NCERT Textbook - Breathing and Exchange of Gases NEET Notes | EduRev

Biology Class 11

Created by: Sushil Kumar

NEET : NCERT Textbook - Breathing and Exchange of Gases NEET Notes | EduRev

 Page 1


268 BIOLOGY
As you have read earlier, oxygen (O
2
) is utilised by the organisms to
indirectly break down nutrient molecules like glucose and to derive energy
for performing various activities. Carbon dioxide (CO
2
) which is harmful
is also released during the above catabolic reactions. It is, therefore, evident
that O
2
  has to be continuously provided to the cells and CO
2 
produced
by the cells have to be released out. This process of exchange of O
2
 from
the atmosphere with CO
2
 produced by the cells is called breathing,
commonly known as respiration. Place your hands on your chest; you
can feel the chest moving up and down. You know that it is due to
breathing. How do we breathe? The respiratory organs and the mechanism
of breathing are described in the following sections of this chapter.
17.1 RESPIRATORY ORGANS
Mechanisms of breathing vary among different groups of animals
depending mainly on their habitats and levels of organisation. Lower
invertebrates like sponges, coelenterates, flatworms, etc., exchange O
2
with CO
2
 by simple diffusion over their entire body surface. Earthworms
use their moist cuticle and insects have a network of tubes (tracheal
tubes) to transport atmospheric air within the body. Special vascularised
structures called gills are used by most of the aquatic arthropods and
molluscs whereas vascularised bags called lungs are used by the
terrestrial forms for the exchange of gases. Among vertebrates, fishes
use gills whereas reptiles, birds and mammals respire through lungs.
Amphibians like frogs can respire through their moist skin also.
Mammals have a well developed respiratory system.
BREATHING AND EXCHANGE OF GASES
CHAPTER  17
17.1 Respiratory
Organs
17.2 Mechanism of
Breathing
17.3 Exchange of
Gases
17.4 Transport of
Gases
17.5 Regulation of
Respiration
17.6 Disorders of
Respiratory
System
2015-16(19/01/2015)
Page 2


268 BIOLOGY
As you have read earlier, oxygen (O
2
) is utilised by the organisms to
indirectly break down nutrient molecules like glucose and to derive energy
for performing various activities. Carbon dioxide (CO
2
) which is harmful
is also released during the above catabolic reactions. It is, therefore, evident
that O
2
  has to be continuously provided to the cells and CO
2 
produced
by the cells have to be released out. This process of exchange of O
2
 from
the atmosphere with CO
2
 produced by the cells is called breathing,
commonly known as respiration. Place your hands on your chest; you
can feel the chest moving up and down. You know that it is due to
breathing. How do we breathe? The respiratory organs and the mechanism
of breathing are described in the following sections of this chapter.
17.1 RESPIRATORY ORGANS
Mechanisms of breathing vary among different groups of animals
depending mainly on their habitats and levels of organisation. Lower
invertebrates like sponges, coelenterates, flatworms, etc., exchange O
2
with CO
2
 by simple diffusion over their entire body surface. Earthworms
use their moist cuticle and insects have a network of tubes (tracheal
tubes) to transport atmospheric air within the body. Special vascularised
structures called gills are used by most of the aquatic arthropods and
molluscs whereas vascularised bags called lungs are used by the
terrestrial forms for the exchange of gases. Among vertebrates, fishes
use gills whereas reptiles, birds and mammals respire through lungs.
Amphibians like frogs can respire through their moist skin also.
Mammals have a well developed respiratory system.
BREATHING AND EXCHANGE OF GASES
CHAPTER  17
17.1 Respiratory
Organs
17.2 Mechanism of
Breathing
17.3 Exchange of
Gases
17.4 Transport of
Gases
17.5 Regulation of
Respiration
17.6 Disorders of
Respiratory
System
2015-16(19/01/2015)
BREATHING AND E XCHANGE OF GASES 269
17.1.1 Human Respiratory System
We have a pair of external nostrils opening out above the upper lips.
It leads to a nasal chamber through the nasal passage. The nasal
chamber opens into the pharynx, a portion of which is the common
passage for food and air. The pharynx opens through the larynx region
into the trachea. Larynx is a cartilaginous box which helps in sound
production and hence called the sound box. During swallowing glottis
can be covered by a thin elastic cartilaginous flap called epiglottis  to
prevent the entry of food into the larynx. Trachea is a straight tube
extending up to the mid-thoracic cavity, which divides at the level of
5th thoracic vertebra into a right and left primary bronchi. Each bronchi
undergoes repeated divisions to form the secondary and tertiary bronchi
and bronchioles ending up in very thin terminal bronchioles. The
tracheae, primary, secondary and tertiary bronchi, and initial
bronchioles are supported by incomplete cartilaginous rings. Each
terminal bronchiole gives rise to a number of very thin, irregular-walled
and vascularised bag-like structures called alveoli. The branching
network of bronchi, bronchioles and alveoli comprise the lungs (Figure
17.1). We have two lungs which are covered by a double layered pleura,
with pleural fluid between them. It reduces friction on the lung-surface.
The outer pleural membrane is in close contact with the thoracic
Bronchus
Lung
heart
Diaphragm
Epiglottis
Larynx
Trachea
Cut end of rib
Pleural membranes
Alveoli
Pleural fluid
Bronchiole
Figure 17.1 Diagrammatic view of human respiratory system (Sectional view of
the left lung is also shown)
2015-16(19/01/2015)
Page 3


