Lymphatic System Flashcards
Specify the types of leukocytes, their functions, origins and relative quantities in normal blood.
The various components of blood are shown in Figure 1. The cellular components of blood are red blood cells (erythrocytes) and white blood cells (leucocytes). Note that the erythrocytes are far more numerous than leucocytes and are smaller than leucocytes. All blood cells begin development in the red bone marrow.
Leucocytes are of two basic types, granulocytes and agranulocytes. Figure 1 illustrates the three types of granulocytes: neutrophils, eosinophils and basophils. Each type has granules in the cytoplasm and each has a complex lobed nucleus.
The other major group of leucocytes are the agranulocytes. Figure 1 illustrates the two types of agranulocytes: lymphocytes and monocytes. Agranulocytes have a clear cytoplasm without granules present. Lymphocytes have very little cytoplasm and have a large circular nucleus which fills up most of the cell. Monocytes are relatively large cells and have a nucleus which fills up almost 2/3 of the cell. The shape of the nucleus is more variable in monocytes than in lymphocytes.
Describe the purpose of a differential count and how to interpret the results.
A differential count is used in the diagnosis of an infection or disease on the basis of an increase or decrease in numbers of specific types of white blood cells.
In adults, an increase in leucocytes is described as leucocytosis (i.e. > 10,000 WBCs/μl) while a decrease is called leucopenia (i.e. < 5,000 WBCs/μl). The normal ranges for the different types of leucocytes and some causes of leucocytosis and leucopenia are indicated in Table 1 in Wk 2 notes.
Describe the major functions and anatomical organization of the lymphatic system.
One function of the lymphatic system is to return tissue fluid back to the circulatory system. About 15% of the fluid filtered from the blood into the interstitial spaces is returned back to the blood via the lymphatic system
Another function of the lymphatic system is defence The lymphatic system contains two types of white blood cells that act in defence: T lymphocytes and B lymphocytes from which plasma cells are produced in the lymph nodes. This will be dealt with in more detail in week 10.
A third function of the lymphatic system is to transport fats, some proteins, and some other molecules from the small intestine to the circulatory system
The lymphatic system consists of networks of capillaries which arise in tissue spaces and form thin vessels and ducts. These vessels are small, dead end tubes into which tissue fluid drains
The vessels contain swellings called nodes. These oval or bean-shaped swellings are situated throughout the lymphatic vessels and serve to filter the fluid within the vessels
The lymphatic system also has tissues and organs associated with it, which include the spleen, tonsils, and thymus.
- The spleen has the largest amount of lymphoid tissue in the body and initiates immune responses to circulating foreign substances
- The tonsils are masses of lymphoid nodules in the pharynx and functions in a filtering and immunological role.
- The thymus is a small, grainy lymphoid organ located behind the sternum. It plays a role in the maturation of certain white blood cells.
Distinguish between the cardiovascular system and the lymphatic system.
The fluid contained in lymph vessels is called lymph. The lymph originates from tissue fluid which, in turn originates from the plasma. The lymph in the vessels eventually drains back into the blood. The lymph enters the circulatory system via two ducts in the neck region, the right lymphatic duct and the thoracic duct. These ducts drain into the right and left subclavian veins respectively
There is no pump to drive lymph through the lymphatic system. Rather, muscle contractions and the movements of the internal organs are responsible for the flow of lymph through the system. Backflow is prevented by valves.
Explain nonspecific (innate) resistance to disease and specify the general components of nonspecific (innate) resistance.
NON-SPECIFIC (INNATE) RESISTANCE General response to trauma, infection
- SKIN and MUCOUS MEMBRANES
* Chemical
* Mechanical - ANTIMICROBIAL
* Interferon
* Complement - PHAGOCYTOSIS
* Microphages
* Macrophages - INFLAMMATION
- FEVER
SPECIFIC (ADAPTIVE) RESISTANCE
Occurs only in response to a particular antigen
HUMORAL IMMUNITY (Antibodies)
CELL MEDIATED IMMUNITY
(cytotoxic T cells)
Explain specific (adaptive) resistance to disease (immunity), and distinguish between T- cell mediated (cellular) immunity and B-cell mediated (humoral) immunity.
Specificity and immunological memory are features that are found in specific (adaptive) immunity but not in non-specific (innate) immunity. Specific immunity also involves the production of specific types of cells and specific antibodies. Among the important cells produced during the development of specific immunity are antigen presenting cells (APCs), T lymphocytes and B lymphocytes.
APCs include phagocytic cells such as macrophages (derived from monocytes), dendritic cells and B cells. They must be present for both cellular and humoral immunity. APCs are responsible for processing and presenting antigens to T cells Antigens are substances that trigger an immune response if introduced into an individual who does not have those particular antigens. APCs also secrete powerful chemicals such as cytokines and interleukins that cause T cells and B cells to proliferate.
T cells are responsible for cellular immunity. It is called cellular immunity because specially activated cytotoxic T lymphocytes directly kill other cells. For example, host cells can be destroyed when infected by viruses or intracellular bacteria or when recognized as abnormal such as some cancer cells and transplanted cells. Helper T cells aid various immune cells fulfill their roles within the immune system.
