be an autoimmune disease that affects the biliary epithelial cells (BECs) of the small bile duct in the liver. Although the cause is yet to be determined, most of the patients (>90%) appear to have auto-mitochondrial antibodies (AMAs) against pyruvate dehydrogenase complex (PDC), an enzyme that is found in the mitochondria.
- Psoriasis is a skin disorder in which rapidly-multiplying skin cells produce itchy, scaly inflamed patches on the skin.
- Rheumatoid arthritis is an autoimmune disorder that causes the body's immune system to attack the bone joints.
- Reiter's syndrome seems to be an autoimmune attack on various body systems in response to a bacterial infection and the body's confusion over the HLA-B27 marker
- Takayasu's arteritis is a disorder that results in the narrowing of the lumen of arteries.
- Temporal arteritis (also known as "giant cell arteritis") is an inflammation of blood vessels, most commonly the large and medium arteries of the head. Untreated, the disorder can lead to significant vision loss.
- Warm autoimmune hemolytic anemia is a disorder characterized by IgM attack against red blood cells
- Wegener's granulomatosis is a form of vasculitis that affects the lungs, kidneys and other organs.
Immunization
Immunization is the process by which an individual is exposed to an agent that is designed to fortify his or her immune system against that agent. The material is known as an immunogen. Immunization is the same as inoculation and vaccination in that inoculation and vaccination use a viable infecting agent like immunization does. Immunization is just the general term for vaccination and such things as what you gain from these process.
When the human immune system is exposed to a disease once, it can develop the ability to quickly respond to a subsequent infection. Therefore, by exposing an individual to an immunogen in a controlled way, their body will then be able to protect itself from infection later on in life.
Antibody
An antibody is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. This is because at the two tips of its "Y", it has structures akin to locks. Every lock only has one key, in this case, its own antigen. When the key is inserted into the lock, the antibody activates, tagging or neutralizing its target. The production of antibodies is called the humoral immune system.
Immunoglobulins are glycoproteins in the immunoglobulin superfamily that function as antibodies. The terms antibody and immunoglobulin are often used interchangeably. They are found in the blood and tissue fluids, as well as many secretions. In structure, they are globulins (in the γ-region of protein electrophoresis). They are synthesized and secreted by plasma cells that are derived from the B cells of the immune system. B cells are activated upon binding to their specific antigen and differentiate into plasma cells. In some cases, the interaction of the B cell with a T helper cell is also necessary.
Immunization is the process by which an individual is exposed to an agent that is designed to fortify his or her immune system against that agent. The material is known as an immunogen. Immunization is the same as inoculation and vaccination in that inoculation and vaccination use a viable infecting agent like immunization does. Immunization is just the general term for vaccination and such things as what you gain from these process.
When the human immune system is exposed to a disease once, it can develop the ability to quickly respond to a subsequent infection. Therefore, by exposing an individual to an immunogen in a controlled way, their body will then be able to protect itself from infection later on in life.
Antibody
An antibody is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. This is because at the two tips of its "Y", it has structures akin to locks. Every lock only has one key, in this case, its own antigen. When the key is inserted into the lock, the antibody activates, tagging or neutralizing its target. The production of antibodies is called the humoral immune system.
Immunoglobulins are glycoproteins in the immunoglobulin superfamily that function as antibodies. The terms antibody and immunoglobulin are often used interchangeably. They are found in the blood and tissue fluids, as well as many secretions. In structure, they are globulins (in the γ-region of protein electrophoresis). They are synthesized and secreted by plasma cells that are derived from the B cells of the immune system. B cells are activated upon binding to their specific antigen and differentiate into plasma cells. In some cases, the interaction of the B cell with a T helper cell is also necessary.
There are five types: IgA, IgD, IgE, IgG, and IgM. (Ig stands for immunoglobulin, which is another name for antibody)
This is according to differences in their heavy chain constant domains. (The isotypes are also defined with light chains, but they do not define classes, so they are often neglected.) Other immune cells partner with antibodies to eliminate pathogens depending on which IgG, IgA, IgM, IgD, and IgE constant binding domain receptors it can express on its surface.
Structure of the antibody
Immunoglobulins are heavy plasma proteins, often with added sugar chains (see glycosylation) on N-terminal (all antibodies) and occasionally O-terminal (IgA1 and IgD) amino acid residues.
The basic unit of each antibody is a monomer. An antibody can be monomeric, dimeric, trimeric, tetrameric, pentameric, etc. The monomer is a "Y"-shape molecule that consists of four polypeptide chains: two identical heavy chains and two identical light chains connected by disulfide bonds.
