Lymphatic System and Immunity

http://quest.arc.nasa.gov/projects/flies/humanImmune.html

 Lymphatic System Immunity and Microbes

I  Microbes and Pathogens

II. Lymphatic System

III. Nonspecific Defenses

IV.  Specific Defenses

V. Acquired Immunity

VI.  Hypersensitivity Reactions

V. AIDS

Lymphatic System Immunity and Microbes

The Lymphatic system works in conjunction with the cardiovascular system in aiding immunity.

Microbes and Pathogens

Bacteria or microbes are everywhere and beneficial to life. However some are harmful to humans and are known as pathogens mainly bacteria and viruses. Bacteria are prokaryotes, don't have a nucleus and are independent cells. They reproduce identical copies by binary fusion. Disease is caused by the growth of bacteria or the release of toxins. Common diseases are strep throat, tuberculosis, syphilis, and food poisoning.

Viruses are chemicals that require a host so they are said to be acellular and cannot live independently. They consist of two parts, an inner core of nucleic acid and the outer caspid of protein units. It relies on the enzymes and ribosomes of the host for reproduction and unlike cellular organisms it doesn't need DNA, but may use various enzymes or an RNA genome. Colds, flu, measles, chicken pox, polio, and AIDS are viral.

Lymphatic System

This system consists of the lymphatic vessels and organs functioning to maintain homeostasis. To do this there are four main functions. Excess tissue fluid is absorbed by the lymphatic capillaries emptying into the bloodstream. Fat is carried to the blood by capillaries in the small intestines called lacteals. Lymphocytes are produced and the system protects against pathogens. 

The Lymphatic vessels consist of capillaries, vessels and ducts that empty lymph into the cardiovascular veins in the shoulder. Lymph is colorless and contains lipids. There are two ducts, the thoracic duct and the right lymphatic duct. 

The primary lymphatic organs are bone marrow and the thymus gland, and the secondary are the lymph nodes and spleen. White blood cells mature in the bone marrow with the exception of T cells which pass through the thymus. The secondary organs purify and monitor the lymph. The spleen is the largest lymphatic organ where macrophages engulf debris and pathogens. Lymph nodes filters lymph in compartments where macrophages also engulf debris and pathogens.

Nonspecific Defenses

All pathogens are met by barriers to entry and the inflammatory response. The body's first line of defense the skin and mucous membranes serves as a barrier to infection. Chemical barriers also defend the body. Secretions from oil glands of the skin have chemicals that weaken or kill bacteria. Lysozyme in saliva, perspiration, and tears is antibacterial. Urine flushes bacteria from the body and stomach acids kill or prevent the growth of bacteria. Lastly, natural flora in the mouth, intestines, and elsewhere create a protective barrier to combat pathogens. Antibiotics reduce the effectiveness of normal flora. The second line of defense the inflammatory response  sends neutrophils and macrophages to engulf pathogens. A group of complement protein assist in the immunity.Blood plasma proteins called complement proteins trigger histamine and attract phagocytes. A membrane attack complex creates holes in bacteria and viruses causing them to burst. Interferons bind to receptors and interfere with viral replication.  

Specific Defenses

If nonspecific defenses are unsuccessful in preventing infection, specific defenses are prompted to destroy the disease causing agent. Antigens are foreign invaders such as bacteria, mold, viruses, molds, and parasitic worms. Some cancer cells are antigens. Lymphocytes are the main specific defense. It is able to differentiate into other types of B cells and T cells. By recognizing antigens their receptors bind with the antigen. Antigens are numerous so there is a large diversity of B cells and T cells to protect the body. B cells and T cells are able to clone themselves if they bind with an antigen.

B cells perform anti-mediating immunity by differentiating into plasma cells and memory B cells. The receptors of the cell must fit the antigens shape for it to expand.  B cells, are made in the bone marrow that become plasma cells that produce and secrete antibodies. As B cells clone they sometimes become memory cells. This enables long term immunity. Apoptosis, the programmed death of cells happens when the likelihood of infection subsides, and the the cells are no longer needed.

Shaped like a Y, antibodies are protein cells with two arms. Each arm having a long polypeptide chain and a short polypeptide chain. At the trunk, there are constant regions, where the sequence of amino acids is set. The structure of the constant region determines the class of the antibody. These proteins are made by transcription

and translation of DNA.

There are five classes of circulating antibodies. IgG are mainly found in the blood, lymph, and tissue fluid. It can cross the placenta giving a newborn partial immunity.IgM antibodies activate the complement system and appear quickly after an infection. IgA  have two Y-shaped structures found in body secretions. IgD antibodies serve as receptors on B-cells. IgE prevent parasitic worm infections and can prompt allergic responses.

T cells attack diseased cells and cancer cells by the action of cell -mediating immunity. T cell receptors (TCR) bind to invaders. Cytotoxic T cells or macrophages then engulf the invading microbe.T-cells recognize antigens with the help of an antigen presenting cell (APC) such as a macrophage. APC' s travel to the spleen and lymph node, after phagocytizing a pathogen. Helper T cells secrete cytokines that assist in the response of all types of immune cells. T cells.

Acquired Immunity

There are two types, active, when the individual produces the antibody and passive, when it is given as an injection. A individual can develop an immunity to a pathogen. It is also common to induce active immunity by immunization. Vaccines have antigens of the pathogens. Active immunity is longer lasting and is dependent on the presence of B cells and T memory cells. Individual with insufficient antibodies can receive injections of antibodies or immune cells but they are short lasting since the body does not produce it's own.

Hypersensitivity Reactions

Allergies can result in tissue damage, brought about by hypersensitivity to substances. Sometimes the reaction is immediate and is caused by the antibody IgE. Anaphylactic shock happens as the allergen enters the bloodstream. Delayed reactions is initiated by memory T cells. Tissue rejection is when the immune system recognizes that a tissue is not "self" as in transplants.        

 

AIDS

Acquired immune deficiency syndrome is a set of symptoms and conditions resulting from the virus caused by (HIV) human immunodeficiency virus. This condition weakens the immune system and leaves the individual susceptible to opportunistic infections. HIV is transmitted through contact bodily fluid to the blood or mucous membrane.  HIV is a retrovirus of a single strand of DNA surrounded by proteins. It enters the cell where it replicates by the transcription of RNA. As it gets into the cell it integrates into DNA. From there it can make hundreds of copies of itself with RNA. As it duplicates it buds out. HIV infects helper T cells calls in cells to kill own cells, thus without T cells immunity is compromised. 

After infection it makes many copies and the helper T cells drop within 3-6 weeks. THe antibodies stimulate a response. HIV in the blood drops to nothing in 12 weeks. The antibodies and helper T cells are ready to attack after 3 months so the illness goes into clinical latency. As the number of helper T cells star to drop there aren't enough cells to mount a response. This is when opportunistic infections take hold. HIV doesn't kill but weakens the body's defenses. 

An estimated 37 million people worldwide live with this disease and it has killed an estimated 2.5 million. AIDS is a pandemic with over three quarters of the deaths occurring in sub-Saharan Africa. Some researchers believe that it originated in sub-Saharan Africa during the twentieth century. It was initially recognized by the Center for Disease Control and Prevention in 1981.