CLASS XI, NCERT and COMPETITVE ASPECT. Chapter - Breathing and Exchange of Gases

1. BREATHING AND
EXCHANGE OF
GASES
BY: DR. PRITIMA GUPTA

2. RESPIRATION
• Respiration is a catabolic biochemical process which involves exchange of
environmental oxygen and body’s carbon – di – oxide through a liquid medium
to utilize the oxygen for the oxidation of glucose in the mitochondria to
produce energy.
• Breaking down of respiratory fuel to obtain energy.
#PRINCIPLE OF EXCHANGE OF GASES –
• It’s a physical process & dependent upon the principle of diffusion.
• PARTIAL PRESSURE of a gas is the pressure it exerts in a mixture of gases
and is calculated as –
Total pressure of mixture of gases x percentage of a gas in mixture
• The partial pressure of a gas is directly proportional to its concentration in the
mixture.

3. TYPES OF RESPIRATION
RESPIRATION
BASED UPON
+NCE/ -NCE OF
OXYGEN
AEROBIC
RESPIRATION
ANAEROBIC
RESPIRATION
DIRECT/
INDIRECT
INVOLVEMENT
OF CELL
CHARAC -
TERS
EXTERNAL
RESPIRATION
(BREATHING)
INTERNAL
RESPIRATION (TISSUE)
SITE OF
OCCURRENCE
At the respiratory
surface.
At the cellular level.
EXCHANGE OF
GASES
Oxygen of air or water &
carbon-di-oxide of blood.
Oxygen of blood & carbon-
di-oxide of cells.
NATURE Physical process. Physico – chemical process.
ENERGY
Food is not oxidised so no
energy is produced.
Food is oxidized in the
mitochondria & energy is
produced.
ENZYMES
Enzymes are not
involved.
A large no. of enzymes are
involved.

4. STEPS WITHIN
RESPIRATION
1. Breathing/ ventilation –
respiratory gases enters our
body.
2. Exchange of respiratory gases
between alveoli and blood.
3. Transport of gases through
blood.
4. Exchange of gases b/w blood
and tissues.
5. Using oxygen – glucose
breakdown to release energy.
CHARACTERISTICS OF
RESPIRATORY SURFACE
1. It must be thin.
2. It must be permeable to O2 & CO2.
3. It must be moist either with water or
mucus.
4. It should have a large surface area.
5. It must be highly vascular.
6. It must be in direct or indirect contact
with source of oxygen.
7. Presence of respiratory pigment
increases the O2 & CO2 carrying
capacity of the blood.

5. ORGANS OF RESPIRATION
1) SKIN – Cutaneous Respiration. Eg:
Earthworm & frogs.
2) TRACHEAE – Chitinous tube.
Tracheal/ Tracheary Respiration. Eg:
Cockroaches.
3) GILLS – Branchial Respiration. Eg:
Fishes, prawns etc.
4) LUNGS – Pulmonary Respiration. Eg:
Higher vertebrates, birds, amphibians,
mammals and reptiles etc.
5) BOOK LUNGS – Eg: Scorpions and
spiders.
6) BOOK GILLS – Eg: Horse shoe crab.
7) PULMONARY SAC – Modified mantle
cavity found in molluscs.

6. HUMAN RESPIRATORY SYSTEM
HUMAN
RESPIRATORY
SYTEM
RESPIRATORY
TRACT
Eternal nares
Nasal chambers
Internal nares
Laryngopharynx
Larynx
Trachea
Primary bronchi
RESPIRATORY
ORGANS
Lungs
1. NOSTRILS/
EXTERNAL NARES –
One pair, small, oval
apertures +nt just above
the upper lip.
2. NASAL CHAMBERS –
These are a pair of large
chambers enclosed in
nasal capsules. These are
separated by a NASAL
SEPTUM.
#RESPIRATORY TRACT

7. #PARTS OF NASAL CHAMBER –
• Each nasal chamber is divided into three parts –
1) VESTIBULAR PART – Anterior & smaller. Lined
by hairy skin.
2) RESPIRATORY PART – Middle part. Lined by
glandular & vascular respiratory epithelium
which acts as an Air- Conditioner.
3) OLFACTORY PART – Posterior part.
Lined by Olfactory epithelium/
SCHNEIIDERIAN MEMBRANE which
helps in smelling.
• Each nasal chamber has three scroll like
processes called CONCHAE or
TURBINALS which increases the surface
area of the chamber.

