Transcript Respiration - Weber State University

respiratory
Partial Pressure
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Primary determinant of diffusion and direction
Describes the pressure of a particular gas within a mixture
Equals the total pressure times the fractional concentration of
the particular gas, according to Whose Law?
respiratory
Partial Pressure
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Concentration of gases in ambient air
– Oxygen 20.93% x PB @ sea level = 159 mm Hg
– Nitrogen 79.04% x PB = 600.7 mm Hg
– Carbon dioxide 0.03% x PB = 0.2 mm Hg
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Tracheal air becomes diluted w/ water vapor
– 760 – 47 = 713 mm Hg
– 713 x .2093 = 149 mm Hg PO2
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Alveolar air is mixed with CO2 leaving blood
– Oxygen concentration = 14.7% (x 713 = 104 mm Hg PO2)
respiratory
Partial Pressure
Alveolar Air Percentages
and Partial Pressures differ
from Ambient Air and
Tracheal Air
1.
2.
3.
Humidification reduces
pressure of gasses
Oxygen is constantly
leaving alveoli in
capillaries
Some residual air is
always left in alveolus in
each breath to mix with
new air.
respiratory
respiratory
Gas Transport
External respiration
Oxygen moves from alveoli
into blood down
concentration gradient (104
mm Hg to 40 mm Hg.
Carbon dioxide moves
from blood into alveoli
down concentration
gradient (46 – 40 mm Hg).
Internal respiration
Carbon dioxide produced in
cells moves from higher
pressure to lower pressure
into blood.
respiratory
Oxygen Transport in the Blood
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Dissolved in plasma
– amount is proportional to partial pressure
– O2 is poorly soluble in plasma
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average .3 ml O2 / 100 ml blood
Combined with hemoglobin
– each hemoglobin molecule combines with 4 O2
– average 20 ml O2 / 100 ml blood
respiratory
respiratory
Oxygen Capacity of Hemoglobin
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Men average grams of
hemoglobin = 15/100 ml
Women average grams of
hemoglobin = 14/100 ml
Amount of O2 per gram of
hemoglobin = 1.34 ml
Maximal amount of O2 that
combine 100 ml blood =
– 20.1 ml O2 for men
– 18.8 ml O2 for women
if 100% saturated.
respiratory
Oxygen Capacity of Hemoglobin
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Percent saturation (%SO2) is
proportion of hemoglobin bound
with oxygen.
Even with sufficient atmospheric
oxygen, adequate pulmonary
ventilation, & optimum diffusing
capacity, Hb not become 100%
saturated.
SO2 arterial blood at rest = 98%
Hemoglobin carries 19.7 ml O2
(.98 x 20.1) and .3 ml dissolved
in 100 ml blood at 100 mm Hg as
in the lungs.
respiratory
Oxygen Capacity of Hemoglobin
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Tissue PO2 in cell fluids at
rest averages 40 mm Hg.
Dissolved oxygen in arterial
blood readily diffuses into
cells.
This causes Hb to release its
oxygen.
At 40 mm Hg, Hb holds
about 75% of total capacity
for oxygen (15 mL O2).
Arteriovenous-oxygen
difference at rest = 5 mL O2
respiratory
Hb Saturation Differences in
Arteries and Veins
Arteriovenous O2 difference
 Reveals the amount of oxygen extracted by
the tissues
Arterial O2
Venous O2
A-V O2 diff
Rest
20 ml/ 100 ml blood
15 ml/ 100 ml blood
5 ml/ 100 ml blood
Exercise
20 ml/ 100 ml blood
5 or 4 ml/ 100 ml blood 15-16 ml/ 100 ml blood
respiratory
Oxygen Capacity of Hemoglobin
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During exercise, tissue
PO2 decreases to about 20
mm Hg.
Hemoglobin retains about
25% or 5 mL O2 (.25 x
20.1).
A-v O2 difference = 20.1
– 5 = 15 mL/100.
During exhaustive
exercise, tissue PO2 about
3 mm Hg, Hb releases all.
respiratory
Blood Conditions Influencing
O2 Saturation of Hemoglobin
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Temperature
pH
PCO2
PO2
2,3-diphosphoglycerate (also called 2,3-DPG
or BPG)
respiratory
Resting Conditions
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Temperature = 37 degrees Celsius
pH = 7.4
Arterial PO2 = 100 mm Hg
Mixed venous PO2 = 40 mm Hg
respiratory
Changes with Exercise
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Temperature rises
pH drops
PO2 at the tissues decreases
PCO2 rises
No change in 2,3-DPG