“Roses are red,
Violets are blue,
Without your lungs
Your blood would be, too.”
David D. Ralph, MD
New England Journal of Medicine

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

Describe the mechanism of respiration
List the non respiratory functions of the lung
Describe the basic structures of the lung

Made up of:
1. Gas exchanging organ – Lungs
2. Pump that ventilates the lungs – consists of:

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Chest wall
Respiratory Muscles – increase and decrease the size of the thoracic cavity
Areas in the Brain – control the muscles
Tracts and Nerves – connect the brain to the muscles

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A process involving:



Taking up of Oxygen from the air.
Utilizing the Oxygen in the tissues.
Removal of the Carbon dioxide formed.
O
2
Tissues:
Use of O
2
Removal
Of CO
2

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The term respiration includes 3 separate functions:
1. Ventilation:
I.
Breathing.
2. Gas exchange:
I.
II.
3. O
I.
2
Between air and capillaries in the lungs.
Between systemic capillaries and tissues of the body.
utilization:
Cellular respiration.

1)
2)
3)
Inspiration: The process of taking in of air (O
2
) from the external environment.
Expiration: Giving out of air (CO
2
) from the body to the external environment.
Exchange of gases between the body and the external environment.

1)
2)
Tissue or Cell level Respiration.
Oxygen is utilized by tissues for the metabolism of organic molecules.
Oxygen Carbon Dioxide
TISSUES

I. Defense & Protection:
1.
Warms & humidifies the air.
2.
3.
4.
5.
Dust particles are trapped by the
Bronchial secretions.
The Ciliary Escalator removes trapped matter by expectoration(Cough)
Secretory Ig.A provides Immunity against airborne microbes.
Pulmonary Alveolar Macrophages(PAMs) engulf foreign bodies by Phagocytosis.

II. Metabolism & Other functions:
1.
Regulation of blood pH.
2.
Synthesis of proteins, Fats &
Carbohydrates.
3.
4.
Fibrinolysis & removal of blood clots.
Phonation or Speech.

7.
8.
9.
5.
6.
Removal of vasoactive local hormones.(Bradykinin, PGE, E
2 etc.)
ACE (from Pulmonary Capillary endothelium) converts Angiotensin I into Angiotensin II.
Destruction of Thrombocytes.
Maintaining Body Water balance
Thermoregulation.

1)
2)
Conducting zone
- All the structures air passes through before reaching the respiratory zone.
Respiratory zone
- Region of gas exchange between air and blood.

Includes terminal respiratory bronchioles and alveolar sacs.


1)
2)
Diaphragm:

Sheets of striated muscle divides anterior body cavity into
2 parts.
Above diaphragm: thoracic cavity:

Contains heart, large blood vessels, trachea, esophagus, thymus, and lungs.
Below diaphragm: abdominopelvic cavity:

Contains liver, pancreas, GI tract, spleen, and genitourinary tract.

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Structures in the central region “ mediastinum ” enveloped by two layers of pleural membranes.
1.
Parietal (superficial) – lines the inside of thoracic wall.
2.
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
Visceral (deep) – covers lung surface
The visceral pushed against parietal pleura
Under normal condition – little or no air
There is potential space “ intrapleural space = pleural cavity ”



A.
B.
Filled with fluid produced by the pleural membranes.
It does 2 things:
Act as lubricants – parietal and visceral pleural past each other
Helps hold parietal and visceral pleural membrane together

For Inspiration
1.
2.
Diaphragm – 75%
External intercostals
3.
4.
5.
Sternocleidomastoid
Serratus (anterior)
Scaleni
For Expiration
1.
2.
Internal intercostals
Abdominal recti

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Ventilation - mechanical process that moves air in and out of the lungs.
Pressure difference induced by change in lung volumes
Air move from high to low pressure between conducting zone & terminal bronchioles

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Active process:

Contraction of diaphragm, increases thoracic volume vertically.
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Contraction of parasternal and external intercostals, raising the ribs; increasing thoracic volume laterally.
Pressure changes:
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Alveolar changes from 0 to –3 mm Hg.
Intrapleural changes from –4 to –6 mm Hg.
Transpulmonary pressure = +3 mm Hg.

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Passive process.
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The diaphragm, thoracic muscles, thorax, and lungs recoil.
Pressure changes:

Intrapulmonary pressure changes from –3 to +3 mm Hg.
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Intrapleural pressure changes from –6 to –3 mm
Hg.
Transpulmonary pressure = +6 mm Hg.

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Definitions
Atmospheric Air: Air at the normal sea level.
Alveolar Air: The inspired air which has reached the alveoli. (Before the exchange of gases)
Expired Air: The air which is exhaled after the exchange process.

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The air that envelopes the
Planet earth.
The air that we normally live in.
Has a pressure of 1 Atmosphere or 760mm of Hg.

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Gas pressure in closed container is inversely proportional to volume of container
Changes in lung volume  changes in intrapulmonary pressure.
Increase in lung volume decreases intrapulmonary pressure.

Air goes in.
Decrease in lung volume, raises intrapulmonary pressure above atmosphere.

Air goes out.

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During inspiration – air enters the lungs
(atmospheric pressure > intrapulmonary
“intrapleural” pressure)
Quiete inspiration – intrapulmonary pressure 3 mmHg sub atmospheric.
During expiration – air goes out of the lung
(intrapulmonary “intrapleural” pressure > atmospheric pressure)
Quiete expiration - intrapulmonary pressure 3 mmHg greater than atmospheric pressure.

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Pressure in the intrapleural space.
It is negative, due to lack of air in the intrapleural space.
More negative during inspiration – expansion of thoracic cavity
It is normally lower than intrapulmonary pressure during both inspiration and expiration


1.
2.

During inspiration, the intrapleural pressure falls further for two reasons: as the lung expands, the elastic recoil increases. This increases the pull on the lung away from the chest wall, dropping the intrapleural pressure further.
the fall in the alveolar pressure is transmitted to the intrapleural space, increasing the pressure drop
During expiration, the intrapleural pressure returns to its resting level


The pressure across the lung wall.
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It is the difference between intrapulmonary and intrapleural pressure.

It keeps the lung against chest wall

Change in lung volume parallel changes in thoracic volume during inspiration & expiration.

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Air sacs - Honeycomb-like clusters
~ 300 million in the two lungs
25-50 mm in diameter
Large surface area (60–80 m 2 ) for diffusion.
Each alveolus: only 1 thin cell layer “airblood barrier = 0.3µm = 1/100 th hair width”.
Total air barrier is 2 cells across (2 m m)
(alveolar cell and capillary endothelial cell).


1)
2)
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 alveoli are lined by two types of epithelial cells
Type I pneumocytes structural cells.
Thin squamous epithelial cells
95-97% (gas exchange)
Type II granular pneumocytes
Round or cup-like secretary cells
Secrete pulmonary surfactant
Reabsorb Na + and H within alveoli”
2
O “prevent buildup of fluid


The alveoli contain pulmonary alveolar macrophages (PAMs)