8. SIGNIFICANCE OF
NASAL BREATHING
FILTRATION
AIR -
CONDITIONING
MOISTENINGSTERILISING
SMELLING
3) INTERNAL NARES/
CHOANAE – These are openings of
nasal chambers in the nasopharynx and
are closed by uvula during swallowing.
# NASOPHARYNX – Upper part of
pharynx, connecting with the nasal
cavity above the soft palate.

9. 4) LARYNGOPHARYNX – Lower part of pharynx &
has a slit like aperture called GLOTTIS, which can
be closed by leaf like bilobed cartilage,
EPIGLOTTIS, during swallowing. It basically
prevents entry of food into trachea.

10. 5) LARYNX/ VOICE BOX/ ADAM’S APPLE – Small, thin walled tubular
part +nt in the neck. Lined by stratified columnar ciliated epithelium. It has 2
elastic flap like structure c/as VOCAL CORDS. To prevent from collapsing, it
is supported by four cartilages.
CARTILAGES
1 CRICOID
1 THYROID
(biggest)
2 ARYTENOID
(smaller)

12. 6) TRACHEA/ WIND – PIPE – 10-11cm long, thin walled, tubular structure.
Lined by pseudo-stratified ciliated epithelium. Supported by 16-20 dorsally
incomplete ‘C’ shaped cartilaginous tracheal rings in order to prevent form
collapsing.
7) PRIMARY BRONCHI – Paired,
small, thin walled tubular structures
formed by the division of trachea at the
level of 5th thoracic vertebra.
RIGHT BRONCHUS LEFT BRONCHUS
2.5 cm long 5 cm long
Wider Narrower
More vertical More horizontal

13. • LUNGS – Respiratory organ in human.
Hence, also c/as PULMONARY
RESPIRATION.
• It is lobulated.
POSITION – Large (PULMONES),
paired, soft, elastic & cone shaped
organs +nt in the thoracic cavity, one
on either side of the heart.
Thoracic cavity boundaries –
Dorsally – Vertebral column
Ventrally – Sternum
Laterally – Ribs
Posteriorly – Diaphragm
Anteriorly – Base of the neck
RIGHT LUNG LEFT LUNG
Bigger Smaller
Weighs 625 gm. Weighs 567 gm.
Cardiac notch -nt +nt
3 lobes – Upper/superior
Middle
Inferior lobe
2 lobes – Superior
Inferior
#RESPIRATORY ORGAN

14. PLEURA – Thin, transparent, two-layered peritoneal serous sac around the
lung. Its inner layer - VISCERAL PLERON (in contact with lung surface)
Outer layer – PARIETAL PLEURON (in contact with thoracic lining)
• B/w these layers, there is a narrow cavity – PLEURAL CAVITY which is
filled with fluid called PLEURAL FLUID.
#FUNCTIONS OF PLEURAL FLUID –
1. Acts as a lubricant.
2. Protects lungs from mechanical shock.
3. Holds the membrane together.

15. BRONCHIAL INTERCOM
• Network present inside the lung formed by
the division and redivision of primary
bronchus.
• The part of respiratory system from
nostrils to terminal bronchioles is called
CONDUCTING PART. It transports air
to alveoli, cleans, humidifies and air –
conditions the air at body temperature.
• The part of respiratory system from
respiratory bronchioles to alveoli is called
RESPIRATORY OR EXCHANGE
PART. Site of gaseous exchange.
• A bronchiole along with its branches –
LOBULE.

16. Each respiratory bronchioles
, divides into finest branches
2-11 in no. called
ALVEOLAR DUCTS, each
of which opens into an
ALVEOLAR SAC/
INFINDIBULUM OR
ATRIUM.
An alveolar sac is formed of
central passage and 6-8
pocket like grape shaped
outgrowths called
ALVEOLI OR AIR SACS
which are about 0.1 mm in
diameter.

17. • Each alveolus is lined by a squamous
epithelium of flat cells called ALVEOLAR
EPITHELIUM.
• Each blood vessel/ capillary is lined by
ENDOTHELIUM.
• Alveolar epithelium, endothelium along
with their basement membranes and
interstitial fluid are collectively k/as
REPIRATORY MEMBRANE.
• Lecithine – surfactant, so that alveoli do
not collapse.
RESPIRATORY
MEMBRANE

