phew, only 5 more minutes left of this 2 hour jog. I'm out of breath.
*cough* (deep breath) phew, i'm tired from that long jog. i need to sit down and rest!
Woo I feel so much better and energized time to jog back home!
the heart(part of the circulatory system) pumps oxygenated blood to working muscles, so that the muscles (part of the respiratory system) can produce movement allowing him to keep running.
As the muscles use the oxygen up, carbon dioxide is produced and absorbed into the blood. And the de-oxygenated blood is pumped back to the heart then on to the lungs. The lungs (part of the circulatory system) then are able to take in more oxygen after all the carbon dioxide is breathed out.
This allows him to catch his breath and breathe easier through his airway (part of the respiratory system), now he isn't as tired and is able to do more.