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                                                                 Disease and the Body

                                                                  A.K Balhara and Sunesh

Pathogen is a microbe capable of causing illness. The most common pathogens are bacteria, fungi, parasites, and viruses.

  • bacteria : are tiny, one-celled creatures that get nutrients from their environments in order to live. Bacteria can reproduce outside of the body or within the body as they cause infections.
  • viruses : need to be inside living cells to grow and reproduce. Most viruses can't survive very long if they're not inside a living thing like a plant, animal, or person. Whatever a virus lives in is called its host.
  • protozoa : are one-celled animals and the smallest of all animals. Most of them can only be seen under a microscope. They live in water or at least where it is damp
  • fungi : are multi-celled (made of many cells), plant-like organisms that lack chlorophyll. Since fungi do not have chlorophyll to make food, they have to absorb food from whatever they are growing on.
  • Parasite :An organism that lives in or on and takes its nourishment from another organism. A parasite cannot live independently.parsites are of two type :ectoparasites and endoparasites
    • endoparasites are those parasites which live inside the body of its host.
    • ectoparasites are those parasites which live outside the body of the host.

The process through which a pathogen, also called an infectious agent, causes illness is pathogenesis.

Diseases can be classified in three ways:

  1. contagious - can spread from one animal to another
  2. infectious - can infect a living organism
  3. non-infectious - are those diseases that are not caused by a pathogen but they may be caused by either the environment, nutritional deficiencies or genetic inheritances.

The body has several lines of defense against disease.

Some body defense mechanisms are :

  1. body designs
  2. skin                
  3. mucous membranes
  4. phagocytic cells              
  5. tissue inflammation
  6. lymph vessels or nodes
  7. white blood cells
  8. red blood cells

Immun System - The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks pathogens that invade body systems and cause disease.

Immunity is the ability of the body to prevent an organism from causing disease.

There are two types of immunity:

  1. Natural immunity - Immunity that is naturally existing in an organism, Natural immunity does not require prior sensitization to an antigen.
  2. Aquired immunity - Immunity acquired by infection or vaccination or by the transfer of antibody or lymphocytes from an immune donor. Acquired immunity is in contrast to natural immunity.   


antibodies - produced by the white blood cells in response to a foreign protein, or antigen