268 BIOLOGY
As you have read earlier, oxygen (O
2
) is utilised by the organisms to
indirectly break down nutrient molecules like glucose and to derive energy
for performing various activities. Carbon dioxide (CO
2
) which is harmful
is also released during the above catabolic reactions. It is, therefore, evident
that O
2
  has to be continuously provided to the cells and CO
2 
produced
by the cells have to be released out. This process of exchange of O
2
 from
the atmosphere with CO
2
 produced by the cells is called breathing,
commonly known as respiration. Place your hands on your chest; you
can feel the chest moving up and down. You know that it is due to
breathing. How do we breathe? The respiratory organs and the mechanism
of breathing are described in the following sections of this chapter.
17.1 RESPIRATORY ORGANS
Mechanisms of breathing vary among different groups of animals
depending mainly on their habitats and levels of organisation. Lower
invertebrates like sponges, coelenterates, flatworms, etc., exchange O
2
with CO
2
 by simple diffusion over their entire body surface. Earthworms
use their moist cuticle and insects have a network of tubes (tracheal
tubes) to transport atmospheric air within the body. Special vascularised
structures called gills are used by most of the aquatic arthropods and
molluscs whereas vascularised bags called lungs are used by the
terrestrial forms for the exchange of gases. Among vertebrates, fishes
use gills whereas reptiles, birds and mammals respire through lungs.
Amphibians like frogs can respire through their moist skin also.
Mammals have a well developed respiratory system.
BREATHING AND EXCHANGE OF GASES
CHAPTER  17
17.1 Respiratory
Organs
17.2 Mechanism of
Breathing
17.3 Exchange of
Gases
17.4 Transport of
Gases
17.5 Regulation of
Respiration
17.6 Disorders of
Respiratory
System
2015-16(19/01/2015)
BREATHING AND E XCHANGE OF GASES 269
17.1.1 Human Respiratory System
We have a pair of external nostrils opening out above the upper lips.
It leads to a nasal chamber through the nasal passage. The nasal
chamber opens into the pharynx, a portion of which is the common
passage for food and air. The pharynx opens through the larynx region
into the trachea. Larynx is a cartilaginous box which helps in sound
production and hence called the sound box. During swallowing glottis
can be covered by a thin elastic cartilaginous flap called epiglottis  to
prevent the entry of food into the larynx. Trachea is a straight tube
extending up to the mid-thoracic cavity, which divides at the level of
5th thoracic vertebra into a right and left primary bronchi. Each bronchi
undergoes repeated divisions to form the secondary and tertiary bronchi
and bronchioles ending up in very thin terminal bronchioles. The
tracheae, primary, secondary and tertiary bronchi, and initial
bronchioles are supported by incomplete cartilaginous rings. Each
terminal bronchiole gives rise to a number of very thin, irregular-walled
and vascularised bag-like structures called alveoli. The branching
network of bronchi, bronchioles and alveoli comprise the lungs (Figure
17.1). We have two lungs which are covered by a double layered pleura,
with pleural fluid between them. It reduces friction on the lung-surface.
The outer pleural membrane is in close contact with the thoracic
Bronchus
Lung
heart
Diaphragm
Epiglottis
Larynx
Trachea
Cut end of rib
Pleural membranes
Alveoli
Pleural fluid
Bronchiole
Figure 17.1 Diagrammatic view of human respiratory system (Sectional view of
the left lung is also shown)
2015-16(19/01/2015)
270 BIOLOGY
lining whereas the inner pleural membrane is in contact with the lung
surface. The part starting with the external nostrils up to the terminal
bronchioles constitute the conducting part whereas the alveoli and their
ducts form the respiratory or exchange part of the respiratory system.
The conducting part transports the atmospheric air to the alveoli, clears
it from foreign particles, humidifies and also brings the air to body
temperature. Exchange part is the site of actual diffusion of O
2
 and CO
2
between blood and atmospheric air.
The lungs are situated in the thoracic chamber which is anatomically
an air-tight chamber. The thoracic chamber is formed dorsally by the
vertebral column, ventrally by the sternum, laterally by the ribs and on
the lower side by the dome-shaped diaphragm. The anatomical setup of
lungs in thorax is such that any change in the volume of the thoracic
cavity will be reflected in the lung (pulmonary) cavity. Such an
arrangement is essential for breathing, as we cannot directly alter the
pulmonary volume.
Respiration involves the following steps:
(i) Breathing or pulmonary ventilation by which atmospheric air
is drawn in and CO
2
 rich alveolar air is released out.
(ii) Diffusion of gases (O
2
 and CO
2
) across alveolar membrane.
(iii) Transport of gases by the blood.
(iv) Diffusion of O
2
 and CO
2
 between blood and tissues.
(v) Utilisation of O
2
 by the cells for catabolic reactions and resultant
release of CO
2
 (cellular respiration as dealt in the Chapter 14).
17.2 MECHANISM OF BREATHING
Breathing involves two stages : inspiration during which atmospheric
air is drawn in and expiration by which the alveolar air is released out.
The movement of air into and out of the lungs is carried out by creating a
pressure gradient between the lungs and the atmosphere. Inspiration
can occur if the pressure within the lungs (intra-pulmonary pressure) is
less than the atmospheric pressure, i.e., there is a negative pressure in
the lungs with respect to atmospheric pressure. Similarly, expiration takes
place when the intra-pulmonary pressure is higher than the atmospheric
pressure. The diaphragm and a specialised set of muscles – external and
internal intercostals between the ribs, help in generation of such gradients.
Inspiration is initiated by the contraction of diaphragm which increases
the volume of thoracic chamber in the antero-posterior axis. The
contraction of external inter-costal muscles lifts up the ribs and the
2015-16(19/01/2015)
Page 4


