respiratory
Bohr Effect



Alterations in hemoglobin’s structure
Shift to the right in the oxyhemoglobin
dissociation curve
Loading of O2 is not affected
– the flat upper portion is not altered

Unloading of O2 is enhanced
– along steep lower portion, more O2 is unloaded at
a given PO2 with the shift
respiratory
respiratory
Myoglobin and Muscle Oxygen
Storage




Skeletal & cardiac muscle
contain compound myoglobin.
Each myoglobin contains only
one heme in contrast to 4 in
hemoglobin (Hb).
Myoglobin binds and retains
O2 at low pressures.
Facilitates oxygen transfer to
mitochondria at start of
exercise and intense exercise
when cellular PO2 ↓ greatly.
respiratory
Carbon Dioxide Transport
in the Blood

Dissolved in plasma
– CO2 is 20 times more soluble than O2
– 7% to 10% of CO2 is dissolved

Combined with amino compounds
– hemoglobin is most common
– Haldane effect: Hb’s de-oxygenation enables bind CO2
– about 20% of CO2 is carried as carbamino compounds

Bicarbonate
– about 70% carried as bicarbonate
respiratory
Carbon Dioxide Transport
in the Blood
respiratory
Formation of Bicarbonate
at Tissue Level

CO2 diffuses into RBC
Enzyme, carbonic anhydrase, absent in plasma
but present in RBC drives reaction of CO2 + H2O
=> H2CO3
H2CO3 dissociates a proton => HCO3- + H+

CO2 + H2O => H2CO3 => HCO3- + H+

HCO3- moves into plasma via HCO3- / Cl- anion
exchanger to prevent electrical imbalance
Hb acts as buffer and accepts the H+



respiratory
Bicarbonate in the Lungs




In lungs, carbon dioxide diffuses from plasma
into alveoli; lowers plasma PCO2.
HCO3- + H+ recombine to form carbonic acid.
H2CO3 dissociates to H2O and CO2, allowing
carbon dioxide to exit through the lungs.
CO2 + H2O <= H2CO3 <= HCO3- + H+
respiratory
Ventilatory Regulation
Two factors regulate pulmonary ventilation:
 Neural input from higher brain centers
provides primary drive to ventilate
 Gaseous and chemical state of blood: humoral
factors
respiratory
Pulmonary Ventilation Control





Clusters neurons in medulla
oblongata referred to as
respiratory center.
Inspiratory center activates
diaphragm & intercostals.
Expiratory center inhibits
inspiratory neurons.
Stretch receptors assist
regulation of breathing
Pneumotaxic & apneustic
centers contribute (depth).
respiratory
Humoral Factors


Chemoreceptors are specialized neurons.
Chemoreceptors monitor blood conditions, provide
feedback
– Peripheral located in aortic arch and bifurcation of
common carotid respond to CO2, “temperature”-no, H+
– Central located in medulla affected by PCO2 & H+


Specialized receptors in lungs sensitive to stretch and
irritants act to provide feedback
Interaction among factors controls ventilation
– CO2 production is closely associated with
ventilation rate
respiratory
Receptor Location and Function

Central chemoreceptors
located within the
medulla
– respond to changes in
PCO2 & H+ in cerebral
spinal fluid
– ventilation increases
with elevations of PCO2
or H+
respiratory
Receptor Location and Function

Peripheral
chemoreceptors
located in aortic arch
and common carotid
arteries
– respond to changes in
PO2, PCO2 and H+
– at sea level changes in
PO2 have little effect
on VE
respiratory
Ventilatory Control at Rest



Carbon dioxide pressure in
arterial plasma (PaCO2)
provides the most important
respiratory stimulus at rest.
Urge to breathe after 40 s
breath-holding results
mainly from increased
arterial PCO2.
Hyperventilation decreases
Alveolar PCO2 to 15 mm
Hg, which decreases PaCO2
below normal, allows
longer breath holding.
respiratory
Ventilatory Control in Exercise



Very rapid increase at start
of exercise
Chemical stimuli cannot
explain initial hyperpnea
during exercise.
Nonchemical factors
mediate the rapid response
– Cortical: motor cortex
– Peripheral:
mechanoreceptors in joints,
tendons and muscles
respiratory
Integrated Response


Control of breathing
is not result of a
single factor but of
combined result of
several chemical and
neural factors.
Composite of
ventilatory response
to exercise.
respiratory
References



Axen and Axen. 2001. Illustrated
Principles of Exercise Physiology. Prentice
Hall.
Kapit, Macey, Meisami. 1987. Physiology
Coloring Book. Harper & Row.
McArdle, Katch, Katch. 2006. Image
Collection Essentials of Exercise
Physiology, 3rd ed. Lippincott William &
Wilkens.