.2 Animal tissues, organs and organ systems

• Health is the state of physical and mental well-being.
• Different types of disease may interact.

  Defects in the immune system mean that an individual is more likely to suffer from infectious diseases.

  Viruses living in cells can be the trigger for cancers.

  Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma.

  Severe physical ill health can lead to depression and other mental illness.