18. MECHANISM OF BREATHING
• Mechanism of breathing involves the alternate expansion and contraction of
chest cavity called RESPIRATORY MOVEMENTS.
• The respiratory movements involves two phases –
• Breathing involves sending
fresh air to respiratory organ
(INSPIRATION) and
expelling the foul air from
them (EXPIRATION).
• Respiratory frequency varies
among individuals. It is
12-16 times/minute in an
adult man.
• Average 12times/minute.
RESPIRATORY
MOVEMENTS
INSPIRATION
PHRENIC
(RADIAL)
MUSCLE OF
DIAPHRAGM
EXTERNAL
INTERCOASTAL
MUSCLE
EXPIRATION
ABDOMINAL
MUSCLES
INTERNAL
INTERCOASTAL
MUSCLES

19. • Involves intaking of fresh air in the alveoli of the lungs. It includes muscle contraction so its
an active process.
#INSPIRATORY MUSCLES –
1. PHRENIC (RADIAL) MUSCLE
OF DIAPHRAGM - Extends from
diaphragm to ribs and vertebral column.
When these contract, the diaphragm is
flattened which increases the thoracic
cavity anteroposteriorly.
2. EXTERNAL INTERCOASTAL
MUSCLE – 11 pairs of muscles +nt b/w
12 pairs of ribs. When these contract, the ribs are pulled upward and outward, so thoracic
cavity increases dorsoventrally and laterally.
INSPIRATION/ INHALATION

20. #MECHANISM OF
INSPIRATION-
Phrenic
muscle
contract
Diaphragm
becomes flat
Volume of
thoracic
cavity
increases
Volume
increases and
pressure
decreases in
lungs (by 2-
6mm Hg)
Atmospheric air pressure
is more and lungs
decreases

21. EXPIRATION/ EXHALATION
• Involves expelling of foul air out of the body. It includes muscle relaxation so it’s
a passive process.
Phrenic muscle
relax
Diaphragm
becomes dome
shaped
Volume of
thoracic cavity
decreases
Pressure
increases in
lungs
Atmospheric pressure is less and
lungs pressure is more
During forceful expiration, two expiratory
muscles also help in expiration –
1. Abdominal muscles
2. Internal intercoastal muscles

22. • After expiration when we try to exhale more air.
• Forceful expiration is an active process.
# MUSCLES INVOLVED –
1. INTERNAL INTERCOSTAL MUSCLES-
These are 11 pairs of muscles +nt b/w the
ribs. When these muscle contract, ribs
are pulled downward & inward, so thoracic
cavity decreases dorsoventrally and
laterally.
2. ABDOMINAL MUSCLES –
These extends from ribs to the abdominal organs. when these contract, the
abdominal visceral organs are pulled upward. So the diaphragm becomes more
convex & thoracic cavity decreases anteroposteriorly.
FORCEFUL EXPIRATION

23. When internal
intercostal
muscles contracts
Rib cage moves
inward
Abdominal
muscles are
attached to the
organs & rib cage
When these
muscles contract
Diaphragm is
pushed upwards
Because the
abdominal organs
are pushed
upwards
Thoracic cavity
volume decreases
more
Which in turn
increases
pressure
Forcefully air
rushes from lungs
to atmosphere
Completenormalonebreathingcycle
iscompletedin5secinadults.
Inadultsundernormalconditions–
12cycles/ministhebreathingrate.

24. PULMONARY AIR VOLUMES
• PULMONARY VOLUMES are the quantities of
air the lungs can receive, hold or expel under
different conditions.
1. TIDAL VOLUME (TD) - 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.
2. INSPIRATORY RESERVE VOLUME (IRV) -
Additional volume of air, a person can
inspire by a forcible inspiration. This
averages 2500 mL to 3000 mL.
3. EXPIRATORY RESERVE VOLUME (ERV) -
Additional volume of air, a person can
expire by a forcible expiration. This averages
1000 mL to 1100 mL.
4. RESIDUAL VOLUME (RV) - Volume of air
remaining in the lungs even after a forcible
expiration. This averages 1100 mL to 1200
mL.
5. MINUTE RESPIRATORY VOLUME – It is
the total amount of air which is moved into
the respiratory passage per minute. It is
equal to the product of tidal volume & the
respiratory rate.
6. ALVEOLAR VENTILATION – It is the rate at
which the fresh air reaches the alveoli and
adjoining areas like alveolar ducts, sacs and
respiratory bronchioles.

25. PULMONARY CAPACITIES
• PULMONARY CAPACITIES are sum of two or more pulmonary volumes.
1. 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).
2. 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).
3. FUNCTIONAL RESIDUAL CAPACITY (FRC) - Volume of air that will remain in the
lungs after a normal expiration. This includes ERV+RV.
4. 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.
5. TOTAL LUNG CAPACITY (TLC) - 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.

