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Respiratory Physiology
TV- (VT) – Tidal volume – amount of air inspired
and expired at rest
=500ml
ERV- expiratory reserve volume – amount of air
that can be expired beyond TV =1200ml
IRV – inspiratory reserve volume- amount of air
that can be inspired beyond TV = 3100ml
RV- residual volume- remains in lungs after
forced expiration = 1200ml
*a fraction of this, called minimal volume,
remains even in a collapsed lung
TLC –total lung capacity
=6000ml
TV+IRV+ERV+RV
IC – inspiratory capacity TV+IRV = 3600ml
maximum amount that can be inspired after
normal expiration
VC – vital capacity TV+IRV+ERV = 4800ml
amount that can physically be inspired or
expired
FRC – functional residual capacity volume
remaining in lungs after normal tidal volume
expiration RV+ERV=2400ml
Anatomic dead space – volume of air remaining
in conducting portion of respiratory system
per breath
30% of TV (150ml)
Minute ventilation - total amount of air that
flows into/out of the respiratory tract per
minute. 12 x (TV)500ml = 6000ml
AVR -Alveolar ventilation rate - part of minute
ventilation that is actually used for respiration
#breaths per minute(12) x (350ml) =4200ml
FEV1.0 - maximum amount of air forcefully
expired in first second. (80% VC is normal)
Respiration types
A) Pulmonary ventilation - breathing
B) External respiration- exchange of gases
between alveolar air/blood
C) Internal respiration – exchange of gases
between blood/tissues
Chemical Regulation of Respiration
A) Central chemoreceptors
-located in medulla oblongata
-respond to changes in H+ in CSF
-therefore, we say they are highly sensitive
to CO2 (+/- 3 mmHg) WHY?
CSF has no proteins to buffer H+.
In blood plasma, about 70% of
carbon dioxide reacts with water
H2O + CO2 H2CO3  (H+) + (HCO3-)
Therefore, detecting hydrogen ion content
indirectly detects carbon dioxide content
More carbon dioxide = lower pH = more acidic
What about the rest of CO2 ?
7% - simply dissolved in plasma
23% - forms carbaminohemoglobin
Compare to oxygen:
99% bound to hemoglobin
1% dissolved in plasma
PO2 and PCO2 values
PO2 of deoxygenated blood= 40 mmHg
PO2 of alveolar air = 105 mmHg
PO2 of oxygenated blood = 100 mmHg
PCO2 of deoxygenated blood = 45 mmHg
PCO2 of alveolar air = 40 mmHg
PCO2 of oxygenated blood = 40 mmHg
• Tissue cells average
• PO2 = 40 mmHg
• PCO2 = 45 mmHg
• 25% of oxygen derived from blood for a
person at rest. 75% still carried
B) Peripheral chemoreceptors
-located in walls of aorta and carotid
arteries
-also sensitive to H+ (CO2) (+/- 3 mmHg)
- also sensitive to O2 , but only substantial
deficiencies (by about 40 mmHg !)
Blood / gas transport physiology
concepts
Bohr effect - hemoglobin can act as a buffer
for H+ as H+ binds to amino acids of
hemoglobin.
This induces shape changes and reduces
hemoglobin’s O2 carrying capacity.
Application: metabolically active tissues
receive more O2 -why?
Haldane effect – amount of CO2 transported
in blood is related to the percent saturation of
hemoglobin by oxygen.
Deoxyhemoglobin can bind more CO2 and
buffer more H+ than oxyhemoglobin.
Application: deoxyhemoglobin removes H+
from solution & promotes CO2 HCO3 but
oxyhemoglobin favors HCO3CO2 (alveoli)
Chloride Shift - carbonic acid formation via
carbonic anhydrase occurs in rbc’s
. Excess HCO3 begins to diffuse to plasma, as Clions from plasma diffuse into rbc’s
Application: maintains electrical balance
between rbc’s and plasma
Physiological terms
a) Hypercapnia -- increased arterial CO2
-results in hyperventilation –why?
b) Hypocapnia -- decreased arterial CO2
-results in hypoventilation and ability
to hold breath for extended periods -why is
this dangerous?
c) Hypoxia - - decreased arterial O2 causes a
decreased tissue level of O2
FOUR types:
1)hypoxic hypoxia-failure to get O2
into blood airway obstruction, CO,
2) anemic hypoxia- low
hemoglobin/hematocrit anemia
3) ischemic hypoxia- failure of blood to circulate
heart failure, clots
4) histotoxic hypoxia- tissues are unable to use
provided O2 -cyanide