Transcript File

Respiratory
System
1
Recap
2
Pressure in Occluded Alveoli Caused
by Surface Tension
• If the air passages leading from the alveoli of the lungs are
blocked, the surface tension in the alveoli tends to collapse
the alveoli→ positive pressure in the alveoli → attempting to
push the air out
• formula:
Pressure=2 X Surface Tension
Radius of Alveolus
• respiratory distress syndrome of the newborn
3
Pulmonary Volumes & Pulmonary Capacities
2
1
2
4
1
3
3
4
4
Values in adult male
• All pulmonary volumes and capacities are
about 20 to 25 per cent less in women
• greater in large and athletic people than in
small and asthenic people.
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Lecture 4
6
Measurement
Value
Calculation
Description
Total lung capacity
(TLC)
= 5.8 L
= IRV + TV + ERV + RV
The volume of gas contained in the
lung at the end of maximal
inspiration. The total volume of the
lung (i.e.: the volume of air in the
lungs after maximum inspiration).
Vital capacity
(VC)
= 4.8 L
= IRV + TV + ERV
The amount of air that can be forced out of
the lungs after a maximal inspiration.
Emphasis on completeness of expiration.
The maximum volume of air that can be
voluntarily moved in and out of the
respiratory system
Forced vital
capacity (FVC)
= 4.8 L
measured
The amount of air that can be
maximally forced out of the lungs
after a maximal inspiration.
Emphasis on speed
Tidal volume (TV) = 500 ml
measured
The amount of air breathed in or out
during normal respiration. The
volume of air an individual is
normally breathing in and out.
Residual volume
(RV)
= 1.2 L
measured
The amount of air left in the lungs after a
maximal exhalation. The amount of air that
is always in the lungs and can never be
expired (i.e.: the amount of air that stays in
the lungs after maximum expiration).
= 1.1L
measured
The amount of additional air that can be breathed out
after the end expiratory level of normal breathing. (At the
end of a normal breath, the lungs contain the residual
volume plus the expiratory reserve volume, or around
7 2.4
litres. If one then goes on and exhales as much as
possible, only the residual volume of 1.2 litres remains).
Expiratory reserve
volume (ERV)
Lung Volumes
Q.Which of these can be measured with a spirometer ?
Boundary Conditions
TLC
VT
VOLUME
ERV
FRC
RV
RV
TIME
Answer : NONE
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Helium Dilution Method
• Determination of Functional Residual
Capacity, Residual Volume, and Total Lung
Capacity
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Abbreviations and Symbols
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Table 37-1
VT = tidal volume
FRC = functional residual capacity
ERV = expiratory reserve volume
RV = residual volume
IC = inspiratory capacity
IRV = inspiratory reserve volume
TLC = total lung capacity
VC = vital capacity
FEV1= Forced Expiratory Volume in 1st second
FVC= Forced Vital Capacity
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Minute Respiratory Volume
• Respiratory Rate X Tidal Volume
• total amount of new air moved into the
respiratory passages each minute
• 12 breaths per minute X 500 milliliters = 6
L/min
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Alveolar Ventilation
• The rate at which new air reaches gas exchange
areas is called alveolar ventilation.
• gas exchange areas:
– where air is in proximity to the pulmonary blood
– alveoli, alveolar sacs, alveolar ducts, and respiratory
bronchioles.
• importance of pulmonary ventilation
– continually renew the air in the
12
"Dead Space" and Its Effect on
Alveolar Ventilation
• areas where gas exchange does not occur
– nose, pharynx, and trachea, bronchi, large
bronchioles
• On expiration, the air in the dead space is
expired first
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Measurement of the Dead Space
Volume
• takes a deep breath
of oxygen
• expires through a
rapidly recording
nitrogen meter
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Normal Dead Space Volume
• 150 milliliters
– ↑ slightly with age.
• Anatomic Versus Physiologic Dead
Space
• nearly equal
• nonfunctional alveoli: physiologic dead
space may ↑
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Rate of Alveolar Ventilation
• Alveolar ventilation per minute is the total volume of
new air entering the alveoli and adjacent gas
exchange areas each minute
• = respiratory rate X amount of new air that enters
these areas with each breath.
• ṼA = Freq . (VT-VD)
–
–
–
–
ṼA = volume of alveolar ventilation per minute
Freq = frequency of respiration per minute
VT = tidal volume
VD = physiologic dead space volume
– normal value
• 12 × (500 - 150), or 4200 ml/min.
• Alveolar ventilation is one of the major factors
determining the concentrations of oxygen and carbon
dioxide in the alveoli.
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Functions of the Respiratory
Passageways
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Trachea, Bronchi, and Bronchioles
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Function of Trachea, Bronchi, and
Bronchioles
1.To keep Respiratory passageways open
to allow easy passage of air to and
from the alveoli
i. Cartilages
ii. Smooth Muscle (Relaxed)
2. Clear the Passageways:
i. Mucus
ii. Cilia
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Smooth Muscle
Smooth muscle↑
Downwards
Cartilage
Trachea
Cartilage ↓
downwards
Bronchi
Bronchioles
Less smooth Muscle
Mainly Epithelium
Terminal
Bronchioles
(Respiratory
Bronchioles)
Clinical:
obstructive diseases:
1.excessive contraction
of the smooth muscle
2. edema
3. mucus
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Nervous Control of the Bronchiolar
Musculature
• Sympathetic:
– Dilation of the Bronchioles
– Direct control
• relatively weak
– norepinephrine and epinephrine
• adrenal gland medulla
– beta-adrenergic receptors
V. Important
• Parasympathetic
– Constriction of the Bronchioles
– vagus nerves
– atropine
• asthma
• irritation of the epithelial membrane
– Reflex Activation of parasympathetic nerves
21
Local Factors that Affect/Control
Bronchiolar Musculature
• Bronchiolar Constriction
• histamine
• slow reactive substance of anaphylaxis
– mast cells
• pollen in the air
• allergic asthma
22
Cough Reflex
• sensitive areas:
– bronchi and trachea
• light touch
• larynx and carina (the point where the trachea
divides into the bronchi) are especially sensitive
– terminal bronchioles and even alveoli
• corrosive chemical stimuli
– sulfur dioxide gas
– chlorine gas
Contd….
23
• Afferent nerve
Cough Reflex
Contd….
– Vagus
• Medulla
• automatic sequence
– .5 liters of air are rapidly inspired
– Epiglottis closes
– Vocal cords shut tightly
– Entrap the air within the lungs
– Abdominal muscles contract forcefully
– Other expiratory muscles, such as the internal
intercostals, also contract forcefully
– Lungs explodes outward
– Velocities ranging from 75 to 100 miles per hour
• Carries with it any foreign matter
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Sneeze Reflex
• much like the cough reflex
• irritation in the nasal passageways
• afferent impulses
– fifth cranial nerve
•
•
•
•
medulla
reactions similar to those for the cough reflex
uvula is depressed
air pass rapidly through the nose
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