B cells produce antibodies that participate in humoral immunity. The term “antibody (Ab)” is short for anti-foreign body. Antibodies are proteins that are produced in response to specific features on pathogens or to substances produced by pathogens such as toxins. After exposure of B cells to such substances, Antibodies are produced and released from the B cells to circulate in the blood until reaching sites of infection. The antibody then attaches and inactivates the substance that caused its creation. Antibodies are particularly effective against extracellular microorganisms such as acute bacterial infections, and during phases of viral infections where viral particles are outside the cell.
Both T cells and B cells originate from lymphocytic stem cells in the embryo’s bone marrow. During embryonic development, half of these stem cells migrate to the thymus gland where they become T (thymus) cells. It is in the thymus gland that these cells mature into different types of T cells such as cytotoxic T cells and helper T cells that perform specific immune reactions. T cells are also educated in the thymus so they can differentiate self from non-self. Just before and shortly after birth, the T cells leave the thymus gland as mature, naive (not yet exposed to antigen) T cells. The T cells become embedded in the body’s lymphoid tissue where they are maintained by hormones released from the thymus. It is at these sites distal from the thymus that the T cells are activated or stimulated by specific antigens to differentiate into effector cells (cells primed to carry out their functions).
There are at least a billion different antigens recognized by T cells, but only the particular T cell that is specifically programmed to react with a particular antigen becomes active when that antigen is present in the body. This indicates that T cells are very selective regarding the antigens that they will bind and thus the specific (adaptive) immune system shows specificity. Furthermore, for activation, the T cell must bind its specific antigen as a fragment on an APC. Following this, activated T cells whether cytotoxic or helper, then grow in size, differentiate, and divide. Activated cytotoxic T cells that leave the lymphoid tissue go to the site of infection, and directly kill the infected or altered host cell. The activated helper T cells produce chemicals and proteins (cytokines and interleukins) that speed up the formation of both cytotoxic T cells and antibody producing B cells (plasma cells). The memory T and B cells develop on first exposure to the antigen but they do not proliferate on this first encounter; instead they lie in readiness and will speedily differentiate and divide upon subsequent exposure to the same antigen. They enable the body to rapidly respond to a second infection.
The origin of B cells is illustrated in Figure 3. As mentioned earlier, half of the original lymphocytic stem cells migrated to the thymus gland to become T cells. The other half migrates to an unknown part of the body where they are processed to become B cells. It is suspected that this processing occurs in the bone marrow, the fetal liver and spleen. The role of B cells in humoral immunity
As in the case with the T cells, there are again billions of antigens to which specific B cells respond. In the case of cellular immunity we discovered that killer or cytotoxic T cells actually leave the lymphoid tissue. However, B cells remain in the lymphoid tissue where they are activated by appropriate antigens and helper T cells. This stimulation leads to their differentiation and clonal expansion into effector plasma cells that are responsible for the production of antibodies. It is the antibodies that circulate in the blood and lymph, (like hormones thus the term humoral immunity) and attack the invading pathogen or toxin.
abbreviated as Ig. There are 5 classes of immunoglobulins in the blood. Each class performs a particular function. For example the immunoglobulins in the IgG class enhance phagocytosis by binding to the surface of microorganisms and making them more “tasty” for macrophages; this is called opsonization. IgG also neutralises toxins and protects the foetus and newborn. IgG is the only immunoglobulin class that is able to cross the placenta. The IgA antibodies provide localised protection on mucosal surfaces. The IgE antibodies play important roles during the elimination of large multicellular parasites and are involved in allergic reactions.
A plasma cell can produce 2,000 molecules of antibody/cell/second. This rate of production is sustained for 4 or 5 days at which time the cell dies. Not all of the B cells are activated into plasma cells. As was the case with T cells, where some differentiated into memory cells, there are also B cells that remain as memory cells. These will react more quickly upon a subsequent invasion of a foreign body.
Antibodies generally do not persist for more than a few months or years. This indicates an important difference between cellular and humoral immunity. The sensitized lymphocytes of cellular immunity have an indefinite lifespan, and can survive as long as the individual.
Discuss the relationship between antibodies and immunization, and specify four ways of conferring immunity.
a) Neutralising the antigen by binding to the pathogen or its toxins. This binding covers sites used to cause disease and/or their attachment to body cells.
b) Immobilizing bacteria by antibodies binding to cilia or flagella. This can prevent movement and therefore the spread of bacteria.
c) Direct opsonization through binding of the antibody to the antigen. This binding enhances phagocytosis and participates in removal of large pathogens such as parasites from the body.
d) Indirect opsonization through multiple binding sites on antibodies for antigens. One antibody may bind several antigens forming a clump (agglutination) or causing antigens to come out of solution (precipitation). Both agglutinated and precipitated antigens are more readily phagocytosed.
e)Activation of the complement system that involves several enzyme precursors and their associated substances. When the antibody attaches to the antigen it begins to activate the complement cascade. The complement proteins will then have a number of effects including lysis of the invading cell, opsonization through a complement component (rather than an antibody), and activation of inflammation.
f) Activation of the anaphylactic system. This system involves a hypersensitivity (or allergic) reaction where the IgE antibodies stimulate other cells (e.g. basophils) to release histamine and prostaglandins. The tissue around the invading agent swells due to fluids and the arrival of various immune mediators that help localise the infection.
