The Respiratory System functions of the respiratory system

The Respiratory System • functions of the respiratory system 1. Breathing (Ventilation): movement of air in and out of the lungs. 2. Gas Exchange. • Supplies body with oxygen • Eliminates carbon dioxide from the tissue. 3. Regulation of p. H.

4. Regulation of body temperature. 5. Metabolic function. 6. Has many important defense mechanisms : hair within the nose, mucus, cough and sneezing.

ventilation It is process of air flowing into the lungs during inspiration and out of the lungs during expiration.

• Air move in and out of the lungs due to pressure gradient ( move from higher pressure to lower pressure ). • Air moves into the lungs when the atmospheric pressure is higher than the intrapulmonary pressure (inspiration). • Air moves out of the lungs when the atmospheric pressure is lower than the intrapulmonary pressure (expiration)

Mechanisms of ventilation Ventilation is a function of the respiratory pump. The components of this pump are: 1 - The lungs 2 - Thoracic cage 3 - bones 4 - intercostals muscles 5 - diaphragm

• Breathing, or pulmonary ventilation, consists of two phases: • Inspiration, the period when air flows into the lungs • Expiration, the period when gases exit the lungs.

MECHANISM OF BREATHING Breathing is produced by rhythmic discharge of signals from the spinal motor neuron that supply the respiratory muscle, this discharge is controlled by 2 mechanisms : 1. An involuntary automatic mechanism : • This is the principal mechanism that control respiration , and is performed by the respiratory centre. •

• 2. A voluntary mechanism : breathing can voluntarily be stopped (e. g. during talking) or accelerated when required this can be performed for only a short time , and produced by signals discharged from the motor area of the cerebral cortex

1. Mechanism of inspiration • Inspiration is an active process because it require contraction of inspiratory muscle. • The inspiratory muscles: 1. The diaphragm and external intercostal muscles: During normal resting breathing. • The phrenic nerves arise from cervical segments (C 3 , 4 & 5) supply the diaphragm • Intercostal nerves arise from the thoracic segments and supply the external intercostal muscle which extend obliquely downward and forward between the ribs

2. The scalene & sternocleidomastoid muscles: In deep inspiration, which help to elevate thoracic cage.

When the diaphragm contracts , it moves down leading to an↑ in the vertical diameter of the chest ( about 1. 5 up to 7 -10 cm ) Movement of the diaphragm accounts for 75% of the change in intrathoracic volume during quiet inspiration. • Contraction of the external intercostal muscle lead to: (a) Elevation of the ribs (b) Movement of the sternum forward and upward. These movement ↑ the anteroposterior diameter of the chest and its transverse diameter.

Vertical and antero-posterior diameters of the chest

• The chest cavity expands in all dimensions • This ↓ the intrapleural pressure , • expansion of the lungs As a result , the intrapulmonary pressure ↓ from zero to about -1 mm. Hg which causes rush of about 500 ml of atmospheric air into the lungs , leading to its inflation

inspiration

2. Mechanism of expiration: • Expiration during normal resting breathing is a passive process. • After relaxation of inspiratory muscles , expiration then follows passively by recoil of the lungs & chest

• As a result of lung & chest recoil and diaphragmatic elevation : • the intrapulmonary pressure increase & becomes positive (about +1 mm. Hg). • leading to air flow out of the lungs ( 500 ml).

Expiration

Expiratory muscles • In case of deep expiration, expiration become active because expiratory muscles contract. • these include the internal intercostal muscles & the anterior abdominal wall muscles. • Deep expiration occur during: 1. exercise. 2. asthma. 3. emphysema.

Figure 37 -16 The Mechanics of Breathing Section 37 -3 Air exhaled Air inhaled Rib cage descends Rib cage rises Diaphragm Inhalation Exhalation

Contraction of inspiratory muscles Expansion of the chest& reduction of IP pressure Air moves out of the lung Increase in the IA pressure Expansion of the lungs& reduction of IA pressure Lungs recoil to expiratory position Air moves into the lungs relaxation of inspiratory muscles Inspiration Expiration Mechanisms of normal quiet ventilation

A. Volumes 1. Tidal volume TV q Is the volume of air inspired or expired each breath. q Normally it is 500 ml (0. 5 L)

2. Inspiratory reserve volume (IRV) q Is the volume of air inspired by maximum inspiratory effort in addition to the tidal volume about 3. 3 L

3. Expiratory reserve volume (ERV) q Is the volume of air expired by maximal expiratory effort about 1. 0 L

4. Residual volume (RV) q. Is the volume of air that remain in the lungs after maximum expiratory effort. q. About 1. 2 L in male and 1. 1 L in female. q. Important in : v. Maintain Continuous gas exchange during expiration. v. Prevent lung collapse. 1/25/2022 28

Residual volume (RV) q Factors affecting it (age, diseases) q Measurement - Helium dilution method - Nitrogen washout

1. Inspiratory capacity: q. Is volume of air that can be inspired by maximal inspiratory effort after normal resting expiration about 3. 8 L q IC = TV+ IRV 2. Expiratory capacity: q. Is volume of air that can be expired by maximal expiratory effort after the end of normal resting inspiration about 1. 5 q. L 30