Respiratory System

Human Respiratory System

Figure 10.1
Respiration
 Process of air exchange
 Oxygen is obtained and carbon dioxide is eliminated
 Gas exchange occurs in the alveoli
 Four parts of respiration
 Ventilation – movement of air between the atmosphere and
alveoli
 Perfusion – blood flow through the lungs
 Diffusion – oxygen and carbon dioxide are transferred
between alveoli and blood
 Regulation – respiratory muscles and nervous system
Function
 The four main processes of respiration. They are:
1. BREATHING or ventilation
2. EXTERNAL RESPIRATION, which is the exchange
of gases (oxygen and carbon dioxide) between inhaled air
and the blood.
3. INTERNAL RESPIRATION, which is the exchange of
gases between the blood and tissue fluids.
4. CELLULAR RESPIRATION
In addition to these main processes, the
respiratory system serves for:
5.REGULATION OF BLOOD pH, which occurs in coordination with the
kidneys, and as a
6. 'DEFENSE AGAINST MICROBES
7. Control of body temperature due to loss of evaporate during expiration
The Respiratory Organs
Conducting zone
 Respiratory passages that
carry air to the site of gas
exchange
 Filters, humidifies and
warms air
Respiratory zone
 Site of gas exchange
 Composed of
 Respiratory
bronchioles
 Alveolar ducts
 Alveolar sacs

Conducting zone labeled

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The conducting zone
 Nose, pharynx, larynx, trachea, bronchi
 Series of tubes that function as airway passages
 Filter, warm and humidify incoming air
 1)Nose
 Provides airway
 Warming and humidification of the inspired air.
 Filtration and cleaning.
 Resonating chamber for speech
 Olfactory receptors
 2)Pharynx
 Contain the tonsils – normal function is to fight infection
 Larynx – voice box
3)Epiglottis
 Flexible cartilage – supported flap that covers the opening of the trachea
or (glottis).
 It automatically closes the opening to the trachea during
swallowing.
 If you eat food too fast it can get lodged in the trachea.
 4)Trachea
 Trachea is lined with ciliated columnar epithelium and mucous
cells.
 The chronic cough of smokers is caused by damage to cilia.
 The Respiratory Zone
 The region where gas exchange occur, includes lungs, respiratory
bronchioles and the terminal alveolar sacs.
 Lungs and Pleura
Around each lung is a flattened
sac of serous membrane called
pleura

Parietal pleura – outer layer

Visceral pleura – directly on
lung
Pleural cavity – slit-like potential space filled with pleural
fluid
 Lungs can slide but separation from pleura is resisted (like film
between 2 plates of glass)
 Lungs cling to thoracic wall and are forced to expand and
recoil as volume of thoracic cavity changes during breathing

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Lungs
 Each is cone-shaped with anterior, lateral and posterior
surfaces contacting ribs
 Superior tip is apex, just deep to clavicle
 Concave inferior surface resting on diaphragm is the base

apex apex

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 Right lung: 3 lobes Abbreviations in medicine:
e.g.” RLL pneumonia”
 Upper lobe Horizontal fissure
 Middle lobe
Oblique fissure
 Lower lobe
 Left lung: 2 lobes
 Upper lobe Oblique fissure
 Lower lobe

Each lobe is served by a

lobar (secondary)
bronchus

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Surfactant
 Essential fluid that lines the alveoli and
smallest bronchioles.
 Reduces surface tension of the lung allowing the
oxygen and carbon dioxide across the membrane.
 Lack of Surfactant
 Premature infants can have Respiratory
Distress Syndrome due to immaturity of
lungs.
 Persons with Chronic Obstructive Pulmonary
Disease (COPD).
Lack of
Surfactant
Bronchi
 Definition: The bronchi are small air
passages, composed of hyaline
that extend from the cartilage, trachea to the
bronchioles. There are two bronchi in the human
body that branch off from the trachea. The
bronchi are lined with mucous membranes that
secrete mucus and cilia that sweep the mucus and
particles up and out of the airways.
Alveoli
 Gas exchange in lungs occur across app. 300 million
tiny( 0.25-0.50 nm in dia) air sacs called alveoli.
 The enormous number provides large surface area(60-80
m2 or about 760 sq. feet) for diffusion of gases.
 Have a very thin membrane that allows rapid diffusion of
oxygen and carbon dioxide between capillary blood and
alveolar air spaces.( average distance of about 2 um)
 Lined with surfactant to prevent alveolar collapse.
Alveoli
 End-point of respiratory tree
 Structures that contain air-exchange chambers are called alveoli
 Respiratory bronchioles lead into alveolar ducts: walls consist of alveoli
 Ducts lead into terminal clusters called alveolar sacs – are microscopic
chambers
 There are 3 million alveoli!

