Remarks 1. Respiratory system is communicating with external environment, so it is susceptible to the diseases 2. All blood from the body will pass through the lung and the biological pathogens and embolus can be trapped in the lung.8 Remarks 1. Respiratory system is communicating with external environment, so it is susceptible to the diseases. 2. All blood from the body will pass through the lung and the biological pathogens and embolus can be trapped in the lung