The document explains the mechanism of breathing, detailing the anatomical structures involved such as the thoracic cage and intercostal muscles. It describes the processes of inspiration, which requires a decrease in lung pressure, and expiration, which can be passive or active, depending on the circumstances. Additionally, it outlines the roles of external and internal intercostal muscles in these processes.

1. BREATHING EXCHANGE OF GASES
MECHANISM OF BREATHING
CLASS - XI
Ajay Kumar Gautam

2. Mechanism of Breathing
• THE LUNGS ARE SITUATED IN THE THORACIC CHAMBER WHICH IS ANATOMICALLY AN
AIR-TIGHT CHAMBER.
• THORACIC CAGE – COVERING OF THORACIC CAVITY MAKES THORACIC CAGE.
ANTERERIOR SURFACE – CLAVICLE BONES, NECK (UPAR)
POSTERIOR SURFACE – DIAPHRAGM (NICHE)
DORSAL SURFACE – CEREBRAL COLUMN AND RIBS (PICHE)
VENTRAL SURFACE – STERNUM & RIBS (SAAMNE)
LATERAL SURFACE – RIBS (SIDE )
• THE ANATOMICAL SETUP OF LUNGS IN THORAX IS SUCH THAT ANY CHANGE IN THE
VOLUME OF THE THORACIC CAVITY WILL BE REFLECTED IN THE LUNGS (PULMONARY)
CAVITY.
• SUCH AN ARRANGEMENT IS ESSENTIAL FOR BREATHING,AS WE CANNOT DIRECTLY
ALTER THE PULMONARY VOLUME.

4. Mechanism of Breathing
 Intercostal muscles (ICM) –
Space between two ribs is called intercostal space in which 2 types of
muscles are present :
 External ICM (EICM)
 Internal ICM (IICM)

5. INTERCOSTAL MUSCLES

6. INTERCOSTAL MUSCLES
 EICM –
 They originate from dorsal part of upper rib & insert on ventral part of lower rib.
 By the construction in this muscles,rib & sternum shifts upward & outward. So they help
in inspiration.
 IICM –
 They originate from dorsal part of lower rib & insert in ventral part of upper rib.
 By the contraction in these muscles, ribs & sternum shifts downward & inward respectively.
 So, it helps in forceful expiration which is a voluntary activity , So contraction of IICM is under the
control of cerebrum.

7. Breathing Mechanism
 Inspiration –
 Inpiratuon can occur if the pressure within the lungs is less than the atmospheric
pressure, i.e, there is a negative pressure in the lungs with respect to atmospheric
pressure.
 Inspiration is initiated by the contraction of diaphragm and goes towards Abdominal
cavity which increases the volume of thoracic chamber in the anterior posterior axis.
 The contraction of external intercostal muscles lifts up the ribs and the sternum causing
an increase in the volume of the thoracic chamber in the Dorso- Ventral axis.

8. Breathing Mechanism

9. Breathing Mechanism
 Expiration:-
1. Normal expiration is a passive activity. It takes around 3 second.
2. Expiration during sneezing, coughing, and yogabhyas is called forcefull expiration.
3. It is an active process.
4. During forcefull expiration internal intercostals muscles contract.
5. At this time these contracted muscles pull the ribs inwards, thus the volume of
thoracic cavity is highly decreased and the air which was filled in lungs rushes towards
outside.
6. Normal breathing is also called abdominal breathing.
7. The volume of air involved in breathing movements can be estimated by using a
spirometer.

13. Difference between Inspiration &
Expiration