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Exercise Physiology > Lecture 17 - Diffusive Oxygen Transport into Muscle > Flashcards

Lecture 17 - Diffusive Oxygen Transport into Muscle Flashcards

1
Q

How is oxygen transferred from the blood to the muscle?

A
  • binds to hemoglobin in the red blood cell
  • hemoglobin releases oxygen to separate the two, this oxygen is diffused into thee tissue
  • diffuses into the plasma then the mitochondria
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2
Q

how is O2 used in the mitochondria?

A
  • must be present to create water by accepting electrons
  • drives the flow of electrons along the chain
  • facilitates proton pumping to create a gradient (for ATP synthase)
  • drawn to complex IV where is accepts electron pairs
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3
Q

what is the flow of O2 from the blood to the muscle tissue?

A
  1. blood plasma
  2. capillary endothelium
  3. interstitial space
  4. sarcoplasm
  5. mitochondria
  6. complex IV
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4
Q

What are the two ways to deliver O2 from the blood to the tissues?

A
  1. convection
  2. diffusion
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5
Q

what is convection?

A
  • transfer of O2 by movement of RBC within arterial blood to the tissue
  • the flow of a fluid (blood)
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6
Q

what is diffusion?

A
  • transfer of O2 from an area of high pressure to low pressure
  • only the gas flows
  • two locations (within the lung and within the tissues)
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7
Q

how does diffusion occur in the lungs?

A
  • O2 diffuses from alveoli into the pulmonary capillaries
  • driven by the gradient between PPO2 in the alveolar space and in the deoxygenated pulmonary capillary blood
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8
Q

how does diffusion occur in the tissues?

A
  • O2 diffuses from the systemic capillaries into the skeletal muscle mitochondria
  • driven by the gradient between PPO2 in muscle capillaries and the mitochondria
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9
Q

What does the variable Q represent?

A
  • flow of O2 rich blood
  • aka oxygen delivery
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10
Q

what is the equation for convection?

A

VO2 = Q x a-vO2 difference
- aka Ficks principle

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11
Q

what is the equation for diffusion?

A

VO2 = DMO2 x (PO2 capillary - PO2 mitochondria)
- decreasing the DMO2 will also raise VO2

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12
Q

What are the two steps of diffusive O2 delivery?

A
  1. diffusion of O2 from blood to sarcoplasm (cytosol)
  2. diffusion of O2 from sarcoplasm to mitochondria
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13
Q

what is the relation between partial pressure and hemoglobin?

A
  • hemoglobin has an affinity for O2 and blood PO2 which creates a pressure gradient between the capillary and the myoglobin
  • the bond between Hb and O2 weakens when O2blood reaches the muscle cells
  • O2 is released from Hb as RBCs pass through capillaries –> it then diffuses into the muscle cells
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14
Q

why is the fall of PO2 in the tissues based on luck/chance?

A
  • fall in PO2 because it reduces the affinity for HBO2 from oxygen desaturation
  • oxygen needs to be released so it can be used by the tissues
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15
Q

How does PO2 change in arterioles, capillaries and veins?

A
  • PO2 lowers in the capillary as dissolved O2 diffuses out of the plasma
  • this facilitates off-loading of O2
  • more O2 leaves the plasma the further along the capillary (nearer to venule) you get
  • during exercise more CO2 is released increasing capillary PCO2 towards the venular end
  • Bohr shift (rightward shift) in HBO2 dissociation curve
  • therefore “end-capillary” PO2 may be quite low relative to “mean capillary”
  • the “driving pressure” is reduced progressively from the arterial to venous end
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16
Q

How is O2 diffused into the mitochondria?

A
  1. dissolved O2
  2. myoglobin-facilitated O2 diffusion
    - oxygen is now in the interstitial space
17
Q

What is myoglobin?

A
  • an iron containing globular protein in skeletal and cardiac muscle fibres
18
Q

what is the role of myoglobin?

A
  • O2 diffusion from blood to sarcoplasm
  • provide an extra O2 source to release O2 at low PO2
  • resembles Hb but differs because Mb molecules contain only 1 iron atom compared to 4
  • Hb can hand off O2 to Mb inside the capillaries through the equation Mb + O2 –> MbO2
19
Q

how is the dissociation curve for Mb different from Hb?

A
  • Mb saturation abruptly increases in percentage, there is little change in saturation following this
  • The Hb line is much less abrupt
  • Mb affinity for O2 is not dependent on other variables
20
Q

what are the 3 factors that affect diffusive O2 delivery?

A
  • the ability of the muscle to extract O2 from the blood to the muscle mitochondria
    1. pressure gradient b/w capillary and mitochondria
    2. contact area b/w RBC and myocyte
    3. distance between capillary and mitochondria
21
Q

what is Fick’s Law of Diffusion?

A
  • muscle diffusion capacity
    1. pressure gradient b/w capillary and mitochondria (“p1-p2”)
    2. contact area b/w RBC and myocyte (“area”)
    3. distance between capillary and mitochondria (“thickness”)
22
Q

What is the effect of driving pressure on VO2 max?

A
  • VO2 max is 25% less in hypoxia
  • decreased pressure = decrease diffusive delivery = decreased vo2 max
  • low oxygen reduces VO2 max
23
Q

Effect of driving pressure on VO2max

A
  1. decreased driving pressure = decreased VO2 max
  2. training increases diffusion capacity such that a greater VO2max can be achieved for the same pressure
24
Q

What is RBC Spacing?

A
  • during exercise, greater convective blood flow increases number of blood cells in a given capillary (less RBC spacing)
  • increased hematocrit = increased functional surface area for diffusion = increased diffusive O2 delivery
  • RBC hemodynamics at onset of electrically stimulated rhythmic contraction of rat spinotrapezius muscle
25
Q

what is capillarization?

A
  • increase capillaries in contact with muscle fibres and decrease diffusion distance
26
Q

what are the 7 stages of diffusive O2 delivery during exercise?

A
  1. when oxygenated blood reaches muscle capillaries, the bond between o2 and Hb molecules weakens
  2. as RBCs pass single file through the tiny capillaries that surround muscle cells, O2 is released from Hb
  3. capillary PO2 > cytosolic PO2 so O2 diffuses into the sarcoplasm
  4. once inside the sarcoplasm, O2 can either diffuse directly into mitochondria or bind to myoglobin
  5. myoglobin shuttles O2 from cytosol to the mitochondria when cytosolic PO2 falls to critical levels during exercise
  6. once in the mitochondria, O2 is drawn to cytochrome c oxidase (complex IV) where it accepts electrons delivered by oxidation of CHO or FAT
  7. reduced O2 then picks up two H+ from the surrounding medium to form water

Exercise Physiology (12 decks)

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