Cause of disease

Microorganism - general term for a single celled organism that is too small to be seen with a microscope. Disease causing microorganisms are called pathogens Disease can be physical, mental or both. It has adverse effects on good health. it also has mental, physical and social aspects.

For a microorganism to be considered a pathogen it must; -gain entry to the host-colonise the host's tissue-resist defences of host-cause damage to host tissuePathogens include -bacteria-viruses -fungiif pathogen enters host and colonises its tissue an infection results. Disease occurs when an infection leads to recognisable symptoms. when the pathogen is transferred from one individual to another, it's known as transmission 

How do microorganisms get into the body?pathogens get into the body by penetrating one of the organisms interfaces with the environment. (interface - surface or boundary linking two systems (internal and external for instance) e.g. skin)some of the interfaces of the body are designed for material exchange from the external and internal environment, so the lining around these areas are supplied with blood vessels, are moist and thin (therefore they are sticky) and they also have a large surface area.Because these features make for easy entry for molecules they also make easy entry for pathogenic microorganisms.common entry points include - the gas exchange system - pathogens that cause influenza and tuberculosis.-the digestive system - food and water carry pathogens into stomach and intestines via mouth. Cholera, typhoid and dysentery pathogens enter body through this way.

The bodies natural defence from entry of pathogens-mucus layer - covers exchange surfaces and forms sticky barrier that is difficult to penetrate- production of enzymes to breakdown pathogen- production of stomach acid to kill bacteria

How pathogens cause disease- Damaging host tissue - many pathogens break down the membranes of host tissue. the sheer number of pathogens cause damage by preventing tissues functioning properly. viruses inhibit the synthesis of DNA, RNA and proteins by the host cell.- Producing toxins -  most bacterial pathogens produce toxins. cholera bacterium produces a toxin that leads to excessive water loss

Pathogens, lifestyle and genetic factors can all cause disease. How quickly the pathogen causes damage depends on how quickly it divides. pathogens like those that cause gastroenteritis only divide about every 30 mins so symptoms become apparent within 24 hours. the gastroenteritis pathogen also only causes damage if  large numbers of the pathogen are present.other pathogens, however, such typhoid bacterium, cause harm in relatively small numbers

Questionswhat is a pathogen?a pathogen is a disease causing microorganismWhy are digestive and respiratory systems often sites of entry for pathogens?they have a good supply of blood vessels they are moist and have a large surface area and are thin so t is easy for pathogens to penetrate themIn which two ways do pathogens cause disease?By producing toxins and damaging host tissuessuggest one reason why oral antibiotics are not normally used to treat gastroenteritis and other diarrhoeal disease.they are not effective as they will not stay in the body long enough to be absorbed as the person is vomiting and has diarrhoea

chapter 1. p 4-5