26. • The graph showing
the changes in the
pulmonary volumes
and pulmonary
capacities under
different conditions
of breathing is
called
SPIROGRAM.
• Changes can be
calculated by
SPIROMETRY.
• Instrument used –
SPIROMETER.

27. EXCHANGE OF GASES
# TRANSPORT OF OXYGEN –
• O2 diffuses in two forms –
a) Dissolved in plasma – 1-3% of total O2.
b) As a complex with Hb –
OXYHAEMOGLOBIN. (97-99%)
• 1 Hb binds to 4 O2 molecules.
• 1 gm of Hb can transport 1.34 ml of O2.
# FACTORS HELPFUL –
1. High pO2 in alveolar air or low pCO2 in
blood.
# TRANSPORT OF CARBON-DI-OXIDE –
a) As bicarbonate of Na and K. (70%)
b) As carbonic acid. (7%)
c) Transported as carbaminohaemoglobin.
• 100 ml of blood transports 3.7 ml of CO2.
• CO2 + Amino group Hb =
CARBAMINOHAEMOGLOBIN.
# OXYGEN DISSOCIATION CURVE –
It shows the
percent
saturation
of
haemoglobin
with the
changes in
pO2 at
constant pH.

29. # FACTORS AFFECTING OXYGEN DISSOCIATION CURVE –
1. CARBON - DI - OXIDE CONCENTRATION - ↑se in CO2 – ODC bends towards
the right. % saturation of Hb will be decreased. And this is k/as BOHR’S
EFFECT.
2. TEMPERATURE
3. pH
# RELEASE OF CO2 –
1. HALDANE’S EFFECT – As more and more concentration of Oxyhaemoglobin
is there – it acts as a strong acid, thereby releasing more H+ ions. These ions
combines with bicarbonate ions forming carbonic acid. This carbonic acid
dissociates into carbon di oxide & water in +nce of carbonic anhydrase.
𝐇
+
+ 𝐇𝐂𝐎𝟑
−
→ 𝐇 𝟐 𝐂𝐎 𝟑
2. High partial oxygen is responsible for dissociation of carbamino Hb.
3. Carbon di oxide is less soluble in arterial blood.

30. CONTROL OF RESPIRATION
I. NERVOUS CONTROL – Basic rhythm of respiration is regulated by 4
respiratory centres +nt in the floor of medulla oblongata and pons varolii. These
centres are collectively c/as RESPIRATORY RHYTHM CENTRES/
RHYTHMICITY CENTRE.
a) INSPIRATORY CENTRE – It lies in dorsal wall of medulla oblongata and
stimulates the inspiratory muscles.
b) EXPIRATORY CENTRE – It lies in the ventral wall of medulla oblongata and
remains dormant during normal respiration but during exercise, it controls the
powerful contraction of expiratory muscles.
c) PNEMOTAXIC CENTRE – It lies in the upper part of pons varolii. When
stimulated, it increases the rate of respiration but decreases the depth of
respiration. Like dog panting.
d) APNEUSTIC CENTRE – It lies in the lower part of pons varolii. It promotes
inspiration by sending excitatory signals to inspiratory centre of medulla. It
controls the intensity of breathing.

31. II. CHEMICAL CONTROL – CHEMOSENSITIVE
BODIES control these.
a) CARBON DI OXIDE CONCENTRATION –
Increase in carbon di oxide concentration
increases the respiration rate.
b) OXYGEN CONCENTRATION – respiratory
centres are less sensitive to oxygen changes in
blood.
• Changes in partial oxygen and partial carbon di
oxide are noted by CAROTID and AORTIC
BODIES, groups of peripheral chemoreceptors
+nt in carotid bodies of carotid sinus and aortic
bodies or aortic arch. These receptors are
stimulated by following changes in the arterial
blood –
1. Significantly decrease in pO2 – HYPOXIA.
2. METABOLIC ACIDOSIS – Increased H+
concentration.
3. Increased pCO2 – RESPIRATORY ACIDOSIS.
• ASTHMA – Narrowing & inflammation of bronchi,
bronchospasm, & difficulty in breathing.
• EMPHYSEMA – The air sacs in the lungs become
damaged and stretched. This results in a chronic
cough and difficulty breathing. Smoking is the
most common cause.
• OCCUPATIONAL RESPIRATORY DISORDERS
–
1. SILICOSIS – Caused by clay, sand and sand
stone grinding.
2. ASBESTOSIS – Caused by inhaling of
asbestos inside the respiratory tract.
3. CO –POISONING
4. OXIDES OF SULPHUR
RESPIRATORY DISORDERS