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Microscopic detail of alveoli
 Alveoli surrounded by fine elastic fibers
 Alveoli interconnect via alveolar pores
 Alveolar macrophages – free floating “dust cells”
 Note type I and type II cells and joint membrane

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 Breathing and Lung Mechanics
 Ventilation is the exchange of air between the external
environment and the alveoli.
 Air moves by bulk flow from an area of high pressure to low
pressure. All pressures in the respiratory system are relative to
atmospheric pressure (760 mmHg at sea level). Air will move
in or out of the lungs depending on the pressure in the alveoli.
 The body changes the pressure in the alveoli by changing the
volume of the lungs. As volume increases pressure decreases
and as volume decreases pressure increases.
VENTILATION
 There are two phases of ventilation; inspiration and
expiration.
 During each phase the body changes the lung dimensions to
produce a flow of air either in or out of the lungs.
 The body is able to change the dimensions of the lungs
because of the relationship of the lungs to the thoracic wall.
 Each lung is completely enclosed in a sac called the pleural
sac. Two structures contribute to the formation of this sac. The
parietal pleura is attached to the thoracic wall where as the
visceral pleura is attached to the lung itself.
Movement of Air In and Out of the Lungs and
the Pressures That Cause the Movement
 The lung is an elastic structure that collapses like a balloon and expels all its
air through the trachea whenever there is no force to keep it inflated.
 Also, there are no attachments between the lung and the walls of the chest
cage, except where it is suspended at its hilum (area having heart
impression on each lung) from the mediastinum (middle section of the
chest cavity).
 The lung "floats" in the thoracic cavity, surrounded by a thin layer of
pleural fluid that lubricates movement of the lungs within the cavity.
 Further, continual suction of excess fluid into lymphatic channels maintains a
slight suction between the visceral surface (front) of the lung pleura
and the parietal (beneath, behind) pleural surface of the thoracic
cavity.
 Therefore, the lungs are held to the thoracic wall as if glued there, except that
they are well lubricated and can slide freely as the chest expands and contracts.
Ventilation
 Air flow through bronchioles is directly
proportional to the pressure difference and
inversely proportional to the frictional
resistance to the flow.
 The pressure difference is induced by changes in
lung volumes.
 What are the different respiratory patterns?
 Quiet breathing (relaxed)

