Human respiration involves two main processes: [1] External respiration which is the exchange of gases between the lungs and blood, and [2] Internal respiration which is the exchange of gases between blood and tissues at the cellular level. The ultimate goal of respiration is to release energy through cellular respiration in which oxygen is used to oxidize nutrients to produce carbon dioxide, water, and ATP as energy is stored.

1. HUMAN RESPIRATION

2. Breathing Respiration
1. Intake of fresh air and Oxidation of food to form carbon
removal of foul air dioxide, water and energy
2. Physical process Biochemical process
3. No energy is released Energy is released in the form of
rather used ATP
4. Extra cellular process Intra cellular process
5. No enzymes involved Large no of enzymes are involved
6. Confined to certain organs Occurs in all the cells of the body
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3. Types of Respiration
1. Anaerobic Respiration :
When nutrients are oxidized without the use of O2 .
In yeast glucose forms ethyl alcohol and CO2.
In bacteria and muscles glucose is converted to lactic acid
Endoparasites are anaerobic in nature
2. Aerobic Respiration :
When nutrients are oxidized with the use of O2 either from air or from water .
i) External respiration : Exchange of gases between Blood and air
ii) Transport of gases to the tissues
iii) Internal respiration : Exchange of gases between blood and tissues
iv) Cellular respiration : Oxidation of nutrients in the cell and release of energy.
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4. Mechanisms of breathing vary among different groups of animals mainly on their habitats
and levels of organisation.
Lower invertebrates
Sponges, coelenterates, flatworms, etc., exchange O2,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
Vascularised bags called lungs are used by the terrestrial molluscs for the exchange of
gases.
Vertebrates
Fishes use gills
Reptiles, birds and mammals respire through lungs.
Amphibians like frogs can respire through their moist skin also
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5. Human Respiratory System
1. Respiratory pathway :
a) Nostrils and Nasal
chamber
b) Pharynx
c) Larynx
d) Trachea
e) Bronchi
f) Bronchioles
g) Alveoli
1. Respiratory Organ :
a) Lungs
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6. Nose
NOSTRILS:
•Nostrils are the external openings of the nose.
These are also called external nares.
Similarly a pair of internal openings is present.
They open into pharynx. These are called internal
nares
NASAL CHAMBERS:
•The space between the external and internal
nares is known as nasal chamber.
•Internally, each one is lined by a mucous
membrane.
•Ciliated epithelium is present in nasal chamber.
•It is divided into right and left parts by a
cartilage known as mesethmoid.
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7. Each nasal chamber is further divided into
three regions:
Vestibule:
This is the anterior most part of the
nasal chamber.
It has hair to trap dust particles and
prevent them from going inside.
Respiratory part:
This is the part richly supplied
with capillaries.
It warms the air and makes it moist.
Sensory part:
This is lined by sensory epithelium for
detection of smell.
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8. Pharynx
•Nasal chamber opens into the pharynx.
•It is a short, vertical tube measuring about 12
cm.in length.
•The respiratory and the food passages cross
each other in the pharynx by two separate
passages.
• Its upper part is known as naso-pharynx
which helps in conduction of air and the lower
part is called laryngo-pharynx or oro-pharynx
conducting food to oesophagus.
In the pharynx, there are tonsils which are
made up of lymphatic tissue. They kill bacteria
trapped in the mucous
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9. Larynx
•It is the sound producing organ, hence also
called the sound box.
•In males, the larynx increases in size at the
time of puberty. Hence, it is called Adam's
apple and can be noticed in the neck region
•.
•From the pharynx, air enters the larynx
through an opening called glottis.
•The glottis is guarded by a flap called
epiglottis.It prevents the entry of food
particles into the respiratory passage
•Along the sides of the glottis are two folds of
elastic tissue called vocal cords. These are
responsible for producing sound.
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10. Trachea
•It is also known as wind pipe.
•It is about 12 cm. long and 2.5 cm. wide.
•It lies in front of the oesophagus and extends
downward into the neck.
•The wall of the trachea is made up of fibrous
muscular tissue supported by 'C'- shaped
cartilage rings. These are 16-20 in number.
They make the trachea rigid.
•The trachea is internally lined with ciliated
epithelium and mucous glands.