268 BIOLOGY
As you have read earlier, oxygen (O
2
) is utilised by the organisms to
indirectly break down nutrient molecules like glucose and to derive energy
for performing various activities. Carbon dioxide (CO
2
) which is harmful
is also released during the above catabolic reactions. It is, therefore, evident
that O
2
  has to be continuously provided to the cells and CO
2 
produced
by the cells have to be released out. This process of exchange of O
2
 from
the atmosphere with CO
2
 produced by the cells is called breathing,
commonly known as respiration. Place your hands on your chest; you
can feel the chest moving up and down. You know that it is due to
breathing. How do we breathe? The respiratory organs and the mechanism
of breathing are described in the following sections of this chapter.
17.1 RESPIRATORY ORGANS
Mechanisms of breathing vary among different groups of animals
depending mainly on their habitats and levels of organisation. Lower
invertebrates like sponges, coelenterates, flatworms, etc., exchange O
2
with CO
2
 by simple diffusion over their entire body surface. Earthworms
use their moist cuticle and insects have a network of tubes (tracheal
tubes) to transport atmospheric air within the body. Special vascularised
structures called gills are used by most of the aquatic arthropods and
molluscs whereas vascularised bags called lungs are used by the
terrestrial forms for the exchange of gases. Among vertebrates, fishes
use gills whereas reptiles, birds and mammals respire through lungs.
Amphibians like frogs can respire through their moist skin also.
Mammals have a well developed respiratory system.
BREATHING AND EXCHANGE OF GASES
CHAPTER  17
17.1 Respiratory
Organs
17.2 Mechanism of
Breathing
17.3 Exchange of
Gases
17.4 Transport of
Gases
17.5 Regulation of
Respiration
17.6 Disorders of
Respiratory
System
2015-16(19/01/2015)
BREATHING AND E XCHANGE OF GASES 269
17.1.1 Human Respiratory System
We have a pair of external nostrils opening out above the upper lips.
It leads to a nasal chamber through the nasal passage. The nasal
chamber opens into the pharynx, a portion of which is the common
passage for food and air. The pharynx opens through the larynx region
into the trachea. Larynx is a cartilaginous box which helps in sound
production and hence called the sound box. During swallowing glottis
can be covered by a thin elastic cartilaginous flap called epiglottis  to
prevent the entry of food into the larynx. Trachea is a straight tube
extending up to the mid-thoracic cavity, which divides at the level of
5th thoracic vertebra into a right and left primary bronchi. Each bronchi
undergoes repeated divisions to form the secondary and tertiary bronchi
and bronchioles ending up in very thin terminal bronchioles. The
tracheae, primary, secondary and tertiary bronchi, and initial
bronchioles are supported by incomplete cartilaginous rings. Each
terminal bronchiole gives rise to a number of very thin, irregular-walled
and vascularised bag-like structures called alveoli. The branching
network of bronchi, bronchioles and alveoli comprise the lungs (Figure
17.1). We have two lungs which are covered by a double layered pleura,
with pleural fluid between them. It reduces friction on the lung-surface.
The outer pleural membrane is in close contact with the thoracic
Bronchus
Lung
heart
Diaphragm
Epiglottis
Larynx
Trachea
Cut end of rib
Pleural membranes
Alveoli
Pleural fluid
Bronchiole
Figure 17.1 Diagrammatic view of human respiratory system (Sectional view of
the left lung is also shown)
2015-16(19/01/2015)
270 BIOLOGY
lining whereas the inner pleural membrane is in contact with the lung
surface. The part starting with the external nostrils up to the terminal
bronchioles constitute the conducting part whereas the alveoli and their
ducts form the respiratory or exchange part of the respiratory system.