 Forced inspirations & expirations

 Respiratory volumes follow these respiratory patterns…

Intra pulmonary and Intra pleural
pressures
 The intra pleural space contain only a film of
fluid secreted by the two membranes.
 During inspiration, enters the lungs
air because atmospheric pressure is greater
than the intrapulmonary pressure.
 The intrapulmonary pressure may
decrease
3 mm Hg below the pressure of the
atmosphere. This is sub atmospheric
pressure and shown as -3mmHg.
 Expiration, conversely occurs when the
intrapulmonary pressure is greater than the
atmospheric pressure and it rise up to + 3
mm Hg over the atmospheric pressure.
 Transpulmonary pressure– difference between
intra pulmonary and intra pleural pressure.
 Since, the pressure within the lungs is greater
than the intra pleural pressure, the difference in
pressure keeps the lungs against the chest wall.
 Inspiration and Expiration
 Inspiration:
diaphragm conrtraction→chest volume↑→intrapleural pressure
↓→lungs expansion→alveolar pressure<atmospheric pressure →air
is sucked into the lungs.
(At the end of an inspiration, alveolar pressure=atmospheric pressure
and airflow stops )
 Expiration:
diaphragm relaxation→chest volume↓→intrapleural pressure ↑→lungs
conrtraction→alveolar pressure>atmospheric pressure→ air is pushed
out of the lungs. Therefore, expiration is a passive process.
(At the end of an expiration, also alveolar pressure=atmospheric
pressure and airflow stops )
 Stronger ventilation:
muscles of the chest wall help produce changes in chest volume
beyond that produced by the contraction and relaxation of the
diaphragm.
Contraction of the external intercostal muscles helps increase the volume
of the chest for stronger inspiration.
while contraction of the internalintercostal muscles helps to
decrease chest volume for stronger expiration.
Mechanism of Pulmonary Respiration
 The lungs can be expanded and contracted in two ways:
 (1) by downward and upward movement of the diaphragm to lengthen
or shorten the chest cavity
 (2) by elevation and depression of the ribs to increase and decrease the
anteroposterior diameter of the chest cavity.
1st method:
 Normal quiet breathing is accomplished almost entirely by the first method
i.e. by movement of the diaphragm.
 Inspiration, contraction of the diaphragm pulls the lower surfaces of the
lungs downward.
 Expiration, the diaphragm simply relaxes, and the diaphragm, chest wall, and
abdominal structures compresses the lungs and expels the air.
 Heavy Breathing extra force is required which is achieved by contraction of
abdominal muscles that push the abdominal contents upwards and thereby
compress the lungs.
 2nd method:
 Raising of the ribs cause expansion of the lungs
When ribcage is in normal position
 Normal position of ribs i.e. slant downwards
 Normal position of sternum i.e. falling backwards close to the spine
When ribcage is elevated
 Ribs project directly forward
 Sternum also moves forward away from the spine
 This make the anteroposterior thickness of the chest about 20% greater during
maximum inspiration.
Muscles
 Muscles of inspiration
1. External intercostal muscle (most important)
2. Sternocleidomastoid muscles (lift sternum)
3. Anterior serrati (lift ribs)
4. Scaleni (lift first 2 ribs)
 Muscles of expiration
1. Abdominal recti (pulling downward the lower ribs)
2. Abdominal muscles (pulling upward the abdominal contents)
3. Internal intercostal muscles
Respiratory
Physiology
Gas Laws
 Basic Atmospheric conditions
 Pressure is typically measured in mm Hg
 Atmospheric pressure is 760 mm Hg
 Atmospheric components
 Nitrogen = 78% of our atmosphere
 Oxygen = 21% of our atmosphere
 Carbon Dioxide = .033% of our atmosphere
 Water vapor, krypton, argon, …. Make up the rest
 A few laws to remember
 Dalton’s law
 Fick’s Laws of Diffusion
 Boyle’s Law
 Ideal Gas Law
 Dalton’s Law
 Law of Partial Pressures
 “each gas in a mixture of gases will exert a pressure
independent of other gases present”
Or
 The total pressure of a mixture of gases is equal to the sum of the
individual gas pressures.
 What does this mean in practical application?
 If we know the total atmospheric pressure (760 mm Hg) and the
relative abundances of gases (% of gases)
 We can calculate individual gas effects!
 Patm x % of gas in atmosphere = Partial pressure of any
atmospheric gas
 PO2 = 760mmHg x 21% (0.21) = 160 mm Hg
 Now that we know the partial pressures we know the
gradients
that will drive diffusion!
 Fick’s Laws of Diffusion
 Things that affect rates of diffusion
 Distance to diffuse
 Gradient sizes
 Diffusing molecule sizes
 Temperature 🗸
 What is constant & therefore out of our realm of
concern? 🗸

So it all comes d🗸own to partial pressure gradients of
gases… determined by Dalton’s Law!

🗸
 Boyle’s Law
 Describes the relationship between pressure and
volume
 “the pressure and volume of a gas in a system are
inversely related”
 P1V1 = P2V2