The respiratory tract has two sources of blood supply. The lungs receive blood from the pulmonary arteries which are under lower pressure. The bronchi receive blood from the bronchial arteries.
These are under normal pressure. Therefore, bleeding from the bronchial arteries gives massive bleeding. On the contrary, when your lungs bleed, it contains blood in abundance. It is so because of the low pressure.
This site offers information designed for educational purposes only. You should not rely on any information on this site as a substitute for professional medical advice, diagnosis, treatment, or as a substitute for, professional counseling care, advice, diagnosis, or treatment. If you have any concerns or questions about your health, you should always consult with a physician or other healthcare professional.