This document summarizes the human respiratory system. It describes the major parts including the nostrils, pharynx, larynx, trachea, bronchi, bronchioles and alveoli. It explains how breathing occurs through inspiration and expiration, driven by contractions of the diaphragm and intercostal muscles. Gas exchange takes place in the alveoli and oxygen and carbon dioxide are transported in the blood and tissues. Regulation of respiration maintains appropriate rates. Common respiratory disorders like asthma and emphysema are also outlined.

1. Respiratory
Organs
Entire Body
surface
Skin
Tracheal system
Gills
Lungs
Organisms
Sponges, coelenterate,
flatworms.
Earthworm.
Insects
Pisces, aquatic arthropods.
Amphibians,mammals.

2. Human Respiratory System
• Human respiratorysystem consists of a
pair of nostrils, pharynx, larynx, bronchi and
bronchioles that finally terminates into
alveoli.
• Nasal chamber open into pharynx that
leads to larynx. Larynx contains voice box
(sound box) that help in sound production.
• The trachea, primary,secondary and
tertiary bronchi and initial bronchioles are
supportedby incompletecartilaginous
rings to preventcollapsing in absence of
air.
• Each bronchiole terminates into an
irregular walled, vascularized bag like
structure called alveoli.

3. Cut end 01rib
18
0
Lu
Eptöottls
Lannx
Tracipa
neural
Pteural fluid
Btotxhtole
• The branching networkof bronchi,
bronchioles and alveoli collectively form
the lungs.
• Two lungs are covered with double layered
pleura having pleural fluid between them to
reduce the friction on lung surface.

4. RespiratorySystem
Conducting Parts Exchange Parts
• Conducting parts include nostrils, pharynx,
larynx and trachea. Main functions include-
1. Transport of atmospheric air to alveoli.
2. Removing foreign particles from air,
humidifying it and bringing it to body
temperature.
• The exchange parts are alveoli. It is the site
of actual diffusion of 02 and C02 between
blood and atmospheric air.

5. Steps of Respiration
1. Breathinginwhich Oxygen rich
atmospheric air is diffused in and C02 rich
alveolar air is diffused out.
2. Diffusion of gases across alveolar
membrane.
3. Transport of gases by blood.
4. Diffusion of 02 and C02 betweenblood
and tissues.
5. Utilization of 02 by cells to obtain energy
and release of C02 (cellular respiration).

6. Mechanism of Breathing
• Breathing involves inspiration and
expiration. During inspiration atmospheric
air is drawn in and during expiration,
alveolarair is released out.
• Movementof air in and outtakes place due
to difference in pressure gradient.
• Inspirationoccurs when pressure inside the
lung is less andexpirationoccurs when
pressure is morein lungs than outside.
• The diaphragmand externaland internal
intercostal muscles betweenthe ribs help
in developing pressure gradient due to
change in volume.

7. Airenteringlungs
Ribsand
sternum Volumeof
raised thorax
Ribcage
Diaphragm
contracted
• The contraction of intercostal muscles lifts
the ribs and sternum causing an increase in
volume of thoracic cavity that results in
decrease in pressure than the atmospheric
pressure.This causes inspiration.
• Relaxation of the diaphragm and
intercostal muscles reduce the thoracic
volume and increase the pressure causing
expiration.

8. • The volume of air involved in breathing
movements is estimated by using
spirometer for clinical assessment of
pulmonaryfunctions.
Airexpelledfromlungs
Ribsand
sternum
returnedto
original VolumeOf
position thorax
14
Diaphragm
relaxed
andarched
upwards
RespiratoryVolumeand Capacities
Tidal volume (TV) - volumeof air inspiredor
expired during a normal respiration. It is about
500mL in healthy man.

9. InspiratoryReserve Volume (IRV) - additional
volumeof air a person can inspireby forceful
inspiration.It is about2500 mL to 3000mL.
ExpiatoryReserve Volume (ERV) - additional
volume of air a person can expire by forceful
expiration.It is about 1000 mL to 1100mL.
Residual Volume (RV) - volume of air remaining
in lungs even after a forcible expiration. It is
about 1100mL to 1200mL.
InspiratoryCapacity (IC) - TV + IRV
ExpiratoryCapacity (EC) - TV + ERV
FunctionalResidualCapacity (FRC) - ERV+ RV

10. Vital Capacity (VC) - maximum volumeof air a
person can breathe in after a forceful expiration.
ERV+ TV+ IRV
Total Lung Capacity (TLC) - total volume of air
accommodated in lung at the end of forced
inspiration.RV+ ERV+ TV+ IRV or Vital capacity
+ Residual Volume.
Insptred atr Exptredair
Alveolar
air
pop 104 mmHg
Pulmonary
artery
Systemjc s•etns
(cartytng deoxygenated blood)
PO. • 40mm lg
pCO, • 43 mm Hg
coao.
co. 02
co, o,
Bodytissues
Alveolus
Pulmonary
Systemic artertes
(carrytng oxygenated blood)
• 95 mm IR
pCO, 40 mm

