We all know that we can get sick, but many of us don’t really understand all the efforts our body goes through to keep us healthy. This post will fill you in on the way that our body defends itself from disease.
We have two kinds of defenses. We have non-specific defenses, which is a defense that just keeps everything out that doesn’t belong. These are general barriers and are regarded to innate defenses. We also have specific defense, which target very specific microorganisms or chemicals. This is regarded to as an active defense.
There are two kinds of non-specific defenses. There are first line defenses and second line defenses. First line defenses include the skin. The skin is a continuous surface with a non living top layer with living cells under the top later. The living layer is continuously working to replace lost cells from the top layer. Sweat glands underneath the living layer of skin evaporate fluids, including antimicrobial fluids, to the surface oil glands. These secrete oils that change the pH environments that are inhibitory to the diseases and bacteria. Electrical energy, in either positive or negative direction, also works to repel any chemicals which may be repelled by either charge. Mucous membranes also work as a first line defense. These membranes are thick and sticky and coat the linings of openings into the body. The mucous is made of goblet cells and is very effective as a defense due to its stickiness so that it can trap things. The mucous is acidic and contains antimicrobial chemicals.
The respiratory system is a good example of first line defenses getting utilized. In the nose, there is a wavy shape called a conch. Unfiltered air comes in through the nose and travels through the conchs, while getting filtered by turbinate. In the back of the throat there is a lymphatic tissue which picks up anything that gets through the nose and the throat. Mucous flows down the back of the throat. When swallowing a flap on the trachea closes and mucous goes through the esophagus to the stomach, where anything foreign remaining gets broken down with the mucous. In the trachea, there are ciliated mucous epitheliums. These are cells with little extensions that face where the air is going through. They have proteins that wave around which catch particles and move them up and out of the trachea. Because mucous is dropping downwards simultaneously, while the cilia are moving particles up, the mucous and particles mix, so that that they can travel down the esophagus together once the reach the top of the trachea and that flap closes.
Second line defenses include sneezing, coughing, vomiting, fever, and inflammation. Sneezing is a violent contraction of the diaphragm to get things out of the system through the nasal passage. Coughing clears the throat, trachea and brachial tubes. Vomiting is a violent contraction of the stomach as a reaction to toxins entering. A fever is an increase in body temperature which stimulates the immune system and inhibits bacteria that doesn’t survive in heat. Fevers also increase chemical reactions in the blood. Inflammation is a first response to any trauma. Signs of inflammation are redness, heat, swelling and pain. This occurs when blood vessels dilate. It is a relaxation of the vessel walls and increases blood flow to bring in healing properties.
There is also a compliment system which acts when something makes it past all these defenses and gets into the blood. There are 20 different proteins which are made by the liver that become very reactive in the presence of certain bacteria. These proteins form on the surface of the bacteria and punch whole in the bacterial wall.
Specific Defense is also known as immunity. Substances are recognized as foreign and provoke immune responses are known as antigens. Immunity has specificity for certain antigens and memory of previously encountered antigens so that the second encounter gives an even faster and harsh response. The body has to decide if something is part of itself or if it is foreign and antibodies are only released by specific cells for specific antigens. The cell identifies these antigens by antigen specific receptors on the cell membrane. In the membrane of cells are MHC antigens. This stands for major histocompatability complex. This is unique to every person. These MHC molecules help T cells and B cells recognize that an antigen is foreign. This is very important to the beginning of an immune response.
T cells and B cells are type of white blood cells that attack bacteria or viruses. T cells begin in the bone marrow. Once the T Cell differentiates, it produces antigen specific receptors and becomes antigen dependant. When it is activated by a certain antigen, it differentiates and becomes a killer T Cell. As a killer T cell, the cell leaves the lymph nodes and goes to the blood stream where it clones itself and attacks. The killer t cells have receptors for specific antigens and MHC proteins. If it identifies in passing that the MHC protein fits its receptor, then it keeps moving. If not, then it attacks. Cells which are infected manufacture viral proteins, but still maintain their MHC markers. The killer t cell notices that that there is a viral protein as well as an MHC-1 and if it is infected with a matching antigen that the killer t cell has a receptor for it, then it will know that even though this is part of self, it is being attacked by a foreign object and will attack it. The killer t cells lock onto the MHC and viral protein and produce perferin which punches holes and sends granules which explode inside the cell and instructs self destruction to the nucleus.
B cells do not exit into the blood stream, but rather remain in the lymph nodes. The virgin b cells are undifferentiated cells. B cells are activated or sensitized once in contact with specific antigens and become plasma b cells. Once they are plasma b cells, they are then antigen dependant. Once they become plasma b cells, and come into contact with a specific antigen, they sprout antibodies on their surface as well as clones. All these clones also produce the same antibodies. The antibodies are then released into the bloodstream, while the plasma b cells continue to clone and produce more antibodies. B and t cells that remain become memory cells that are programmed to be ready to respond the next time there is an attack by the same antigen. 
APCs are Antigen Presenting Cells. These cells have the eaten the antigen and display and present them by synthesizing a modified form of an MHC marker. This is a type II marker. It’s a combo on the surface of the MHC and the antigen. Microphages carry this combo out to t and b cells to the lymphatic system. B cells can be activated by direct contact by unprocessed antigens, meaning the not eaten by macrophage ones, and processed antigens, meaning ones attached to APCs. T cells only recognize antigens with APCs attached.
Helper t cells are required for co stimulation for the t and b cells. They reside in the lymph nodes and do not kill anything. They become activated by APCs. These are the cells that HIV targets. Eventually the helper t cells stop doing their job with HIV present and there is no more immune system, since the t cells and b cells are helpless without the helper t cells.
pictures taken from:
yaflamingalah.wordpress.com/category/health/
http://hr-is-back.blogspot.com/2008_07_01_archive.html
www.biooncology.com