Monoclonal antibodies
Monoclonal antibodies (mAb) are antibodies that are identical because they were produced by one type of immune cell, all clones of a single parent cell. Given (almost) any substance, it is possible to create monoclonal antibodies that specifically bind to that substance; they can then serve to detect or purify that substance. This has become an important tool in biochemistry, molecular biology and medicine.
Antigen
An antigen is a substance that stimulates an immune response, especially the production of antibodies. Antigens are usually proteins or polysaccharides, but can be any type of molecule, including small molecules (haptens) coupled to a carrier-protein.
Types of antigen
Immunogen - Any substance that provokes the immune response when introduced into the body. An immunogen is always a macromolecule (protein, polysaccharide). Its ability to stimulate the immune reaction depends on its commoness to the host, molecular size, chemical composition and heterogeneity (e.g. similar to amino acids in a protein).
Tolerogen - An antigen that invokes a specific immune non-responsiveness due to its molecular form. If its molecular form is changed, a tolerogen can become an immunogen.
Allergen - An allergen is a substance that causes the allergic reaction. It can be ingested, inhaled, injected or comes into contact with skin.
Cells present their antigens to the immune system via a histocompatibility molecule. Depending on the antigen presented and the type of the histocompatibility molecule, several types of immune cells can become activated.
Complement System
The complement system is a biochemical cascade of the immune system that helps clear pathogens from an organism. It is derived from many small plasma proteins work together to form the primary end result of cytolysis by disrupting the target cell's plasma membrane.
The actions of the complement system affect both innate immunity and acquired immunity.
Activation of this system leads to cytolysis, chemotaxis, opsonization, immune clearance, and inflammation, as well as the marking of pathogens for phagocytosis. The complement system consists of more than 35 soluble and cell-bound proteins, 12 of which are directly involved in the complement pathways. The proteins account for 5% of the serum globulin fraction. Most of these proteins circulate as zymogens, which are inactive until proteolytic cleavage. The complement proteins are synthesized mainly by hepatocytes; however, monocytes, macrophages, and epithelial cells in the gastrointestinal and genitourinary tracts also produce significant amounts.
Vaccination
Vaccination is the process of administering weakened or dead pathogens to a healthy person, with the intent of conferring immunity against a targeted form of a related disease agent.
The term was coined by Edward Jenner and adapted by Louis Pasteur for his pioneering work in vaccination.
Triggering immune sensitization
In the generic sense, the process of artificial induction of immunity, in an effort to protect against infectious disease, works by 'priming' the immune system with an 'immunogen'. Stimulating immune response, via use of an infectious agent, is known as immunization. Vaccinations involve the administration of one or more immunogens, in the form of live, but weakened (attenuated) infectious agents, which normally are either weaker, but closely-related species (as with smallpox and cowpox), or strains weakened by some process. In such cases, an immunogen is called a vaccine.
Some modern vaccines are administered after the patient already has contracted a disease, as in the cases of experimental AIDS, cancer and Alzheimer's disease vaccines. Vaccinia given after exposure to smallpox, within the first four days, is reported to attenuate the disease considerably, and vaccination within the first week is known to be beneficial to a degree. The first Rabies immunization was given by Pasteur to a child bitten by a rabid dog, and then and subsequently postexposure immunization to Rabies has generally been followed by survival. The essential empiricism behind such immunizations is that the vaccine triggers an immune response more rapidly than the natural infection itself.
Most vaccines are given by hypodermic injection as they are not absorbed reliably through the gut. Live attenuated Polio, some Typhoid and Cholera Vaccines are given orally in order to produce immunity based in the bowel.
Adult Immunization Schedule
(Anyone over 18 years old)
Vaccines for adults include
Tetanus-diphtheria Vaccine (all adults, every 10 years)
Influenza (Flu) Vaccine (adults 50 and older)
Pneumococcal Vaccine (adults 65 and older)
Hepatitis B Vaccine (adults at risk)
Measles-Mumps-Rubella (MMR) Vaccine (susceptible adults)
Varicella (chickenpox) Vaccine (susceptible adults)
Vaccines for travelers
AIDS - Acquired immunodeficiency syndrome.
AZT - Azidothymidine (zidovudine).
CMV - Cytomegalovirus.
ddI - Didanosine.
EBV - Epstein-Barr virus.
ELISA - Enzyme-linked immunosorbent assay.
HIV - Human immunodeficiency virus.
HSV - Herpes simplex virus.
IgA - Immunoglobulin
KS - Knee society (aaos specialty societies).
PCP - Pneumocystis carinii pneumonia.
T4 - Thyroxine.
ZDV - Zidovudine.
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