Describe conditions that may result due to a compromised immune system.
Normally the immune system operates only against foreign substances that enter the body. The immune system can recognize its own tissues and chemicals as belonging to the host and therefore does not mount an immune attack against itself. Immunologic tolerance
describes the mechanisms through which the host’s immune system does not attack its own cells and proteins because they are not recognized as foreign. This tolerance is developed during the processing of the T lymphocytes that occurred in the thymus gland, and the B lymphocytes in their processing areas. The tolerance may develop from the destruction of any precursor lymphocytes specific to the body’s own tissues during the period of education. Another mechanism of tolerance is to have “immunologically privileged” sites where host immune cells do not enter, such as the cornea of the eye.Normally the immune system operates only against foreign substances that enter the body. The immune system can recognize its own tissues and chemicals as belonging to the host and therefore does not mount an immune attack against itself. Immunologic tolerance
describes the mechanisms through which the host’s immune system does not attack its own cells and proteins because they are not recognized as foreign. This tolerance is developed during the processing of the T lymphocytes that occurred in the thymus gland, and the B lymphocytes in their processing areas. The tolerance may develop from the destruction of any precursor lymphocytes specific to the body’s own tissues during the period of education. Another mechanism of tolerance is to have “immunologically privileged” sites where host immune cells do not enter, such as the cornea of the eye.
Unfortunately immunologic tolerance is sometimes lost. This can happen for a number of reasons. For example, not all self-reactive immune cells may be destroyed during development, and later autoimmune disease may develop in genetically susceptible individuals. In addition, if body cells that are not normally exposed to the immune system during fetal development become damaged later in life, the resulting newly exposed antigens can induce autoimmunity. As a result, when antigens from damaged tissues are released into the circulatory system in significant quantities, the tissues are then attacked by the immune system as if they were foreign to the body. For example, the proteins from the cornea do not circulate in the fluids of a fetus. If the cornea is damaged later in life it may be attacked by the immune system and cause corneal opacity.
Other examples of autoimmune diseases include; rheumatoid arthritis, thyroiditis, rheumatic fever, hemolytic and pernicious anemia, Addison’s disease, Grave’s disease, and possibly some forms of diabetes and multiple sclerosis.
Probably one of the best known immune system deficiencies is Acquired Immune
Deficiency Syndrome (AIDS) was first recognised in 1981 and is caused by a virus called
human immune deficiency virus (HIV). The virus infects helper T cells, which are then unable to carry out their important role in immunity. They produce the chemical interleukin II that stimulates the proliferation of cytotoxic T cells. Helper T cells also help amplify antibody production by cooperating with B cells.
Describe the basis of the ABO blood groups and Rh factor and explain the significance of this to transfusions and hemolytic disease of the newborn.
The surfaces of erythrocytes contain a variety of genetically determined antigens composed of glycoproteins and glycolipids. These antigens are also called isoantigens or agglutinogens. There are more than 50 different surface antigens that may be present on the surface of erythrocytes. The presence or absence of various antigens is used to classify blood into various blood groups. There are about 24 different blood group systems that have been identified. Two blood groups of particular importance in transfusions are the ABO blood group involving A and B antigens and the Rhesus (Rh) blood group involving the D antigen.
The four blood types associated with the ABO blood group, are based on the presence or absence of the A and B antigens. Individuals with only antigen A (but no antigen B) on their erythrocytes are identified as having blood type A. Those with only antigen B (but no antigen A) are blood type B. Those with both antigen A and antigen B on their
erythrocytes are identified as having blood type AB. Individuals with neither antigen A nor antigen B on their red cells have blood type O.
Blood types are determined by mixing serum containing specific antibodies with blood and watching for agglutination (clumping) of cells. Table 1 summarizes the antigens present in A, B, AB, and O blood types and the agglutination reactions that would occur with serum containing particular antibodies.
The reason that blood groups are significant in blood transfusions is because of potential interactions between antigens present on the surfaces of erythrocytes of donors and antibodies present in the plasma of recipients. For each antigen there may be specific antibodies in plasma that could cause agglutination (clumping) of erythrocytes carrying a specific antigen. Antibodies called anti-A antibodies will cause agglutination of erythrocytes carrying A antigens and anti-B antibodies will cause agglutination of erythrocytes carrying B antigens.
Individuals do not carry or produce antibodies against their own antigens but do have antibodies against blood group antigens which are not present on their own cells. Individuals with blood type A have anti-B antibodies in their plasma; those with blood type B have anti-A antibodies, those with blood type AB have neither anti- A or anti-B antibodies and those with blood type O have both anti-A and anti-B antibodies.
