Respiratory System and Muscle Movements

Mechanism of Respiration (Breathing)

• Movement of air in and out of lungs occurs by changes in size of thoracic cavity and followed by lung changes.
• Changes take place by activity of a group of muscles called “Respiratory Muscles" including:
  • Diaphragm (most important)
  • Inter-costal muscle (less important)
  • Abdominal muscles

Respiratory Muscles

• Diaphragm muscle:
  • Descends 1-5 cm during quiet respiration, up to 7cm during deep respiration
  • Contracts and pushes up into thoracic region, increasing length of thoracic cavity
  • Relaxes and ascends, decreasing length of thoracic cavity
• External intercostal muscles:
  • Contract, raising ribs and increasing transverse diameter of thorax
  • Relax, passing downwards and forwards from their articulation
• Internal intercostal muscles:
  • Relax, passing downwards and forwards from their articulation
  • Contract, pulling ribs downwards and decreasing transverse diameter of thorax
• Abdominal muscles:
  • Relax, pushing abdominal contents down
  • Contract, pushing abdominal contents up and into inside (regaining tone)

Volume of Respiratory Air

• Measured by "Spirometer"
• Types of volumes:
  • Tidal air volume (TV): 500 ml (C.C.)
  • Inspiratory Reserve volume (IRV): 3000 ml (C.C.) = 3 liter
  • Expiratory Reserve volume (ERV): 1200 ml
  • Residual air volume (RV): 1200 ml (can't be measured by spirometer)

Lung Capacity

• Total Lung Capacity: 6000mL = 6 Liter (TV + IRV + ERV + RV)
• Functional Residual Capacity: 2-3 liter (ERV + RV)
• Inspiratory capacity: 3500 ml (TV + IRV)
• Expiratory Capacity: 1700 ml (TV + ERV)
• Vital capacity: 4700 ml (TV + IRV + ERV)

Factors affecting vital capacity

• Condition of respiratory muscles
• Elasticity of lung
• Posture of body
• Expansion and recoil of thoracic cage
• Volume of blood in pulmonary circulation
• Resistance to air flow in respiratory passage

Lungs

• Paired organs in the chest that perform respiration
• Right lung has 3 lobes and 2 fissures, while the left has 2 lobes and 1 fissure
• Each alveolus has an average diameter of 200 micrometres, increasing during inhalation
• 700 million alveoli, producing 70m2 of surface area
• Alveoli are wrapped in a fine mesh of capillaries covering about 70% of its area

The Pleura

• Thin double membrane: fibro-elastic and invest lung
• Parietal pleura: lined on outside lung by simple squamous epithelium
• Visceral pleura: lined on inside lung by simple squamous epithelium
• Separated by thin film of fluid for lubrication of sliding movements