BREATHING AND EXCHANGE OF GASES

POINTS TO REMEMBER :

 

  • Breathing: (External respiration) the process of exchange of O2 from the atmosphere with CO2 produced by the cells.

RESPIRATORY ORGANS :

  • Direct respiration by diffusion from the environment – sponges, coelenterates, flat worms etc.
  • Cutaneous or by skin – earthworm.
  • Tracheal system – insects.
  • Gills – aquatic arthropods mollusks
  • Lungs – terrestrial forms.

HUMAN RESPIRATORY SYSTEM:

  • External nostril opens into the nasal chamber through nasal passage.
  • The nasal chamber opens into the nasopharynx.
  • Nasopharynx opens through glottis of the larynx into the trachea.
  • Larynx is a cartilaginous box which produce sound hence called sound box.
  • Cartilaginous epiglottis covers the glottis during swallowing to prevent entry of food into trachea.
  • Trachea is a straight tube extending up to themed-thoracic cavity, which divides into right and left primary bronchi at the level of 5th thoracic vertebra.
  • Each bronchus undergoes repeated divisions to form the secondary and tertiary bronchi and bronchioles ending up in very thin terminal bronchioles.
  • Trachea, primary, secondary and tertiary bronchi and initial bronchioles are supported by cartilaginous rings.
  • Each terminal bronchiole gives rise to a number of very thin, irregular-walled and vascularised bags like structures called alveoli.
  • The branching network of bronchi, bronchioles and alveoli comprises the lungs.
  • There are two lungs which are covered by a double layered pleura, with pleural fluid in them.
  • Lungs are situated in the thoracic chamber which is anatomically a air tight chamber.
  • The thoracic chamber is formed  –
    • Dorsally by vertebral column.
    • Ventrally by sternum.
    • Laterally by ribs.
    • On the lower side by dome shaped diaphragm.

  • Respiration involves in following steps –
    • Breathing or pulmonary ventilation by which atmospheric air is drawn in and CO2 rich alveolar air is released out.
    • Diffusion of gases (O2 and CO2) across alveolar membrane.
    • Transport of respiratory gases by blood.
    • Diffusion of O2 and CO2 between blood and tissues.
    • Utilization of O2 by the cells for catabolic reactions and resultant release of CO2.

MECHANISM OF BREATHING :

Inspiration :

  • Intake of atmospheric air into the lungs.
  • It occurs if the pressure within the lungs (intra-pulmonary pressure) is lower than the atmospheric pressure.
  • Contraction of diaphragm which increases the volume of thoracic chamber in the anterior posterior axis.
  • The contraction of external intercostals muscles lifts up the ribs and the sternum causing an increase in the volume of thoracic chamber in the dorso ventral axis.
  • It causes an increase in pulmonary volume decrease the intra-pulmonary pressure to less than the atmospheric pressure.
  • It forces the air out side to move in to the lungs, i.e, inspiration.

Expiration :

  • Relaxation of diaphragm and inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic and pulmonary volume.
  • It increases in intrapulmonary pressure slightly above the atmospheric pressure.
  • It causes the expulsion of air from the lungs, i.e, expiration.
  • A healthy man breathes 12-16 times/minutes.
  • The volume of air involved in breathing is estimated by spirometer.

Respiratory Volumes and Capacities :

  • Tidal volume: volume of air inspired or expired during a normal breathing. It is about 500 ml.
  • Inspiratory reserve volume: Additional volume of air, a person inspire by a forceful inspiration. It is about 2500-3000 ml.
  • Expiratory reserve volume: Additional volume of air, a person expires by a forceful expiration. It is about 1000-1100 ml.
  • Residual volume: Volume of air remaining in the lungs even after a forceful expiration. It is about 1200 ml.
  • Inspiratory capacity: it includes tidal volume and Inspiratory reserve volume.
  • Expiratory capacity: it includes tidal volume and expiratory reserve volume.
  • Functional residual capacity: This includes ERV+RV.
  • Vital capacity: IRV + TV + ERV.
  • Total lung capacity: RV + IRV + TV + ERV

 

CBSE Biology (Chapter Wise) Class XI ( By Mr. Hare Krushna Giri ) 
Email Id : [email protected]