The conducting part transports the atmospheric air to the alveoli, clears
it from foreign particles, humidifies and also brings the air to body
temperature. Exchange part is the site of actual diffusion of O
2
 and CO
2
between blood and atmospheric air.
The lungs are situated in the thoracic chamber which is anatomically
an air-tight chamber. The thoracic chamber is formed dorsally by the
vertebral column, ventrally by the sternum, laterally by the ribs and on
the lower side by the dome-shaped diaphragm. The anatomical setup of
lungs in thorax is such that any change in the volume of the thoracic
cavity will be reflected in the lung (pulmonary) cavity. Such an
arrangement is essential for breathing, as we cannot directly alter the
pulmonary volume.
Respiration involves the following steps:
(i) Breathing or pulmonary ventilation by which atmospheric air
is drawn in and CO
2
 rich alveolar air is released out.
(ii) Diffusion of gases (O
2
 and CO
2
) across alveolar membrane.
(iii) Transport of gases by the blood.
(iv) Diffusion of O
2
 and CO
2
 between blood and tissues.
(v) Utilisation of O
2
 by the cells for catabolic reactions and resultant
release of CO
2
 (cellular respiration as dealt in the Chapter 14).
17.2 MECHANISM OF BREATHING
Breathing involves two stages : inspiration during which atmospheric
air is drawn in and expiration by which the alveolar air is released out.
The movement of air into and out of the lungs is carried out by creating a
pressure gradient between the lungs and the atmosphere. Inspiration
can occur if the pressure within the lungs (intra-pulmonary pressure) is
less than the atmospheric pressure, i.e., there is a negative pressure in
the lungs with respect to atmospheric pressure. Similarly, expiration takes
place when the intra-pulmonary pressure is higher than the atmospheric
pressure. The diaphragm and a specialised set of muscles – external and
internal intercostals between the ribs, help in generation of such gradients.
Inspiration is initiated by the contraction of diaphragm which increases
the volume of thoracic chamber in the antero-posterior axis. The
contraction of external inter-costal muscles lifts up the ribs and the
2015-16(19/01/2015)
BREATHING AND E XCHANGE OF GASES 271
sternum causing an increase in the volume of
the thoracic chamber in the  dorso-ventral axis.
The overall increase in the thoracic volume
causes a similar increase in pulmonary
volume. An increase in pulmonary volume
decreases the intra-pulmonary pressure to less
than the atmospheric pressure which forces
the air from outside to move into the lungs,
i.e., inspiration (Figure 17.2a). Relaxation of
the diaphragm and the inter-costal muscles
returns the diaphragm and sternum to their
normal positions and reduce the thoracic
volume and thereby the pulmonary volume.
This leads to an increase in intra-pulmonary
pressure to slightly above the atmospheric
pressure causing the expulsion of air from the
lungs, i.e., expiration (Figure 17.2b). We have
the ability to increase the strength of
inspiration and expiration with the help of
additional muscles in the abdomen. On an
average, a healthy human breathes 12-16
times/minute. The volume of air involved in
breathing movements can be estimated by
using a spirometer which helps in clinical
assessment of pulmonary functions.
17.2.1 Respiratory Volumes and
Capacities
Tidal Volume (TV): Volume of air inspired or
expired during a 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.
Inspiratory Reserve Volume (IRV):
Additional volume of air, a person can inspire
by a forcible inspiration. This averages 2500
mL to 3000 mL.
Expiratory Reserve Volume (ERV):
Additional volume of air, a person can expire
by a forcible expiration. This averages 1000
mL to 1100 mL.
Figure 17.2  Mechanism of breathing showing :
(a) inspiration  (b) expiration
2015-16(19/01/2015)
Page 5


