Respiratory system

• During inspiration the diaphragm and external intercostals contract increasing the volume of the thoracic cavity, decreasing pressure causing air to enter the lungs.
• Inspiration during exercise involves the recruitment of the sternocleidomastoid and pectoralis minor further increasing the volume of the thoracic cavity, creating a pressure gradient so air enters the lungs more quickly.
• Expiration is a passive process where the diaphragm and external intercostals relax reducing the volume of air in the thoracic cavity, increasing air pressure causing air to be expelled.
• Expiration during exercise involves the recruitment of the internal intercostals and abdominals decreasing the volume of the thoracic cavity further, increasing pressure more so air if forced out of the lungs more quickly.
• Breathing rate is the number of times we breathe in or out per minute. A normal resting value is between 12 and 15. A normal maximal value is between 40 and 60.
• Tidal volume is the volume of air inhaled or exhaled per breathe. A normal resting value is 500ml. A normal maximal value is between 2.5 and 3.5L per breathe.
• Minute ventilation is the volume of air breathed in or out per minute. A normal resting value is 5.5 to 7.5L per minute. A normal maximal resting value is 15 to 20L per minute.
• The alveoli are designed for gas exchange because thin walls result in a short diffusion pathway, extensive capillary network provides good blood supply and a large surface area results in greater O2 uptake.
• Partial pressure of O2 in the alveoli is higher than in the capillaries because O2 has been removed by the working muscles. It's concentration in the blood is lower and therefore PP. The difference in PP is called the concentration/diffusion gradient. The steeper the difference the faster diffusion will be.
• O2 will diffuse from the alveoli into the blood until the pressure is equal in both. PP of CO2 in the blood entering alveolar capillaries is higher than in the alveoli. CO2 therefore diffuses into the alveoli from the blood until pressure is equal in both.