The document summarizes the physiology of respiration and the mechanism of breathing. It describes that breathing consists of two phases: inspiration and expiration. Inspiration is the active process of inhaling air which involves contraction of the diaphragm and intercostal muscles to enlarge the thoracic cavity and decrease lung pressure, drawing air in. Expiration is the passive process of exhaling air which involves relaxation of these muscles, shrinking the thoracic cavity so lung pressure exceeds atmospheric pressure, expelling air out.

1. Respiratory system
Physiology of Respiration-Mechanism of
Breathing
Mr N.JEGAN
Associate Professor
K.M.COLLEGE OF PHARMACY.
MADURAI.

2. Breathing mechanism
Breathing consist of two Phases
1.Inspiration:
The process of taking in air.
2. Expiration:
The process of expel out the air.

3. Muscles of respiration
The main muscles of respiration in normal quiet breathing
are
1. Intercostal muscles
2.Diaphragm
During difficult or deep breathing they are assisted by
1. Muscles of the neck
2.Shoulders muscle
3.Abdominal muscles

4. Intercostal muscles
 There are 11 pairs of intercostal muscles that
occupy the spaces between the 12 pairs of ribs.
 They are arranged in two layers
1. External intercostal muscles
2. internal intercostal muscles

5. Diaphragm
 The diaphragm is a dome-shaped muscle
structure.
 It separating the thoracic and abdominal cavities

6. Inspiration
In this process air enter into the lungs from atmosphere.
This process is active and requires energy for muscle
contraction.

7. Inspiration-Mechanism
Intercostal muscles contract they pull all the other ribs towards the
first rib.
Ribs move up
Diaphragm contract and move down
Thoracic cavity is enlarged
Decrease the alveoli pressure(lungs pressure)
Drawing air into the lungs in an attempt to equalize the atmospheric
and alveolar air pressures.
Air enter in to Lungs
Inspiration

10. Expiration-Mechanism
Relaxation of the intercostal muscles and the
diaphragm
Downward and inward movement of the rib cage
Pressure inside the lungs exceeds that in the atmosphere
Air is expelled from the respiratory tract.
Expiration

11. Expiration