268 BIOLOGY
As you have read earlier, oxygen (O
2
) is utilised by the organisms to
indirectly break down nutrient molecules like glucose and to derive energy
for performing various activities. Carbon dioxide (CO
2
) which is harmful
is also released during the above catabolic reactions. It is, therefore, evident
that O
2
  has to be continuously provided to the cells and CO
2 
produced
by the cells have to be released out. This process of exchange of O
2
 from
the atmosphere with CO
2
 produced by the cells is called breathing,
commonly known as respiration. Place your hands on your chest; you
can feel the chest moving up and down. You know that it is due to
breathing. How do we breathe? The respiratory organs and the mechanism
of breathing are described in the following sections of this chapter.
17.1 RESPIRATORY ORGANS
Mechanisms of breathing vary among different groups of animals
depending mainly on their habitats and levels of organisation. Lower
invertebrates like sponges, coelenterates, flatworms, etc., exchange O
2
with CO
2
 by simple diffusion over their entire body surface. Earthworms
use their moist cuticle and insects have a network of tubes (tracheal
tubes) to transport atmospheric air within the body. Special vascularised
structures called gills are used by most of the aquatic arthropods and
molluscs whereas vascularised bags called lungs are used by the
terrestrial forms for the exchange of gases. Among vertebrates, fishes
use gills whereas reptiles, birds and mammals respire through lungs.
Amphibians like frogs can respire through their moist skin also.
Mammals have a well developed respiratory system.
BREATHING AND EXCHANGE OF GASES
CHAPTER  17
17.1 Respiratory
Organs
17.2 Mechanism of
Breathing
17.3 Exchange of
Gases
17.4 Transport of
Gases
17.5 Regulation of
Respiration
17.6 Disorders of
Respiratory
System
2015-16(19/01/2015)
BREATHING AND E XCHANGE OF GASES 269
17.1.1 Human Respiratory System
We have a pair of external nostrils opening out above the upper lips.
It leads to a nasal chamber through the nasal passage. The nasal
chamber opens into the pharynx, a portion of which is the common
passage for food and air. The pharynx opens through the larynx region
into the trachea. Larynx is a cartilaginous box which helps in sound
production and hence called the sound box. During swallowing glottis
can be covered by a thin elastic cartilaginous flap called epiglottis  to
prevent the entry of food into the larynx. Trachea is a straight tube
extending up to the mid-thoracic cavity, which divides at the level of
5th thoracic vertebra into a right and left primary bronchi. Each bronchi
undergoes repeated divisions to form the secondary and tertiary bronchi
and bronchioles ending up in very thin terminal bronchioles. The
tracheae, primary, secondary and tertiary bronchi, and initial
bronchioles are supported by incomplete cartilaginous rings. Each
terminal bronchiole gives rise to a number of very thin, irregular-walled
and vascularised bag-like structures called alveoli. The branching
network of bronchi, bronchioles and alveoli comprise the lungs (Figure
17.1). We have two lungs which are covered by a double layered pleura,
with pleural fluid between them. It reduces friction on the lung-surface.
The outer pleural membrane is in close contact with the thoracic
Bronchus
Lung
heart
Diaphragm
Epiglottis
Larynx
Trachea
Cut end of rib
Pleural membranes
Alveoli
Pleural fluid
Bronchiole
Figure 17.1 Diagrammatic view of human respiratory system (Sectional view of
the left lung is also shown)
