Chapter 16 Lymphatics and Immunity

1. Chapter 16 � Lymphatics and Immunity

2. Lymphatics and Immunity The Lymphatic System is a network of vessels that is closely associated with the cardiovascular system. This system picks up excess fluid from the interstitial spaces and transports it back to the bloodstream. Fluid inside the lymph vessels is called Lymph. The lymph vessels start with lymphatic capillaries and these merge to form successively larger pathways. They terminate in the collecting ducts which are the largest of the lymphatic vessels. Flow of lymph is one way, and ends with the lymph entering a large vein.

3. Lymphatics and Immunity Lymphatic capillaries are similar to blood capillaries in some ways. They consist of a single endothelial layer, but are blind ended. They are usually very intimately associated with blood capillaries. Lymphatic vessels are rather similar to veins. They have an outer connective tissue layer, a smooth muscle layer, and an endothelial lining. They also have semilunar valves like veins. The larger lymphatic vessels have specialized organs called Lymph Nodes.

4. Lymphatics and Immunity

5. Lymphatics and Immunity The two largest lymphatic ducts are the Thoracic Duct and the Right Lymphatic Duct. The Thoracic Duct is the larger and longer of the two main lymph ducts. It drains the entire lower torso, upper left torso, left arm, and the left side of the head and neck. It empties its lymph into the left subclavian vein. The Right Lymphatic Duct is smaller, and drains the right arm, right side of the head and neck, and the right upper torso. It empties its lymph into the right subclavian vein. Once returned to the venous system, lymph then becomes a part of the plasma of blood.

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7. Lymphatics and Immunity Capillary blood pressure generally creates interstitial fluid by pushing water and many other substances out of the bloodstream and into interstitial spaces. This fluid has much of the same composition as plasma, minus the plasma proteins. The formation of this fluid will accumulate over time and could lead to edema if it were not for the ability to drain it. This interstitial fluid is usually picked up by the lymphatic system in response to an increase in pressure from outside the lymphatic vessel.

8. Lymphatics and Immunity Lymph is the fluid in the lymphatic vessels and the lymph nodes. Most of it is formed due to hydrostatic pressure in the interstitial fluid. This fluid pressure causes the fluid to move �downhill� into the lymphatic vessel thru special valve-like flaps that simply open in the presence of increased fluid pressure in the tissues. The flaps of the valves are not attached to each other and so move freely to open and close as needed. Lymph flow functions to absorb dietary fats, small proteins that may escape blood flow from time to time, and transport foreign particles such as bacteria to the lymph nodes.

9. Lymphatics and Immunity Lymph flow (inside the vessels) is largely due to muscular activity and the pressure changes caused by breathing. This is greatly similar to the action of blood returning to the heart in the veins. Lymph vessels, like veins, have semilunar valves that prevent the backflow of fluid.

10. Lymphatics and Immunity Lymph Nodes Lymph nodes have afferent and efferent vessels that lead into and out of the node. Arteries, veins, and nerves join the node at the hilum. Each node is enclosed by a connective tissue capsule. Lymph sinuses are spaces within the node thru which lymph circulates.

11. Lymphatics and Immunity Lymph nodes serve to filter foreign particles and monitor body fluids (immune surveillance) via the lymphocytes and macrophages. The lymph nodes are home to the lymphocytes (B-cells and T-cells) and the macrophages.

12. Lymphatics and Immunity The Thymus Gland is located in the midiastinum and is usually anterior and somewhat superior to the heart. It secretes hormones called thymosins. The thymus gland is usually larger and more active in children than in adults. It is during childhood that the immune system is developing, and it is in the thymus gland that the T-cells develop in the presence of thymosins.

13. Lymphatics and Immunity The Spleen is the largest of lymphatic organs. It resembles a large lymph node in that it is surrounded by a connective tissue covering and has a hilum on one surface. The spleen has two different types of tissues, white pulp and red pulp. The white pulp is dispersed as islands of tissue among the remaining tissue which is red pulp. White pulp contains many lymphocytes whereas the red pulp contains a lot of red blood cells. The spleen is known to be the graveyard of the red blood cells. Many of the older cells are destroyed as they make their way thru the capillaries system of the red pulp. The spleen functions to filter blood such as the lymph nodes filter lymph.

14. Lymphatics and Immunity Defenses against infection There are two types of defense mechanisms in the body: Innate: these defenses are very general and function against many types of potential invaders. They function the same way regardless of the type of invader. Adaptive: these defenses are very specific, acting on only one type of invader. Their methods are directed, rather than automatic, and much more specialized in nature.

15. Lymphatics and Immunity Types of Innate Resistance Species Resistance: Humans cannot catch some diseases such as Dutch Elm Disease or Feline Immunodeficiency Virus. Genetics is at play here. Mechanical Barriers: the skin is a non-specific mechanical barrier. If an invader cannot penetrate the skin, then it most likely cannot cause infection. Chemical Barriers: a chemical barrier is similar to a mechanical barrier, but has the added advantage of being possibly caustic to the potential invader (i.e. gastric juice and tears). Natural Killer Cells: a type of non-specific lymphocyte that produces perforins. These chemicals attack the cell membrane of a virus infected cell or tumor cell causing it�s destruction.

16. Lymphatics and Immunity Inflammation: this is a process that has some very specific signs and symptoms. These include localized redness, swelling, heat, pain, and loss of function. The redness and heat are from increased localized blood flow. Swelling is generally due to increased interstitial fluid due to both increased capillary permeability and damage done to cells in the area. The pain is the result of pressure being put on nearby nociceptors. Phagocytosis: this is the mechanism whereby certain leukocytes ingest and destroy invaders and left over cellular debris. Chemicals are released from injured tissues that attract phagocytes via chemotaxis. A macrophage can engulf up to 100 bacteria! Fever: this process indirectly counters microbial growth in that it causes a retardation in their growth rate. Also, phagocytes are more active and aggressive during times of higher temperature.