11. Exchange of Gases
• Exchange of gases takes place at two sites
1. Alveoli to blood
2. Between blood and tissues.
• Exchanges of gases occur by simple
diffusion due to pressure/ concentration
gradient, solubility of the gases and
thickness of membrane.
• Pressure contributed by individual gas in a
mixtureof gas is called partial pressure
representedby pc02 and p02
• Partial pressure of Oxygen and carbon
dioxide at different part involved in
diffusion varies from one part to another
and moves from higher partial pressure to
lower partial pressure.

12. • Solubility of C02 is 20-25 times morethan
solubilityof 02 , so C02 diffuse much
faster through membrane.
• Diffusion membrane is three layered thick,
that is alveolarsquamous epithelium,
endothelium of alveolar capillaries and
basement substance betweenthem.
Alveolar
wall Basement
(one-celledthick) substance
Alveolarcavity
Blood Q
capillary O 0 Redblood

13. Transport of Gases
• Blood is the mediumof transportfor C02
and 02 Mostof oxygen (97%) is
transported through RBC and remaining 3%
by blood plasma.
• 20-25%of C02 is transportedby RBC, 70%
as bicarbonateand rest 7% in dissolved
state by bloodplasma.
Transport of Oxygen
• Haemoglobin in RBC combines with02 to
form Oxyhaemoglobin.Each haemoglobin
combine with four oxygen molecules.
• Binding of 02 is relatedwith partial
pressure of 02 and C02, hydrogenion
concentration and temperature.
• Percentage saturationof haemoglobinand
partialpressureof oxygenforms sigmoid
curve (oxygen dissociation curve).
• Inthe alveoli,p02 is moreand pc02 is

14. • In the alveoli, p02 is more and pc02 is
less, less H+ ions concentrationand lower
temperature favour the binding of 02 with
hemoglobin. Where opposite condition in
tissues favour the dissociation of
Oxyhaemoglobin.
Transport of Carbon dioxide
• Carbon dioxide is transported by
haemoglobin as carbamino-haemoglobin.
Intissues pc02 is highand p02 is less
that favour the binding of carbon dioxide
with haemoglobin. Opposite condition help
in dissociation of carbamino- haemoglobin
in alveoli.

15. • Carbon dioxide is transported by
haemoglobinas carbamino-haemoglobin.
Intissues pc02 is highandp02 is less
that favour the binding of carbon dioxide
with haemoglobin. Opposite condition help
in dissociation of carbamino- haemoglobin
in alveoli.
• Enzymecarbonic anhydrase helpin
formation of carbonate ions to transport
carbon dioxide.
Regulation of Respiration
• Human beings have ability to maintain and
moderate the rate of respiration to fulfill the
demand of body tissues by neural system.
• Respiratory rhythmcentre is located in
medulla regionof hindbrain.Pneumotaxic
centre in pons moderatethe function of
respiratory rhythm centre.
• Chemo-sensitive area near rhythmcentre
is highlysensitive to C02 and H+ ions that
ultimately control the respiratory rate.
Oxygen do not play major role in controlling
rate of respiration.

16. Functions of Respiration-
1. Energy production
2. Maintenance of acid-base balance.
3. Maintenance of temperature
4. Returnof bloodand lymph.
Mountain Sickness is the condition
characterisedbythe ill effectof hypoxia
(shortage of oxygen) inthe tissues at high
altitudecommonlyto person going to high
altitude for the first time.

17. Symptoms-
• Loss of appetite, nausea, and vomiting
occurs due to expansion of gases in
digestive system.
• Breathlessness occurs because of
pulmonary oedema.
• Headache, depression, disorientation, lack
of sleep, weakness and fatigue.
Disorderof RespiratorySystem
1. Asthma- it is due to allergic reaction to
foreign particles that affect the respiratory
tract. The symptoms include coughing,
wheezing and difficulty in breathing. This is
due to excess of mucus in wall of
respiratory tract.

18. 2. Emphysema- is the inflation or abnormal
distension of the bronchioles or alveolar
sacs of lungs. This occurs dueto
destroying of septa between alveoli
because of smoking and inhalation of other
smokes. The exhalationbecomes difficult
and lung remains inflated.
3. Occupational Respiratory Disorders-
occurs dueto occupation of individual.This
is caused by inhalationof gas, fumes or
dust present in surrounding of work place.
This includes Silicosis, Asbestoses dueto
exposer of silica and asbestos. The
symptom includes proliferation of fibrous
connective tissue of upper part of lung
causing inflammation.