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Many factors affect respiratory capacity forexample, a persons size, sex, age, and
physical
condition.
The normal quit breathing movesapproximately
500 ml of air into and out of the lungs witheach breath. This respiratory volume isreferred to as the tidal volume (TV)
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A person can inhale much more than istaken during a normal, or tidal breath . Theamount of air that can be taken in forciblyover the tidal volume is the inspiratoryreserve volume (IRV)
After a normal expiration, more air can beexhaled. The amount of air that can be
forcibly exhaled after a tidal expiration, theexpiratory reserve volume (ERV)isapproximately 1200 ml.
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Even after the most strenuous expiration,
about 1200 ml of air still remains in the
lungs, and it cannot be voluntarily expelled.
This is the residual volume.
Residual volume is important because it
allows gas exchange to go on continuously
even between breaths and helps keep the
alveoli open. (inflated)
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The total amount of exchangeable air is
typically around 4800 ml in healthy young
males, and this respiratory capacity is the
vital capacity
Much of the air that enters the respiratory
tracts remains in the conducting zone
passageways and never reaches the alveoli.This is called the dead space volume
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Lung Volume
The average total lung capacity of an adulthuman male is about 6 litres of air, but onlya small amount of this capacity is used
during normal
Lung volumes and lungcapacities refer to the volume of air
associated with different phases of therespiratory cycle. Lung volumes are directlymeasured. Lung capacities are inferredfrom lung volumes.
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Control of Respiration
Control of ventilation (control of
respiration) refers to
the physiological mechanisms involved
in the control of physiologic ventilation.
Gas exchange primarily controls the rate
of respiration.
Ventilation is normally controlled bythe autonomic nervous system, with only
limited voluntary override
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The activity of the respiratory muscles, thediaphragm and the external intercostals, is
regulated by nerve impulses transmitted to
them from the brain by the phrenic and
intercostal nerves.The neural centers that control the
respiratory rhythm and depth are located in
the medulla and pons.
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The medulla, which sets the basic rhythm
of breathing, contains a self-exciting
respiratory centers, as well as other
respiratory centers.The pons centers appear to smooth out
the basic rythym of inspiration and expiration
set by the medulla.
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Abnormal Reflexes
Asthma
common chronic inflammatorydisease of
the airways characterized by variable
and recurring symptoms, reversible
airflow obstruction,
and bronchospasm. Symptoms
include wheezing, coughing, chesttightness, and shortness of breath
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Bronchospasm
- bronchial spasm is a suddenconstriction of the muscles in the
walls of the bronchioles
- causes difficulty in breathing which `
can be very mild to severe
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Apnea
- is a term for suspension ofexternal breathing
- there is no movement of
the muscles of respiration and thevolume of the lungs initially remains
unchanged
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Hypercapnia
- known as hypercarbia, is a conditionwhere there is too much carbon
dioxide (CO2) in the blood. Carbon
dioxide is a gaseous product of
the body's metabolism and is normally
expelled through the lungs.
- normally triggers a reflex which
increases breathing and access tooxygen, such as arousal and turning the
head during sleep
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