Biology BREATHING MECHANISM AND RESPIRATORY VOLUMES

KEY TOPICS

star Breathing Mechanism
star Respiratory Volumes and Capacities

MECHANISM OF BREATHING

● color{violet}("Breathing") involves two stages :

● color{brown}("Inspiration") during which color{violet}("atmospheric air") is drawn in and color{brown}("Expiration") by which the alveolar air is released out.

● The movement of air into and out of the color{violet}("lungs") is carried out by creating a pressure gradient between the color{violet}("lungs") and the color{violet}("atmosphere.")

● color{violet}("Inspiration") can occur if the pressure within the color{violet}("lungs (intra-pulmonary pressure)") is less than the color{violet}("atmospheric pressure,") i.e., there is a negative pressure in the color{violet}("lungs") with respect to color{violet}("atmospheric pressure.")

● Similarly, expiration takes place when the color{violet}("intra-pulmonary pressure") is higher than the color{violet}("atmospheric pressure.")

● The color{brown}("diaphragm") and a specialised set of muscles – color{brown}("external and internal intercostals") between the ribs, help in generation of such color{violet}("gradients.")

● color{violet}("Inspiration") is initiated by the color{brown}("contraction") of color{violet}("diaphragm") which increases the volume of color{violet}("thoracic chamber") in the antero-posterior axis.

● The color{violet}("contraction") of external inter-costal muscles lifts up the color{violet}("ribs") and the color{violet}("sternum causing") an increase in the volume of the color{violet}("thoracic chamber") in the color{violet}("dorso-ventral axis.")

● The overall increase in the color{violet}("thoracic volume") causes a similar increase in color{violet}("pulmonary volume.")

● An increase in color{violet}("pulmonary volume decreases") the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the color{violet}("lungs,i.e., inspiration.")

● Relaxation of the color{violet}("diaphragm") and the color{violet}("inter-costal muscles") returns the color{violet}("diaphragm") and color{violet}("sternum") to their normal positions and reduce the color{violet}("thoracic volume") and thereby the color{violet}("pulmonary volume.")

● This leads to an increase in color{violet}("intra-pulmonary pressure") to slightly above the color{violet}("atmospheric pressure causing") the expulsion of air from the color{violet}("lungs,") i.e., color{brown}("expiration.")

● We have the ability to increase the strength of color{violet}("inspiration and expiration") with the help of additional color{violet}("muscles") in the color{violet}("abdomen.")

● On an average, a healthy human breathes color{brown}("12-16 times/minute.")

● The volume of air involved in color{violet}("breathing movements") can be estimated by using a color{violet}("spirometer") which helps in clinical assessment of color{violet}("pulmonary functions.")

Respiratory Volumes and Capacities

● color{brown}("Tidal Volume (TV):") Volume of air inspired or expired during a color{violet}("normal respiration"). It is approx. 500 mL., i.e., a healthy man can inspire or expire approximately 6000 to 8000 mL of air per minute.

● color{brown}("Inspiratory Reserve Volume (IRV):") color{violet}("Additional volume") of air, a person can inspire by a forcible inspiration. This averages 2500 mL to 3000 mL.

● color{brown}("Expiratory Reserve Volume (ERV):") Additional volume of air, a person can expire by a color{violet}("forcible expiration.") This averages 1000 mL to 1100 mL.

● color{brown}("Residual Volume (RV):") Volume of air remaining in the color{violet}("lungs") even after a color{violet}("forcible expiration"). This averages 1100 mL to 1200 mL. By adding up a few respiratory volumes described above, one can derive various color{violet}("pulmonary capacities"), which can be used in color{violet}("clinical diagnosis.")

● color{brown}("Inspiratory Capacity (IC):") Total volume of air a person can inspire after a color{violet}("normal expiration.") This includes tidal volume and inspiratory reserve volume ( TV+IRV).

● color{brown}("Expiratory Capacity (EC):") Total volume of air a person can expire after a color{violet}("normal inspiration"). This includes tidal volume and expiratory reserve volume (TV+ERV).

● color{violet}("Functional Residual Capacity (FRC):") Volume of air that will remain in the color{violet}("lungs") after a color{violet}("normal expiration.") This includes ERV+RV.

● color{brown}("Vital Capacity (VC):") The maximum volume of air a person can breathe in after a color{violet}("forced expiration.") This includes ERV, TV and IRV or the maximum volume of air a person can color{violet}("breathe") out after a color{violet}("forced inspiration.")

● color{brown}("Total Lung Capacity:") Total volume of air accommodated in the color{violet}("lungs") at the end of a forced inspiration. This includes RV, ERV, TV and IRV or color{violet}("vital capacity + residual volume.")