2015-16(19/01/2015)
270 BIOLOGY
lining whereas the inner pleural membrane is in contact with the lung
surface. The part starting with the external nostrils up to the terminal
bronchioles constitute the conducting part whereas the alveoli and their
ducts form the respiratory or exchange part of the respiratory system.
The conducting part transports the atmospheric air to the alveoli, clears
it from foreign particles, humidifies and also brings the air to body
temperature. Exchange part is the site of actual diffusion of O
2
 and CO
2
between blood and atmospheric air.
The lungs are situated in the thoracic chamber which is anatomically
an air-tight chamber. The thoracic chamber is formed dorsally by the
vertebral column, ventrally by the sternum, laterally by the ribs and on
the lower side by the dome-shaped diaphragm. The anatomical setup of
lungs in thorax is such that any change in the volume of the thoracic
cavity will be reflected in the lung (pulmonary) cavity. Such an
arrangement is essential for breathing, as we cannot directly alter the
pulmonary volume.
Respiration involves the following steps:
(i) Breathing or pulmonary ventilation by which atmospheric air
is drawn in and CO
2
 rich alveolar air is released out.
(ii) Diffusion of gases (O
2
 and CO
2
) across alveolar membrane.
(iii) Transport of gases by the blood.
(iv) Diffusion of O
2
 and CO
2
 between blood and tissues.
(v) Utilisation of O
2
 by the cells for catabolic reactions and resultant
release of CO
2
 (cellular respiration as dealt in the Chapter 14).
17.2 MECHANISM OF BREATHING
Breathing involves two stages : inspiration during which atmospheric
air is drawn in and expiration by which the alveolar air is released out.
The movement of air into and out of the lungs is carried out by creating a
pressure gradient between the lungs and the atmosphere. Inspiration
can occur if the pressure within the lungs (intra-pulmonary pressure) is
less than the atmospheric pressure, i.e., there is a negative pressure in
the lungs with respect to atmospheric pressure. Similarly, expiration takes
place when the intra-pulmonary pressure is higher than the atmospheric
pressure. The diaphragm and a specialised set of muscles – external and
internal intercostals between the ribs, help in generation of such gradients.
Inspiration is initiated by the contraction of diaphragm which increases
the volume of thoracic chamber in the antero-posterior axis. The
contraction of external inter-costal muscles lifts up the ribs and the
2015-16(19/01/2015)
BREATHING AND E XCHANGE OF GASES 271
sternum causing an increase in the volume of
the thoracic chamber in the  dorso-ventral axis.
The overall increase in the thoracic volume
causes a similar increase in pulmonary
volume. An increase in pulmonary volume
decreases the intra-pulmonary pressure to less
than the atmospheric pressure which forces
the air from outside to move into the lungs,
i.e., inspiration (Figure 17.2a). Relaxation of
the diaphragm and the inter-costal muscles
returns the diaphragm and sternum to their
normal positions and reduce the thoracic
volume and thereby the pulmonary volume.
This leads to an increase in intra-pulmonary
pressure to slightly above the atmospheric
pressure causing the expulsion of air from the
lungs, i.e., expiration (Figure 17.2b). We have
the ability to increase the strength of
inspiration and expiration with the help of
additional muscles in the abdomen. On an
average, a healthy human breathes 12-16
times/minute. The volume of air involved in