17. Lymphatics and Immunity Adaptive Resistance Immunity is a resistance to a particular pathogen, it�s toxins, or metabolic by-products. This process is based on the bodies ability to distinguish self from non-self. Molecules that are capable of eliciting an immune response are called Antigens. Antigens may be proteins, polysaccharides, glycoproteins, or glycolipids. All are generally from a source foreign to the body.

18. Lymphatics and Immunity Lymphocytes There are 2 types of Lymphocytes: T-lymphocytes B-Lymphocytes T-lymphocytes start their life in red bone marrow (as do all blood cells), but early on they migrate to the thymus. They mature from an immature blastic cell to T-lymphocytes under the influence of the thymus hormones. T-lymphocytes reside richly in the lymph nodes, the thoracic duct, and the white pulp of the spleen. They make up about 70-80% of all lymphocytes.

19. Lymphatics and Immunity Some t-cells secrete toxins that kill invaders. Some t-cells act in the Cellular Immune Response. There are a few types of t-cells, including Helper T-cells, Cytotoxic T-cells, and Memory T-cells. Cytotoxic T-cells release perforin proteins that cute openings into the cell membrane of invading organisms. Memory T-Cells are the cells that are produced on first contact with a new antigen. They provide a no-delay response to future exposures of the same antigen.

20. Lymphatics and Immunity B-Lymphocytes begin their life in red bone marrow and also mature therein. They make up the remaining 20-30% of lymphocytes. B-cells will sometimes act in the Humoral Immune Response. These cells will proliferate themselves rapidly upon detection of an antigen. They secrete chemicals called antibodies or immunoglobulins. Some B-cells develop into Memory Cells and react only to a specific antigen.

21. Lymphatics and Immunity Immunoglobulins These molecules are made up of protein with a three dimensional structure (globular). The specialized regions of these molecules are made to fit the shape of a specific antigen molecule. The antigen binding site binds to the idiotype of a specific antigen. Antibodies act against antigens in one of three ways. They either directly attack the antigen, activate complement, or stimulate inflammation.

22. Lymphatics and Immunity Types of Immunoglobulins: IgG accounts for about 80% of all immunoglobulins. It is particularly active against bacteria, viruses, and some toxins. IgG acts to activate compliment when necessary. IgA accounts for about 13% of all immunoglobulins. IgA is commonly found in the secretions of exocrine glands (i.e. breast milk, tears, gastric juice). IgM accounts for about 6% of all immunoglobulins. This antibody also activates complement. IgD is found on the surface of most B-cells, and is responsible for activating most B-cells. IgE appears in exocrine secretions also, and appears to be tied into allergic reactions.

23. Lymphatics and Immunity Immune Responses Primary Immune Response � this takes place when B-cells or T-cells become activated after first encountering an antigen for which they are specialized to react. During this response, plasma cells release antobodies IgM and IgG. These are then transported by the blood throughout the body where they help destroy antigen bearing agents.

24. Lymphatics and Immunity Following a primary immune response, some B-cells produced during the original proliferation phase will remain dormant and serve as Memory B-cells. Secondary Immune Response � this is a second or later encounter with an antigen that takes place after the original exposure to the original antigen. This helps to maintain memory and serve to continue stimulating immunity.

25. Lymphatics and Immunity Practical Classification of Immunity Natural Active Immunity � this takes place when a person catches an illness and makes their own antibodies to counteract it. Natural Passive Immunity � this takes place when a baby is breast fed and enjoys the mother�s immunity. Artificial Active Immunity � this is a case of being exposed to an antigen via artificial means (the antigen is usually attenuated). This commonly happens via vaccine. Artificial Passive Immunity � this takes place when a person receives an injection of antibodies or antitoxins. This type of immunity is usually very short lived.

26. Lymphatics and Immunity Allergic Reactions Allergic reactions are triggered by Allergens. An allergic reaction is an immune response against a non-harmful substance and can be life threatening. Anaphylaxis or a Type I Reaction occurs within minutes after contact with an allergen. Persons with this reaction have an inherited ability to over produce IgE antibodies. The initial exposure is usually a point of sensitization, with subsequent exposures leading to anaphylaxis. The usual response of the body to this reaction is to cause swelling in the face, tongue and larynx will swell and cause difficulty breathing. This is the life threatening part of the reaction. Epinepherine injection is called for immediately. The person may also experience, diarrhea, vomiting, and an itchy rash. Other allergic reactions of Types II thru IV exist also.

27. Lymphatics and Immunity Tissue Transplantation 4 varieties exist: Isograft: takes place when getting tissue from an identical twin. Autograft: takes place when getting tissue from your own body. Allograft: takes place when someone accepts tissue from another person. Xenograft: takes place when someone accepts tissue from another species.

28. Lymphatics and Immunity Autoimmunity This is a case in which the body cannot tell friend from foe and initiates an attack on it�s own tissues via the production of autoantibodies and cytotoxic T-cells. Some theories say that a virus is responsible, others state that a body cell may for some reason come to resemble a known antigen. Many imply a factor of heredity. Almost all of these disorders are accompanied by pain or malfunction of a body part. All research on these ideas are still in theory stages, and the field is wide open to interpretation and further research. Some autoimmune diseases include RA, AS, Lupus, Scleraderma, Myasthenia Gravis, Reiter�s Syndrome, and many others.