•If any foreign particle enters, it is
immediately expelled out by coughing action.
Dust particles get trapped by the mucous. By
ciliary movement, they are swept towards the
larynx and finally they enter the oesophagus
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11. Bronchi & Bronchioles
•The distal end of the trachea is divided into
two bronchi behind the sternum.
•
•Each bronchus is supported by a complete
ring of cartilage.
•It enters into the lung of its respective side.
•On entering the lung, each bronchus further
divides into secondary and then tertiary
bronchi.
•Tertiary bronchi divide into many minute
bronchioles.
•Wall of each bronchiole does not have
cartilage rings.
•Each bronchiole ends into a balloon-like
alveolus.
•These alveoli make the lungs spongy and
elastic.
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12. Lungs
These are the principal respiratory
organs, located in the thoracic cavity.
Lungs are paired, hollow, elastic organs.
Each lung is enclosed in pleural sac.
Pleural sac is made up of two
membranes ,outer parietal and inner
visceral. The enclosed cavity is called
the pleural cavity. It is filled with a
pleural fluid, which lubricates the
pleura and prevents the friction when
the pleural membranes slide over each
other.
Lungs are pink in colour, soft, elastic
and distensible.
They are highly vascular (richly
supplied with blood capillaries).
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13. Each sac has about twenty alveoli
which look like grapes. They are
covered with a network of capillaries
from the pulmonary artery and vein.
The alveoli have very thin (0.0001 mm)
wall composed of simple non-ciliated,
squamous epithelium. It has collagen
and elastin fibres. This makes the
alveoli very flexible.
Each alveolus is about 0.1 mm in
diameter.
The human lung has about 750 million
alveoli, which increase surface area for
exchange of gases. The total area
covered by them is about 50 times the
surface area of skin.
Alveoli are supplied by a network of
pulmonary capillaries.

14. Mechanism of Breathing
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15. INSPIRATION :
•It is an active process brought about by ribs, intercostal muscles, sternum
and diaphragm.
•The intercostal muscles contract, pulling the ribs outward and increase the
space in the thoracic cavity.
•
•The lower part of the breast bone (sternum) is also raised.
•The diaphragm contracts and becomes almost flat
•.
•Volume of the thoracic cavity is further increased, pressure on the lungs
decreases. The lungs expand and their volume increases. Atmospheric air
rushes into the lungs through the respiratory passage to make the pressure
equal. Thus the air enters the lungs.
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16. EXPIRATION:
It is a passive process.
The inter-costal muscles relax pulling the ribs inwards.
The diaphragm relaxes and again becomes dome shaped.
Thus collective contraction of intercostal muscle and diaphragm reduces the
volume of the thoracic cavity. The pressure on the lungs increases. The
lungs get compressed and the air in the lungs, rushes out through the
external nares.
Alternate inspiration and expiration together form the respiratory cycle.
It occurs16-20 times per minute in man.
Breathing is under the control of the medulla oblongata of the brain
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17. RESPIRATORY QUOTIENT (RQ)
The ratio of the vol of CO2 / O2 used in unit time is called respiratory quotient
It varies for different substrates used for respiration
GLUCOSE has RQ = 1
FAT has RQ = 0.7
PROTEIN has RQ = 0.85
ORGANIC ACIDS has RQ = 1.3 or 1.4
In ANAEROBIC respiration RQ = infinity
RQ is determined by means of Ganong’s respirometer
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18. TRANSPORT OF GASES
The transport of respiratory (O2 and CO2) gases takes place in the following events:
1.External respiration
2.Internal respiration
3.Cellular respiration
1. External respiration
•It includes the respiratory processes which take place in the lungs
O2 from the lungs diffuses in the lung capillaries and
CO2 from the lung capillaries diffuses into lungs
External respiration includes three events:
a. Exchange of gases
b. Formation of oxy-haemoglobin
c. Release of carbon-di-oxide:
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19. 1.Exchange of gases
•Concentration of oxygen is higher in the
inspired air than in the alveolar blood and
the concentration of carbon-dioxide is
higher in the alveolar blood than in the
inspired air.
•This results in the exchange of oxygen
from the air into the blood and carbon-
dioxide from blood into the air which is
exhaled out.
