Transcript Chapter 10 PED 304 Exercise Physiology

Chapter 10
PED 304 Exercise Physiology
COMPOSITION OF AMBIENT AIR
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20.93% OXYGEN
79.04 % NITROGEN
.03 CARBON DIOXIDE
All exert pressure from the air
column, referred to as barometric
pressure (760 mmHg at sea level)
Partial pressure = percent
concentration of a gas x total
pressure
CONCENTRATION AND PRESSURE
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As air travels to the alveoli, it mixes
with residual air, is moistened, and
heated/cooled, resulting in a
reduction in the partial pressures of
oxygen and an increase in the
partial pressure of carbon dioxide
PASSIVE DIFFUSION
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Blood entering the capillaries
surrounding the alveoli has an
oxygen partial pressure of around
40mmHg. In the alveoli, the partial
pressure of oxygen is around
100mmHg. The old move from
higher to lower concentration takes
place, and oxygen enters the blood.
PASSIVE DIFFUSION
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Carbon dioxide comes into the
alveoli at around 46mmHg; the
carbon dioxide in the alveoli has a
partial pressure of around 40mmHg.
Same thing—higher to lower
concentration, except it doesn’t
require as high a difference
because…
AT THE MUSCLE
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Same thing happens at the muscle—
higher to lower concentrations. Partial
pressure of oxygen in the muscles is
around 40 (a bunch lower if exercising),
and arterial blood is around 100.
During intense exercise, partial pressures
of oxygen in the muscles can go down to
3mmHg, while carbon dioxide can rise to
90mmHg.
Oxygen Dissociation
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Four things contribute to oxygen
dissociation at the tissues:
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Partial pressures of oxygen and
carbondioxide
Temperature
pH
2,3 Diphosphoglycerate
Ventilation & Oxygen Transportation
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Respiratory center
is located in the
medial medulla
with influences
from the
hypothalamus
Ventilatory control
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Influenced by:
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Temperature
Baroreceptors
Chemoreceptors
Proprioceptors
Ventilation & Oxygen Transportation
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Fick Equation (oxygen uptake) – Helps
determine the difference in arterial vs mixedvenous blood
Starlings Law – A muscle which is Preloaded will
provide a more forceful contraction
Henry’s Law – Movement of Gas in Air & Fluids
 Pressure differential between the gas above
the fluid and the gas dissolved in the fluid
 Oxygen requires higher pressure gradient
because it’s not very soluble in blood
Bohr Effect – Heat & pH, relatively unchanged
HOW IT’S CARRIED
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A very small amount of oxygen is
dissolved in plasma.
Most is carried attached to
hemoglobin.
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The four iron atoms each bind to an
oxygen to form oxyhemoglobin
It binds tightly and does not require an
enzyme
The partial pressures alone help to
accomplish this
How much is carried?
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Given an average hemoglobin of 15
g/100mL (females average around
14; males 15-16), with each Hb
carrying 1.34mL of oxygen, the
total oxygen carried is around 20.1
mL/100 mL of blood.
Ventilation & Oxygen Transportation
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Hemoglobin (Hb) – Contains four iron
atoms which carry oxygen.
Myoglobin – Found in skeletal and
cardiac muscle – but only contains one
iron molecule
Capillaries – Gas exchanged by allowing
one RBC through at a time.
Alveoli – Structure which allows gas
exchange in lungs
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Anatomic Dead Space vs Physiologic Dead
Space
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Carbon dioxide pressure in arterial plasma
provides the most important stimulus for
increased minute ventilation at rest.
If you lower this through hyperventilation,
the stimulus to breathe is reduced.
During exercise, it appears that increased
acidity (and with it, carbon dioxide
formed when buffering is completed)
stimulates ventilation.
VENTILATORY CONTROL
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Neurogenic stimuli from the cerebral
cortex and exercising limbs cause an
initial, abrupt increase in breathing when
exercise starts. (Cortical Influence pg.
253)
After a short plateau, minute ventilation
gradually increases to a steady state,
controlled through hypothalamus,
chemoreceptors, and baroreceptors.
VENTILATORY CONTROL
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The final phase of control involves
fine tuning through peripheral
sensory feedback mechanisms
(temperature, carbon dioxide,
hydrogen ions)
VENTILATION DURING EXERCISE
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During light to moderate exercise,
ventilation increases linearly with
oxygen uptake, with most of the
contributions from tidal volume.
The point at which ventilation
increases dramatically when
compared to oxygen uptake is
known as the ventilatory threshold.
OBLA & VT
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This takeoff from oxygen uptake
represents lactic acid buffering (R>1.0)
Normally occurs around 55-65% of VO2max
in untrained, and more than 80% in
trained.
Is considered to be 4mM per L
May be due to muscle hypoxia, inability to
clear enough lactate, or production of too
much lactate to clear
OBLA will increase as a function of
training without an increase in VO2max
Additional Terms
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Physiological Dead Space – Portion
of alveolar volume with poor
profusion of tissue.
Anatomical Dead Space – Air that
fills the nose, mouth and trachea
Tidal Volume – Volume inspired or
expired per breath during normal
respiration
Additional Terms
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Inspiratory Reserve Volume
Expiratory Reserve Volume
Total Lung Capacity – Volume in
lungs after max. insp
Residual Lung Volume – Volume in
lungs after max exp.