Lakhasly

Respiration Part 1
Dr. Ashfaq Bukhari
Assistant Professor, Physiology
RAKCOMS
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Objectives
At the of the lecture, students will be able to:
• 1. Describe the anatomical physiology of lungs.
• 2. Explain the process of inspiration and expiration.
• 3. Explain the role surfactant.
• 4. Understand pulmonary elastic recoil and compliance.
• 5. Understand alveolar surface tension and pulmonary surfactants.
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Respiration is the process by which
the body takes in and utilizes
oxygen (O2) and gets rid of carbon
dioxide (CO2).
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An Overview of Key Steps in Respiration
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Respiration can be divided into
four major functional events
• Ventilation: Movement of air into and out of
lungs
• Gas exchange between air in lungs and blood
• Transport of oxygen and carbon dioxide in the
blood
• Internal respiration: Gas exchange between
the blood and tissues
Respiratory System Functions
• Gas exchange: Oxygen enters blood and carbon dioxide leaves
• Regulation of blood pH: Altered by changing blood carbon dioxide levels
• Voice production: Movement of air past vocal folds makes sound and speech
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ANATOMY OF THE RESPIRATORY
TRACT
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Respiratory System Divisions
• Upper Airway
– Nose, pharynx,
larynx and
associated
structures
• Lower Airway
– trachea, bronchi,
lungs
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Conducting Zone
• All the structures air
passes through before
reaching the
respiratory zone.
• Cartilage holds tube
system open and
smooth muscle
controls tube
diameter
• Warms and
humidifies inspired
air.
• Filters and cleans:
Insert fig. 16.5
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Respiratory Zone
• Region of
gas exchange
between air
and blood.
• Includes
respiratory
bronchioles
and alveolar
sacs.
BLOOD SUPPLY TO THE LUNG
• Two separate blood supplies:
• Pulmonary circulation
• Bronchial circulation
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Pulmonary circulation
• Brings deoxygenated blood from the right ventricle to the gas-
exchange units
• At the gas-exchanging units, oxygen is picked up and carbon dioxide
is removed from the blood
• The oxygenated blood returned to the left atrium for distribution to
the rest of the body
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Bronchial circulation
•Arise from the aorta
•Provides nourishments to the lung
parenchyma
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MUSCLES OF RESPIRATION
•Inspiratory muscle:
•Diaphragm and Abdominal breathing
•external intercostal muscle and thoracic breathing
•accessory muscle of inspiration
•Expiratory muscle
•relax during normal breathing
•Internal intercostal muscle
•Muscles of the abdominal wall
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Thoracic Walls and Muscles of Respiration
Breathing Rate
•At rest: 10-20 breaths / minute
•During exercise: 40 - 45 at maximum
exercise in adults
•What about Kids?
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•Pleural fluid produced by pleural
membranes
–Acts as lubricant
–Helps hold parietal and visceral pleural
membranes together
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Ventilation
• Movement of air into and out of lungs
• Air moves from area of higher pressure to
area of lower pressure
• Pressure is inversely related to volume
Inspiration
• Diaphragm and intercostals muscles contract
• Diaphragm moves inferiorly and flattens during contraction,
causing height of thoracic cavity to increase
• Intercostals contraction lifts the ribcage and thrusts sternum
forward, increasing anterioposterior and lateral dimensions
(circumference)
• Lungs adhere tightly to the thorax walls (due to surface
tension of fluid between pleural membranes), they are
stretched to the new, larger size of the thorax.
• As intrapulmonary volume increases, gases with in the lungs
spread out to fill the larger space.
• Resulting decrease in the gas pressure in the lungs produces a
partial vacuum (pressure less than atmospheric pressure),
which sucks the air into the lungs.
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Expiration
• Passive process that depends mostly on natural elasticity of the
lungs than on muscle contraction.
• As inspiratory muscles relax and resume normal resting length, rib
cage descends and lungs recoil.
• As the thoracic and pulmonary volume to decrease, gases inside the
lungs are forced closer together and intrapulmonary pressure rises
to above atmospheric pressure.
• This causes gases to flow out to equalize pressure inside and
outside of the lungs.
• Normally this is a passive process, but if passageways are
narrowed due to spasms of bronchioles (asthma) or clogged
with mucus/fluid (bronchitis/pneumonia), it becomes an
active process, using intercostal muscles to help depress rib
cage and abdominal muscles to help squeeze air out of lungs.
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Events of Inspiration
Steps of Expiration
Boyles Law
• The volume of gas is inversely proportional to pressure
(when temperature is constant).
Therefore:
• When the volume of the thoracic cavity increases–
the volume of the lungs increases and the pressure
within the lungs decreases.
• When the volume of the thoracic cavity decreases–
the volume of the lungs decreases and the pressure
within the lungs increases.
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SURFACTANT AND SURFACE
TENSION
• Surface tension: a measure of the attraction force of the surface
molecules per unit length of the material to which they are attached
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Surface Tension
•Force exerted by fluid in alveoli to resist
distension
•Lungs secrete and absorb fluid, leaving a
very thin film of fluid.
•H20 molecules at the surface are attracted to
other H20 molecules by attractive forces.
–Force is directed inward, raising pressure in
alveoli.
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Surface Tension
• Law of Laplace:
– Pressure in alveoli
–directly proportional
to surface tension
–inversely
proportional to radius
of alveoli (pressure exerted by
the surface tension increases as the
radius of the alveolus goes down)
Insert fig. 16.11
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Surfactant
• Phospholipid produced
by alveolar type II cells.
• Lowers surface tension.
– Reduces attractive
forces of hydrogen
bonding
– by becoming
interspersed between
H20 molecules.
• Surface tension in
alveoli is reduced.
Physiological Importance of Surfactant
• Reduce the work of breathing
• Stabilize alveoli
• Prevent collapse and sticking of alveoli
• Maintain the dryness of the alveoli
• Prevent the edema of the alveoli
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Mechanics of breathing
• Compliance:
• This the ability of the lungs to stretch during inspiration
• lungs can stretch when under tension.
• Elasticity:
• It is the ability of the lungs to recoil to their original
collapsed shape during expiration
• Elastin in the lungs helps recoil
Dr . Zulfania 32
Elastic Recoil
• Elastic recoil is the tendency of an elastic structure to oppose
stretching.
• The lungs naturally have a tendency to collapse because of
elastic recoil. They are held open by the negative pleural
pressure (established by lymphatic pumping of fluid).
• The chest wall naturally expands, but is also held by the
negative pleural pressure.
Punctured Lung
• What would happen if the pleura was punctured, but the lung
was not damaged?
• Air would rush into the intrapleural space and the lung would
collapse – a pneumothorax.
Lung Compliance
• Compliance is the magnitude of the change in volume
produced by a given change in pressure.
• The greater the lung compliance, the easier it is to expand the
lung at any given change in transpulmonary pressure.
• During inspiration the lungs are stretched
• Compliance is measure of effort that has to go into stretching
or distending the lungs
• Volume change per unit of pressure change across the lungs
• The less compliant the lungs are, the more work is required
to produce a given degree of inflation
• Decreased by factors such as pulmonary fibrosis
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Lung Compliance Diagram
Elastic Forces of the Lungs
• Characteristics of the compliance diagrams are determined by
2 elastic forces:

• Elastic properties of the lung tissue itself (fairly straight
  forward).


• Elastic forces caused by the surface tension of the fluid
  that lines the inside walls of the alveoli.
  Reference
  • Guyton and Hall 15th Ed.
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