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20. 2.Formation of oxy-haemoglobin
The absorbed oxygen combines with the
haemoglobin of RBC's.
Haemoglobin is a respiratory protein
pigment. It forms the unstable
oxy-haemoglobin.
Haemoglobin+ Oxygen = Oxy-Hb
Hb + 4 O2 Hb (4O2)
15 gms of Hb is present in 100 ml of blood
1 gm of Hb can carry 1.34 ml of O2
Thus 100 ml of blood (15 gm of Hb) can carry approx
20 ml of O2
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21. 3. Release of carbon-dioxide
Carbon-dioxide from the blood is released
outside into the air.
CO2 is brought by the blood from the tissue
cells in the form of sodium and potassium
bicarbonates in the blood plasma.
Some amount of CO2 is also brought by
haemoglobin in the form of carbamino-
haemoglobin.
CO2 brought in all these forms is released.
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23. 2. Internal respiration
•It includes the respiratory processes
which take place in the tissue cells.
•Oxygen brought by the blood is given to
the tissue cells and carbon-dioxide from
the tissues, is passed into the blood.
•When the blood reaches the tissue cells,
the unstable oxy-Haemoglobin breaks
down to form haemoglobin and oxygen.
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24. O2 – Hb Dissociation Curve

25. 3. Cellular respiration
The ultimate purpose of respiration is to release energy. This is carried out in the cells
by oxidation of food.
It results in the formation of ATP molecules. Energy is stored in this form. This energy is
used to carry out vital life processes
So ,ATP is called energy currency of cell.
ATP is formed as the main product using mitochondria, while by-products are CO2 and
water vapour which are transported by the blood to the lungs.
Energy released as heat to certain extent is used to maintain the body temperature.
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26. PULMONARY AIR VOLUMES AND
CAPACITIES:
•The quantities of air the lungs can receive, hold or
expel under different conditions are called
pulmonary or lung volumes.
•Pulmonary capacity refers to a combination of two
or more pulmonary volumes
•.
SPIROMETRY is the process of recording the
changes in the volume of air into and out of lungs and
the instrument used for this purpose is called
SPIROMETER
The graph showing the changes in the pulmonary
volumes and pulmonary capacities under different
conditions of breathing is called a SPIROGRAM.
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27. PULMONARY AIR VOLUMES AND CAPACITIES
(TV + IRV)
(TV + IRV + ERV)
(RV + ERV)

28. TIDAL VOLUME (TV)
•It is the volume of air inspired or expired (both) with each normal breath (effortless). It
amounts to about 500ml in the average adult man.
•Of the 500ml of inspired air, only 350 ml of fresh air reaches the lung alveoli and is called
alveolar volume while about 150 ml of the inspired air remains in the respiratory tract
from the nasal chambers to terminal bronchioles which is often called anatomical dead
space and is called dead space volume.
•Physiological dead space includes anatomical dead space and the space in the non-
functional alveoli. It is not useful for the gas exchange process as no gas exchange
occurs in the dead space.
•During exercise, tidal volume is about 4-10 times higher than normal.
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29. INSPIRATORY
RESERVE VOLUME (IRV)
It is the extra volume of air which can be inspired by forced inhalation beyond
the normal tidal volume.
It is about 2500-3000 ml.
It is the deepest possible inspiration
EXPIRATORY
RESERVE VOLUME (IRV)
It is the amount of air that can be expired by forceful expiration after the end of
a normal tidal expiration.
It is about 1000 – 1100 ml.
RESIDUAL VOLUME (IRV)
It is the volume of air left behind in the lung alveoli and respiratory passage
even after the most forceful expiration.
It is about 1500 ml.
This volume can never be expelled out by respiration.
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30. INSPIRATORY CAPACITY (IRV)
It is the amount of air that a person can inhale to the maximum level.
It is the sum of the inspiratory reserve volume(IRV) and the tidal volume (TV)and
is about 3500 ml. (Range 3 – 3.5 L)
IC = IRV + TV
FUNCTIONAL
RESIDUAL CAPACITY (IRV)
It is amount of air left in the lungs after normal expiration.
It is equal to the sum of expiratory reserve volume and the residual volume.
