The document describes the structure and function of the respiratory system. It details the major components including the nasal passages, pharynx, larynx, trachea, bronchi, bronchioles, respiratory bronchioles, alveolar ducts, and alveoli. It explains how air moves through the respiratory tree from the trachea down to the alveoli where gas exchange occurs. It also discusses cellular respiration and the role of oxygen and carbon dioxide exchange between the alveoli and blood in the pulmonary capillaries. Finally, it covers the mechanics of ventilation including atmospheric pressure, intra-alveolar pressure, intra-pleural pressure, and the importance of transmural pressure gradients.

1. STRUCTURE AND FUNCTION
Lecture—1
Dr.Zahoor Ali Shaikh
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2.  Nasal passages (Nose)
 Pharynx (Throat )
 Larynx (Voice box)
 Trachea –Divides into Right main bronchus and
Left main bronchus
 Bronchi
 Bronchioles—large and small
 Terminal Bronchioles
 Respiratory Bronchioles
 Alveolar Duct
 Alveoli
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3. 3

4. 4

5.  Trachea divides into Right and Left Bronchi
which enter Right and Left Lungs
 Within each lung, bronchi continue to branch
into narrow (small diameter),shorter and
more numerous airways like branching of a
tree.
 Small braches are known as Bronchioles-
lastly Terminal bronchioles
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6.  At the end of Terminal Bronchioles, are
Respiratory Bronchioles , Alveolar duct,
Alveoli.
 Tiny sacs(Alveoli) where gas exchange takes
place between alveolar air and blood
capillaries
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7.  Trachea and large bronchi have cartilaginous
rings that prevent these from compressing
 Very small bronchioles have no cartilage to
hold them open. Their wall has smooth
muscle
 This smooth muscle is innervated by
Autonomic Nervous System, and is also
sensitive to some hormones and local
chemicals, which affect the air flow in small
bronchioles
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8.  1- Breathing Oxygen in, and breathing out
Carbon dioxide
 Helps in regulation of pH of blood (Acid –base
balance) , by adjusting the rate of removal of
CO2.
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9.  -- Cellular Respiration ( Internal Respiration)
 --External Respiration
 Cellular Respiration
 It refers to intracellular metabolic process in
the Mitochondria, which uses O2 and
produces CO2 and energy ATP from food.
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10. CELLULAR
RESPIRATION
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11.  On a mixed diet ( Carbohydrate, Fat, Protein ) O2
used is 250 ml/min and CO2 produced is 200
ml/min.
 We use the Term Respiratory Quotient (RQ)
CO2 produced = 200
RQ=
O2 used = 250
- On a mixed diet RQ = O.8
-- RQ depends on the type of food used
-- when Carbohydrate is used RQ= 1
-- when Fat is used RQ= 0.7
-- when Protein used RQ=0.8
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12.  Exchange of O2and CO2 between External
environment and cells of body. It has 4 steps.
 1 – Gas exchange between the atmosphere
and alveoli.
 2- Exchange of O2 and CO2 between air in
the alveoli and blood in pulmonary
capillaries.
 Transport of O2 and CO2 by the blood to the
tissues.
 4 – Exchange of O2 and CO2 between system
capillaries and tissue cells
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13. 13

14.  It is route for water loss and heat elimination.
Inspired air is humidified and warmed by the
respiratory airways before it is expired .
 Respiratory pump – helps in venous return.
 Helps in regulation of PH of blood.
 It enables speech, singing .
 It defends against inhaled foreign material.
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15.  Prostaglandins are inactivated in the lungs.
 Conversion of angiotensinI to angiotensinII
hormone, by ACE ( angiotensin converting
enzyme ).
 Nose– part of respiratory system , organ of
smell.
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16.  O2 and CO2 diffuse through alveoli.
 Rate of diffusion depends on thickness of
alveolar membrane, surface area and partial
pressure of O2 and CO2.
 Alveolar wall consists of single layer of
alveolar cells [type 1].
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17.  Each alveolus is surrounded by a network of
pulmonary capillaries, which is also single
layer .
 The interstitial space between an alveolus and
capillary is very thin 0.5 µm which facilitates
gas exchange.
 Respiratory Membrane [Alveolar wall and
Capillary wall].
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18.  Lungs contain about 500 million alveoli, each
about 300 µm in diameter [surface area
exposed between alveolar air and pulmonary
capillary blood is about 75 m2, size of tennis
court].
 In alveoli, there are Type II alveolar cells .
They secrete Pulmonary Surfactant.
 Pulmonary Surfactant is a phospholipoprotein
complex that helps in lung expansion.
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19. 19

