Anatomy and Physiology The Immune System Anatomy and Physiology

The Immune System (IS) Our bodies have a protective system that defends us against harmful invaders, called pathogens. Pathogens are “disease causing” agents or “sickness makers” A Disease is any change other than an injury that disrupts the normal functions of the body. Some diseases are produced by agents such as bacteria, viruses, and fungi. Others are caused by materials in the environment such as cigarette smoke, while others can be inherited, like sickle cell.

The Immune System The immune system is the body’s main defense against pathogens. It recognizes, attacks, destroys, and “remembers” each type of pathogen that enters the body. The function is to fight off infection through the production of cells that inactivate foreign invaders or cells. This process is called immunity,

Two Categories of Defense NonSpecific Defense its like the “wall” – its job is to keep things out of the body by physical and chemical barriers Specific Defense its like the “CIA”- it tracks down specific and harmful pathogens that enter the body

NonSpecific Defense- 1st line 1st line of defense: to keep things out of the body  skin, mucus, sweat, and tears The body’s most important nonspecific defense is the skin. When something does break the skin barrier, pathogens can enter the body and multiply  leads to infection (swelling, redness, pain) Many secretions of the body (mucus, saliva, tears) contain lysozyme, which is an enzyme that breaks down the cell walls of bacteria. Oil and sweat glands produce an acidic environment that kills many bacteria.

NonSpecific Defense- 1st line Pathogens can also enter the body through your mouth and nose. Mucus in the nose and throat trap pathogens, the cilia that line your nose and throat push pathogens away from your lungs, stomach acid and digestive enzymes destroy the pathogens that make their way to your stomach.

NonSpecific Defense- 2nd line If pathogens do enter the body, they multiply and release toxins into the tissue. When this happens, your inflammatory response is activated. The inflammatory response is a nonspecific defense reaction to tissue damage cause by injury or infection

NonSpecific Defense- 2nd line When pathogens are detected, the immune system produces millions of white blood cells (WBC). Blood vessels around a wound widen and WBCs enter the vessels to fight the infected tissue. Most of the WBC that enter are phagocytes (a cell that eats bacteria)

NonSpecific Defense- 2nd line The IS also releases chemicals that increases the body’s core temperature (fever). The increased temperature is a benefit to the body because it can kill the bacteria that can only live in a specific temperature range. The higher temperature also increase the heart rate and blood pumping so WBCs can get to the infected site faster.

Specific Defense Specific defenses are called immune responses (specific defenses that attack a disease-causing agent). Antigens are the substances that trigger theses responses. Viruses, bacteria, and other pathogens are antigens

Specific Defense 2 types of lymphocytes (WBC) that recognize specific antigens are: B Lymphocytes (B cells) and T Lymphocytes (T cells) B cells provide immunity against antigens and pathogens in the body fluids  humoral immunity T cells provide a defense against abnormal cells and pathogens inside living cells  cell mediated immunity

Humoral Immunity When a pathogens invades the body its antigens are recognized by a small portion of the body’s B cells. Those that do recognize it, grow and multiply rapidly producing large amounts of plasma cells and memory B cells. Plasma cells release antibodies, which are proteins that recognize and bind to antigens.

Humoral Immunity The antibodies get carried in the bloodstream to attack the pathogen. As the antibodies overcome the infected area, the plasma cells die and stop producing antibodies. Once the body has been exposed to a pathogen, millions of memory B cells remain able to recognize that specific pathogen and reduce the chance that the disease will occur again.

The Antibody Shaped like a “Y” 2 identical binding sites (shape makes it possible for it to recognize a specific antigen)

The Antibody

Cell Mediated Immunity Cell Mediated Immunity The body’s primary defense against its own cells when they have become cancerous or infected by viruses. It is also important when fighting infection caused by fungi and protists. When pathogens get inside a living cell it is difficult for antibodies alone to “fight” them off.

Cell Mediated Immunity During this process, T cells divide and differentiate into: Killer T cells  tracks down and destroys the “bad guy” that contains the antigen Helper T cells  produce memory T cells Suppressor T cells  releases substances that shut down the killer T cells once the “bad guy” is under control Memory T cells  cause a secondary response if the same antigen enters the body again