It is about 2500 ml. (2.5 Litres)
FRC = ERV + RV = 1000 + 1500 = 2500 ml
VITAL CAPACITY (VC)
It is the maximum amount of air that can be expelled from the lungs by forced
exhalation after a forced inhalation.
It is equal to the sum of tidal volume, inspiratory reserve volume and expiratory
reserve volume.
Vital Capacity of lung = TV + IRV + ERV = 500 + 3000 + 1100 = 4600 ml
Range of vital capacity = 3.5 – 4.5 Litres in a normal adult person.
VC is higher in athletes, mountain dwellers, men and young ones
VC is lower in non-athletes, plain dwellers, women,old and cigarette smokers

31. TOTAL LUNG CAPACITY (TLC)
It is the amount of air in the lungs and the respiratory passage after a maximum
inhalation effort.
It is equal to the sum of vital capacity and the residual volume.
TLC= VC + RV = 3.5 – 4.5 L + 1.5 L = 5 – 6 litres (Average 5800 ml)
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32. CARBON MONOXIDE POISONING
Haemoglobin has about 250 times more affinity for carbon monoxide than for
oxygen.
In the presence of carbon monoxide, it readily combines to form a stable
compound called carboxy-haemoglobin.
The oxygen combining capacity with Hb decreases and as a result tissue suffers
from oxygen starvation.
It leads to asphyxiation and in extreme cases to death.
Treatment : The person needs to be administered with pure oxygen-carbon
dioxide mixture to have a very high O2 level to dissociate carbon monoxide from
haemoglobin.
Causes:
Carbon monoxide poisoning occurs often in closed room with open stove
burners or furnaces or in garages having running automobile engines.
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33. CONTROL OF RESPIRATION
Respiration has 2 control mechanisms :
Nervous and Chemical regulation
NERVOUS :
The respiratory center in medulla and pons
consist of
1) Dorsal respiratory group :
Located in the dorsal portion of medulla
Mainly causes Inspiration
2) Ventral respiratory group :
Located in the ventrolateral portion of
medulla
Causes Inspiration or expiration
3) Pneumotaxic centre:
Located in the dorsal portion of pons
Mainly limits Inspiration
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34. CONTROL OF RESPIRATION
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35. CHEMICAL :
Chemoreceptors are located in the carotid
and aortic bodies
Afferent nerve fibres of carotid bodies pass
through Glossopharyngeal nerve to the dorsal
respiratory area
Afferent nerve fibres of aortic bodies pass
through vagus nerve to the dorsal respiratory
area
Excess CO2 and H+ stimulate the respiratory
center and accordingly alter the inspiratory
and expiratory signals to the respiratory
muscles
Increased CO2 lowers the pH resulting in
acidosis
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37. RESPIRATORY DISORDERS
ASTHMA
- inflammatory disease of the air ways
- reversible over-reactivity of the airway smooth muscle.
- The mucous membrane and muscle layers of the bronchi become thickened and the
mucous glands enlarge reducing airflow in the lower respiratory tract.
- During an asthmatic attack, spasmodic contraction of bronchial muscle -(Bronchospasm)
constricts the airway and there is excessive secretion of thick sticky mucus, which further
narrows the airway.
- Inspiration is normal but only partial expiration is achieved so that lungs become hyper-
inflated and there is severe dyspnoea(difficulty in breathing, a.k.a. air hunger) and
wheezing.
- The duration of attacks usually varies from a few minutes to hours (status asthmaticus).
In severe attacks the bronchi may be obstructed by mucus plugs, leading to acute
respiratory failure, hypoxia (deficiency in the amount of oxygen reaching body tissues)
and possibly death.
Non - specific factors
Cold air, Cigarette smoking,
Air pollution, Upper respiratory tract infection,
Emotional stress and Strenuous exercise.
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39. PHARYNGITIS:
The inflammation of the upper respiratory
tract can be caused by inhaling different micro-
organisms.
Streptococcus pyogenes are common cause of
inflammation of palatine tonsils and walls of
pharynx.
Pharyngitis usually accompanies common
cold.
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40. LARYNGITIS:
It is an inflammation of larynx due to viral or
bacterial infection.
It occurs in all the ages but more common in
children.
Symptoms:
The voice becomes husky initially.
Severe infection may lead to aphasia.
