Respiration - Weber State University
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Transcript Respiration - Weber State University
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.