Main muscles of respiration are diaphragm and intercostal muscles (muscle between the ribs). The diaphragm is the principle muscle of breathing.
Abdominal muscles are also important in mechanism of breathing.
Abdominal muscle can help increase and decrease strength of inspiration and expiration.
Inspiration/ Inhalation
Active process, it involves the muscular contraction.
At rest inspiration about 2s
Breathing in is called inspiration.
1. When muscle of diaphragm contracted
Contract; lower the diaphragm and enlarge the thoracic cavity (verticle diameter).
External Intercostal muscle are contracted, enlarging thoracic cavity (anteroposterior and lateral diameter).
Internal intercostal muscle relaxed.
When diaphragm contracts , it flatten, pressing down on the abdominal content and lifting thoracic cavity.
O2 less - O2 high
Increase size in thoracic cavity causes decrease in intra-alveolar pressure and higher pressure in environment (atmosphere).
Lungs expand and pressure in their tube and alveoli decreases.
Air rushes through respiratory passage into lungs, equalizing pressure (Inspiration occurs).
After inspiration, pressure in lungs and in the atmosphere is equal.
Accessory muscles also contract-
Sternocleidomastoid
Scalene muscle
Pectoralis major muscles
More concentration O2 Less concentration CO2 Expiration of air
Atmospheric pressure 760mmHg. Alveolar pressure increases to 762 mmHg
Thoracic cavity - increases lung expand
Alveolar pressure - Inspiration of air. Thoracic cavity decreases in size and lung recoil.
Decreases to 758mmHg
Expiration / Exhalation
Passive process, no muscular contraction is involved.
At rest expiration last about 3 second.
After expiration there is pause before next cycle begins.
Breathing out is called expiration.
Diaphragm relaxes causing decrease in vertical diameter of thoracic cavity.
External intercostal muscles relax, causing decrease in lateral and anteroposterior diameters of thoracic cavity.
Decreased size of thoracic cavity causes the decrease in lung volume.
Causes increase in intra-alveolar pressure (762 mmHg)
Air flows from area of higher pressure in alveoli to are of lower pressure in atmosphere.
Expiration becomes active only during forceful breathing. As the abdominal and internal intercostal muscles contract.
0 Comments