The immune system is made up of specialized organs, cells, and tissues that all work together to destroy these invaders

The immune system helps to protect us against diseases caused by tiny invaders (called pathogens) such as viruses, bacteria, and parasites. cells, and tissues that all work together to destroy these invaders.

Consist of Physical and Chemical Barriers, Specialized cells and special biological weapons

A pathogen is an organism that causes disease.Your body is naturally full of microbes. However, these microbes only cause a problem if your immune system is weakened

Pathogenic organisms are of five main types: viruses, bacteria, fungi, protozoa,

Virus is microorganism that is smaller than a bacteria and it cannot grow or reproduce apart from a living host. A virus invades living cells and uses their chemical machinery to keep itself alive and to replicate itself.

Bacteria is a pathogen which infects an organism. It tries to take the nutrients and also control the host. In the end it tries to kill it

Diseases that are caused by pathogens can usually be passed from one person to another. They are called transmissible diseases.
Once inside the body, some pathogens may damage our cells by living in them and using up their resources.

Direct contact
The passing of a pathogen to an uninfected person is called transmission. The entry of the pathogen into the body is known as infection. The person in which the pathogen lives and breeds is said to be a host for that pathogen.

The skin consist 4 layers of thick cells which help keep foreign particles and pathogens.

Blinking is a method to help keep the eyes moist and also help in flushing out the pathogens

Lysozyme is an enzyme in the eye which kills pathogens

Has acid which helps to neutralize the Pathogen and also Vomiting and Diarrhea help flush out the Pathogen

Celia are hair like structures which catch Foreign Particles which is expelled by a cough.

Mucus swallows the pathogen and killing it

All the cells in the Second Line of Defense are Phagocytes

2. Phagocytes recognize pathogen and encloses it in itself
   
   

3. Phagocytes release the digestive enzymes present in it sac
   

5. Absorb the destroyed pathogen for its own metabolism
   

Contains granules (small particles) with enzymes that are
released during infections, allergic reactions, and asthma

enzymes in the granules damage or digest pathogens and release inflammatory mediators into the bloodstream

act as bridge between the innate immune system and the adaptive immune system

that can leave the circulatory system by
moving across the walls of capillary vessels

Release special proteins called as cytokines in order to
signal and recruit other cells to an area with pathogens

Inflammation is a process by which your body's white blood cells and the things they make protect you from infection from outside invaders, such as bacteria and viruses.

1. When tissue damage occurs, macrophages
   release a chemical called cytokines

2. Cytokines causes local vasodilation (widening of blood vessels) and increases capillary permeability (ability of solids and liquids to pass through) to improve the recruitment of leukocytes (white blood cells) to the region

3.Damaged cells also release chemotactic factors (chemicals that attract other molecules/cells) which attract leukocytes to the site of infection. Phagocytosis takes place.

4. While inflammation is necessary to allow immune cells access to damaged tissue, there are unavoidable side effects

This line of defense has specialized cells which can detect only pathogens and kill them

1. When an antigen is detected by a macrophage (as describe above under phagocytosis), this causes the T-cells to become activated.

2. The activation of T-cells by a specific antigen
   is called cell-mediated immunity.
   The body contains millions of different T-cells,
   each able to respond to one specific antigen.

3. The T-cells secrete interleukin 2.
   Interleukin 2 causes the
   proliferation of certain cytotoxic T cells and B cells.

4. From here, the immune
   response follows 2 paths: one path uses
   cytotoxic T cells and the other uses B cells.

The T cells are capable of recognizing antigens on the surface of infected body cells.

The T cells bind to the infected cells and secrete cytotoxins that induce
cell suicide in the infected cell and cause holes in the infected cells.

Both of these mechanisms destroys he pathogen in the infected body cell.

Antibodies ) are Y-shaped proteins that circulate through the bloodstream and bind to specific antigens, thereby attacking pathogens.

The antibodies are transported through the blood
and the lymph to the pathogen invasion site.

The body contains millions of different B cells, each able to respond to one specific antigen.

There are 4 classes of antibodies (listed from most common to least common):

These cells secrete a certain enzyme which stimulates cell division of T cells and B cells. In other words, these cells recruit even more cells to help fight the pathogens

These cells remain dormant after the initial exposure to an antigen. If the same antigen presents itself again, even if it is years later, the memory cells are stimulated to convert themselves into T cells and help fight the pathogen.

An airborne disorder is any disease that is caused by a microorganism that is transmitted through the air. There are many airborne diseases that are of clinical importance and include bacteria, viruses, and fungi.

Foodborne illness is caused by consuming contaminated foods or beverages. Many different disease-causing microbes or pathogens can contaminate foods, so there are many different types of foodborne illnesses. Most foodborne diseases are infections caused by a variety of bacteria, viruses, and parasites.

Infectious diseases commonly spread through the direct transfer of bacteria, viruses or other germs from one person to another. This can happen when an individual with the bacterium or virus touches, or coughs or sneezes on someone who isn't infected.