There is a feeling of rawness in the throat.
Stridor may be present in children.
Cough of an irritating type may be present.
Cause:
Vocal misuse or overuse are common causes
of acute laryngitis
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41. ALLERGRIC RHINITIS (HAY FEVER):
In this condition, atopic (immediate)
hypersensitivity develops to foreign proteins
(antigens) e.g. pollen, mites in pillow feathers,
animal dander.
The acute inflammation of nasal mucosa and
conjunction causes rhinorrhoea (excessive
watery exudate from the nose), redness of the
eyes and excessive secretion of tears.
Atopic hypersensitivity tends to run in families
but no genetic factor has yet been identified.
Other forms of atopic hypersensitivity include:
Childhood onset asthma,
Eczema in infants and young children and
Food allergies
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42. PNEUMONIA:
Infection of the alveoli.
protective processes fail to prevent microbes reaching lungs.
Causes:
IMPAIRED COUGHING:
Coughing is an effective cleaning mechanism, but if it is impaired if the person is
unconscious, damage to respiratory muscles or the nerves supplying them, or painful
coughing, then respiratory secretions may accumulate and become infected.
Ciliary action may be impaired or the epithelium destroyed by tobacco smoking, inhaling
noxious gases, infection etc.
Depressed macrophage (W.B.Cs) activity may be caused by tobacco smoking, alcohol, and
anoxia(a condition characterized by an absence of oxygen supply to an organ or a tissue).
Other factors:
These include reduced resistance, leucopoenia (decreased W.B.C count) and chronic
diseases like cardiac failure, cancer, chronic renal failure.
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43. SOME PATHOGENS ASSOCIATED WITH
PNEUMONIA:
Streptococcus pneumoniae:
This is the commonest causative organism in
pneumonia, particularly Lobar Pneumonia
(acute bacterial pneumonia).
Mycoplasma:
It is the second commonest causative
organism, and affects mainly children and
young adults.
Other organisms:
Some viruses, protozoa and fungi may cause
pneumonia in people whose general resistance
is lowered or whose immune system is
depressed by HIV, immunosuppressant drugs
etc.
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44. OCCUPATIONAL LUNG DISEASES
This group of lung diseases is caused by inhaling atmospheric pollutants at work place
.
To cause disease, particles must be so small that they are carried in inspired air to the
level of the respiratory bronchioles and alveoli, where they can only be cleared by
phagocytosis.
Larger particles are trapped by mucus in upper part of the respiratory tract and
expelled by ciliary action and coughing.
Recognition of the damaging effects of these substances has led to legislation that
limits workers exposure to these pollutants.
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45. SILICOSIS:
This may be caused by long-term exposure to dust containing silicon compounds.
High-risk industries are quarrying, granite, slate, sandstone-mining, stone masonry, sand
blasting and glass and pottery work.
Inhaled silica particles accumulate in the alveoli.
The particles are ingested by macrophages, and are actively toxic to these cells.
The inflammatory reaction is triggered when the macrophages destroy the particles and this
result in significant fibrosis.
Silicosis appears to predispose to the development oftuberculosis, which rapidly progresses
to tubercular bronchopneumonia and possibly military TB (a form varying in severity, in
which minute tubercles form in different organs due to dissemination of bacilli through the
body by the blood stream).
Gradual destruction of lung tissue leads to progressive reduction in pulmonary function,
pulmonary hypertension and heart failure.
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46. ASBESTOSIS:
Asbestosis is caused by inhaling asbestos
fibres, usually develops after 10 to 20 years
exposure, but sometimes after only 2 years.
Asbestos miners and workers involved in
making and using some products containing
asbestos are at risk.
There are different types of asbestos, but blue
asbestosis is associated with the most serious
disease.

47. SOME RESPIRATORY TERMS
Eupnea – normal breathing
Hypopnea – Slow breathing
Hyperpnoea – rapid breathing
Apnoea – No breathing
Dyspnoea – Difficult breathing
Tachypnoea – Rapid shallow breathing
Orthopnoea – Inability to breathe in horizontal position
Asphyxia – Combination of hypoxia and hypercapnea
Hypercapnea – Increased CO2 content of blood
Hypocapnea – Decreased CO2 content of blood

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