20.  Also in alveolar lumen, present are alveolar
macrophages which help in defense
[Phagocytosis].
 Pore of Kohn – are present between adjacent
alveoli. Their presence permits air flow
between adjacent alveoli. This process is
called Collateral Ventilation.
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21.  Two lungs
- Right lung is divided into 3 lobes [upper,
middle, lower] by oblique and transverse
fissure.
- Left lung is divided into 2 lobes [upper,
lower and has lingula] by oblique fissure.
 Lung – has alveoli, blood vessels and large
quantities of elastic connective tissues.
 Changes in lung volume and alveolar volume
are brought about through changes in
dimensions of thoracic cavity.
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22.  The outer chest [Thorax] is formed by 12
pairs of curved ribs, which join the sternum
anteriorly and thoracic vertebrae posteriorly.
 Diaphragm – forms floor of thoracic cavity.
Diaphragm is sheet of skeletal muscle that
separates thoracic cavity from abdominal
cavity. It is penetrated by esophagus and
blood vessels.
 In the lung and chest wall, there is
considerable amount of elastic connective
tissue.
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23.  Pleura – separates each lung from the thoracic wall.
 Pleura which surround each lung has two layers –
Visceral Pleura [inner layer] which surrounds the lung
and Parietal Pleura [outer layer] which is under
thorax.
 Interior of pleural sac(space between parietal and
visceral pleura) is known as Pleural Cavity.
 Surfaces of pleura secrete intrapleural fluid which
lubricates surfaces as they slide on each other during
respiratory movements.
 Clinical application – pleurisy – [inflammation of
pleura]. It causes pain during inspiration and
expiration, and friction rub.
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24. 24

25.  Ventilation - air flow into and out of lungs.
 We will consider
1. Atmospheric [barometric] pressure
2. Intra-alveolar pressure or Intra-pulmonary
pressure
3. Intra-pleural pressure
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26.  It is pressure exerted by weight of air in the
atmosphere on objects on Earth, as Earth
surface.
 At sea level, atmospheric pressure is
760mmHg.
 Atmospheric [Barometric] pressure decreases
at high altitude as layers of air decrease in
thickness.
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27.  It is pressure within alveoli. It is 760mmHg. It
decreases slightly during inspiration and
increases during expiration.
 Intra-Pleural Pressure or Intra-thoracic Pressure
 It is pressure within pleural sac.
 It is pressure exerted from outside the lungs
within thoracic cavity.
 Intra-pleural pressure is -4 mmHg [756mmHg
which is 4mmHg less than atmospheric pressure
of 760mmHg]
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28. 28

29.  Flow of air into and out off lung occurs due to
cyclic changes in intra-alveolar pressure.
 Intra-alveolar pressure is less than
atmospheric pressure during inspiration.
 Intra-alveolar pressure is greater than
atmospheric pressure during expiration.
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30. 30

31.  When thorax expands, the lungs also expand that
is lungs follow the movements of chest wall.
Transmural Pressure Gradient
 It is the pressure difference between alveolar
pressure and intra-pleural pressure in the lungs.
 Intra-alveolar pressure equals to atmospheric
pressure of 760mmHg.
 Intra-pleural pressure is 756mmHg.
 So there is greater pressure in the lungs as
compared to pleura.
 This Transmural pressure of +4mmHg causes
stretching or opening of alveoli ,therefore lungs
are always forced to expand.
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32.  Pneumothorax – air in the pleural cavity.
 If there is chest injury, air rushes into the
pleural cavity from high atmospheric pressure
when chest is punctured e.g. broken rib or
stab wound.
 In Pneumothorax, pressure in the pleural
cavity increases and causes the collapses of
the lung.
 Pleural Effusion – Abnormal collection fluid in
the pleural cavity e.g. Tuberculosis
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33.  Functional Anatomy of Respiratory System
 Functions of Respiratory System
 External and Cellular Respiration
 Non-respiratory functions of respiratory system
 Gas Exchange between alveoli and pulmonary
capillaries
 Respiratory membrane (Alveolar wall & capillary wall)
 Lungs and Thoracic Cavity
 Visceral, Parietal Pleura and Pleura Cavity
 Atmospheric pressure, Intra-alveolar pressure and
Intra-pleural pressure
 Transmural Pressure and its importance
 Applied Aspects – Pleurisy, Pneumothorax, pleural-
effusion
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34. THANK YOU
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