Respiratory anatomy
- The thoracic cage is formed by
- 12 thoracic vertebrae
- 12 ribs - the top 10 attach directly or indirectly to the sternum
- Sternum
- Diaphragm muscle
- Within the thoracic cage are 3 compartments
- The 2 pleural cavities, each with a lung
- The mediastinum, containing the heart
- Gases enter and leave lungs through
- Mouth and nose
- Pharynx and larynx
- Trachea
- Bronchi
- Bronchioles
- These tubes expand at their ends into alveoli, where gas exchange
takes place
- There are about 23 branchings which lead to about 300 million
alveoli
Respiratory mechanics
- Contracting the diaphragm or raising the ribs expands the thoracic
cavity
- At rest contraction of the diaphragm accounts for most of
inspiration
- The diaphragm is supplied by phrenic nerve which originates from
cervical spinal cord (C3-C5)
- The external intercostal muscles also aid inspiration
- At rest expiration is mostly passive and lungs contract due to
elasticity
- During exercise the internal intercostal muscles and others aid
expiration
- Pull ribs downward and inward, reducing thoracic cavity
Pulmonary ventilation
- The total amount of air moved in and out of the lungs each minute
depends upon two factors
- Tidal volume
- Respiratory rate
- Pulmonary ventilation = RR x TV
- During exercise both RR and TV can be increased
- The extra inspiration available is called the inspiratory reserve
volume (IRV)
- The extra expiration available is called the expiratory reserve
volume (ERV)
- After maximum expiration some air is still present in the lungs and
is know as the residual volume (RV)
- The maximum volume available for breathing is the vital capacity
(VC)
- Vital capacity = IRV + TV = ERV
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