When you are running at high intensity many body systems are being influenced by running and providing some responses in your body.
Running stimulates the cardio respiratory system, making your heart work harder by pumping a large amount of blood into your body, the blood flow starts to be fast and to compensate for this effort you will have to breathe more, taking more oxygen for your organs and tissues.
The muscular and bone systems are stimulated and trained providing greater resistance and strength for your muscles and lower bones.
During the run, the urinary system is also affected, because running is able to improve kidney function, allowing the expulsion of toxic substances from your body to be done more efficiently.
Finally, running stimulates the endocrine system by causing it to release hormones of well-being and relaxation that help you rest and feel good after running.