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A pathogen is any organism that causes disease. Pathogens include microorganisms and some larger organisms such as tapeworms. Pathogenic microorganisms include some bacteria, some fungi and all viruses

Pathogens can penetrate an organisms interface with the environment. Pathogens need to enter the body in order to cause disease, they get it through an organism surface of contact (interface) with the environment, eg-nose, eyes or a cut.

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The three main interfaces with the environment

An organism has three main interfaces with the environment:

  • The Gas Exchange System- If you breathe in air that contains pathogens, most of them will be trapped in the mucus lining of the lung epithelium. These cells also have cilia that beat and move the mucus up the trachea to the mouth, where it is removed. Unfortunately, some pathogens are still able to reach the alveoli where they can invade cells and cause damage.
  • Skin- If you damage your skin, pathogens on the surface can enter your bloodstream. The blood clots at the area of damage to prevent pathogens from entering, but some may get in before the clot forms. 
  • The Digestive System- If you eat or drink food that contains pathogens, most of them will be killed by the acidic conditions of the stomach. However some may survive and pass into the intestines where they can invade cells of the gut wall and cause disease.
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Producing Toxins and Damaging Cells

Despite our protective mechanisms, pathogens can still successfully enter out bodies. Once inside, they can cause disease in two ways. 

  • Production of Toxins- Many bacteria release toxins (harmful molecules) into the body. For example; the bacteria which causes tetanus produces a toxin that blocks the function of certain nerve cells, casing muscle spasms.
  • Cell Damage- Pathogens can physically damage the host cells by;
    • Ruputuring them to release nutrients (proteins etc.)
    • Breaking down nutrients inside of the cell for their own use. This starves and eventually kills the cell. 
    • Replicating inside the cells and bursting them when they're released, eg-some viruses do this.
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Lifestyles that affect the risk of developing dise

CHD- Cornary Heart Disease- This is a disease that affects your heart. There are plenty of lifestyle factors that increase your risk of developing CHD: 

  •  Poor Diet- a diet high in saturated fat or salt increases the risk
  • Smoking, or lack of exercise and excessive alcohol intake- these can lead to high blood pressure, which can damage the heart and the blood vessels, incerasing the risk of CHD.

Cancer is the result of uncontrolled cell division. Factors that can increase the risk of developing cancer include:

  • Smoking- This is the main cause of mouth, throat and lung cancer.
  • Excessive exposhure to sunlight- This can cause skin cancer. Using sunbeds or sunbathing without suncream increases the risk.
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