Health And Diseases Flashcards
What are Pathogens?
Pathogens areorganismsthat cause disease. They include microorganisms such as bacteria, viruses, fungi and protozoa.
Fungi?
Larger fungi include moulds and mushrooms. Microscopic fungi can cause diseases such as athlete’s foot.
Viruses
Viruses are many times smaller than bacteria. They consist of a fragment of genetic material inside a protective protein coat.
Viruses cause diseases such as influenza - flu.
Bacteria
Bacteria are microscopic organisms that come in many shapes and sizes. But even the largest ones are only 10 micrometres long - 1 micrometre = 1 millionth of a metre.
Bacteria cause diseases such as cholera.
Protozoa
Protozoa are single-celled organisms. Food contaminated with protozoa can cause infections such as amoebic dysentery, of which severe diarrhoea is a symptom.
Some protozoa areparasites. These organisms live on, or inside, another organism and cause it harm. Malaria is a disease caused by protozoa that live in the blood. It is passed to a person by an insect vector, the mosquito.
Body defences
Thebody has several defences against pathogens so we do not fall ill with the diseases they cause.
The Skin
The skin covers the whole body. It protects the body from physical damage, microbe infection and dehydration. Its dry, dead outer cells are difficult for microbes to penetrate, and the sebaceous glands produce oils which help kill microbes.
Blood clotting
If microorganisms get into the body through a cut in the skin, the most important thing to do is close the wound quickly so that no more microorganisms can enter. A scab does just that. The blood contains tiny structures called platelets, and a protein called fibrin. A scab is basically platelets stuck in a fibrin mesh.
Mucous membranes
The respiratory system is protected in several ways. Nasal hairs keep out dust and larger microorganisms. Sticky mucus traps dust and microbes, which are then carried away by cilia - tiny hairs on the cells that line the respiratory system.
Stomach Acid
Hydrochloric acid in the stomach kills harmful microorganisms that might be in the food or drink that we swallow.
Immunity
Once inside the body, pathogens reproduce. Viruses reproduce inside cells and damage them, while escaping to infect more cells. Bacteria producetoxins- poisons. Cell damage and toxins cause the symptoms of infectious diseases.
Once pathogens enter the body, theimmune systemdestroys them. White blood cells are important components of the immune system.
White Blood cells can?
Engulf pathogens and destroy them. Produce anti-bodies to destroy Pathogens. produce antitoxins that neutralise the toxins released by pathogens.
What do pathogens contain?
Pathogens contain certain chemicals that are foreign to the body, called antigens. White blood cells - lymphocytes - carry antibodies - proteins that have a chemical ‘fit’ to a certain antigen. When a white blood cell with the appropriate antibody meets the antigen, it reproduces quickly and makes many copies of the antibody that neutralises the pathogen.
What does Immunity do?
Once you have been infected with a particular pathogen and produced antibodies against it, some of the white blood cells remain. If you become infected again with the same pathogen, these white blood cells reproduce very rapidly and the pathogen is destroyed. This isactive immunity. Sometimes you may be treated for infection by an injection of certain antibodies from someone else. This ispassive immunity.
Antibiotics
Antibiotics are drugs that kill bacteria, but not viruses. Certain antibiotics can be used to treat fungal infections, such as thrush.