breathing movements can be estimated by
using a spirometer which helps in clinical
assessment of pulmonary functions.
17.2.1 Respiratory Volumes and
Capacities
Tidal Volume (TV): Volume of air inspired or
expired during a 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.
Inspiratory Reserve Volume (IRV):
Additional volume of air, a person can inspire
by a forcible inspiration. This averages 2500
mL to 3000 mL.
Expiratory Reserve Volume (ERV):
Additional volume of air, a person can expire
by a forcible expiration. This averages 1000
mL to 1100 mL.
Figure 17.2  Mechanism of breathing showing :
(a) inspiration  (b) expiration
2015-16(19/01/2015)
272 BIOLOGY
Residual Volume (RV): Volume of air remaining in the lungs even after a
forcible expiration. This averages 1100 mL to 1200 mL.
By adding up a few respiratory volumes described above, one can
derive various pulmonary capacities, which can be used in clinical
diagnosis.
Inspiratory Capacity (IC): Total volume of air a person can inspire after
a normal expiration. This includes tidal volume and inspiratory reserve
volume ( TV+IRV).
Expiratory Capacity (EC): Total volume of air a person can expire after
a normal inspiration. This includes tidal volume and expiratory reserve
volume (TV+ERV).
Functional Residual Capacity (FRC): Volume of air that will remain in
the lungs after a normal expiration. This includes ERV+RV.
Vital Capacity (VC): The maximum volume of air a person can breathe in
after a forced expiration. This includes ERV, TV and IRV or the maximum
volume of air a person can breathe out after a forced inspiration.
Total Lung Capacity: Total volume of air accommodated in the lungs at
the end of a forced inspiration. This includes RV, ERV, TV and IRV or
vital capacity + residual volume.
17.3 EXCHANGE OF GASES
Alveoli are the primary sites of exchange of gases. Exchange of gases also
occur between blood and tissues. O
2
 and CO
2
 are exchanged in these
sites by simple diffusion mainly based on pressure/concentration
gradient. Solubility of the gases as well as the thickness of the membranes
involved in diffusion are also some important factors that can affect the
rate of diffusion.
Pressure contributed by an individual gas in a mixture of gases is
called partial pressure and is represented as pO
2
 for oxygen and pCO
2
 for
carbon dioxide. Partial pressures of these two gases in the atmospheric
air and the two sites of diffusion are given in Table 17.1 and in
Figure 17.3. The data given in the table clearly indicates a concentration
gradient for oxygen from alveoli to blood and blood to tissues. Similarly,
TABLE 17.1 Partial Pressures (in mm Hg) of Oxygen and Carbon dioxide at Different
Parts Involved in Diffusion in Comparison to those in Atmosphere
Respiratory Atmospheric Alveoli Blood Blood Tissues
Gas
Air (Deoxygenated) (Oxygenated)
O
2
159 104 40 95 40
CO
2
0.3 40 45 40 45
2015-16(19/01/2015)
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Important questions

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study material

,

shortcuts and tricks

,

mock tests for examination

,

Semester Notes

,

ppt

,

Extra Questions

,

Free

,

Sample Paper

,

video lectures

,

Exam

,

pdf

,

NCERT Textbook - Breathing and Exchange of Gases NEET Notes | EduRev

,

practice quizzes

,

NCERT Textbook - Breathing and Exchange of Gases NEET Notes | EduRev

,

Summary

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Previous Year Questions with Solutions

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MCQs

,

Viva Questions

;